The Sky at Night (Patrick Moore's Practical Astronomy)

The Sky at Night

Patrick Moore

The Sky at Night



Patrick Moore Farthings 39 West Street Selsey, West Sussex PO20 9AD UK

ISBN 978-1-4419-6408-3 e-ISBN 978-1-4419-6409-0 DOI 10.1007/978-1-4419-6409-0

Springer New York Dordrecht Heidelberg London Library of Congress Control Number: 2010934379 © Springer Science+Business Media, LLC 2010 All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com)

Foreword

When I became the producer of the Sky at Night in 2002, I was given some friendly advice: “It’s a quiet little programme, not much happens in astronomy.” How wrong they were! It’s been a hectic and enthralling time ever since:, with missions arriving at distant planets; new discoveries in our Universe; and leaps in technology, which mean amateurs can take pictures as good as the Hubble Space Telescope. What a privilege it is to work on a programme with such a huge heritage! I am constantly amazed looking back at the flotilla of excellent programmes which have gone out over the past five decades. The Sky at Night has always been at the sharp end of science broadcasting, whether it’s showing the first view from the far side of the Moon or pictures of a new comet which has swept into our sky. Viewers can depend on Sir Patrick to tell them the latest news and explain what it means. It’s an outstanding achievement and Sir Patrick still holds the world record for being the same presenter on the longest running TV programme. Our guests love coming down to Farthings, Sir Patrick’s home. For them, meeting him is like meeting their astronomical hero. Over the past five decades, the Sky at Night has managed to talk to the space scientists and astronomers making the landmark discoveries. No matter how busy they are, they make room for Sir Patrick. We have been privileged to record astronomical history as it is made. For example, when NASA’s spacecraft hits comet Tempel 1, the Sky at Night was given exclusive access to film the astronomers using the Palomar Telescope, thanks to its Director, Professor Richard Ellis. I will never forget the night the Huygens probe landed on Saturn’s moon, Titan. Professor John Zarnecki, Principal Investigator for the surface science package on board Huygens, gave us the ‘nod’ to set up our camera in the dining room at ESA’s mission control. The world’s media was camped out next to the press room, but we trusted John and moved our camera. It paid off when the astronomers came rushing in to us for an impromptu presentation of the first images of Titan, from a distance of some 900 million miles. Filming the Sky at Night every month is always a challenge. First, there is the setting of our main interview with Sir Patrick and the guests. To make room in Sir Patrick’s study for our three cameras and lights, we have to clear much of his furniture and move his work. I always try to make sure that the Woodstock typewriter is in shot. Patrick still uses it for the programme scripts and, of course, his many books. v

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Foreword

Secondly, there is the programme budget. I like to remind my BBC colleagues that daytime TV programmes get more money than we do. We do not have the money to commission CGI graphics; instead, we use simpler and much cheaper props to explain complex theories. Professor Fred Watson rose to the challenge when explaining the transit of Venus with a lemon and two hoops. Dr Dave Rothery juggled coloured ping pong balls to great aplomb when discussing the formation of the Solar System. Professors Carlos Frenk and Derek Ward-Thompson resorted to dinner plates to illustrate the grand collision between our Galaxy and Andromeda. When our dear friend Dr Allan Chapman from Oxford comes on the programme, he always steals the show. He managed to cover Sir Patrick in sloppy plaster when creating craters on the Moon. When Health and Safety said he couldn’t use sulphuric acid to recreate an historic Robert Hooke experiment about understanding comets, he used vinegar instead. The bubbles may not have been as explosive, but they did the job! Another show stealer was comic and impersonator John Culshaw, who became Patrick Moore from the year 1957 for our ‘Time Lord’ programme. Seeing him adopt Patrick’s mannerisms, including the monocle, was quite unnerving. Sir Patrick, in 2007, was more than happy to admit that Patrick Moore in 1957 had got a few things wrong and told him so! There are many people I would like to thank on behalf of the programme. First and foremost are the viewers, who search the schedules for our monthly time slot and stay up late to watch us. Without their loyalty and dedication, we would not have had a programme. There are the amateur astronomers who share images and observations, with their endless enthusiasm and good humour when the clouds role in on our observing sessions; the BBC team who work behind the scenes and who love the show, and put every effort to make it the best science programme that’s all year round. I would like to thank the other man who presents the programme, Dr Chris Lintott. He has been with the programme since 2003, and reports from far flung observatories, asking the astronomers all the right probing questions, and helping me understand the complexities of the Cosmos. Finally, there is Sir Patrick himself. The past few years have been the most exciting and most enjoyable period of my career. It’s been a pleasure and honour to work with Sir Patrick. Every time I meet him, I am bowled over by the enormous breadth of knowledge, grasp of the subject and his ability to explain it simply and succinctly. He is a wonderful broadcaster. I look forward to many, many more Sky at Night programmes, with Sir Patrick at the helm presenting the show, reminding us why we should step outside and look up at the night sky. There is a whole universe out there, and Sir Patrick Moore is going to tell us all about it. Jane Fletcher Producer, the Sky at Night

Introduction

This new book, the Sky at Night series is the 13th – I hope this is not an omen! It covers an eventful period, and I hope that we have managed to cover it successfully. It is interesting to look back to the early days of the Sky at Night; after all, our programme goes back to before the start of the Space Age. There has been one important change. Chris Lintott who helped me join as copresenter, now plays a more major role than I do – which is exactly how I planned it. Unlike me, he is now a leading research astronomer. It is good to have him with me, and he will still be around long after I have faded from view. My special thanks go to Jane Fletcher (in private life Mrs Segar) for guiding the programme throughout this period, and for masterminding that never-to-be-forgotten Fiftieth Anniversary. Well, here’s to the next half-century … Patrick Moore

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About the Author

Sir Patrick Moore is one of the world’s leading popularisers of astronomy. He has written more than 100 books and presented his BBC TV programme The Sky at Night every 4 weeks since 1957, making it the world’s longest running television program of any kind. While still in school, he became a member of the British Astronomical Association (BAA) and was later appointed director of Brockhurst Observatory. He served as director of the Armagh Planetarium between 1965 and 1968. He is a fellow of the Royal Astronomical Society (and a Jackson Gwillt medallist), a member of the International Astronomical Union, a holder of the Goodacre medal, and former president and current vice president of the BAA. A minor planet (# 2602) has been named after him. He was knighted in November 2000. He was also made a Fellow of the Royal Society. As the presenter of the record-breaking The Sky at Night series, Patrick was awarded a BAFTA in 2000. The most important research Patrick has carried out has been about the Moon. He is credited with independently discovering the Mare Orientale. He did this with his “traditional” 12½-in. reflector, which still sits proudly in his front garden. His maps of the Moon were among those used by the Russians in 1959 to correlate the first Lunik 3 pictures of the far side. He was also at NASA for the lunar mapping prior to the Apollo missions. Chris Lintott, the co-star of the latest episodes of The Sky at Night, has a massive fan base that derives equally from The Sky at Night and from his paradigmshifting astronomy website Galaxy Zoo, which has some 150,000 members.

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Acknowledgements

My most grateful thanks to those who have joined me on the programme during this period. I give them in order of first appearance – of course many have joined me in several programmes. I hope I have not turned professors into doctors, or doctors into professors – if I have, please forgive me! Dr Chris Lintott Prof. Gerry Gilmore Prof. John Brown Mr Ninian Boyle Mr Alan Clitheroe Mr Keith Johnson Prof. Richard Ellis Dr James Bauer Prof. Iwan Williams Prof. Andrew Coates Prof. Monica Grady Dr Simon Conway-Morris Prof. Carlos Frenk Dr Robert Nicoll Prof. John Zarnecki Dr Carolyn Porco Prof. Michelle Dougherty Prof. Bernard Foing Dr Steven Squyres Dr Mark Kidger Mr Damian Peach Mr Pete Lawrence Mr Ian Sharp Mr David Tyler Prof. Richard Harrison Prof. Lucie Green Dr John Mason Dr Harriet Jones xi

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Prof. Michael A’Hearn Dr Andrew Adamson Dr Geoff Marcy Mr Bruce Kingsley Mr Alan Schultz Mr Tim Wright Dr Carl Murray Prof. Niall Tanvir Dr Julian Osborne Dr Helen Fraser Mr Tom Boles Prof Richard Nelson Dr David Rothery Prof Fred Taylor Dr Don Kurtz Dr Yvonne Elsworthy Dr Piers Sellers Mr John Culshaw Prof. Andrew Collier-Cameron Dr Fiona Spiritz Prof. Sir Bernard Lovell Dr Ian Morrison Dr Phil Diamond Mr Bernard Baruch Prof. Derek Ward-Thompson Mr Nik Szymanek Dr Eugene Cernan

Acknowledgements

Contents

  1  Eye on the Universe..................................................................................

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  2  The Turbulent Sun...................................................................................

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  3  Comet Crash.............................................................................................

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  4  The Search for Life Elsewhere................................................................

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  5  Mapping the Sky......................................................................................

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  6  News from the Planets.............................................................................

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  7  Spanish Ring.............................................................................................

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  8  The Sizes of the Stars...............................................................................

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  9  The Edge of the Solar System.................................................................

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10  The Telescopes of Mauna Kea.................................................................

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11  Turkish Delight.........................................................................................

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12  Ringed World...........................................................................................

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13  Matter We Cannot See.............................................................................

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14  Gamma-Ray Bursters..............................................................................

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15  Wandering Giants....................................................................................

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16  The Problem of Pluto...............................................................................

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Contents

17  Non-identical Twins.................................................................................

65

18  The Sounds of the Stars...........................................................................

69

19  Space-Man................................................................................................

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20  Exploring Mars........................................................................................

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21  The Lakes of Titan...................................................................................

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22  Fiftieth Anniversary.................................................................................

87

23  SuperWASP..............................................................................................

91

24  Scorpion in the Sky..................................................................................

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25  The August Perseids.................................................................................

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26  Black Holes: And Black Magic............................................................... 103 27  Jodrell Bank: Fiftieth Anniversary........................................................ 107 28  The Grand Collision................................................................................ 109 29  Holmes’ Comet......................................................................................... 113 30  Cosmic Debris........................................................................................... 117 31  Nearest Star.............................................................................................. 121 32  The Flight of the Phoenix........................................................................ 125 33  Devil’s Advocate....................................................................................... 129 34  Galaxy Zoo................................................................................................ 133 35  Four Hundred Years of the Telescope.................................................... 137 36  The Merry Dancers.................................................................................. 141 37  The Fountains of Enceladus.................................................................... 145 38  The Herschel Telescope........................................................................... 149 39  Onward to the Moon................................................................................ 153

Contents

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40  Forty Years on.......................................................................................... 159 41  Impact!...................................................................................................... 161 42  Life?........................................................................................................... 163 Index.................................................................................................................. 167

Chapter 1

Eye on the Universe

Hubble Space Telescope (NASA)

The Hubble Space Telescope – named after the great American astronomer who proved that our Galaxy is only one of many – was launched on 24 April 1990 and was put into a near-circular path 366 miles above Earth. Ever since then, it has been orbiting the world, moving at a speed of 16,800 mph, and completing one circuit every 96.5 min. It seemed appropriate to devote a programme to it on its 15th anniversary, and I was joined by Dr. Gerry Gilmore, who has long been associated with it. The Hubble Space Telescope is now 15 years old and working almost as well as ever. I say “almost” because there are some parts which need attention, and this would have been carried out by a servicing mission, but at the moment no manned flights have been authorised, mainly because of the risks involved. The Columbia tragedy, when the returning capsule broke-up on entering the atmosphere, is still P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_1, © Springer Science+Business Media, LLC 2010

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fresh in everyone’s minds. The astronauts are all prepared to go up, and have said so, but of course the NASA authorities have the last word. Hubble did not have an auspicious beginning. I well remember sitting with the audience in 1990 and watching the telescope launched; that was a great moment, but a few weeks later it became painfully clear that something was wrong. The images were blurred. It was found that mirror had been wrongly made – not by much (less then the width of a human hair) but enough to ruin the telescope’s performance. It was a straightforward case of human error, one of the most embarrassing in the history of science, and some sections of the media made the most of it. I am delighted to say that the Sky at Night took a very different view. Hubble might be flawed, but it was still an instrument of immense value. Then came a daring repair mission. Astronauts went to the telescope, and to all intents and purposes fitted it with spectacles. The results were amazing. Hubble was not only repaired, but was also performing better than had ever been expected. Regular servicing missions have kept it in peak condition, until now. Some people do not realise that by the standards of the present day, Hubble is not a giant telescope. It has “only” a 94 in. mirror and is dwarfed by the reflectors such as the Keck twins in Hawaii and the VLT ( Very Large Telescope) in the Atacama Desert in northern Chile, which is made up of four 8-m mirrors working together. But Hubble is above the main part of our atmosphere so that there are no problems caused by the unsteadiness of the air – and it can receive all radiations from space, whereas on terra firma many wavelengths are blocked, leaving astronomers in the unenviable position of a pianist who is trying to play a concerto on an instrument that lacks everything apart from its middle octave and a few isolated notes in the treble and the bass. For many investigations, then, Hubble is supreme. There is nothing particularly unusual about its optical system, and there are no real problems in sending the images and data down to the Earth. Also, there have so far been no major hits from meteoroids and harmful interplanetary “dust”. The planners have always been worried about the possibility of a collision with a piece of debris the size of say, a teapot – which would cause serious damage and might even put Hubble out of commission permanently. After 15 years, it is starting to look as if the risk was overestimated. I remember making the comments before Yuri Gagarin became the first man in space; in 1961, pessimists were sure that he would be seared by cosmic rays and battered to pieces by meteoroids, as well as being hopelessly space-sick. None of these “Bogeys” happened. Hubble has paid attention to all branches of astronomy. Until the recent Mars rockets, the Hubble pictures of the Red Planet surpassed all others and the famous “canals” were finally laid to rest (though by 1990 I doubt if anyone still believed in Percival Lowell’s brilliant-brained Martians). Amazing views were obtained of Jupiter and Saturn, and for the first time a certain amount of surface detail was seen on Pluto. Hubble was also ready to monitor an exceptional event. When Comet Shoemaker-Levy crashed into Jupiter in 1994, leaving vast scars on the Jovian clouds, Hubble was able to obtain the best pictures, and when the Deep Impact probe was aimed at Tempel 1 in 2005, Hubble was very much a part of the observational programme. But it was in “deep space” that

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the telescope really excelled. The images of clusters, nebulae and galaxies are the best ever taken. Also, pictures sent back of the remotest galaxies within range showed that we were looking back at the very early history of the universe. In every way, the Hubble Space Telescope has been an astounding success – and remember, it has cost less then a nuclear submarine! Originally, it was planned to operate for 15 years, and this it has now done, but all the time it is sending back new data, and to lose it would be a scientific disaster. Moreover, no replacement can be sent up before 2012 at the earliest, and probably not for some years after that. The planned James Webb Space Telescope will be larger than Hubble, but will concentrate upon infra-red research. Unlike Hubble it will not orbit the Earth. It will be sent to one of the “Langrangian points”, a position near the Earth’s orbit which is stable. It will be well away from any terrestrial interference, but it will be a million miles away from us, and no servicing missions will be possible so that the designers must do their best to get everything right first time! Whatever happens, Hubble will continue to work for several years yet. It was at first planned to bring it back to Earth without damaging it. When this was deemed to be too difficult, there was a proposal to boost it into a higher orbit above all the resting part of the atmosphere, and simply leave it there until we developed techniques to make it possible to fish down. Now alas, there is a serious proposal to de-orbit it and allow it to burn away as it comes down. There are dangers here too, because it is a relatively massive structure, and it could well fall into an inhabited area. I know that all astronomers – and indeed all non astronomers, too – would be sad to see us destroying one of our very best achievements. Let us hope this does not happen. The threat seemed imminent in 2005, when our programme was transmitted, but receded when NASA changed its mind and authorised a further servicing mission. So HST is safe for the moment; it cannot remain aloft forever, but it is a vital part of scientific history, and it will never be forgotten.

Chapter 2

The Turbulent Sun

The Sun (SOHO)

It had been some time since a programme had been devoted entirely to the Sun, and it seemed that one now would be appropriate. For this, I was joined by Professor John Brown (the Astronomer Royal for Scotland), Dr Lyndsay Fletcher of Glasgow university and (from La Palma in the Canary islands) Dr Goran Scharmer, who talked to Chris Lintott. In my garden, outside my observatory dome, were Keith Johnson, Alan Clitherow, Ninian Boyle and others, suitably equipped with telescopes. As usual, the Selsey weather was kind. P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_2, © Springer Science+Business Media, LLC 2010

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To us, the Sun is the most splendid object in the sky; it is all-important, and without it the Earth would not have been born. True, it is only a normal star – 1 of 100,000 million in our Galaxy – but it is the only star close enough to be studied in detail; it is a mere 93 million miles away, and light from it can reach us in only 8.6 min. Light from the nearest star beyond the Sun, Proxima Centauri, takes over 4 years to reach us. Represent the Earth–Sun distance by one inch, and Proxima will be over 4 miles away. The Sun is large; its diameter is around 865,000 miles, and it could hold over a million bodies, the volume of the Earth. It is also very hot. At its surface the temperature is not less than 6,000°, and at its core a thermometer would register about 15 million degrees – assuming that a thermometer could survive there! The Sun is a gaseous throughout. It is not burning in the conventional sense; a Sun made up of coal and radiating as fiercely as the Sun actually does would turn to ashes in a million years or so. But we know that the age of the Earth is 4,600,000,000 years, and the Sun is certainly older than that. According to modern theory, it was formed from a cloud of dust and gas inside a nebula 5,000 million years ago, and it will be another 5,000 million years before anything dramatic happens to it so that by cosmological standards, it is no more than middle-aged. The core is the Sun’s power house, where its energy is being created. It contains a vast amount of hydrogen, which is the most plentiful element in the universe (atoms, of hydrogen outnumber the numbers of all other elements combined). At the core, where the temperature and pressure are so high, the nuclei of hydrogen atoms are combining to make up nuclei of another element, helium. It takes four hydrogen nuclei to form one helium nucleus; every time this happens, a little energy is set free and a little mass is lost. It is this liberated energy that makes the Sun shine, and the mass-lost amounts to four million tons per second so that the Sun now “weighs” much less than it did when you began to read this page. However, please do not be alarmed – there is plenty of hydrogen fuel left. To quote Corporal Jones, “Don’t panic!” The Sun’s bright surface is known as the photosphere. It is not as placid as it may seem; it shows granular structure, and very often there are dark patches known as sunspots. The spots are huge by terrestrial standards, but are not permanent; even large spots-groups seldom last for more than a few weeks or months. Neither is then in view continuously. The Sun is spinning on its axis, taking an average of 28 days to complete one turn so that a spot will be carried slowly across the disk until it passes over the limb. A fortnight or so later, it will reappear at the opposite limb, provided that it still exists. Spots generally appear in groups, though single spots are not uncommon; some spots are regular in shape, others irregular. A regular spot will have a dark central “Umbra”, surrounded by a lighter “Penumbra”. Many Umbrae may be contained in one penumbral mass; a typical group has two main spots, a leader and a follower. Sunspots are essentially magnetic phenomena. Lines of magnetic force run below the solar surface; when they break through the photosphere they cool it down, and a sunspot is the result. In fact a spot is not really dark; It appears so only because it is around 2,000° cooler than its surroundings. If it could be seen shining on its own,

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its surface brightness would be greater than that of an arc-lamp. Spots are usually associated with brilliant, high attitude clouds known as faculae (Latin, torches). A word of warning here: Solar observing can be dangerous, and to look straight at the Sun through any telescope or binoculars will result in eye damage – perhaps blindness – unless careful precautions are taken. Fitting a dark filter over the telescope eyepiece is not recommended for the newcomer; filters may not give full protection and are liable to splinter without warning. Mylar filters can be used – but make sure you know exactly what you are doing. To use the telescope as a projector and send the Sun’s image on to a card held or fixed behind the eye piece is far better. In general, a refracting telescope is better than a reflector for solar work. Remember, too, that the Sun is still dangerous when it is low in the sky, veiled by haze, and looks deceptively mild and harmless. A moment’s carelessness may have tragic results, and, sadly, accidents of this kind have happened in the past. (Some small, cheap telescopes are sold together with dark “Sun caps” for direct viewing. If you have one of these caps, throw it away.) Above the photosphere comes the layer known as the chromosphere, and above the chromosphere we come to the corona, made up of very tenuous gas. Normally, the chromosphere and the corona cannot be seen with the naked eye, or with a straightforward telescope; we have to wait for a total solar eclipse when the Moon passes directly in front of the Sun and obligingly blocks out the photosphere for a brief period (never as long as eight minutes and usually much less). Unfortunately, total eclipses are rare as seen from any particular location, and generally we have to depend upon instruments based upon the principal of the spectroscope. Consider flares, for example, which occur in the chromosphere, and are immensely energetic. Very few have been observed with ordinary telescopes; the first was seen in 1859 by one of the great pioneer solar observers, Richard Carrington. I have never seen one myself. A flare begins in the lower chromosphere; it rises upwards, sending out charged particles that cross the 93,000,000-mile gap and reach the Earth, meeting the top of the atmosphere and causing the lovely aurorae or polar lights as well as causing magnetic storms and interfering with radio communication. Flares are usually (not always) associated with spot-groups, which means that they are commonest when the Sun is most active. Equipment now is less expensive than it used to be; for example, the serious solar observer will need a telescope design to cut out all light except that from, say, incandescent hydrogen. If you can afford £400, you can set up a proper solar observing station. This may sound a large sum – until you compare it with a new laptop or a couple of railway tickets between London and Glasgow! There are also phenomena such as Coronal Mass Ejections (CMEs), when huge quantities of gas are sent out, never to fall back into the Sun. There is a reasonably well-defined solar cycle with a mean period of 11 years; at maximum, many spot-groups may be on view at the same time, while at minimum the disk may be clear for several consecutive days or even a week or two. The last maximum fell in 2001 so that the next is due in 2012, but we cannot be precise, because the cycle is not perfectly regular. Moreover there have been protracted minima in the past, for reasons which are not known; for example there were few

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spots between 1645 and 1715, and this so-called Maunder Minimum (named after E.W. Maunder, who was one of the first to draw attention to it) also marked a cold spell nicknamed the Little Ice Age. In England, during the 1680s, the Thames froze every winter, and frost fairs where held on it; in Holland, canals also froze. There have been earlier cold spells, obviously less well documented, which also seemed to be linked with solar activity, and many evidences are accumulating that shows global warming and cooling is due to the Sun and not of human activity as Politically Correct politicians claim. (En passant, similar effects apply to Mars – and there are no Martian factories as yet!) Today the Sun is under constant surveillance from Earth, and there are many solar observatories such as the Swedish station at La Palma. There are also satellites such as immensely successful Solar and Heliospheric Observatory (SOHO). New space missions and new methods of investigations are being planned, and we may hope that in the reasonably, near future we will solve some of the problems which still baffle us. There is a role here for amateur astronomers, but never forget the dangers; a cat may look at a king, but an observer must always be wary of looking directly at the Sun.

Chapter 3

Comet Crash

Deep impact (Credit: NASAJPLUMDP at Rawlings)

The impact of the Deep Space probe on Comet Tempel 1 caused a great deal of interest, and we devoted two programmes to it – one before the collision, and one at the actual time. Chris Lintott was at Palomar, where the 200 in. reflector was being used; with him were Richard Ellis and James Bauer. They saw the flash and the expanding cloud of debris. Back at home, I was joined by Iwan Williams and Andrew Coates. It was a memorable event and we had a ringside view, even though we were 83,000,000 miles away. P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_3, © Springer Science+Business Media, LLC 2010

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On July 4th, 2005, one section of NASA’s Deep Impact Probe crashed into the nucleus of a periodical comet, Tempel 1. This was not the first cometary mission – as long ago as 1986, the Giotto spacecraft had flown into the heart of Halley’s Comet – but this was the first collision, and nobody knew quite what would happen. Earth– based astronomers 83 million miles away waited anxiously. The comet itself was not particularly distinguished. It had been seen on the 3rd of April 1867 by the German astronomer Ernst Wilhelm Tempel; it was then of the 9th magnitude and there was nothing special about it. (Tempel was a skilful and energetic observer; altogether, he discovered 21 comets plus 5 asteroids; a crater on the Moon is named after him.) It has a current period of 5.5 years, and its orbit lies wholly between those of Mars and Jupiter. Its nucleus is around 6 miles long by 4 miles broad, and there is seldom an appreciable tail. At its best it can easily be seen with binoculars, but it has never attained naked eye visibility. Comets are insubstantial things and have been appropriately described as “dirty ice-balls”, though “dirty snowballs” might sound better. A typical comet has a dark surface overlying a nucleus made up of ices of various kinds, naturally including water ice. When at the far part of its orbit, the comet is inert; as it moves in towards perihelion, the ice is warmed and activity begins. Jets spout out through the crust from below, and a tail or tails may develop. Most comets, unlike planets, move in paths which are markedly eccentric; Tempel’s is no exception. Really brilliant have been periods of centuries, or thousands of years; Halley’s is the only bright comet to be seen regularly (it was last at perihelion in 1986, and will be back in 2061). The Deep Impact Space craft was made of two sections; the impactor itself and the flyby. The pair began their journey on 12th of January, sent up by a Delta 2 rocket from Cape Canaveral; there were (inevitably) a few alarms, but in the end the journey to the comet was remarkably uneventful. The mean cruising speed was 64,000 mph. After 174 days in space, the probe neared its target, and the two sections were separated. The impactor used its own thrusters to put it into a collision course, and it crashed down on schedule at a relative speed of 23,000 mph. Soon afterwards the flyby swooped past the nucleus at a range of just over 300 miles, taking pictures of the chaos below. It then veered off to avoid being damaged. Obviously, the impactor was destroyed immediately it hit! The results were spectacular and recorded by observatories all over the world as well as from space telescopes such as the HST. For the Sky at Night, Chris Lintott was at Palomar, where the 200-in. Hale reflector was aimed at the comet. Precisely on schedule there was a brilliant flash and an expanding cloud of ejecta could be seen. The impactor with a mass of just over 800 pounds produced the same effects as four and a half tonnes of TNT would have done; a large crater was blasted out, though it could not be seen until the debris cloud had cleared. There were two surprises: much more dust was ejected than anyone had expected, and the crust was firmer – there had been suggestions that the impactor might plough straight through the comet, like a bullet passing through a meringue. The ices were of the expected kind, and there were complex hydrocarbons, plus silicates. The collision shed new light on cratering, particularly with the pristine material of the interior. Comets are incredibly ancient; they date back to the origin of the Solar System.

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Let it be stressed that there was no danger to the Earth or any other planet. Neither was there any danger to the comet; as I commented at the time, one cannot derail a speeding express train by hurling a baked bean at it. Apart from (probably) temporary shift in the positions of a few jets, the comet was completely oblivious to what had happened, and is at this moment continuing its placid journey round the Sun. It will be interesting to take some new photographs, from close range, to see whether the crater is still visible. No doubt, this will be done at a suitable time. Future comet missions are being planned in 2014; if all goes well, the Rosetta spacecraft will land upon one of these ghostly objects. When that time comes, astronomers will have every reason to be grateful for what they learned from Deep Impact.

Chapter 4

The Search for Life Elsewhere

Search for life (NASA)

All of us are anxious to know whether life exists beyond Earth – and if so, what will it be like. We periodically return to it in our programmes, and this time I was joined by Drs Monica Grady and Simon Conway-Morris. As yet, we have no ­definite ­evidence that aliens are around, but I admit that I hope there are; I would love to welcome a Martian or Europan on the Sky at night! There was a time, not so very long ago, when the Earth was thought to be the centre of the universe; everything else, Sun, Moon, stars, planets, had been created especially for our benefit. We know better now. The Earth is an ordinary planet, moving around an ordinary star in an ordinary galaxy. But what about mankind?

P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_4, © Springer Science+Business Media, LLC 2010

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Are we important in the overall scheme of things? This is what we do not know. As yet, we have found no sign of life upon any world other than our own. We know that other stars have planetary systems of their own. They are of course hard to see, because they are so far away, but by now we have tracked them down in other ways – either by their gravitational effects upon their parent stars, or by a slight dimming of the star as the orbiting planet passes in transit across it. From Earth we can see transits of the inner planets, Mercury and Venus, but these two are far too small to block an appreciable amount of the Sun’s. However, our watcher on a planet in a system of another star – say Alpha Centauri – might well be able to detect the slight fade caused by a transit of Jupiter or Saturn. In our search for life we must obviously begin by considering the planets in our Solar System. Few of them are welcoming. Venus, almost the Earth’s twin in size and mass, has a surface temperature of around 1,000°F, a crushing carbon-dioxide atmosphere, and clouds rich in sulphuric acid. Mercury and the Moon are virtually airless; the four giant planets have gaseous surfaces and radiation belts, which at least in the case of Jupiter would be quick to kill any astronaut unwise enough to venture inside them. The satellites are slightly more promising. Europa, in Jupiter’s family, has an icy surface beneath which there is probably an ocean of ordinary water, kept liquid by the heat from the core; Europa is flexed by the changing pull of Jupiter. Another satellite, Callisto, may also hide an extensive ocean. In Saturn’s family there is one member, Titan, which has an atmosphere thicker than ours and is composed mainly of nitrogen, which makes up well over 70% of the air we breathe; the tiny Enceladus surprises by the fountains which shoot upward from its pole. Triton, the main satellite of Neptune, has nitrogen geysers gushing from below its crust. But can any living organisms survive there, or on the methane-drenched surface of Titan, or in the sunless sea of Europa? We have to agree that life can exist in the most unlikely places. We have found it for instance, in our Antarctic rocks, and in the hydrothermal vents of the ocean floor. Here we have a scalding hot temperature and an acidic environment which would be immediately fatal to any life forms which we encounter from day to day. Yet, these vents teem with life. There is at least a possibility that there are similar vents in the Europan oceans. This means that there could conceivably be life. And what about Titan, with its rivers of liquid methane and, chemical lakes? This is all very well, but as yet we have not yet established the existence of life anywhere except on Earth, and until we do so, we can come to no definite conclusions. Plans for drilling through the ice layer on Europa and reaching the water beneath are projects for the future; we must first practice with Lake Vostok in Antarctica – at least we know exactly where it is, and how far down it lies. But there can be no doubt that the key to the whole problem is Mars. Rovers are exploring it; there has been open water there; for a period in its history – we are not sure how long – conditions were suitable for Earth-type life. For quite a number of reasons, life cannot now be expected on the surface (radiation is one objection), but it may well survive under water. Many Mars probes are being planned, and before long, we should be able to bring back material for analysis. The results could hardly be of

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greater significance. If there are any organisms on Mars, however lowly, they will show that life will appear wherever conditions are tolerable and this will be true even if we find nothing more than extinct life – we must not be parochial; our Solar System is a tiny unit in a galaxy of 100,000,000,000 stars. We now know that many of these stars are attended by planets. Up to now, we have not found systems similar to ours, and most of the planets found seem to be giants, more like Jupiter than like the Earth, strangely close to their central stars, but it is surely premature to suggest that the Sun’s family is unusual; our techniques are not yet able to detect small, rocky, close-in planets, but our new telescopes should do so. On the other hand, we cannot tell whether intelligence will develop even upon worlds suitable for it – and the presence of life need not necessarily mean the presence of intelligent life. We may be rarer than we think! Moreover, how long will an intelligent civilisation endure? It may destroy itself – as Homo sapiens is in danger of doing that the moment. Questions of this sort will be settled only when, or if, we make contact with another race, which means looking beyond our immediate neighbourhood. There are alas, no Martians, Venusians or Jovians. (If there were, no doubt some of our present political leaders would be making preparations to drop bombs on them.) Physical contact is pure science fiction. Sending a twenty-first century type rocket to another star would take an impossibly long time. Exotic methods of travel such as spacewarps, time-warps, teleportation and thought-travel are equally beyond us; I suppose they may come along eventually, but at the moment speculation is endless and, frankly, pointless. And though we hear a great deal about flying saucers, UFOS, alien visitations and abductions, I will take such stories seriously only when a Saucer lands in my garden and a little green man calls in for a cup of tea (or, if he prefers a glass of chlorine). Fortunately, there are other courses of action which are much more promising. Radio contact is one. If there are radio operators on a planet moving around, say, Epsilon Eridani, 11 light-years away and their equipment is as good as ours, then they could pick up our signals and we could pick up their’s. If we recorded something too rhythmically and mathematical to be natural, we would know what an intelligent being had lived there 11 years ago, though our Eridanian would not receive our reply for another 11 years, and any conversation would inevitably be stilted. I wonder how people in general would react if told? Religious leaders would be nonplussed and would have to find a way to wriggle out of a delicate situation. Scaremongers would issue lurid warnings about a possible invasion, disregarding the fact that any race advanced enough to master interstellar travel would be far too sane to take part in warfare of any kind. Politicians would start plotting ways of “cashing in” and so on. Altogether, it would be fascinating. There is another possible avenue in SETI, the Search for ExtraTerrestrial Intelligence. We can make optical lasers of immense power, and so presumably can advance races elsewhere. We might watch out for a very brief but repeated signal. Optical SETI is being taken very seriously, though in my opinion at least the chances of success are slim. I have so far been discussing life of the kind we can understand. But suppose there are beings of totally different type – such as an inhabitant of, say, Polaris Q made of gold which lives on a diet of crushed rock and sulphur cocktail? BEMs (Bug Eyed

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Monsters) have been popular with SF writers ever since they were introduced by H.G. Wells in “The War of the Worlds”, and I suppose we cannot say that they are impossible, but we can say that they are very, very unlikely. If they exist, then the whole of our modern science is wrong, and the weight of evidence is overwhelmingly against anything of the sort. Right out to the depths of the universe, visible material is composed of the familiar elements, and life must be made up of these. Finally, there remains the possibility that we really are alone in the universe, and that there is absolutely no life elsewhere. I find this illogical as well as conceited, but all we can do at the moment is to keep looking, in the hope that either we will contact other beings or they will contact us. I say “hope” because of my firm belief that any race capable of communicating will be far cleverer and civilised than we are. We have not been good guardians of the Earth, and I would be the first to ­welcome an extraterrestrial who would be willing to teach us how to do it better.

Chapter 5

Mapping the Sky

Samuel Oschin Telescope (Credit: Caltech) P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_5, © Springer Science+Business Media, LLC 2010

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Celestial mapping methods have been revolutionised in recent years, and for this programme, I was joined by three of the astronomers most deeply involved, Carlos Frenk, Bob Nichol, and (from Palomar, with Chris Lintott) Richard Ellis. The first really useful star maps date back to the second century ad. Around the year 150, Ptolemy, last of the great astronomers of Classical times, produced charts which were the basis of others for many years, and which gave us the constellations which we still in use today. All 88 of Ptolemy’s constellations are still there, admittedly with altered outlines. In pre-telescopic times with the maps drawn by the Danish astronomer Tycho Brahe, between 1576 and 1596 were much the best and were amazingly good. Even so, they could not rival maps by telescopic observers and this was why Greenwich observatory was founded, by express order of King Charles II, so that British seamen could use them in navigation. The RGO survived as the headquarters of British astronomy until the end of the twentieth century, when it was wantonly destroyed by the Labour Government. Meanwhile in 1881, David Gill, in South Africa, had realised that the best way to map the stars was to use photographic methods. At the time this was certainly true. A major project was undertaken during the second half of the twentieth century at the Palomar Observatory in California. Of course, Palomar is best known because of its two great reflectors, the Hooker 100-in. and the Hale 200-in., each of which was supreme in its day, but today there are also various other large instruments there – one is the 60-in. reflector, which was brought into action in 1970 to relieve the 200-in. of some of its routine work. I was once at Palomar on a night when the 60-in. was “between programmes” and was not being used. To the amusement of the ­resident astronomers, we inserted an eyepiece and observed Saturn and Uranus. I am prepared to bet that the telescope has not since been used visually! There is also the 48  in. Schmidt, now christened the Samuel Oschin Telescope, and it was this which was used for the Palomar Sky survey; it has a 72-in. mirror and a 49.75-in. Schmidt corrector plate. The first survey extended from 1948 into 1958. In the end the survey, with a slightly more southerly extension, included 937 high-quality plate pairs. Now, of course, photography has given way to electronics, and so far as the survey is concerned the Oschin has completed its task. However, it has been given a new and valuable role searching for supernovae in external galaxies and monitoring near-Earth asteroids and also Kuiper Belt Objects in our own Solar System. It has already shown that it is ideally suited to work of this kind; for instance, it has been responsible for discovering two particularly interesting trans-Neptunians – Eris, which is larger than Pluto and is officially classed as a dwarf planet, and Sedna, which has a period of around 10,000 years and travels a long way out towards the Oort Cloud. It is in action every clear night.

Chapter 6

News from the Planets

Enceladus from Cassini (Credit: NASA)

P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_6, © Springer Science+Business Media, LLC 2010

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In October 2005, a major international planetary conference was held at Cambridge. Sadly, I was not mobile enough to attend, but Chris Lintott did and reported on all the latest news from the Solar System. Among those, he interviewed were John Zarnecki, Carolyn Porco, Michelle Dougherty, Bernard Foing and Steven Squyres. Dr Squyres was in a gleeful mood; the Spirit rover on Mars had been handicapped by dust accumulating on top of it; just as things were becoming really critical, a gust of wind swept down and cleaned the panels as efficiently as any hoover could have done. Mars can sometimes be unexpectedly helpful! It sometimes seems strange to realise that the Space Age began only in October 1957, with the ascent of Russia’s Sputnik 1 – an event which was by no means universally popular in the USA. Remember, this was the time of the Cold War; the USSR was a super power, and the American space programme was in trouble. The Sky at Night had started earlier and it is worth looking back at some of the ideas then current. This applies particularly to the bodies of the Solar System. Venus could be a welcoming world, with a reasonably temperate climate and broad, possibly life-bearing oceans; Mars had extensive vegetation tracts, and through the canal-building Martian engineers had vanished, the canals themselves had a basis of reality; the lunar seas might be deep, treacherous dust-drifts, much too soft to support the weight of a spacecraft; Pluto was a true planet, at least comparable with the Earth in size; satellites such as Io and Europa were mere chunks of barren rock, and so on. We had no idea that the Sun’s family would turn out to be as exciting as it actually is. The rate of progress is not steady; it is accelerating as quickly as the universe itself. Even with our nearest neighbour, the Moon, we are learning. SMART-1, the first ion-powered lunar probe, has provided new data about the make up of the rock, and at the end of its career was successfully crashed into a southern lava-plain, the Lacus Excellentiae, not too far from the great walled formation Schickard. At almost the last moment it was realised that instead of plumping down in the plane, it would strike the wall of a well-formed crater, Clausias. This was not what NASA wanted, and so the space-craft was given a last burst of power with the final scrap of xenon “fuel”, lifting it over the wall and the crater-floor. A cloud of dust was thrown up, and well seen (though almost all observers in Britain were clouded out). NASA hoped to see traces of water ice. They did not, and I for one am utterly convinced that there has never been any water on the Moon. It is simply not that kind of world. Mars remains very much a focal point of attention. The Rovers, Spirit and Opportunity, go on and on; they are still operating excellently, far beyond their expected life times. Initially, Opportunity was the “glamour probe”; it landed in a small crater with interesting rock structures, while Spirit came down in a crater, Gusev, believed to be an ancient lake. By now Spirit is proving equally valuable. After 156 Martian days, it has reached the Columbia Hills and has sent back amazing panoramic views – even though the Columbia Hills are hardly Himalayan in attitude! One expected hazard was cleared by courtesy of Mars itself. The Red Planet has a decidedly dusty atmosphere, and dust was expected to accumulate on Spirit, putting the instruments out of action. The dust fell, but before it could do any real harm an

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obligingly wind blew it away. No doubt mechanical or electronic ­breakdown will eventually end Spirit’s active career, but during 2005 everything went according to plan. Opportunity, in Meridiani Terra on the opposite side of Mars, had problems of its own, and spent some time a treacherous dune before managing to extricate itself, but it looked forward to an extended programme during the next Martian season. It is just as well that the instruments on Spirit and Opportunity were so reliable, because few of them were backed up – partly because of weight constraints, and partly for financial reasons. The same is true for the various orbiters, of which the latest are Odyssey, Mars Express and MRO. The NASA designers have reasons to congratulate themselves. Further, the Cassini probe at Saturn has also been tremendous success. The ring system is amazingly complicated; the tiny embedded moonlets cause “waves” in the ring outlines. Perhaps the most startling results have come from the satellites. The soft landing on Titan by the Huygens space-craft must rank as one of NASA’s greatest achievements to date. Released from Cassini, the Lander plunged down through the satellite’s thick atmosphere and touched down upon a surface, which seemed to have about the consistency of wet sand. The landscape showed what were obvious drainage channels – but of liquid methane rather than water. Later analyses taken together with the results from fly-by encounters indicate that there is almost constant “methane drizzle”, and there are chemical lakes. Life? It seems unlikely, but we cannot be sure, though any Titanian organisms would be quite unlike ours. Yet, the results from two of the smaller satellites have been even more surprising. Iapetus, the outermost of the eight fairly large satellites known before the Space Age, is over 800 miles in diameter, and takes 79 days to complete one orbit. At its best, when west of Saturn, it is a very easy telescopic object, but when the eastern elongation it fades to below the 11th magnitude-Giovanni Cassini, the Italian astronomer who discovered it in 1671 (and after whom the present space-craft is named) believed, wrongly, than it disappeared completely for 7 days in each revolution. The reason is that one part of the surface is as bright as snow, while another part is blacker than a blackboard. Like all the major satellites apart from Hyperion, Iapetus has captured or synchronous rotation, so that it keeps the same face turned towards Saturn all the time, just as our Moon behaves with respect to Earth. At western elongation the bright hemisphere is turned towards us, while at eastern elongation we see the dark area. We already knew that both bright and dark regions were hilly and cratered; appropriately, the dark area was named Cassini Regio. But was Iapetus a dark world with an icy coating, or an icy world with a dark stain? I remember referring to this as the “zebra problem”. When it became clear that the overall density of the globe is low, the second of these alternatives had to be right, but we had no idea of the composition of the dark material, or its depth. In fact we still have not, though the material is generally believed to be organic. The Cassini results indicated that the material had not been “sprayed on”. There have been suggestions that it had been knocked off the more distant satellite Phoebe, which is a full 8,000,000 miles from Saturn and is dark; it has retrograde motion, and is undoubtedly a captured body, either an ex-asteroid or else an escapee from the Kuiper Belt. But the colours do not match, and at present the puzzle is still unsolved.

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This is not at all. Cassini showed that a high mountain ridge runs for a long distance round Iapetus, making it look rather like a table-tennis ball which has been broken in half and then unskilfully glued together. The ridge is high, rising to a maximum of 8 miles above the surrounding terrain, running for 800 miles almost among the geographical (should it be the Iapetographic?) equator. It is unlike anything else known in the Solar System, so how was it formed? Could it be that it is due to icy material which welled up from below and then solidified? Could it be that, as suggested by Paulo Frerie of Arecibo observatory, Iapetus once grazed the outer edges of the ring system, and later retreated to its present distance? It has even been suggested that Iapetus itself may have had a ring – a ringed satellite orbiting a ringed planet. Less plausibly, some UFO enthusiasts have claimed that Iapetus itself is artificial, put together by the usual nebulous aliens from afar. Certainly, it may be a popular sight for future interplanetary tourists because its orbit is inclined to the plane of Saturn’s equator by almost 16°, and travellers will see the rings well displayed – while the inner satellites, including Titan, orbit almost in the equatorial plane so that seen from them the ring system will always be edgewise-on. Perhaps, the greatest surprise of all came from Enceladus, discovered in 1787 by William Herschel. It is a mere 310  miles across (about the distance between London and Penzance) and was expected to be icy and inert. This is certainly true of the even smaller Mimas, discovered by Herschel at the same time; incidentally, these were the first of the few important results coming from Hershel’s largest telescope, the 40-foot focus reflector with its 49-in. mirror. Mimas is dark with one vast crater, which had led to its being compared with Darth Vader’s “Death Star”. Enceladus has the highest albedo of any Solar System body; there are no large craters and wide areas where there are no craters at all. This must mean that these areas are young, and have been resurfaced in comparatively recent times. When Cassini flew past Enceladus on 17th of February 2005, at a range of 725 miles, it detected a tenuous but appreciable atmosphere – totally unexpected for a world with so weak a gravitational pull; In fact no atmosphere could be retained for long, and so there must be continual replenishment from below. Next came the discovery of ice geysers spouting from the south polar region; the jets rise to hundreds of miles above the ground. At NASA, they caused great excitement. To quote Carolyn Porco, head of the Cassini imaging team: “I think this is important enough to see a redirection in the planetary exploration programme. We’ve just brought Enceladus to the forefront as a major target of astrobiological interest.” The readings from Enceladus’ geyser plumes indicate that all of the prerequisites for life as we know it could exist below Enceladus’ surface. “Living organisms require liquid water and organic materials, and we know we have both on Enceladus now”. A few tens below the surface the temperature and pressure may be sufficient to keep water in a liquid state. Further evidence comes from the so-called “tiger stripes”, which indicate cracks. The ice here is a more amorphous and virtually crater-free, so that it must have welled up comparatively recently. The geysers rise upward for several 100 miles, so that they are violent – and violence was the last thing to be expected on a world as small as Enceladus. Most of the ice crystals fall back as snow, but some break and free altogether to become part of the wide, thin

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E-ring. It is not yet clear whether the venting and the geyser activities confined to the South Pole region. If so, this must be the hottest part of the whole globe. Can there be hydrothermal vents below? At any rate, Enceladus is one of the only two bodies active enough for its heat to be detected by remote-sensing instruments – the other is Jupiter’s satellite Io, but Io and Enceladus are very different worlds. Certainly, the past few months have been of immense interest. So many new phenomena have been seen. Which is the most intriguing? Make up your own mind – but I have to say that my personal vote must go to the fountains of Enceladus.

Chapter 7

Spanish Ring

Spanish ring eclipse team (Credit: Pete Lawrence)

On 3 October 2005, there was annular eclipse of the Sun. The track of the annularity began in the Atlantic and crossed Spain, which was convenient enough. I have to admit that my travelling days are over, but the Sky at Night team led by Chris Lintott was well represented in Madrid, and was rewarded with a perfect view. I had to stay at home and make do with my very small partial… An annular eclipse occurs when the Earth, Sun and Moon line up, with the Moon in mid position – but with the Moon in the further part of its orbit, so that its disk is not quite big enough to cover the Sun completely. The Sun’s mean angular diameter is

P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_7, © Springer Science+Business Media, LLC 2010

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32 min 1 s of arc; the apparent diameter of the Moon ranges between 33 min 21 s and <30 min, with a mean of 31 min 8 s. The length of the Moon’s shadow varies between 237,000 and 227,000 miles, with a mean of 231,000 miles. The Moon’s mean distance from the Earth is 238,700 miles, and from this distance the shadow is too short to reach the Earth’s surface. It follows that annular eclipses are more frequent than totals in the ratio of 5:4. This is brought out by the dates of totals and annulars in Great Britain between 1800 and 2100; six annulars (1820, 1836, 1847, 1858, 1921 and 2003) and only two totals (1927 and 1999), though it is true that the track of totality on 30 June 1954 just grazed the tip of the northernmost of the Shetland Isles (I do not believe that ­anyone actually saw it from there). The next British totalities will be on 3 September 2081(Channel Islands) and 23 of September 2090 (Southern Ireland and Cornwall). I saw my first annular eclipse on 29 April 1976, from the Greek island of Santorini – the site of the devastating volcanic outburst which probably destroyed the Minoan civilisation on Crete, than just about the most advanced in the whole word. (The Santorini volcano, Nea Kameni, is still smouldering, though for a long time now it has been reassuringly placid.) With a party of friends, I was stationed in the courtyard of the excellent Atlantis Hotel, under a perfect sky. Frankly, I did not know quite what to expect. Annularity can last for more than 12 min so that things are less frenetic than with a total eclipse, and strict precautions must be taken all the time. Of course, there is no chance of seeing the corona, though naked-eye prominences have been recorded, and so have Baily’s Beads – in fact the first description of these beads was given by Francis Baily at the annular eclipse of 15 May 1836, though they had been seen much earlier by MacLaurin at the annular eclipse of 1 March 1737. I did not know whether the sky would darken sufficiently for planets or bright stars to be seen; at the Santorini eclipse it did not, and the diminution in light was so slight that many of the locals failed to realise that anything unusual was happening. Still it was enthralling to see that the jet-black disk of the Moon circled by a ring of sunlight. I saw another annular from Mexico, on 10th of May 1994; this time the sky became darker, but I could see no prominences and certainly no sign of corona. Eclipse-chasing is addictive, and even an annular is well worth seeing, so I was very sorry not to be able to join the 3 October party, in Madrid. At least the Sky at Night was well represented; Chris Lintott and Mark Kidger were our commentators, and the photographers included Damien Peach, Pete Lawrence, Ian Sharp and Dave Tyler, all armed with equipment much more sophisticated than anything I could have taken to Santorini almost 30 years earlier. Nowadays, good results can be obtained even with a simple digital camera, but digitals belong strictly to the twenty-first century. The track of annularity passed right through Madrid, and the eclipse took place in the late morning, so that the Sun was pleasingly high in the sky. The annular phase lasted for 4 min 11 s, and 90% of the solar surface was covered, but the drop in the light-level was surprisingly pronounced. It so happened that neither of our main commentators had seen an annular eclipse before, and they were suitably impressed, notably by the crescent-shaped shadows which were cast as the Moon crept slowly and gracefully on to the Sun.

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The sky never became dark enough for Jupiter to be seen (Venus was badly placed), but the landscape became very dim, and at Madrid was probably about the same as the light-level to the late twilight – according to those who were there; watching the picture on my television screen could not give me any real idea. Baily’s Beads were well seen, and a very interesting set of observations were made by Pete Lawrence. The “beads” are produced when shafts of sunlight cast through the lower-lying parts of the Moon’s uneven limb. Careful timing showed that the main “bead” was seen as the sunlight streamed past a very large, deep depression which could be identified as Mare Orientale, the Eastern Sea. This is a major sea, almost all of which lies on the Moon’s far side; only a tiny section of it can ever be seen from Earth, and then only under the most favourable liberation. (I first drew it in 1949, and suggested its name, American observers rediscovered it later.) It is a huge ring structure apparently, the youngest of the principal Maria and the only one of its kind on the far side. It is so large that from Madrid it was able to produce an obvious and persistent “bead”. It cannot honestly be said that a great deal of valuable work can be done during an annular eclipse, but what does this matter? Everyone at Madrid enjoyed it – including the town band, who came into the main city square to join the astronomers, and played with great gusto without quite matching the standard of the Royal Philharmonic. At least the Sky at Night team, their appetites whetted, could look forward to the much grander spectacle of a total eclipse in March 2007.

Chapter 8

The Sizes of the Stars

The “Plough” in Ursa Major, photographed by Nik Szymanek

Look up into the sky, and you will see the stars as tiny, twinkling points. The twinkling is due entirely to the Earth’s atmosphere; from space (or on the Moon) stars do not twinkle (scintillate) at all, and if you have the chance of seeing stars while you are travelling in a high-flying jet you will find that the twinkling is much less then it is at sea level. But with the naked eye, no star appears as anything but a dot. If you use a star as an obvious disk, you may be assured that there is something wrong. Almost certainly the telescope is out of focus. This being so, it takes an effort of the imagination to appreciate that some of the stars are huge enough to contain the whole orbit of the Earth round the Sun – while admittedly others are so tiny that they could fit comfortably into the ring road of a small city. For the last the programme of 2005 I was joined by Professors Richard Harrison and Lucy Green to say something about the Sun, the only star close enough to be examined in a great deal, and then by Drs John Mason and Barrie Jones, to discuss the sizes of the various types of stars. P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_8, © Springer Science+Business Media, LLC 2010

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If no stars show obvious disks, then how do we measure their diameters? There are various methods. Of course, there is no problem at all with the Sun, which is a normal Main Sequence star of Type G; it is 865,000 miles across. We may not have discovered all its secrets, but we do know a great deal about it, and it gives us a guide to other stars – though the stars are amazingly diverse. Some are much larger than the Sun, others much smaller; some are far more luminous, others remarkably feeble. Let us deal first with exceptionally luminous stars – which are not necessarily the largest. According to one set of measurements, the record holder is a remote celestial search light catalogued as LBV 1906-20, said to be the equal of 40 million Suns, which is about as powerful as a star could be without disrupting itself by the pressure of radiation. (LBV, by the way, stands for Luminous Blue Variable.) This does seem rather dubious. Then we have the Pistol Star in Sagittarius, so nicknamed by the shape of the nebula, which it illuminates. It is approximately 25,000 light years away, in the direction of the galactic centre, and it is certainly very powerful and massive. Were it is not so masked by interstellar dust, it would be an easy naked-eye object; in fact, it remained undetected until the Hubble Space Telescope imaged it in infra-red. Its mass seems to be about 150 times that of the Sun, and its diameter has been given as around 300 times that of the Sun, i.e. roughly 250,000,000 miles, so that it could contain the whole of the Earth’s orbit. However, the data for Eta Carinae, the erratic variable in the southern hemisphere of the sky, are more reliable. The luminosity is at least 5,000,000 times that of the Sun, and it is one of the most massive stars known. It is also wildly unstable; for a while around 1840 it shone as the most brilliant star in the sky apart from Sirius, though for well over a century now it has hovered on the brink of naked-eye visibility. In the foreseeable future – perhaps tomorrow, perhaps not for a million years – it will explode as a supernova, ending up as either a neutron star or a black hole. The largest of all stars are red supergiants. A star begins its career by condensing out of the material inside nebula; it shrinks, under the influence of gravitation, and the inside heats up. When the core temperature reaches about ten million degrees, nuclear reactions are triggered off. The main “fuel” is hydrogen, the most abundant element in the universe; the hydrogen atoms combine to form helium, and the star begins to shine. (Yes, I know this is horribly oversimplified, but it will suffice for the moment!) When the supply of the available hydrogen runs low, different reactions begin, and elements heavier than helium are built up. With a modest star such as the Sun, the process is halted before it can go too far. The star will briefly become a red giant (not a supergiant) and will puff off its outer layers and become a beautiful “planetary nebula”. When the outer layers are finally lost, what is left of the star collapses into what is known as the white dwarf stage. It will then go on shining feebly until all its light and heat have gone, leaving it as cold, dead globe – a black dwarf; – it is quite possible that the universe is not yet old enough for any black dwarfs to have formed. But with a much more massive star, equal to (say) over ten Suns, the story is different. The star evolves much more quickly, and the element-building process is not halted so soon. The star heats up until its core is at a temperature of millions of degrees, and the globe is blown out to produce a supergiant. The surface has

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cooled-hence the red colour – but the luminosity is immense, though without matching Eta Carinae. The best known red supergiant is Betelgeux in Orion (the star marks the great hunter’s shoulder, the name can be spelt in various ways and some people pronounce it “Beetle Juice”). Its apparent magnitude varies slowly between 0.2 and 1; sometimes it equals Rigel, the other brilliant star in Orion, while at others it is comparable with Aldebaran, in Taurus, which looks like the same colour but is a giant rather than a supergiant. Betelgeux is just over 500 light-years away, it must have a diameter of around 550 million miles, and shine 15,000 times more powerful as the Sun. In luminosity it cannot match Rigel, well over 40,000 Sun power, but Rigel is hot, bluish white star, and it is not nearly as large as a red supergiant. But Betelgeux, vast though it is, is by no means the record-holder. Even larger is Mu Cephei, in the far north of the sky not far from the W of Cassiopeia; over Britain if it never sets. It is variable between magnitudes 3.6 and 6, but as its seldom drops between the fifth magnitude it is almost always within naked-eye range. It is so red that William Herschel christened it the “Garnet Star”, and the nickname has stuck; through binoculars it looks rather like a glowing coal. It is further away than Betelgeux (perhaps 5,000 light-years) and much larger, more massive and more luminous, since it could equal 350,000 Suns. For a long time it was said to be the largest star known but we have now found that it is outmatched by four others – VV Cephei, V354 Cephei, KW Sagittari and KY Cygni – and possibly also a fifth, VY Canis Majoris, though the various measurements used here do not agree really well. Consider KY Cygni around 5,200 light years away in the constellation of the Swan. The diameter is thought to be around 1,000,000,000 miles. Imagine that you could stand upon the surface and go for a walk, how long would it take you to go right around, walking at a steady 3 mph and never stopping? The answer – 150,000 years. Yet, although KY is 300,000 times as luminous as the Sun, it has only 25 times the solar mass. Large stars are always less dense than smaller ones; it is almost like balancing a lead pellet against a meringue. Go and look for KY Cygni by all means; its position is RA 20h 26m 52s2, dec. +38° 21¢11″, but I warn you that it will not be easy. It lies in a rich area, but its apparent magnitude is a modest 13.3. Rather surprisingly, the star with the largest known apparent diameter is none of these supergiants, but R Doradus in the far southern constellation of the Swordfish. The distance is 200 light-years, the luminosity 6,500 times that of the Sun and the diameter 150 million miles. It is red, and a variable star of the pulsating type. From incredibly large stars to very small ones, we have noticed that a modest star like the Sun will become a white dwarf when its supply of hydrogen fuel is exhausted. We know a great many white dwarfs, the most famous is the faint companion of Sirius which was also the first to be identified. All the atoms are crushed and broken, and the component parts packed together with almost no wasted space; matter of this sort is termed “degenerate”, and a cupful of it would balance the weight of an ocean liner. Atoms in a normal state are mostly empty space. The best analogy I can give – not a good one, I know – is to picture a snooker table upon which the balls are set out ready for a game. They take up a good deal of room – but pack all the balls together, and

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you can cram them into a suitcase. The white dwarf companion of Sirius is slightly smaller than the Earth, but as massive as the Sun. It is a mere 8.6 light years away, and would easily be seen with binoculars where it not so drowned by the glare of its primary; even so, a modest telescope will show it. Smaller white dwarfs are known, with diameters comparable of that of the Isle of Wight. Finally – the neutron stars left as the remnants of supernova explosions. Here, protons and electrons – the main constituents of atoms – have been unable to withstand the pressure and have been forced to merge, producing neutrons. The density is unimaginable; our cupful of neutron star material would weigh thousands of millions of tons. The most celebrated neutron star is the remnant of the supernova of 1054, now seen as the Crab Nebula, without much doubt the most studied object in the sky. The diameter of a neutron may be less than a dozen miles. If the centre of one of these curious bodies lay in the village of Sidlesham, the globe would barely hold the city of Chichester on one side of my home at the end of Selsey Bill on the other. Indeed the stars are of many kinds. It is strange to reflect that to the early civilisations, even the Greeks, they were no more than tiny lamps attached to an invisible crystal sphere.

Chapter 9

The Edge of the Solar System

Launch of the New Horizons probe to Pluto (Credit: NASA)

How far does the Solar System extend? The answer to this question is not as straightforward as it might be expected. Neptune, the outermost planet, moves around the Sun at a mean distance of 2,793 million miles; beyond come the members of the Kuiper belt, of which Eris is the largest known and Pluto the brightest, and

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there are various trans-Neptunians, such as Sedna, which travels out to immense distances, almost to the fringe of the Oort Cloud, where the Sun’s gravitational pull has become relatively weak. Some comets range much further and may leave the Solar System permanently. Comet Arend-Roland, the subject of my very first Sky at Night programme, will never return. There is one reasonable definition. The nearest stars, those of the Alpha Centauri system, are just over four light-years away. It seems to me, therefore, that the Sun’s dominance may end at a distance of around 2 light-years, 12 million miles. We cannot hope to track a spacecraft out as far as that, but the Kuiper Belt ought to be within range, and our probe New Horizons is on its way there. It was launched on 19 January 2006, and this seems to be a good time to devote a programme to it. I was joined by Professor Mike A’Hearn of the University of Maryland, who gave us the latest news about the Deep Impact spacecraft which had hit comet Tempel 1, and then by two of our regular visitors, Drs Mark Kidger and Lucie Green. Solar System bodies are of many kinds. Planets and comets are certainly very different, but there may well be a link between comets and small asteroids; it is widely believed that some small asteroids are the cores of old comets which have lost all their volatiles, and that one of these, Phaethon, may be the parent of the Geminid meteor stream. There are a few bodies which have “dual nationality” and the distinction is not so clear-cut as used to be thought. The Deep Impact probe to Tempel 1 was immensely informative. One surprise was the abundance of organic material. As expected, the comet was made up chiefly of ices, with water dominant and plenty of ices such as methanol and carbon dioxide; assembling it must have been a gentle process. But what about more massive bodies which in some ways behave like comets? Chiron, which spends most of its time between the orbits of Saturn and Uranus, is well over 50 miles in diameter and has been given an asteroid number (2060), but when it draws into perihelion, it develops what may be called either an atmosphere or a coma and has also been given a cometary number, though to me this seems irrational. And then what about Pluto, way out in the Kuiper Belt? Pluto has an eccentric orbit. When near perihelion, it has a thin but surprisingly extensive atmosphere, though its companion, Charon, has not. (Do not confuse Sharon with Chiron; it is a pity that two names are so alike; in mythology Chiron was the wiser centaur while Charon was the gloomy boatman who ferried departed souls across the river Styx into the underworld.) Pluto was last at perihelion in 1989. Its orbital period is 248 years, and it is generally believed that in near future it will temporarily lose its atmosphere, which again would be a cometary behaviour. Recent doubts have been voiced, because as it swings outward Pluto’s temperature seems to have increased rather than fallen, and this is probably due to slight fluctuations in the output of the Sun, another indication of “global warming”. (P.C fanatics, please note – there are no factories on Pluto to produce greenhouse gases!) We must wait and see what happens during the next few decades, but in any case Pluto is an interesting world and is due to be bypassed by the New Horizons spacecraft in 2015. Perhaps significantly, New Horizons was planned when Pluto was still regarded as

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a true planet rather than KBO. It has been allotted an asteroid number, 134340, though together with Eris and Ceres it is still called a “dwarf planet”. New Horizons has an ambitious programme. After launch, on 19 January 2006 from Cape Canaveral, it was put into its planned orbit. In size and shape NASA likened it to a grand piano, or better, a grand piano glued on to a cocktail-sized bar satellite dish. It was launched by a three-stage rocket, of which the bottom section was an Atlas V 551, and it was sent out towards Jupiter, so that the pull of the Giant Planet could help New Horizons on its way. It was equipped with a radioscope thermoelectric generator; solar power cannot be used at these vast distances, in the wastes of the Solar System. The first encounter was with the mile-wide asteroid 132524 APL, on 13 June 2006 at a range of 64,000 miles. (NB: of course, this and subsequent events took place after the broadcast of our programme in January 2006. I have suitably updated this account.) On 4 September 2006, this spacecraft took its first images of Jupiter, and then, on the following 28 November had its first glimpse of Pluto. All was going well. The Jupiter encounter was extremely successful. Details on the disc were well seen – notably the Little Red Spot, a newcomer to the Jovian scene, which has taken planetary observers by surprise. Io, the wildly active satellite, was surveyed, and its huge volcano Tvashtar obligingly produced a plume rising to a height of 200 miles above the caldera. “Galileo orbited Jupiter for 6 years and never saw a plume like that,” commented John Spencer, of the imaging team. “We just happened to breeze by, and there it was”. The distance from New Horizons was 1,400,000  miles. Clumps of debris in the ring system were seen, trailing the small inner satellite Adrastea “like ducklings following their mother”. A spectacular picture was obtained of Europa, perhaps the most intriguing of the Galileans inasmuch as it may well have a vast ocean of ordinary water beneath its icy crust.

Chapter 10

The Telescopes of Mauna Kea

UKIRT Mauna Kea (Credit: ROE)

Our first programme of 2006 took us back to Mauna Kea. Alas, I am no longer able to travel as far as that, but Chris Lintott can, and to Hawaii he went. Atop the ­volcano he was joined by a number of eminent astronomers, including the director Andy Adamson. Mauna Kea is an amazing place; there is nowhere quite like it. Think of Hawaii, and you will conjure up a picture of palm trees, guitars, bikinis and an azure blue sea. Many parts of it really are like this, but go to Big Island and you will find a different scene. There are two towering volcanoes, one dormant and the other violently active. You will also find one of the world’s greatest observatories. Why Mauna Kea? Because it is so lofty, and pokes above the thickest and unsteadies layers

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of an atmosphere. Not much life can survive – but astronomers love it, and the summit positively bristles with domes. Mauna Kea has not erupted for about 4,000 years, and (we hope!) it is not likely to do so again in the foreseeable future, if ever, but the view is nothing if not picturesque, with cider-stones and lava flows everywhere. From the top you can see the twin volcano Mauna Loa, which is erupting all the time. On one occasion a flow reached the outskirts of Hilo, the largest town on Big Island, and according to local lore was stopped only by the timely intervention of Hawaii’s most powerful witch-doctor. Mauna Kea is just over 14,000 ft high, and there is a good road for most of the way to the summit; all of it is drivable, but there is one thing to be borne in mind. The air at 14,000 ft is thin, and one’s lungs take in only 39% of the usual amount of oxygen. Some people cannot tolerate this, and I will remember that one young, fit, rugby-playing BBC assistant had to be brought hastily down to sea level. Most people have headaches for a while, but I was unaffected because I was an old (wartime) flyer who used to fly high altitudes. Nobody actually sleeps at the summit, and most visitors on the way up stay for a day or so in the “half-way house”. Hale Pohaku is at the height of about 10,000  ft. To drive from Hale Pohaku from the summit takes a mere 20 minutes, but that extra 4,000 ft makes all the difference. The air at the volcano top is not only very thin, but also very dry because you are above 97% of the atmospheric water vapour, and this is a boon to astronomers working at short wavelengths; water vapour is extremely effective at absorbing such radiations. Several telescopes suited to these conditions have been sited here, notably UKIRT, the UK Infra-Red telescope, and JCMT, the James Clerk Maxwell telescope. (Maxwell, a Scot, was one of the greatest scientists of the nineteenth century.) Among others are Kecks 1 and 2, which were for some time the largest telescopes in the whole world. There is a great deal to see, and there have been major developments ever since I was last able to go there, around 10 years ago. Chris Lintott’s first report was from UKIRT, which was brought into action in 1978. It has a 50-in. mirror and was designed to work in the infra-red. The mirror need no to be so accurate as with an optical telescope, which means that it can be thin and therefore cheap – but in the event it turned out to be so good that it can also be used visually, which was sheer bonus. It is continuously upgraded, and not long before our programme a new instrument has been added, the Wide Field and Planetary Camera, WFPC (annoyingly, people will insist on referring to it as “wiffpick”). It has the largest field of view of any astronomical infra-red telescope ever made, and in a single exposure it can cover an area equal to that of the full Moon, which is 1,200 times larger than that covered by the infra-red camera of the Hubble Space Telescope. Spectacular pictures have been taken with it, particularly the so called Chicken Nebula, IC 2044/48, whose shape really does resemble that of a running hen! There is also a dramatic view of the Orion Nebula, M42, with numbers of brown dwarfs i.e. – low mass stars whose interiors never became hot enough to trigger nuclear reactions. A brown dwarf will glow freely for an immense period and will end up as cold, dead globe – a black dwarf, though it is quite likely that the universe is not yet old enough for any black dwarfs to have evolved. M42 is a stellar nursery. Very young stars are associated with dust clouds which block out visual light, but infra-red radiations can slice through them, and give us

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views of star forming regions. Calm though it may look, the Orion Nebula is really in a state of turmoil because star-birth is an energetic process. Around 5,000 million years ago our own Sun was born inside a nebula, but by now it has overcome the instabilities of youth, and has settled down to sober, middle-aged existence. It will not change dramatically for over a thousand million years yet, whereas UKIRT can show us definite, short-term changes in part of M42. Deep inside the nebulosity, there are immensely powerful stars which we can never see, but which betray their presence by pouring out infra-red radiation. You will never see them because they will not live long enough for the light to “burn its way” through the gas and dust which envelopes them, but we know that they are there. The next call during the programme was to the JCMT, which functions at submillimetre wavelengths. This does not resemble an ordinary telescope, and one cannot look through it because it operates in the region of infra-red and the radio range, so that it has the look of a radio telescope dish. Clouds do not bother it, and neither does daylight. It was completed in 1987, and like UKIRT, it has been a tremendous success. One of its many observational programmes concerns stars which may be attended by planets, and here its latest camera, Scuba – installed just before the Sky at Night team arrived – has been particularly informative. An early target was Fomalhaut in Piscis Australis (the Southern Fish), the southernmost of the first-magnitude stars visible from Britain. Look for it during autumn evening below the Square of Pegasus, but even from southern England it is always low down, and from northern Scotland you will be lucky to see it at all. It is a white star, 25 light-years away and 16 times as luminous as the Sun; its mass is 2.3 times that of the Sun, and its diameter size is 1,600,000 miles. It is thought to be no more than 300 million years old, and to be surrounded by a torodial-shaped dust ring with a very sharp edge. The dust is distributed in a belt between two and 3,000,000 miles wide, which is significant; can this belt contain a planer or even a swarm of smaller objects of asteroid size? Scuba has found that the band is “warped”, possibly – even probably – due to the gravitational pull of a planet. If so, there may well be other planets, some of them similar to the Earth in size and mass. Of course, this is a speculation, but it is reasonable speculation. Less than a light-year from Fomalhaut there is a faint star, TW Piscis Australis, which moves at the same speed and in the same direction through space, so that it may be a true companion. Any inhabitants of a planet in the Formalhaut system will have a spectacular view of the sky. Two of our closest stellar neighbours, both 10–11 light years away, have been surveyed by Scuba and found to be unlike each other, though both are considerably smaller, cooler and redder than the Sun. These two, Epsilon Eridani and Tau Ceti, have long been regarded as promising planetary centres. Epsilon Eridani undoubtedly does have planets, but Tau Ceti has been a disappointment. It can only be ten million years old, but there is no well-defined dust disk, and instead the star appears to be associated with a cloud of debris – comets if you like. Jane Greaves, one of the Scuba team, has suggested that there may be thousands or even millions of comets, so that if a planet exists it will be a most uncomfortable place, subjected to constant bombardment – any inhabitants will be used for seeing comets streaking across the sky. When efforts were first made to pick up radio messages from extra-solar planets, way back in 1960, these two stars were the prime candidates. Messages in

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the form of mathematical codes were transmitted, but so far the Tau Cetians and the Epsilon Eridanians have remained obstinately silent. During the programme, Chris also went to another of the great observatories, the Keck, where there are two of the largest telescopes in the world. There he talked to Geoffrey Marcy, widely (and justifiably) regarded as our leading planethunter. One way to detect them is to measure their gravitational pulls on their parent stars; the star will move to and fro very slowly and very slightly, provided that the planet is massive enough. Lightweight bodies comparable with the Earth are obviously much more elusive, but surely they must exist. Geoff Marcy discussed a particular star, IL Aquarii, otherwise known as Gliese 876, which is 15 light years away, with a diameter of 300,000 miles and luminosity little more than 1/100 that of the Sun. Three planets are definitely known. Two are gas giants comparable in mass to Jupiter; both are very hot because they are so close to the star, and have what is termed 2:1 resonance – that is to say, the inner planet makes two orbits in the same time that the inner planet takes to complete one. There is also a third planet, even closer-in, which may be no more than seven times as massive as Earth, much less substantial than Uranus or Neptune. Since the star is a feeble red dwarf, its planet must be bathed in an eerie glow and heated to a temperature of around 800°C. IL Aquarii itself is thought to be ten million years old and, like many red dwarfs, is slightly variable. There is an interesting aside. In 1998, Kevin Apps, an undergraduate student at Sussex University, paid a visit to Mauna Kea and went to the Keck Observatory. He drew up his own list of possible planetary centres, and in particular noted a faint star in Cygnus, over 150 light-years away. Diffidently, he sent his list to Geoff Marcy and his colleague Paul Butler, who used the Keck telescope, observed the star and found the planet. Its official designation is HD 187123b, but it is always known as Planet Kevin. Marcy was impressed; “It is great to have him as a colleague”. After all, not many people have made a major discovery before completing a degree. The first Scuba has been replaced by its successor, Scuba 2 (In case you are wondering what the name means, it stands for Submillimetre Common-User Bolometer Array.) Far beyond the Milky Way, we come to the outer galaxies, and in this field of research, Scuba is unrivalled. It is being used to study very remote systems which are now called Scuba galaxies; they are hard to detect at optical or infra-red wavelengths, but submillimetre radiation is more effective at passing through the dust, We see them now as they used to be when the universe was young, and apparently the larger galaxies are cannibals, swallowing up the smaller systems. Scuba galaxies are frenetically active, with intense star formation in progress all the time. To give anything like an adequate account of the observatories on Mauna Kea would take a very long time – and our programme was only an hour long. There was barely time even to mention the new, huge Gemini South telescope, with its ­segmented mirror, or the HARP spectrometer; we had to gloss over technical advantages such as adaptive optics – there was so much we had to leave out, but I hope we did enough to show that Mauna Kea is one of the world’s greatest scientific adventures. Go there if you have a chance, but do not forget that at 14,000 ft it is definitely wiser to walk rather than to run.

Chapter 11

Turkish Delight

Turkish eclipse (Credit: Pete Lawrence)

In the Sky at Night, I have covered several total eclipses, and the first of these way back in 1961, was a pioneering effort. In 2006, the sky was clear, and in our television programme all went well. P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_11, © Springer Science+Business Media, LLC 2010

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There are many glorious sights in Nature, but to me, as I have often said there is nothing even remotely comparable with a total eclipse of the Sun. For the few moments, when the brilliant solar disk is fully covered by the Moon, everything seems to be put into a state of suspended animation; only the sky changes. I am not surprised that ancient peoples were frightened and in backward countries this is still true. An annular eclipse is fascinating, but no more, and it is hard to become really enthusiastic about one that is partial. I am lucky that I have seen seven totalities, and have presented Sky at Night programmes for most of them; the first, way back in 1961, was a real pioneering effort. But the eclipse of 23 March 2006 was one that I knew I would have to miss; I simply wasn’t fit to travel to the track of totality, which ran from Brazil across to Africa, cutting through Turkey and grazing Egypt before going on to end in Mongolia. John Mason and his team from the South Downs Planetarium opted for Egypt; the Sky at Night contingent, with Chris Lintott and including Pete Lawrence and Bruce Kingsley, preferred the coast of Turkey. For once in a way, politics did not interfere. I was envious. From Selsey there was a small, partial eclipse – <20%, but as a matter of principle I decided to photograph it. Joined by Alan Schultz and Tim Wright, I watched it from my garden outside the observatory, talking to Chris enjoying the pleasant Turkish heat. I had a mediocre view through scattered cloud... In Turkey, the sky was crystal-clear and conditions could not have been better. Totality was due just before 2 o’clock in the afternoon Turkish time, and the expedition members began to make their final preparations. No two totalities are alike. Sometimes, the sky becomes really dark; generally, the light-level at mid-totality is about equal to full moonlight, but one never knows quite what to expect. The shape of the corona is more predictable because it is linked with the solar cycle; at sunspot maximum it is fairly symmetrical, while at spot-minimum it is “spiky”, with streamers stretching out in all directions. In March 2006 we had just passed the low point of the cycle, so that the corona should have been of the spot-minimum type, but Pete Lawrence’s H-alpha telescope showed several prominences, so that the Sun was not entirely quiet even though no spotgroups could be seen on the disk. Quite apart from the corona, there are various phenomena to be observed. Before totality there are shadow bands, wavy lines on the Earth’s surface seen when the disk has been reduced to a narrow crescent. Then, there are Baily’s Beads, when the sunlight streams through low-lying areas of the Moon’s limb; they were seen very clearly at the last annular eclipse. The Moon’s shadow rushes across the landscape at almost 200 mph, both before and after totality. I remember seeing that, at the Cornish eclipse of 11 August 1999, though from our site the eclipse itself was clouded out (a gentle rain fell throughout totality), and we sheltered under umbrellas, muttering words such as “Tut, tut!” and “Most annoying!”. And just as totality ends there is the wonderful “Diamond Ring”, as the first segment of the photosphere pokes out from behind its temporary screen. All these marvels were seen by the observers in Turkey, and they were suitably impressed; “awesome” and “emotive” were two of the adjectives used by our

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commentators. The temperature dropped sharply by 5 or 6°, and just before the corona shone out there was what was described as “a strange twilight”. The corona itself was of typically minimum variety, with long streamers, and there were two naked-eye prominences. This time the sky remained bright; Venus was prominent, and Mercury could be glimpsed, but Chris reported that he could not see any of the stars of Orion. Not that there was much time to look around; totality lasted for a mere three and a half minutes – and as I know from experience, the time seems to flash by. One of the most interesting experiments was undertaken by Pete Lawrence. During totality, he photographed the Moon, which was of course directly in front of the Sun and so was illuminated solely by Earthlight. The pictures he obtained were very good indeed; the outlines of the main maria were unmistakable, together with some of the craters. Totality is the only time to see the completely New Moon. Yes, Turkey was a great success, both as a television programme and, far more importantly, to give dedicated observers a chance to carry out useful work. Nobody who took part in the expedition is ever likely to forget it. Moreover, eclipse chasing is addictive, and all the team members who went to Turkey began to make plans for the next totality, on 1 August 2008, even though it did mean the slight inconvenience of travelling to North Greenland.

Chapter 12

Ringed World

Saturn from Cassini (Credit: NASA)

In the spring and summer of 2006, Saturn was well-placed, with the ring system still widely open. For this programme, I was joined by John Zarnecki, Carl Murray, and photographers Pete Lawrence, Damian Peach and Dave Tyler. Indications of liquid areas on Titan had been found, but true revelations about the “Lake District” came later – see The Lakes of Titan. What is the most beautiful object in the sky? Many people will favour a spiral galaxy, such as the Whirlpool; others will opt for a lunar crater, or a great comet with a glowing head and long, gently-curved tail – but my vote goes unhesitatingly

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to Saturn, the planet with the rings. There are plenty of spirals, many lunar craters and the occasional spectacular comet, but there is only one Saturn. It is a giant world, almost 75,000  miles across; it has a gaseous surface, and though there is a hot, presumably silicate core, the overall density of the globe is less than that of water. It is often said that if you could drop Saturn into an ocean, it would float – but finding an ocean of sufficient size would be quite a problem! Saturn’s mean distance from the Sun is 886 million miles, but even from this range it still outshines most of the stars; when it is at its best, only Sirius and Canopus outrank it. Its slow movement and its dull, yellowish glare led to its being named after the God of Time – Jupiter’s father, and his predecessor as ruler of Olympus. Saturn takes 29½ years to compete one journey round the Sun, but its day is only 10¼ days long, shorter than for any other planet apart from Jupiter; the quick spin means that the equator bulges out, and any small telescope will be good enough to show that the disk is markedly flattened. The upper atmosphere, rich in hydrogen together with some helium, is very cold, at a temperature of about −180°C. Eight satellites can be seen with a good, modern amateur-owned telescope, but of these only one (Titan) is bigger than our Moon. There are over 30 much smaller satellites, some of which have retrograde motion and are almost certainly captured asteroids. In some ways, Saturn is not unlike Jupiter. It also has cloud belts and brighter zones, but the surface is less obviously varied than Jupiter’s, and neither are there any vivid colours, so that the disk seems comparatively bland, and there has never been anything to rival the Jovian Great Red Spot. However, there are strong winds and storms, and between latitudes 35 and 36 we find a turbulent region nicknamed “Storm Alley”. It has to be admitted that for really detailed views we have to rely on space probes, notably the Voyagers of a quarter of a century ago and now the Cassini mission, which was launched in 1997 and was still sending back invaluable data over 10 years later (of course, it carried the Huygens lander which made a gentle touch-down on Titan). But we must not forget the Hubble Space Telescope, which has monitored Saturn and has sent back remarkable pictures of aurorae there. Like ours, the aurorae are caused by particles of the solar wind which are trapped by Saturn’s strong magnetic field and plunged down into the upper atmosphere, making it glow. Saturnian aurorae are brightest in high latitudes north and south because the rotational axis and the magnetic axis virtually coincide. White spots sometimes appear on the disk. The brightest of modern times have been those of 1933 (discovered by W.T. Hay, better remembered by most people as Will Hay, the stage and screen comedian) and 1990, but there was a reasonably noticeable white spot in 1996. When a new white spot appears, as no doubt will happen before too long, there is a good chance that it will be first seen by an amateur. When I began the Sky at Night series, in 1957, there was no telescope anywhere which could be used to match these – but we have entered the Electronic Era, and it has to be said that photography now looks decidedly old-fashioned. Cassini, now happily moving round the planet, is the first Saturn orbiter; Pioneer 11 and the Voyagers were fly-by missions because the Pioneer encounter was really an afterthought on the part of NASA and the Voyagers were on their way to the outer Solar System. Cassini began its main work immediately after arriving, and

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one picture was particularly spectacular; viewed from the space-craft, the Sun passed directly behind Saturn, so that Cassini lay in the planet’s shadow and the rings were brilliantly back-lit. This lasted for twelve hours, and the NASA planners wasted no time. An entirely new ring was discovered, engulfing the midget satellites Janus and Epimetheus, and this was something of a surprise. It had been suggested that meteoritic impacts on both these satellites might send a certain amount of fine material into orbit, but nobody had really expected a complete ring, albeit a very tenuous one. (En passant, I could have been the discoverer of Janus. In 1966, I was using the 10-in. refractor at Armagh Observatory, in Northern Ireland, and made three observations of the then-unknown Janus, but as I did not recognise it as being new I can claim absolutely no credit!) Early images from Cassini also showed the diffuse, extensive E-ring, with one of the familiar satellites, Enceladus, sweeping through its outer part. Cassini also took a picture of our Earth, the first time our world had been imaged from a range of over 900 million miles. It appears as a tiny, featureless dot. The F ring, outside the main system, is both “clumpy” and variable. The particles are kept in their orbits by two small shepherd satellites, Prometheus and Pandora. Cassini showed that Prometheus, a mere 63 miles in diameter, is interacting with the ring and actually pulling particles off it: Pandora is rather smaller, but no doubt acts in the same way. Enceladus, discovered by William Herschel as long ago as 1787, proved to be an amazing world even though it is so small (300 miles in diameter). There is an excessively thin atmosphere; the surface is icy, and reflects almost 100% of the sunlight falling upon it, so that the albedo is higher than for any other body in the Solar System. The main surprise was the discovery of geysers in the South Polar Region, sending water-ice particles high above the surface, so that there must be a heatsource below – just about the last thing that anyone had expected. Earlier, it had been found that Enceladus causes disturbances in Saturn’s magnetic field as it moves along in its orbit, and this indicated the presence of a conducting medium (water?) below the ice-sheet. Very probably, there really is an underground sea of ordinary water, though it would be premature to speculate about Enceladan life-forms. Hyperion and Iapetus, the two outer satellites of the “original eight”, have also perplexed us. Hyperion is cratered, and does not have captured or synchronous rotation; it takes 21½ days to complete one orbit, but is “tumbling along”, and at the moment it spins round in a mere two days. This is not the main puzzle. Hyperion is not regular in shape; it measures 255 × 162 × 137 miles, but because its density is 1½ times that of water it ought to have become a sphere. Why hasn’t it? And if it is the broken-off half of a larger body, where’s the other half? There is no sign of it... Iapetus is larger, almost 900 miles across, and has an orbital period of 79 days; this is the same as the axial rotation period. The distance from Saturn is 2,200,000 miles. Parts of its surface are bright and icy, while other parts are as black as a blackboard. Cassini results indicated that the blackness is due to a surface deposit rather than material welling up from below. (Why Cassini? Because the Italian observer G.D. Cassini paid close attention to Saturn during the seventeenth century; he discovered Iapetus, Rhea, Dione and Tethys, plus the main division in the ring

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system, now named after him. Rather confusingly, perhaps, the main dark area on Iapetus has been christened Cassini Regio.) Iapetus is curiously-shaped; 928 × 930 × 891 miles, making it seem slightly squashed. The most peculiar feature is the equatorial ridge running over 800  miles through the middle of the Cassini Region; it follows the equator almost perfectly, but does not extend on to the bright areas. It is around 12 miles wide, and in places rises to 12 miles above the ground, making it much higher than Everest and comparable with anything on Mars. All sorts of theories have been put forward to account for it. One involves a collision between two smaller bodies which merged, while according to another idea both the ridge and the dark patches were created when Iapetus grazed the outer edge of the ring system long ago. Or could Iapetus itself have had a ring? We have to admit that we simply do not know. Titan is the giant of Saturn’s family, and is unique among planetary satellites inasmuch as it has a thick atmosphere, denser than ours. The Huygens lander, carried most of its way by Cassini, made a controlled touch-down upon “spongy” ground, and sent back excellent images; obviously, it could not transmit for long, but it exceeded all expectations. Since then Cassini has made regular passes, and radar has shown beyond reasonable doubt that there are extensive seas, not of water but of a mixture of ethane and methane. Saturn and its satellites have already given us plenty of surprises, and no doubt more are in store. Which intrigues you most? The new ring, the chemical seas of Titan, the polar aurorae, the towering equatorial ridge of Iapetus or the spongy tumbling Hyperion... It is not easy to decide, but all in all I would choose the fountains of Enceladus. When William Herschel first glimpsed the satellite over 200 years ago, he surely could not have expected that the tiny speck seen in his home-made telescope would prove to be an active world, with geysers hurling ice-crystals high into space.

Chapter 13

Matter We Cannot See

Fritz Zwicky (Caltech)

Of all the problems faced by a modern astronomer, that of “dark matter” is one of the most baffling. In the Sky at Night we return to it periodically, and for this programme I was joined by Professors Gerry Gilmore and Bob Nichol. Look up into the sky, and you will see bodies of all kinds – planets, stars, galaxies. The Universe seems to be a crowded place. Yet, we now know that most of it is invisible. We can make out less than 10% of it. The rest cannot be seen at all. The man who first realised this, during the second half of the twentieth century, was Fritz Zwicky, who was Swiss by blood, born in Bulgaria, and spent most of his P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_13, © Springer Science+Business Media, LLC 2010

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working life in America. It is fair to say that he was one of the most eccentric astronomers of his (or any other) time, but of his brilliance there was no doubt at all. He examined the cluster of galaxies in the constellation Coma, measured their motions, and realised that they were moving around so quickly that they should fly apart. Yet they didn’t. Something was “glueing” them together; the cluster must contain a vast amount of invisible material. Next, the stars in rotating galaxies were not moving as they ought theoretically to do, because they did not obey Kepler’s laws. In the Solar System the centre of motion is the Sun, which also contains over 99% of the mass. Kepler’s Laws state that planets closest to the Sun must move the fastest, and the furthest must be the slowest, which is exactly what we find; Mercury is the quickest (which is why it was named after the scurrying Messenger of the Gods) and remote Neptune is the most leisurely. Now consider a spiral galaxy, such as M.31 in Andromeda or, for that matter, our own Milky Way Galaxy. The stars are rotating round the nucleus of the system, and Kepler’s Laws should apply. The Sun is about 25,000 light-years from the galactic centre, and takes 225 million years to complete one orbit, a period often referred to as the “cosmic year”. Stars further out should move more slowly, but this is not true. The rotation is more like that of a solid, spinning cartwheel. How can this be so? Again Zwicky had the answer. In a galaxy, the mass is not concentrated at the centre, but is spread through the entire system. This explains why the stars behave in the way that they do, but what precisely is the unseen material – Zwicky’s “missing mass”? He did not know, and neither do we, well over 50 years later. All kinds of suggestions have been made. Among these are vast numbers of low-mass stars, too dim to be detected; material locked up in Black Holes and therefore cut off from the rest of the universe; ordinary matter, but so tenuous that it evades us; neutrinos, with a certain amount of “rest mass” – all these were investigated, and found to be wholly inadequate. More popular today are “WIMPs” – Weakly Interacting Massive Particles, which are not the same as the matter we know, and are beyond the reach of our equipment. This may sound plausible, but it is really fudge, and an admission that we simply do not know. The one certain fact is that unless all our measurements are wrong, dark matter definitely exists. Back to Zwicky. In our Galaxy we have occasional stellar explosions which are far more violent than ordinary “new stars”, or novae, which are not really new at all; what happens is that the white dwarf component of a binary system suffers an outburst which makes it flare temporarily up to many times its normal brilliancy before subsiding back to its former state. The more cataclysmic outbursts are different; for them, Zwicky coined the term “supernovae”. They are of several different kinds, but a Type 1a supernova involves the total destruction of a white dwarf, which literally blows itself to pieces. All supernovae of this kind reach about the same luminosity, which means that we can find their distances – and since a 1a can become as powerful as all the stars in a galaxy combined, it can be seen across vast stretches of the universe. During the past 1,000 years only three supernovae have been seen in our Galaxy, the stars of 1006, 1054, 1572 and 1604 (the most celebrated of these was that of 1054, which was not a 1a; we see its remnant now as the Crab Nebula). Zwicky

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believed that he would be able to detect supernovae in external galaxies, and as usual he was right. Much later, it was found that these explosions could tell us something more. We know that the universe is expanding, and has been doing so ever since the Big Bang 13.7 thousand million years ago, and we know the speeds at which the galaxies are racing away from us, but the 1a supernovae show that they are further away than they ought to be if the rate of expansion is constant. The recessional velocities of far-away systems ought to slacken off, because of the effects of gravity. Instead, the velocities are increasing. We live in an “accelerating universe”. Albert Einstein once introduced a force which he called the cosmological constant – the opposite of gravitation. He subsequently rejected it, but it now seems that it really does exist, and is known as dark energy. There is a tug-of-war between gravitation and dark energy, and gravitation seems to be losing. What will eventually happen we do not know. And if we are puzzled by dark matter, we are even more so by dark energy. Its nature is completely unknown, and we cannot even make reasonably plausible speculations. For the moment we have to admit defeat – but only for the moment. New techniques, new instruments, new theories come along with almost bewildering rapidity, and moreover there may well appear a new Newton or a new Einstein to make a fundamental breakthrough. If so, I hope he will be willing to come to a Sky at Night studio, and talk to whoever has succeeded me as presenter of the programme!

Chapter 14

Gamma-Ray Bursters

Gamma-ray burster grb080916 NASA Swift (Stefan Immler)

The universe is a violent place, calm though it may often look. Supernovae are powerful enough, but gamma-ray bursters are even more so. I was joined by Nial Tanvir and Julian Osborn; we also heard from Helen Fraser, and Chris Lintott went down to see Tom Boles, working hard in his observatory during one of his nightly supernova hunts. P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_14, © Springer Science+Business Media, LLC 2010

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The role of an amateur astronomer has changed. When I started out, in 1930 (!), an amateur was concerned mainly with the Solar System, and usually with one particular object, in my case the Moon. There were some amateurs who were variable star enthusiasts, but not many and amateur photography was rudimentary. Today all this has changed, and though the Solar System is not neglected, amateurs have extended their scope. Photography has given way to electronics; the modest 15-in. reflector in my observatory can be used to produce images far better than any professional could have managed a couple of decades ago. Sadly, I have to admit that these developments came just too late for me; all I can do now is to watch – and admire. Searching for supernovae in outer galaxies is one favourite pastime. When a supernova appears, observations are needed quickly, and this sort of investigation does have to be left to the professionals, but a supernova cannot be predicted, and this is where amateur help is invaluable. Two amateur hunters – Tom Boles in England and the Reverend Robert Evans in Australia – have each made over a 100 discoveries. But powerful though they are, supernovae are outmatched by gammaray bursters, which are unbelievably violent. Gamma-rays are ultra-short and energetic. Fortunately for us, our atmosphere shields us, and gamma-ray astronomy could not really begin until space research became practicable, but during the late 1960s it was found that US satellites, sent up to search for evidence of Soviet nuclear tests, were picking up bursts of gamma-rays. The Russian nuclear tests proved to be as unreal as Iraq’s weapons of mass destruction, but the gamma-ray bursts were genuine, and astronomers were intrigued. On 5 April 1991 NASA launched the Compton Gamma-Ray Observatory to study them (it was named after the American Nobel Prize winner Arthur Holly Compton, a pioneer in gamma-ray research). The CGRO orbited until 4 June 2000, and carried out a full survey of the sky, discovering almost three hundred sources. Many of these could be identified; for example, the Crab Nebula is a gamma-ray emitter. But the brief, super-energetic flashes, detected by BATSE (the Burst sand Transient Source Experiment) were quite different, and nobody could make out what they were. For a time it was thought that they might be relatively local, but on 23 January 1999 Compton found that one violent burst left an “afterglow” which could be examined spectroscopically, and was obviously a long way away; its distance was given as 4.5 thousand million light-years. Now we have the Swift satellite, which was launched on 20 November 2004 and was put into an almost circular orbit at an altitude of 370 miles (600 km). It was an immediate success, and its BAT (Burst Alert Telescope) is on average detecting one burst per day. When a burst is found, Swift can slew round and use its X-ray and ultra-violet telescopes to follow the sequence of events. So far, the remotest burst observed lies at a distance of 12.3 thousand million light-years. Gamma-ray bursts (GRBs) are of two main types: short (less than 2 s in duration) and long (several seconds). Their origins are different. A long burst is believed to be due to the collapse of a hypergiant star, at least 40 times as massive as the Sun, to form a black hole. When the star runs out of fuel and energy production comes to an abrupt stop, its matter swirls downwards towards the core, and the infall results in a pair of jets emerging from the rotational poles of the doomed star; the

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shock waves break into space, and their immense energy is released in the form of gamma-rays. A short burst is more probably due to a collision between two neutron stars; which hit each other and fuse to form a black hole. The whole process takes only a second or two, and there is no afterglow. It is also possible that some flashes are due to flares from magnetars, which are stars with unusually strong magnetic fields, but we know little about magnetars, because only five had been discovered by the end of 2006. Could we be in danger from a gamma-ray burst? If it occurred within a few lightyears from us, the answer is “yes”. Even a supernova would make things very uncomfortable from a range of, say, 200 light-years, and comparing a supernova with a GRB is like comparing a match with a searchlight. However, our Galaxy does not seem to be of the type prone to GRBs, and our particular region is reassuringly quiescent. We can survey them from a respectful distance, and see how they behave – the biggest bangs since the original Big Bang almost fourteen thousand million years ago.

Chapter 15

Wandering Giants

Jupiter, photographed by Damian Peach

Jupiter was prominent in the night sky during the summer of 2006, so this seemed to be a good time to devote a programme to the giant planets and their past wanderings. I was joined in my study by Drs Richard Nelson, David Rothery and John Rogers, while in my observatory Chris Lintott and a group of observers including Pete Lawrence, Damian Peach, Bruce Kingsley and Ian Sharp turned the 15-in. reflector toward Jupiter, now showing two Red Spots instead of only one. Our Solar System is in some respects an orderly place. There are eight planets, in two well-defined groups. The four inner planets, Mercury to Mars, are rocky and comparatively small; beyond them comes the main belt of asteroids, of which only one Ceres is over 500 miles in diameter, and the only one, Vesta is ever visible with the naked eye. Next come the four giants, Jupiter to Neptune, and then the Kuiper Belt objects, of which the best-known, though not the largest, is Pluto. But things have not always been as straightforward as this. We have a good idea of the age of the Solar System, because we are confident that the Earth is about four and a half thousand million years old. The planets were formed in a rotating disk of material round the youthful Sun, which was not then as P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_15, © Springer Science+Business Media, LLC 2010

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luminous as it is now. Instabilities in this disk led to the gradual formation of “cores” containing both ice and water. These cores built up to bodies around 15 times the mass of the Earth, a process which took at least a million years. Their gravitational pulls were now great enough to collect more material from the solar nebula, and the cores or “protoplanets” making up our Jupiter and Saturn were particularly massive. The growth must have been quick by comical standards; even so, the cores of our Uranus and Neptune did not become gravitationally powerful until much of the nebular material had been dispersed. These two are composed largely of ices, and each may have no more than two Earth masses of gas. There was also the “left-over” material, with a total mass which was far from negligible; at least 35 times that of the Earth, and this had a very marked influence upon the sequence of events. Initially, Neptune may have been closer-in than Uranus. Interactions between the ice-giants and the scattered material meant that there may have been what is usually termed planetary migration, which obviously took a long time; Uranus and Neptune were driven outward, possibly exchanging places, though Jupiter and Saturn were less affected because they had built up to bodies of much greater mass. By now the migrations have stopped, and the Solar System has settled into its current stable form, but in its early history the situation was chaotic. At one time, Jupiter and Saturn may have been in a 2:1 resonance, Jupiter making two orbits round the Sun for every one of Saturn’s. Uranus has an unusual axial tilt – 98°, more than a right angle to the orbital plane. It has been generally assumed that this was due to the impact of a large body which literally “tipped Uranus over”. This does not sound very plausible. Moreover, the Uranian satellites share the same inclination, and an impact could hardly have taken them along. It is much more likely that interactions with the other giants and with the debris caused a slow, steady tip-over. In the inner part of the forming Solar System, another important factor had to be taken into account. The Sun went through a period of great activity, sending out a strong “wind” – known as a T Tauri wind, because it has been identified in other stars, of which the faint variable T Tauri was the first. Most of the light gas (hydrogen, with some helium) was blown away, leaving only the rocky materials. This is why the Earth is comparatively deficient in hydrogen, which is the most plentiful element in the universe as a whole (atoms of hydrogen far outnumber the atoms of all the other elements put together). There was a period too, when debris bombarded all the newly formed planets; we still see the effects in as much as solid planets and satellites are crater-scarred, though in some cases (notably Earth) most of the craters have been eroded away, while in others (Venus, and Jupiter’s satellite Io) the craters have been removed because volcanic activity has provided total re-surfacing long after the Great Bombardment ended, 3.9 thousand million years ago. No large planet could be formed in the zone now occupied by the main-belt asteroids, because of the disruptive pull of Jupiter. In the Kuiper Belt, the bodies are widely spaced; so far as we know there is no dense swarm. Eris is the largest known KBO at present, but even so it is no more than about 1,500 miles in diameter. There may be another major planet way out beyond the Kuiper Belt; this now seems

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unlikely, but is not impossible. If it exists, is bound to be so faint that its discovery will be largely a matter of luck. There are “irregular” objects, often with highly eccentric and inclined orbits, such as Sedna, which has an orbital period of over 10,000 years, and whose path it takes from rather beyond the Kuiper Belt out to the region of the much more distant Oort Cloud, far beyond the reach of even the Hubble Space Telescope. Some satellites of the giant planets have retrograde motion, and are certainly captured bodies rather than bona-fide satellites. The most important of these is Neptune’s attendant Triton, which is larger than Eris or Pluto. Neptune could not have captured it from the Kuiper Belt had it been single; it was probably one member of a pair – in fact a binary KBO. When approaching Neptune the two were wrenched apart; one component was “kicked away”, and the other put into a path round the ice-giant which was initially eccentric, but gradually became more circular. Binary KBO’s are very common, and indeed Pluto and its companion Charon make up such a binary; two more members of the group, Nix and Hydra, have recently been found, though both are very small. At the moment the Solar System is going through a “calm” period. Migration is to all intents and purposes suspended, and there is little chance of dramatic change in the near future. But this state of affairs cannot continue indefinitely, because the Sun itself will eventually change. In perhaps a thousand million years it will have become so luminous that our Earth will be too hot for mankind to survive; subsequently it will swell out to change into a red, giant star. However, it will have lost an appreciable amount of mass, and its gravitational pull will have weakened, so that the orbits of the planets will spiral outward, and the Earth’s distance from the Sun may increase enough to save it from being incinerated. After this may come the planetary nebula stage, and when the nebulosity has dispersed, the Sun will be reduced to a tiny, super-dense globe – a white dwarf, still orbited by the ghosts of its remaining planets. This may sound depressing – but we will not be there to see. Humanity may have departed to find a better home. At least the crisis is not imminent. We have plenty of time to work out what we can do!

Chapter 16

The Problem of Pluto

Clyde Tombaugh at the blink comparator (Credit: Lowell)

In August, there was a meeting of the Nomenclature Commission of the International Astronomical Union, held in Prague. I could not go – particularly disappointing because I was, for many years, a member of that Commission, and enjoyed working with it. John Mason did attend, and on return told us what had been decided. In 1930 Clyde Tombaugh, at the Lowell Observatory in Arizona, was carrying out a systematic search for a planet moving beyond the orbit of Neptune using a telescope which had been obtained specially for the purpose. The existence of “Planet X” had been predicted by Percival Lowell, founder of the Observatory, from slight irregularities in the movements of Neptune and (particularly) Uranus. It was not long before Tombaugh found a body not far from the position given by Lowell. It was P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_16, © Springer Science+Business Media, LLC 2010

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certainly moving far beyond Neptune, and was thought to be considerably larger than the Earth. Naturally, it was assumed to be a planet, and it was named after the God of the Underworld. (Conveniently, the symbol, PL, also fitted in with Percival Lowell’s name.) From the outset Pluto was an enigma. Its orbit was much more eccentric than those of the other planets, and was also more highly inclined (17°). Its orbital period was almost 248 years, and at perihelion it moved closer-in than Neptune; the last perihelion fell in 1989, and between 1979 and 1999 its distance from the Sun was less than that of Neptune, though its orbital inclination meant that there could be no chance of collision. More worrying was the revelation that it was not only smaller than the Earth but even smaller than our Moon and Triton, the main satellite of Neptune. With a diameter of only 1,444 miles, it simply did not fit in with the general pattern of the Solar System. A satellite, Charon, was found in 1977; its diameter was more than half that of Pluto, and its orbital period, 6.3 days, was the same as Pluto’s axial rotation period, so that the two were tidally locked. To an observer standing on the surface of Pluto, Charon would remain stationary in the sky. Could the pair be regarded as a double planet – and in any case, could the diminutive Pluto really deserve full planetary status? There was no general agreement, but the situation changed in 1992 when another planetary object was found moving further-out than Neptune. For some reason or other it has never been given a proper name, and is still known by its catalogue listing, 1992 QB1. It proved to be the first of many. By now over a thousand Trans-Neptunians are known. Much earlier, the existence of a swarm of asteroid-sized bodies in this remote part of the Solar System had been mooted by the Dutch astronomer Gerard Kuiper, and today we refer to the Kuiper Belt. (In fact, a less positive suggestion had been made previously by Kenneth Edgeworth, in Ireland, and we still sometimes hear it called the Edgeworth-Kuiper Belt.) Pluto is the brightest KBO (Kuiper Belt Object) but it is not the largest. That distinction, so far as we know, belongs to Eris, which is around 1,500 miles across, while others such as Quaoar and Varuna are comparable. If Pluto is to be ranked as a planet, then so must Eris, Quaoar and the rest. This seems to make no sense at all. I wish I had been at that IAU meeting – I would have had a great deal to say! The first official proposal was illogical; Pluto was to be retained as a planet and to add three more: Charon and Eris together with Ceres, the largest of the main-belt asteroids, even though Ceres is a mere 600  miles in diameter and Charon is the satellite of Pluto (the excuse here, that the centre of gravity of the Pluto-Charon system lies between the two bodies, was surely irrelevant; after all, the centre of gravity of the Jupiter-Sun system lies above the solar surface). It was fairly clear that the idea of keeping Pluto as a bona fide planet was due to sentiment and tradition. The proposal was put to a general vote, and was defeated. The Commission then came up with a new recommendation: A planet would be a body moving round the Sun, massive enough to assume a spherical form, and to have cleared other bodies out of its orbit. A dwarf planet would be in orbit round the Sun and to have assumed a spherical form, but without clearly its orbit. All others would be lumped together as Small Solar System bodies.

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This meant that the only accepted planets would be the familiar ones, from Mercury to Neptune; nobody was likely to quarrel with that. The dwarf planets would be Eris, Pluto and Ceres. The Committee’s proposal was accepted, but to me it seems to muddy the waters. Why should Ceres be a dwarf planet, and Pallas, the second main-belt asteroid, simply an SSSB? My suggestion would have been to class all the minor bodies orbiting the Sun as “planetoids”. But the IAU is the controlling body of world astronomy, and the die is cast. Despite this, there is still considerable resentment about the demotion of Pluto. It is now known to have three satellites, though the two new discoveries, Nix and Hydra, are very small, and a certain amount of surface detail has been made out with the Hubble Space Telescope; we will know much more in 2015 when, if all goes well, the New Horizons space-craft will swoop past it. But insofar as its status is concerned, we have to be logical rather than sentimental, and relegate it from the Premiership of the Solar System. A planetoid, certainly; A remote asteroid, possibly; A KBO, undoubtedly; But a planet it isn’t.

Chapter 17

Non-identical Twins

Venus South polar from Venus express (Credit: NASA)

Earth and Venus have often been regarded as twins. In so far as size and mass are concerned this is true enough, but they are certainly not identical. Drs Fred Taylor and David Rothery joined me to talk about the results from the latest mission there, Venus Express. During the early years of planetary space research Venus was regarded as a prime target, because it did not seem to be really hostile – probably more welcoming than Mars. Without going back 80 years to the ideas of Svante Arrhenius, who believed Venus to be in a state similar to that of the Earth during the Carboniferous P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_17, © Springer Science+Business Media, LLC 2010

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Period, when the coal measures were being laid down and the lands were covered with lush tropical vegetation, there seemed no reason to doubt that there might be oceans, and that the climate was no more than tolerably hot. The probes of the 1960s and 1970s showed that this attractive picture was very far from the truth; the atmosphere was made up chiefly of carbon dioxide, the surface pressure was around 100 times that of the Earth’s air at sea-level, and the temperature was far too high for advanced life-forms of our kind. Moreover, the clouds were rich in sulphuric acid. The U.S. Magellan orbiter surveyed the whole surface in detail, and as a potential colony, Venus was ruled out; the main attention swung back to Mars. Venus is a world dominated by vulcanism. There are lava-flows everywhere, and there are craters together with deep valleys – though impact craters are rare; there is overwhelming evidence that the whole landscape is “young”, and has been re-surfaced in what we may call the relatively recent past. Whether the volcanoes are active now is a matter for debate, but most people believe they are. Astronauts may well be able to survey Venus from a safe distance, but certainly not yet awhile, and a manned landing there is obviously quite out of the question. Venus may have been named after the Goddess of Beauty and is a glorious sight when shining down in the evening or morning sky, but conditions there are much more akin to the conventional idea of the Inferno. Now we have a new probe, Venus Express, which was launched on 9 November 2005 from the Baikonur Cosmodrome in Kazakhstan, by a Soyuz-Fregat rocket. It reached Venus on 11 April 2006, after a journey lasting 150 days, and was put into closed orbit round the planet. The orbit is eccentric; the distance from Venus ranges between 156 and 41,000 miles (250–66,000 km) and is polar, with a period of 24 h. Transmissions began immediately, and it was clear that the mission was a complete success. It was scheduled to operate until May 2009, but was still working perfectly in 2010. There is no lander; this is purely an atmospheric space-craft. In addition to analysing the atmosphere, and measuring its temperature, Venus Express carries a camera to operate in the visible, ultra-violet and near-infra-red regions of the spectrum. One early surprise was that the polar vortex, already known to exist, is like a hurricane with two “eyes” instead of one; nothing of this kind has ever been known on Earth. There is also a magnetometer. This may seem rather strange in view of the fact that Venus (unlike Mercury) has no magnetic field strong enough to be detected, but the magnetometer should be able to study the interactions between the solar wind and the uppermost part of Venus’ carbondioxide “air”. An observer standing on the surface would be able to see the Sun dimly through the clouds, and this leads on to a new theory about the Ashen Light – that is to say the faint visibility of the night side of Venus, seen from the Earth during the crescent stage. Its reality is not in doubt, but its origin has led to many explanations, some plausible and others bizarre. In the nineteenth century Franz von Paula Gruithuisen maintained that they were illuminations lit by the Venusians to celebrate the accession of a new Emperor, while others believed that there were electrical storms in the upper atmosphere, similar in nature to our aurorae but much stronger. Of course, the “Earthshine” on the non-sunlit side of the Moon is familiar

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enough, but Venus has no satellite. It is now believed that the cause is simply the glow from the fiercely hot surface passing through the atmosphere. Why are Venus and Earth so different? Surely it must be due to Venus’ lesser distance from the Sun, 67 million miles against our 93 million. When the planets were formed from the solar nebula, the two worlds may well have been similar, starting to evolve along similar lines. The Sun then was not as powerful as it is now, and probably both Venus and Earth developed seas, pleasantly warm but no more. But as time went by, the Sun’s luminosity increased. Earth was at a safe distance; Venus was not. The oceans boiled away and the carbonates were driven out of the rocks, so that the atmosphere became thick with carbon dioxide. In a very short time, astronomically speaking Venus was transformed into the inferno of today; there was what may be called a “runaway greenhouse” effect. If life had ever started there, it was ruthlessly snuffed out. This sequence of events may or may not be accurate, but it does seem plausible. Venus Express will help us to solve some of the problems which still puzzle us, but no further specialised probes there have been funded as yet, though in 2008 Messenger is due to make some observations as it flies by Venus on its way to Mercury. We may not be able to go there, and perhaps this will never be possible, but we must surely be deeply interested in the Earth’s non-identical twin.

Chapter 18

The Sounds of the Stars

Coronal loops (Credit: NASA SOHO)

Some time ago we did present a “musical” programme, but that was conventional music on cosmic themes. Our last programme of 2006 was different – the music of the stars themselves. I was joined by two leaders in the field of astroseismology, Drs Don Kurtz and Yvonne Elsworth.

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The concept of the “Music of the Spheres” is far from new; it goes back to the time of Pythagoras, and survived until a surprisingly late stage in astronomical history. Kepler, for example, took it very seriously indeed. Today everyone knows about radio waves from space, and there are people who fondly imagine that you can fit up a receiver and listen to the Pole Star. Alas, this cannot be done. Sound waves cannot travel in a vacuum, and there is very little air above a few tens of miles. On Mars, where the atmospheric pressure is very low (less than 10 mbar, against around 1,000  mbar at sea-level on Earth), even the most raucous auctioneer or football referee would struggle to make himself heard. Sound-waves are pressure waves, and depend upon a medium of some sort. The more rarefied the medium, the higher the frequency of sound waves within it. Blow up a balloon filled with the light gas helium, inhale some helium from the balloon, and your voice will be very squeaky until you clear your lungs! Helioseismology is the study of the propagation of acoustic (pressure) waves in the Sun; it has turned out to be immensely valuable. The waves are generated by convection near the Sun’s surface – that is to say, in the convection zone – and some of the frequencies make the Sun “ring like a bell”. They reach the bright surface or photosphere, and set up oscillations which we can detect by means of the familiar Doppler principle. Even from close range, we would be unable to hear the solar music. Our ears can detect sounds over only a limited range of frequencies. For example, not many people can hear the squeaks of bats. (I can, but even now, when I am over 80, I still have rather exceptional hearing.) Explosive events at or near the Sun’s surface seem to trigger acoustic waves which penetrate to a certain depth and are then bounced back when they encounter gaslayers of different densities. A sort of “loop” forms, and the Sun would be a noisy place – if we could hear it. The acoustic waves which bounce between the ends of the loops produce a phenomenon known as a standing wave. The loops – essentially magnetic phenomena – have been said to be analogous to a simple guitar string; pluck the string, and you will hear a musical note. In the cosmic version, the sound waves generated travel in the Sun and are linked with vibrations, which can be tracked. Among the results from helioseismology is the revelation that the Sun spins in a rather unexpected way. Of course, it has long been known that we are dealing with differential rotation; at the equator, the rotation period is 26 days, while at the poles the period is 9 days longer – to measure this, all we have to do is to track sunspots as they are carried across the disk. Obviously, we cannot see the far side – the Sun is not transparent! – but sound waves travel through the globe comparatively quickly, and by studying them we can actually find out what is happening there. This is important, because outbursts such as solar flares can not only cause disruption of radio communications, but can also prove really dangerous to astronauts who are outside the protective shield of the Earth’s atmosphere. If the new methods can locate an active area on the far side, we can easily tell when the rotation will bring it on to the Earth-facing side – and astronauts can make sure that they are protected. It takes an acoustic wave only one and a half hours to travel right through the Sun, and the inner regions of the Sun rotate in the way that a solid sphere would do.

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The Sun is a normal star, and other stars may be expected to show the same acoustic phenomena – and so they do, provided that they are not too hot or too cool. On star which has been studied with particular care is the brightest component, of the Alpha Centauri system. Alpha Centauri shines as the third brightest star in the sky, inferior only to Sirius and Canopus; it is too far south to rise over Europe (our two brightest stars are Sirius and Arcturus). At a range of 4.3 light-years, Alpha Centauri is the nearest of our stellar neighbours; there are two bright components, one rather more luminous than the Sun and the secondary (B) rather less so. The third member, Proxima, is a dim red dwarf. Alpha Centauri A is of solar type, and acoustically it seems to be very much the same. The sounds are far too deep to affect the ears of beings like ourselves, but we have enough information to work out what they would sound like if they could be brought into our range. A comparatively small star will have a higher note, while a huge, red supergiant such as Betelgeux in Orion will be deep and sonorous. An interesting recording has been made from the sounds of the stars – it has been likened to a rather obscure piece of classical music; every vibrating star makes its own particular contribution. One wonders what Pythagoras or Kepler would have thought!

Chapter 19

Space-Man

Piers Sellers assembling the ISS (Credit: NASA)

I have had many guests on the Sky at Night, but none more welcome than the British astronaut Piers Sellers. You can imagine my reaction when the BBC scheduler, Mr  George Dixon relegated the programme to two o’clock in the morning. On the previous month he had forgotten to schedule the Sky at Night at all, with the result that the programme was transmitted a week late. Mr Dixon has been deleted from my Christmas card list. At least he could not stop the Piers Sellers programme repeats on BBC4 and BBC2. I will say no more! The first space-man was a Russian, Yuri Gagarin. Since then, many astronauts have flown; all nationalities have been represented, and that includes Britons. Our first true astronaut was Michael Foale; the second was Piers Sellers, who did me the honour of joining me for the first Sky at Night programme of 2007. He would not have been able to join me for my first programme, in 1957, as he was then at P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_19, © Springer Science+Business Media, LLC 2010

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the early age of two! Like Michael, he had to take American citizenship before being allowed to start training, but he was born at Crowborough in Sussex; educated at Cranbrook School in Kent, and graduated with degrees from the Universities of Edinburgh and Leeds. It would be difficult to be more British than that – and his wife is English. He was selected by NASA in 1996, and flew his first mission in 2002, during which he performed three space-walks. His second foray, in 2006, took him to the International Space Station, and he was not long down when he broadcast with me from my study. No guest could possibly have been more welcome, and this was also a very special Sky at Night in another way; it was our 650th programme. Quite a milestone. Of course I had to ask him the standard questions, and rather than trying to quote him verbatim, I will do my best to summarise what he told me. First, the Earth as seen from space: “glorious – blue, and glowing”. One can see that our world really is a huge ball in space. Everyone expects you to see stars, but you don’t, because the Sun is blindingly bright, and staring at it is not to be recommended. Of course, the sky is jet-black. When you are working in the shadow of the Station, there are bright lights to make sure that you can see what you are doing. The only answer is to find a secluded niche and turn out your helmet light. Zero gravity – weightlessness – can be initially uncomfortable, but one soon becomes used to it, and it becomes fun. Remember, the ISS is not like the early, cramped space-craft; it is as roomy as a 747, and one can have the feeling of flying around, though it is important not to forget inertia. The American section of the station is a little like a workplace, while the Russian quarters are decidedly more homely. Food? Well, it is palatable enough, and there can be unexpected delicacies; the Russians, for example, are rather fond of jellied eels in aspic. At present the crew of the ISS usually consists of three people, but this is increased when a Shuttle arrives, and eventually there will be six resident astronauts. Sleeping is not a problem, though care must be taken to avoid drifting around; with no definite “up” or “down”, things can seem rather curious until you get used to it. There is plenty of work to do in the Station – for example medical tests and experiments, and researches into the behaviour of various materials under conditions of zero gravity; for example it is easier to produce perfect crystals. Piers has taken part in two missions so far, one lasting for eleven days and the other for thirteen, and no doubt there will be more. I asked him whether he would like to pay a visit to the Hubble Space Telescope, and he replied that he most certainly would, but the astronauts for the next repair mission had already been selected. The HST must be somewhere near the closing stages of its career, and its successor, the James Webb Space Telescope, will be in a different sort of orbit, staying in one of the so-called Lagrangian Points, where the gravitational pulls of the Earth and the Sun cancel each other out. This means that the JWST will always be about a million miles from the Earth – out of reach of any repair mission. Piers currently holds the “space-walking” record from the ISS; he has made six forays, adding up to a total of 42 h. He enjoyed them. Things were not very different from what he had expected; for his first walk (more properly called EVA, Extra-

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Vehicular Activity) he had the impression of “flipping over” as soon as he emerged from the hatch. Working during an EVA can be tiring; you move around by finger pressure on the Station’s rail, but a jet-pack is carried in case of emergencies. I asked him whether he had had any alarming experiences; he told me that on one occasion he found that his oxygen was running low, so that he had only nineteen minutes to re-enter the Station, but was not anything in the way of a crisis, as his work programme had already been completed. The jet pack could actually be used outside, but this was never done under normal circumstances. One more question about space-walks: Is there anything you had to do that you didn’t want to do? His reply: “Yes – come back inside!” One point he made was that from space, you realise how shallow the layer of atmosphere is. Thunderstorms give the impression of extending about half-way up from the ground. Aircraft condensation trails over the Atlantic could be made out, and the scene was always changing. I could not resist asking Piers what he expected to happen in the foreseeable future. I wondered whether he would be more accurate than Arthur Clarke was in a very early Sky at Night programme (about 1960?) when he anticipated men on the Moon before 1970, Lunar Bases by 1980 and the first trips to Mars well before the end of the twentieth century. He was right about the first of these predictions, but not, alas, the other two. (I was even less correct; I doubted whether men would reach the Moon much before 1990.) According to Piers, the ISS will last until 2020 at least; its main function has been to show that habitable stations really are practicable. Within ten years there could be the first Lunar Base, probably in Shackleton Crater in the south polar region, where there are areas which are in almost permanent sunlight. Before then, unmanned missions will have deposited equipment on the surface ready for the astronaut’s arrival. The first journeys to Mars – between 2030 and 2035. It is an alluring prospect. I will not be around to see it, but I have no doubt that Piers will. He may now carry an American passport, but it is good to know that he is British-born, British trained and thinks in a British way. I am proud to know him, and proud to have welcomed him as a guest on Sky at Night.

Chapter 20

Exploring Mars

Spirit on Husband Hill (Credit: NASA)

Mars was very much in the news at the start of 2007. Of course we had devoted plenty of programmes to it over the years, but it seemed a good moment to bring viewers up to date, and a major conference that was being held at the Jet Propulsion Laboratory in California, so Chris went there and talked to some of the leading astronomers, including Dr Steve Squyres. P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_20, © Springer Science+Business Media, LLC 2010

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In a way it seems strange to recall that our ideas about Mars have changed so dramatically over the past few decades. Opinions oscillated wildly to and fro. First, the polar caps were snowdrifts, then they were solid carbon dioxide, then they were due to hoar-frost no more than a millimetre thick, then they were back to snowdrifts, made of water ice mixed with CO2 ice; the dark areas were old seabeds coated with vegetation, then made up of hygroscopic salts which darkened with the arrival of moisture-laden winds from the poles, then areas where the dusty covering had been blown away, and then areas covered with lava-flows; the bright regions were dustdeserts made of sand, then coloured minerals such as felsites and limonite; Phobos and Deimos, the two midget satellites, were captured asteroids or (according to one eminent Soviet astronomer) artificial space-stations, built by Martians. The best advice was “Make up your own mind!” For our February programme, there seemed no point in repeating what we had said earlier; it seemed best to take a few salient points, and deal with them properly. First, there is the all-important question about the nature of the polar caps, which, remember, can be very extensive, and which wax and wane with the Martian seasons. A life-supporting world must provide a few essentials, and in particular there must be water in some form. If the caps had turned out to be carbon dioxide, we would probably have had to abandon any ideas not only about Martians, but about even the most elementary, single-celled organisms. Steve Squyres was quite definite. The caps are of ordinary ice, and they are thick, so that from this point of view Mars is much more co-operative than the Moon or, for that matter, Venus. Also, there is no longer the slightest doubt that Mars was once much wetter and much warmer than it is today. Rivers flowed – and the great volcanoes were active too. The Red Planet was anything but changeless and sterile. Not that it is quite changeless at the present moment; small new impact craters have been found, and there is strong evidence that water occasionally gushes out from below the surface, running down through valleys in crater-walls before evaporating or freezing. “If you were standing there and saw a torrent of this kind coming toward you”, was one comment, “you’d probably want to get out of the way”. Many of the recent missions – Global Surveyor, Odyssey, Mars Explorer, Mars Reconnaissance Orbiter and so on – have either searched for life, or have concentrated upon areas where it might be expected, assuming of course that it exists at all, which is still a very open question. Britain’s Beagle 2 failed, alas; nothing was heard from it after arrival, and though we are fairly sure that it did land, and it may be done so either intact, or else in a shower of fragments. (There have been other failures too, notably a very ambitious Soviet mission, and NASA’s Mars Observer, while another US probe, Mars Climate Orbiter, was lost because of confusion between Imperial and Metric units!). Up to now there have been no positive results, and surface life may be ruled out because of radiation levels, but the jury is still deliberating. The NASA rovers, Spirit and Opportunity have been triumphantly successful, and were still functioning perfectly when our February programme was transmitted – long after the end of their expected lifetimes. Both have had problems; for instance one of Spirit’s wheels is “dragging”, while Opportunity spent some time stuck in a

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drift, and extricated itself only with difficulty. But Mars has been helpful too. Dust accumulating upon their upper panels threatened to cut off all transmissions, but in the nick of time convenient winds blew the dust away. Both rovers have been photographed from orbit, and both have traversed fascinating and varied territory. One of the most spectacular features is Victoria Crater, visited by Opportunity, with its bays and inlets, while Spirit scaled the Columbia Hills inside Gusev Crater, probably an ancient lake. Everywhere there is evidence of past water activity – and, of course, past eruptions. The giant volcanoes of Tharsis must indeed have been awesome, and we cannot be sure that they are now extinct. They may merely be dormant. There was also the “Face on Mars”, originally imaged by the Viking orbiters of the 1970s. One has to admit that it did look like a face – and predictably caused great excitement among flying saucer enthusiasts. Perhaps disappointingly, new images taken from different angles show that it is a very ordinary rock structure. There is nothing in the least unusual about it. Plans for returning to Mars are well advanced, both by NASA and by the European Space Agency. The search for life will continue, and talk of a fully fledged Martian Base can no longer be dismissed as science fiction. When this will be possible depends partly upon progress in technology, and partly upon politics. Of one thing I am certain: the world of 2080 will not be the same as that of 2008. Either we will be preparing to set up bases on Mars, or else the remnants of Homo sapiens will be trying desperately to survive in radioactive caves. I have always felt that the first travellers to Mars will not go straight there, but will stop-off first at Deimos which is after all a natural space-station and might have been put there especially for our benefit. I would favour Deimos rather than Phobos mainly because it is further out, whirls along at a less giddy speed, and would give us a better overall view. However, the Russians prefer Phobos, and even hope to bring samples back for analysis. Phobos is only about as far from the surface of Mars as London is from Aden, and it has even been suggested that when a Martian crater is formed some material may have been hurled upward violently enough to spatter on Phobos. Studies of Stickney, the largest crater on Phobos, link it with the 300-mile impact crater Lyot on Mars, which is well-formed and is thought to be between 3 and 3½ million years old. Whether this is true or not, Phobos and Deimos may eventually turn out to be remarkably useful. Next year – before this edition of the Sky at Night is published, I am sure that we will have to do yet another Mars update. Much of what I have written here will need modification, but I doubt whether much of it will be downright wrong, as our ideas of 1957 have turned out to be.

Chapter 21

The Lakes of Titan

Lakes of Titan (Credit: NASA JPL)

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The Lake District of Triton (Credit: NASA JPL)

It was only a year since our last programme about Saturn, but as the planet was high in the sky, and the Cassini spacecraft was sending exciting new data, we decided to return to it, but this time to concentrate upon Titan. As before, John Zarnecki and Michelle Dougherty joined me. I think it is fair to say that Cassini has been one of the most successful of all space missions up to the present time. Quite apart from carrying the Huygens lander, it has carried out a prolonged survey of Saturn and its satellite system; it has imagined the clouds which look rather like “a string of pearls”, it has looked for the strange spokes in Ring B, which seem to be very variable; it has given new information about the fountains of Enceladus, which are now thought to be fuelling the E Ring, and it has provided us with firm evidence about the existence of broad seas on Titan. Titan, remember, is much larger than the Moon, and slightly larger than Mercury, though not so massive. Alone among planetary satellites, it has a thick atmosphere – denser than ours, made up largely of nitrogen, though the lack of free oxygen, together with the intense cold, rules out advanced life-forms of our type. Huygens, which made a controlled landing, touched down upon a surface with “about the consistency of wet sand”, and there were indications of drainage channels. It was thought possible that the area was part of a coastline, but there was no clear sign of a sea or a lake within the range of the grounded probe’s cameras. There had almost certainly been a fairly recent shower, not of water but of liquid methane; cloudcover on Titan is constant (which is why we had never before been able to see the actual surface), and there may well be methane drizzle all the time.

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Long after Huygens had lost contact, Cassini itself went on with its programme, during which it flew past the satellites and sent back pictures and data. On 22 July 2006 Titan was the target, and Cassini returned radar images of areas in high northern latitudes which caused great excitement at Mission Control – and beyond, because the images showed numerous very dark patches with sharply edged boundaries. A rough area will look bright in radar, while a smooth area will look black. The Titan patches were so featureless that they could hardly be anything other than liquid areas: in other words, lakes. They were of considerable size, in one case at least 40 miles long. Finer details could be made out. At a second pass, on 23 September 2006, Cassini showed two lakes at latitude 73°N, 40°W, which were each about 15 miles across, and were joined by a narrow channel (somebody at JPL called them “kissing lakes”). The right-hand lake had lighter patches within it, indicating that it may be starting to dry out with the approach of northern summer, and patchy lakes were also found elsewhere, so that we are presumably seeing deep lakes, shallow lakes and lakes which have either dried up completely or else are in the process of doing so. The Saturnian seasons are different from ours. The tilt of the planet’s axis is much the same as that of Earth, but Saturn takes 29.5 years to complete one journey round the Sun so that the seasons are a great deal longer. This also applies to Titan because like all the other major satellites (except Iapetus) its orbit lies almost in the plane of Saturn’s equator, and a lake there has ample time to form and then dry out again partially or completely. Everything happens at a very leisurely pace. Let us admit that we have no final proof that the radar-smooth areas are lakes, but I would estimate that the odds in favour are around 99.9%, and it is very difficult to suggest any other explanation. At Titan’s surface temperature of −180°C, the lakes cannot contain water and must consist of methane mixed with a certain amount of ethane. They are thought to be the source of the methane gas which accounts for 5% of the satellite’s atmosphere. Over millions of years sunlight breaks down atmospheric methane, and there has to be a way of replenishing it. Much more work remains to be done, both by Cassini and future missions, and no doubt there will be other surprises in store, but at least we have found a world unlike any other in the Solar System. It is a fascinating place – and one day, perhaps, astronauts will go there and explore the Lake District of Titan. Saturn was past opposition, but still prominent in the evening sky, with the rings practically edgewise on. The Cassini probe was still orbiting, and in full order, sending back amazing data. Clearly we should discuss it. I had two regular and distinguished guests: Carl Murray and Michelle Dougherty. Carl had been making special studies of the rings, and of course the main revelation was the discovery of the new ring associated with Phoebe. It is extensive and very tenuous, with retrograde motion, and formed from material knocked off Phoebe itself. Some material is wafted inward and falls on Iapetus, darkening the leading hemisphere; at least this solves the problem of Iapetus yin-yang appearance. But even more exciting are the chemical lakes of Titan, and here Michelle is the leading expert.

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Glint from sunlight reflected from a lake adjoining Kraken Sea

What is the loveliest object in the sky? Opinions differ, but my vote would unhesitatingly go to Saturn. It is not the only ringed planet, but it is in a class of its own. It is a gas giant, much larger than any other planet apart from the other gas giants. Jupiter (Uranus and Neptune are better classes as ice giants). Its equatorial diameter is almost 75,000 miles, but its rapid rotation – less than 11 h – makes the equator bulge out so that in shape Saturn resembles a slightly squashed orange. The orbital period is 29½ years. The axial inclination is slightly greater than that of the Earth, and the rings and the orbits of all the main satellites apart from Iapetus lie practically in the plane of the equator. There is a strong magnetic field, and it is worth noting that the magnetic axis is virtually coincident with the axis of rotation. The rings are made of water-ice particles, ranging in size from tiny pebbles up to blocks at least as large as a car. Three rings are within the range of a small telescope, two bright (B and A) and one semi-transparent (C). Others, much more elusive, lie closer in or further out. The bright rings, A and B, are separated by a gap known as the Cassini Division in honour of its seventeenth century discoverer; the Italian astronomer G.D. Cassini, a pioneer telescopic observer of Saturn. The current spacecraft is also named after him.

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Saturn has a wealth of satellites, but only a few are over 100 miles in diameter, and most of the rest are probably captured asteroids. The larger members of the family have differing features of interest; tiny Enceladus with its geysers of ice particles, Mimas with its “death star” crater, Dione with its icy cliffs, Iapetus with its weird equatorial mountain range… But Titan is really big and actually larger than Mercury. It has an atmosphere twice as dense as ours, made up chiefly of nitrogen, and it is of course bitterly cold. Saturn’s mean distance from the Sun is 886,000,000 miles. It is difficult to visualise any life, at least of our kind. The first spacecraft to pass by-pass Saturn were Pioneer 11 (1979), Voyager 1 (1980) and Voyager 2 (1981). Good images were obtained, but those of Titan were not particularly informative, because they could do no more than show the uppermost clouds of the dense atmosphere. What the surface was like remained a mystery. The existence of “seas” was not ruled out, but not filled with water; they would be chemical, with methane and/or ethane. Cassini was the first Saturn orbiter. It arrived in 2004, and was an immediate success. It carried a small lander, Huygens (named after the Dutch astronomer who discovered Titan in 1655) which released and made a controlled landing on Titan’s surface. It came down on solid ground, said to have the same consistency as damp sand. There were features that looked like drainage channels. Presumably, there had been a recent methane shower. Contact could not be maintained for long, but the landing was certainly one of NASA’s greatest achievements to date. Cassini continued happily on its way, and regularly sent back data and images of Saturn and the satellites. Titan was a prime target. It was expected to be fascinating, and it did not disappoint us. The existence of chemical seas and lakes was proved beyond all doubt. Radar results gave the essential clue. Smooth areas are radar-dark, and a sea-surface is obviously, completely smooth. Most of the seas and lakes seem to be in the polar regions. Anything over about 250 miles in diameter is conventionally classed as a sea (mare) anything smaller as a lake (lacus). In the north, there are three seas, Kraken Mare, Ligeia Mare and Punga Mare – huge features filled with methane plus some ethane. Kraken, the largest of them is about 730  miles in diameter, roughly the size of the Caspian Sea. It was named after a legendary Norwegian sea monster. It seems to be rather irregular in shape, and contains an island, Mayda Insula. On 8 July 2009 Cassini’s instruments observed a spectacular reflection from a lake Jingpo Lacus, adjoining the northern coast of Kraken. Ligeia and Punga are of the same type as Kraken, though smaller. The real “lake district” is far north. There are more than a dozen named lakes, notably Jingpo Lacus (diameter 150  miles). There are fewer known lakes in the south, of which the largest is Ontario Lacus (145 miles), about equal to our Lake Ontario. Ontario was actually the first lake to be identified, on 21 December 2008. However, we must remember that our mapping of Titan’s surface is very incomplete, and the long seasons mean that there will be major changes in the seas and lakes over the course of a Saturnian year. Whether men will ever reach Titan remains to be seen, but it will certainly not be yet awhile. Frankly, it must be a gloomy place, with permanent cloud cover and

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probably persistent methane drizzle. There may be a gentle lapping of waves at the shore, but that is all, and indeed the calm may be constant. I suppose that life in the chemical seas cannot be entirely ruled out, but it does seem highly unlikely. Of one thing I can be certain; no future astronauts will be able to organise fishing parties in the Kraken Mare!

Chapter 22

Fiftieth Anniversary

Fiftieth anniversary

When the first episode of the Sky at Night was transmitted (live!) on 24 April 1957, it never occurred to me that I would still be broadcasting after an unbroken run of half a century. But I was – and believe me, my Fiftieth was a joyous occasion. There were in fact three programmes, one of which was organised separately by the BBC and about which I knew little before it was transmitted. I was both honoured and staggered by the number of people who were on it – including most of our leading astronomers; some distinguished MPs – Charles Kennedy, Lembit Opik; equally distinguished public figures – Sir Richard Branson, Sir Tim Rice; musical and theatre figures – Dame Evelyn Glennie, Mylene Klass; pioneer astronauts – Neil Armstrong, Buzz Aldrin; space pioneer Sir Arthur Clarke, plus almost all my true, personal friends. It was overwhelming. There were also some who are no longer with us, notably one of the closest friends I have ever had, Michael Bentine. I was seen doing a sketch with Morecambe and Wise, and there was even a clip taken during P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_22, © Springer Science+Business Media, LLC 2010

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a cricket match, just as I came on with my leg-breaks, delivered at the end of my long, leaping run. On film I tiptoed through the tulips with Magnus Pyke. Memories aplenty … Special tribute to Jonathan Ross for his expert comparing, and to Philip (Pip) Jennings, aged 12, who spoke on behalf of the British Astronomical Association. I append here (a) a list of the people at my actual party on 21 April; I hope I have not left anyone out, and (b) a list of the participants in the programme who were not actually present in person. I am particularly proud because I doubt whether there has ever before been such a gathering organised to pay tribute to one person – and an amateur astronomer at that. What more can I say – except “Thank you?” There was a good deal of discussion about our actual Fiftieth programme, and eventually it was decided to look back and forward in a novel way. First we would return to 1957 and give as accurate a reconstruction as we could; John Culshaw, wellknown for his TV impersonations, would play me as I used to be then, and using a Time Machine the PM of 1957 could talk to the PM of 2007. Next, look forward at the next fifty years; a suitably age-increased Dr Chris Lintott would give reports from Lunar Base, and from Port Lowell on the surface of Mars. There would follow a broadcast from the Sky at Night studio in 2057, with Professors Chris Lintott, John Zarnecki and Brian May… Initially I was afraid that the programme would end up something like out of Monty Python, but at the end most viewers felt that the recipe worked, even though I have to add that there were a few dissenters. John Culshaw was brilliant; he really did look like the 1957 version of me, and he had all my mannerisms. Chris Lintott and John Zarnecki demonstrated their very considerable acting skills, and of course Brian May is unique (incidentally he was in the throes of completing his PhD thesis at Imperial College, London, put on hold years earlier when the Queen Group monopolised his main attention; his subject was Zodiacal dust). The programme was tricky to produce. Jane Fletcher and her team coped admirably, and got everything absolutely right. I think that our reconstruction of the 1957 studio was accurate, and as a “Time Lord” I felt nostalgic. The opening music, “At the Castle Gate” by Sibelius, has never changed; I chose it, and we have only twice used anything else, though for our last programme about Halley’s Comet in 1986, the Band of the Royal Transport. Corps played us out with the march which I had composed for the Halley’s Comet Society. (This flourished between 1968 and 1988 and was great fun, perhaps because it had no aims, objects or ambitions, and claimed to be the only completely useless society in the world with the obvious exception of the European Parliament. It really ought to be revived.) Let me add here that one thing absent from an ordinary Sky at Night programme is background music. At the present moment, all producers seem to be obsessed with it; it destroys the credibility of a science programme, and dumbs it down to the level of Listen with Mother. It also sounds so amateurish, and does its best to swamp the participants in the programme; even news bulletins are not immune. We did once have a background “executive producer” who wanted to make extensive

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changes, and to “modernise” everything. I firmly declined, but she was an unmitigated nuisance for a couple of months before being chased away. Back to 1957; by good fortune (nothing more I assure you!) we were greeted by a bright comet, Arend-Roland, distinguished by its sunward spike, which looked like a reverse tail but was in fact due to the illumination of material left in the comet’s orbit as it moved along. Alas, even if the Sky at Night lasts for a million years, we will never see Arend-Roland again. As it moved outward after perihelion, it was affected by the gravitational pull of Jupiter and thrown out of the Solar System, to wander permanently among the stars. Where it is now, I know not – but it was a good omen, and I wish it well… I had what I hope was an informative conversation with my 1957 self. So much has happened since then, and there many older ideas have been found to be wrong. For example, it was widely believed that there were extensive vegetation tracts on Mars, that Venus was partly covered by ocean, that the four Galilean satellites of Jupiter were barren and rocky, that Pluto was a bona-fide planet, and that many of the Moon’s craters were volcanic. I was wrong there, but at least I was right about the far side of the Moon, which proved to be just as cratered and just as bleak as the regions we have always known. In 1957, I was predicting that the first lunar journeys would be made around 1980–1985, so I was over-pessimistic; Arthur Clarke got it right. Dealing with the 1957–2007 period was at least factual, but 2007–2057 was speculation, and I would love to know how good our speculations were. Chris Lintott and John Zarnecki tramped around Mars, and enthused about the discovery of lowly life-forms there; the great Martin Rees radio telescope on the far side of the Moon picked up radio signals from the Milky Way that seemed to be non-natural; Bob Nichol explained how the nature of dark energy had been solved – and so on. We did not want to go too far, but at the same time we wanted to be bold. Perhaps, whoever is presenting the Sky at Night in 2057 will look back at these recordings and chuckle “How quaint!” On the other hand, he may say “However did they hit that nail on the head?” I will not be around, but Chris Lintott will be younger than I am today. Well, I hope that our programmes have helped some people, and at least we hold the record for longevity. No doubt it is a record that will be broken eventually, but not, I think… for a long time yet, because half a century’s continuous run is the sort of thing now becoming rarer and rarer. The programme must have been officially classed as a success, but I can claim no personal credit for this because all the cards were stacked in my favour, and I know quite well that I was simply the link-man who happened to be in the right place when space research suddenly became part of everyday life.

Chapter 23

SuperWASP

SuperWASP (Credit: David Anderson)

P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_23, © Springer Science+Business Media, LLC 2010

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Are there other worlds similar to Earth? There probably are, and searches are being carried out using programmes such as SuperWASP. Dr Andrew Collier-Cameron joined me to give me the latest news. Have you heard about SuperWASP? I assure you that it has nothing to do with insects. WASP here stands for Wide Angle Search for Planets – that is to say, planets of other stars. When I presented the first Sky at Night programme, we had no proof that there were such bodies; we thought they were probably there, but we did not definitely know. Today we have detected over 200, and one of these, known by its catalogued number of Gliese 581c, may well be suited to the development of our kind of life. Direct observation is remarkably difficult. A planet is much smaller than an ordinary star, it shines only by reflected light, and its feeble glow is drowned by the presence of its parent star. This means that we have to track them down by less direct methods, and there are several ways of doing this. The first is gravitational. A planet orbiting a star will make the star move to and fro to either-side of its mean position – very slightly and very slowly, but by an amount which is detectable with modern equipment. This method, known as the “wobble,” has been used to make the greatest number of discoveries up to the present time. The second is the “transit” technique. When a planet passes across the face of its parent star, as seen from Earth, a tiny fraction of the star’s light will be blocked, and the star will show a slight, brief drop in magnitude. Obviously, the amount of dimming will depend on the size of the planet. Most of the planets tracked down by these two methods, plus a third which involves “gravitational lensing,” are much larger than the Earth, and much more akin to Jupiter; in general, they are very close to their parent stars and are fiercely heated, so they are usually called “hot Jupiters.” What we really want to find, of course, is an Earth sized world at an Earth-type temperature. We may be on the verge of success, but first let us look briefly at some of the stars which have been regarded as promising candidates as centres of what we may call solar systems. The first two were Tau Ceti and Epsilon Eridani, both of which are within a dozen light-years of us, both of which are easily visible to the naked eye, and both are not too unlike our Sun, though smaller, redder and less luminous. In 1960, radio astronomers in America actually tried to see whether they could pick up signals from any operators living on planets there. They failed, which is no surprise, and it has now been found that the two stars are very different. Tau Ceti has been a distinct disappointment. No planet has been found, but in 2004 Jane Greaves and her team of British astronomers found that there is a large amount of orbiting debris – comets, if you like – so that a planet would be under constant bombardment, and living there would be most uncomfortable. However, Epsilon Eridani is much more promising (it does have an old Arab proper name – Al Sadirah “the Returning Ostriches” – though it is hardly ever used). The spectral type is K, and the luminosity little more than a quarter that of the Sun. A dust disc was found round it in 1988, before the discovery of the first extra-solar planet, at about the same distance as that between our Sun and the Kuiper Belt, and there is definitely one planet, 1½ times as massive as

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Jupiter, with indications of another. Searches will be made for a lower-mass planet where conditions may be tolerable. This means that it would have to move round the star in which is variously termed the star’s ecosphere, zone of habitability or Goldilocks zone: the region where water would neither boil or freeze, naturally assuming the presence of an atmosphere of sufficient density. In our Solar System, Venus is at the extreme inner edge of the zone, Mars at the extreme outer edge and Earth comfortably in the middle. Since Epsilon Eridani is less massive than the Sun, its ecosphere will be closer-in, while with a more powerful star the ecosphere will be further out. Actually, few giant stars are known to have planets. The first was Iota Herculis, otherwise Edasich (the Male Hyena), which has evolved through its main sequence stage and has become a K2-type orange giant, 100 light-years away; it is currently 40 times as luminous as the Sun but is much larger. In 2002, a massive planetary companion was found, with a mass of over eight times that of Jupiter, moving in a highly eccentric orbit and with a period of 1½ years. But – at least eight Jupiter masses and possibly rather more – could Edaisch be attended by a brown dwarf star rather than a planet? A star is formed from a collapsing cloud of dust and gas. As it shrinks, the core temperature rises; when it has reached 10,000,000°, nuclear reactions begin, and the star starts to shine. But if the initial mass is too low, the core temperature will not soar to the critical value, and nuclear reactions will never be triggered off. A star of this kind is known as a brown dwarf (misleadingly, because it is actually dull red) and will go on glowing for an immensely long period before all its energy leaves it, and it ends up as a cold, dead black dwarf. A planet, on the other hand, builds up by accreting from debris associated with a star, and its surface will never become hot enough to shine. Jupiter, Saturn and Neptune in the Solar System so have hot cores, but their temperatures amount to a few thousands of degrees rather than millions. Structurally and in evolution, a planet is quite different from a brown dwarf. The companion body of Edasich is quite definitely a planet, though not a very inviting one. Other naked eye stars are believed to be planetary centres, among them Vega, Fomalhaut and Pollux, but to date we have found only one planet whose surface temperature seems to be much the same as that of Earth. The parent is a dim red dwarf in Libra, Gliese 581, 20½ light-years from us. The star’s luminosity is a mere one-hundredth that of the Sun, so that it really does rank as a cosmic glowworm and its zone of habitability will be close in. The planet, around five times as massive as the Earth, moves in an almost circular orbit well within the zone, at a range of around 7,000,000 miles. If there is an iron-rich core and rocky mantle, the surface gravity would be about twice ours, which would be tolerable and would no doubt suit any inhabitants. The trouble is that we do not know the axial rotation period, and if it is “locked,” so that the same hemisphere is always turned starward, the chances of finding life there will be greatly reduced. As yet this is as far as we can go. Unquestionably many more extra-solar planets will be discovered during the next few years, and it will be surprising if some of them are not Earthlike, but we have to find out whether life will appear wherever conditions are suitable for it. Time will tell – we hope.

Chapter 24

Scorpion in the Sky

Scorpio (Credit: Angel Lopez, Jose Caballero)

Scorpius is undoubtedly one of the most magnificent of all the constellations. It is never high up from Britain, but at least we can see part of it. It is at its best during the summer, so with John Mason I decided to have an in-depth look at it. There are not many constellations that have the slightest resemblance to the objects they are meant to represent. One of the exceptions is Scorpius, the Scorpion, where the long, curved line of bright stars may be said to conjure up the image of an insect – provided you have a fairly lively imagination. Moreover, the area is crossed by the Milky Way and abounds in rich star fields. Unfortunately it is always low down as seen from Britain, and the southernmost part of it never rises at all. If you go South and see the Scorpion high in the sky, you will appreciate how magnificent it is. It is of course one of Ptolemy’s original constellations and is in the Zodiac (during the summer of 2007, it played host to Jupiter). There is an old legend about it. P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_24, © Springer Science+Business Media, LLC 2010

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Orion, the great hunter, boasted that he could kill any creature in Earth, but he forgot the Scorpion, which crawled out of a hole in the ground and stung him fatally on the heel. Orion was then placed in the sky, and in the interests of fair play the scorpion was also elevated to celestial rank – but put as far away from Orion as possible so that there could be no ill-feeling. From Britain, at least, Scorpius and Orion can never be above the horizon together. The leading star is Antares (Alpha Scorpii), a vast red supergiant; magnitude 1.06 – very slightly variable, but not by more than a tenth of a magnitude, in which it differs from Betelgeux in Orion, whose fluctuations are very marked. Antares is the reddest of the first magnitude stars and indeed its name means “the Rival of Mars” (Ares). Its spectral type is M1, and it is truly immense, with a diameter of about 500 times that of the Sun – that is to say, well over 400 million miles. If its centre lay in the Solar System, its outer edge would extend out to the asteroid belt, and the inner planets, including Earth, would be engulfed. Yet its mass is only about 15 times that of the Sun, because, like all supergiants, most of its globe is very rarefied. If you could go there and cycle right round its surface, travelling at a steady 6 mph, your ride would take 3,000 years, so that as you crossed the finishing line you would be rather weary! Antares is an evolved star which has long since left the main sequence; eventually, it will explode as a supernova and will be intensely bright in our sky while the outburst lasts, but it is 600 light-years away, too far to do us any damage. At present, its luminosity is 10,000 times that of the Sun, but much of its energy is radiated in the infra-red. Antares is flanked on both sides by two-third magnitude stars, Sigma (Alniyat) and Tau, which has never been given a proper name, but it is interesting because it is known to have an unusually strong magnetic field. Altair, in Aquila, also has a fainter star on either side, but there is little danger of mis-identification, because Altair is a pure white star and as seen from Britain is always much higher up than any part of the Scorpion. Antares is not a solitary traveller in space. It has a 5.5-magnitude B-type companion at a separation of 3 s of arc, but the companion is not so easy an object as might be thought, because it is so overpowered by the red glare of the primary. I find it difficult with any telescope below 6 in. aperture. It is at least 170 times as luminous as the Sun, and to me it always looks decidedly green, but this is no doubt a contrast effect; other red stars also have early-type secondaries which appear greenish (e.g. Alpha Herculis). The only single star usually said to have a true greenish hue is Beta Librae, though I admit that to me it appears colourless. The Scorpion’s head is marked by Beta (Akrab), Delta (Dzuba) and Pi (Vrishika). Beta – alternative proper name Graffias, magnitude 2.6 – is an easy double, and a second easy double, Nu, lies close by. Delta Scorpii, which has several alternative names – Dzuba, Dschubba, Al Jabba, Iclarkrau – was long regarded as a normal B-type star of magnitude 2.3, but in June 2000 it suddenly brightened up to magnitude 1.6, changing the whole look of that part of the sky. It has proved to be a variable of the Gamma Cassiopeiae type, throwing off “shells” at unpredictable intervals. Since then it has faded slightly from the outburst maximum, but is still definitely brighter than it was before the outburst, and how it will behave in future we know

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not. Gamma Cassiopeiae, the middle star in the famous W pattern, also flared up from 2.3 to 1.6 – in 1936 – but then sank to below three for several months before returning to its former magnitude, where it has remained ever since. Whether Dzuba will show a similar temporary dimming remains to be seen. The line of stars representing the Scorpion’s body curves south from Antares and dips below the British horizon; its southernmost star, Theta Scorpii (Sargas), magnitude 1.9, has a declination of −43°. We cannot see Iota Scorpii (Apollyon) which shines modestly at magnitude 3.0, but is in fact immensely powerful – much more luminous than Antares – and is 1,800 light-years away. However, the “Sting,” with two bright stars close together – Lambda (Shaula) and Upsilon (Lesath) – does just rise, though I admit that from my Selsey home I have never seen it distinctly. The two are not true neighbours, because Shaula is much more remote (700 lightyears) and is a bluish-white B-type star almost as luminous as Antares. En passant, Scorpius adjoins much smaller constellations such as Norma (the Rule) and Telescopium, and by edict of the International Union has purloined several of their stars; N and H Scorpii (each of magnitude 4) used to be known as Alpha and Beta Normae, respectively, while G Scorpii (Basanismus, magnitude 3.2) used to be Gamma Telescopii. The Scorpion is rich in clusters, both open and globular. Open clusters usually consist of from a few dozen to a few hundred stars, with no particular form even though their stars are of the same age and were formed from the same nebula; of course, the most celebrated examples are the Pleiades and Hyades in Taurus and Praesepe in Cancer. In Scorpius, we find two naked eye open clusters, M6 (the Butterfly) and M7 (Ptolemy’s Cluster); M7 was recorded by Claudius Ptolemy, last of the great astronomers of Classical times, in the second century AD, while M6 possibly was. Both are low in British skies, but are easy to locate, particularly M7; look for it to the east of the main body, and you should be able to find it with no trouble at all when the sky is reasonably dark and clear. The main portion contains at least 80 stars; at its distance of about 1,000 light-years, this corresponds to a real diameter of about 20 light-years. M6 is not so prominent, but is much further away – of the order of 1,600 light-years; the real diameter has been given as 12 light-years. Most of its main stars are white or bluish, but there is one K-type orange giant, BM Scorpii, which varies between magnitudes 5.5 and 7. Photographs bring out the contrast well, and although M6 does not look like a butterfly, it has a more distinctive pattern than its bright neighbour. Globular clusters are huge symmetrical systems, most of which lie round the edge of the main Galaxy and some of which contain over a million stars. Not many are visible with the naked eye; the three brightest are Omega Centauri and 47 Tucanae in the southern hemisphere and M13 Herculis in the north. Two notable globulars lie in the Scorpion. M4 is easy to find with binoculars, since it lies a mere 1.3 degrees west of Antares and has as integrated magnitude of 7. Ata distance of 7,200 light-years is the closest known globular; real diameter 70 light-years. It is much less densely packed than others of its type, and for some time astronomers wondered whether it should really be classified as an unusual open cluster. M80, midway between Antares and Akrab, is more typical; it is 32,600 light-years away

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and contains several hundred thousand stars. The full diameter is 95 light-years, and near the centre the individual stars are so close together that collisions must sometimes occur. In May 1861, a nova flared up in the cluster and briefly outshone all the other cluster members combined; it was given a designation – T-Scorpii – but has never reappeared. It was probably an ordinary nova, a one-off, but M80 is worth monitoring. Adjoining Scorpius are the beautiful clouds of the star Rho Ophiuchi, and the whole region is exceptionally rich. So, when the sky is clear, go and seek out the Scorpion, with its red leader, its chain of bright stars, and its wonderful star fields. There is no other constellation quite like it.

Chapter 25

The August Perseids

Perseids 2006 (Credit: Pete Lawrence)

The Perseids provide the most reliable of all the annual meteor showers. Conditions in 2007 were expected to be good, so we planned a meteor watch at my observatory. It turned out to be a distinct success. Meteors can be seen on almost any clear night, and there can be few people who have not been impressed with shooting stars flashing across the sky and vanishing in a second or two. Yet not everybody knows what they are, and only during the past couple of centuries have we been able to learn much about them. They are phenomena of the upper atmosphere, and each streak indicates the last moments of a tiny object, generally no larger than a grain of sand, dashing into the upper air from outer P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_25, © Springer Science+Business Media, LLC 2010

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space and burning away by friction against the atmospheric particles. It enters the air at a speed of anything up to 45 miles per second and is destroyed by the time it has penetrated to about 40 miles above sea level, ending its journey in the form of ultrafine “dust.” Meteors are cometary debris. A comet has a nucleus made up of ice and solid particles; its mass is very slightly compared with that of a planet or even an asteroid, and I once described a comet as being “the nearest approach to nothing that can still be anything”. Some move round the Sun in elliptical orbits, in periods of a few years; these so-called short-period comets are old friends, and we know when and where to expect them. Others have much longer periods, so that we cannot predict them. I well remember the lovely green comet of 1996, discovered by the Japanese astronomer Yuji Hyakutake, and named after him. It will return to the inner Solar System in about 15,000 years time; remember to look out for it! As a comet draws in towards the Sun, its outer ices begin to evaporate, and the comet may develop a tail of immense length, so that it may become spectacular despite its negligible mass. However, a comet loses material at ever perihelion passage, and it wastes away; some periodical comets have been seen to disintegrate. The most famous case of this was that of Biela’s Comet, which is seen every 6 ¾ years – until 1846, when it broke in half. The pair came back on schedule in 1852, but this was their final appearance. The comet is dead, but when the Earth passes close to the place where it ought to be, we pick up particles which it has left behind – and the result is a shower of shooting stars. Actually, it is more accurate to say “when the Earth passes through the orbit of the defunct comet,” because dust particles have been left all along the orbit. Few periodical comets ever become bright enough to be seen with the naked eye even when they are relatively close to us, and only one – Halley’s Comet – can ever become brilliant. It returns to perihelion every 76 years, but at its last visit, in 1986, it was badly placed and some people were disappointed (it will be back again in 2063). But comets are clearly linked with meteor showers, and this brings me on to the August Perseids and our Sky at Night programme for that month in 2007. The particles left behind by a comet are moving along in parallel paths, and so the resulting meteors appear to emanate from one definite point in the sky, known as the radiant. The best demonstration I can give you is to picture the scene from the top of an arc overlooking a motorway. The lanes seem to diverge from a point near the horizon – the “radiant” of the lanes, and approaching cars will come from that point. The August meteor issue from a radiant in the constellation Perseus, and I always regard this as the richest of all annual showers – of which there are many. The Perseids were not identified until 1835, when attention was drawn to them by a Flemish scientist, Adolphe Quetelet, who was an interesting man; he was an enthusiastic astronomer, but was also a leading criminologist and statistician. After he drew attention to the August shower, others took notice of it, and in 1864 the Italian astronomer Giovanni Schiaparelli (best remembered, perhaps for his observations of the “canals” of Mars) found that the meteors moved in the same orbit as a comet, SwiftTuttle, which had been discovered in 1862, and was thought to have a period of well

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over 100 years (Lewis Swift and Horace Tuttle were both renowned comet hunters). The inference was obvious; Swift-Tuttle was the parent comet of the Perseids. Every year, the shower meteors begin to appear around July 23 and become more and more plentiful until maximum activity is reached on August 12–13. After that subsides, though a few Perseids may still be seen as late as August 20. The ZHR, or Zenithal Hourly Rate, may be as high as 80 (the ZHR is defined as the number of naked-eye shower meteors which would be seen by an observer under ideal conditions, with the radiant at the zenith or overhead point. In practice, these conditions are never attained, so that the observed rate is always less than the theoretical ZHR). There are three more points to be noted here. First, although the meteors radiate from Perseus – but are not confined to Perseus – they flash along to any point in the sky. Second, not all the meteors that you see will be Perseids; some belong to other, less prolific showers, while there are also sporadic meteors, which may appear from any direction at any moment, and are not linked with known comets. You can identify Perseids by plotting their paths against the stars and tracing them “backwards” to their starting point. Finally, what we see in the sky is not the particle itself, which is too small to be visible, but the luminous effects which it produces during its headlong dash through the atmosphere. For 2007, the prospects were as good as they could possibly be. The weather forecast was favourable, and – most important of all – there was no interference from moonlight; the Moon was new. Maximum was due at 2 a.m. on the morning of August 13. So for a Sky at Night “special,” we assembled a group of experienced meteor observers, headed by John Mason, plus others (such as me) who were less dedicated, but were determined to enjoy the display of cosmic fireworks. The two groups were doing different programmes. I was merely carrying out a television commentary plus counting the meteors, noting their magnitudes, their colours (if any) and other exceptional features; some meteors leave trains which persist for some seconds, or even less frequently, a minute or two. The more serious members of the party were carrying out photography. The method here is to point the camera in a suitable direction and take time-exposure. You will record star trails, and perhaps an artificial satellite or two. We were lucky; we had barely settled down when the ISS – the International Space Station – passed overhead. You could not possibly miss it; it shone more brightly than Venus. What did we hope to see? Well, a decent shower; the Perseids are usually co-operative. There was always the chance of a “fireball” which would light up the landscape; I have seen a few of these, produced by particles the size of grapes or even golf-balls, but they are rare. Otherwise, we had to wait and see. The sky was cloudless and transparent, and the lawn surrounding my observatory is shielded from any obtrusive artificial lights, so that it was pleasingly dark. Meteors began to appear; apart from one brief period, the clouds stayed away. Gradually activity increased. There were some bright meteors, though no fireballs. None of us felt inclined to give up; as usual on these occasions, there was rather a party atmosphere. Coffee was most welcome, and we

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remained until the approach of dawn, when we adjourned indoors to refresh ourselves with drinks which were rather more potent than coffee. The end of an enjoyable evening. What had we achieved? Scientifically not a great deal, though routine observations are always useful; our main point was that we had spoken to a large audience of around a million people, some of whom went outside and watched a spectacle which they would otherwise have missed. That in itself, I feel, justified our special programme. Of course, the Perseids will be with us again next year, but in 2008 the conditions will not be nearly so favourable, as meteor watchers will have to contend with strong moonlight. Finally, spare a thought for Comet Swift-Tuttle, responsible for it all. It was not seen for many years after 1862, and calculations indicated that although it had been missed at several intervening returns, it should be back in 1981. Careful searches gave negative results, and I thought that it had simply been overlooked. John Mason disagreed; he believed that the orbit had been wrongly worked out, so that the real date of the next perihelion passage would be early in the 1990s. We had a modest bet about this (a bottle of Irish Whisky, I recall) and I was confident – until 1992, when the comet turned up. The period is now known to be 135 years, Swift-Tuttle has not been conspicuous lately, but a good deal will be heard about it in the twenty-second century, when it will pass alarmingly close to us. Wait for an end-of-the world scare then – but don’t blame the Perseids!

Chapter 26

Black Holes: And Black Magic

Einstein’s cross (Credit: ESA)

Everybody is fascinated by black holes. Who better to give us the latest news than professor John Brown, the Astronomer Royal for Scotland, who as well as being a world-renowned solar physicist is also an expert amateur magician. Joined by Drs Fiona Spititz and Chris Lintott, we attired ourselves suitably and did our best to forge a link between black holes and Dark Forces. P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_26, © Springer Science+Business Media, LLC 2010

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Black Holes and Black Magic? No true connection, needless to say, but black holes are so bizarre that they really do seem to be magical. Even now we cannot pretend that we have anything like a full understanding of them. Then first concept of them seems to have been due to an English amateur scientist, the Rev. John Michell, who lived from 1724 to 1793 (of course, most people misspell his name as “Mitchell”). His activities were very varied – someone ought to write a really good biography of him – and one of his suggestions was that a body of sufficient mass would pull hard enough to prevent even light escaping from it. A similar comment was made later by the great French mathematician Laplace, but the term “black hole” dates from only 1968, when it was introduced by the American scientist John Wheeler. It caught on and is now part of our language, but in a way it is misleading because a black hole is not black at all. It emits no light and so cannot really be said to have any colour. If we cannot see a black hole, we have to locate it by means of its gravitational pull upon objects that we can see. Black holes are incredibly massive – thousands of millions of times more massive than the Sun – so that they can certainly make their presence felt. We have every reason to believe that there is a black hole in the centre of our Galaxy, because we can measure the speeds at which objects fairly close to it whirl around it, and this allows us to calculate its mass. It seems that a black hole is the end product of a very massive star. Normal stars create their energy by nuclear reactions taking place inside them, as our Sun is doing now. Eventually the supply of available nuclear “Fuel” will run out, and the whole situation must change. A modest star such as the Sun will lose its outer layers and subside into a white dwarf, where the atoms are crushed and packed together so tightly that the star is extremely dense; the final state will be as cold, dead black dwarf. We know plenty of white dwarfs, one of which, the faint companion of Sirius, is no larger than the Earth but is as massive as the Sun, but the whole course of stellar evolution is so slow that the universe may not yet be old enough for any dwarfs to have formed. After all, the Big Bang happened a mere 13.7 thousand million years ago! A star much more massive than the Sun will die in a much more spectacular fashion; it will explode as a supernova, blowing much of its material away into space while the remnant, now composed of neutrons, will spin round and send out beams of radio emission. If these beams sweep over the Earth, just as the beams of a rotating lighthouse will sweep across the watcher on the beach, we pick up pulsed radio waves – hence the term “pulsar” (there is a pulsar in the famous Crab Nebula, 6,000 light-years away; the supernova responsible was seen to blaze out in the year 1054). Pulsars, too, must end up as black dwarfs. But if the mass of the dying star is greater still, it cannot even produce a pulsar. Once the final collapse starts, nothing can stop it. The star becomes smaller and smaller, denser and denser – and the escape velocity goes on increasingly until it reaches 186,000 miles per second, the speed of light. Light is the fastest thing in the universe, at least so far as we know, and so nothing can break free from the doomed star. It has become a black hole. The underlying principle is not the same as was believed by Michell, because the modern idea of gravity is different. To Michell, and also to Newton, gravity was a

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force which enabled one body to affect another even when the two were widely separated; this “action at a distance” was often regarded as a form of scientific black magic. Albert Einstein changed all this and interpreted gravity as a distortion of “space-time.” Consider a bowl with paper stretched across its top; roll a marble across the paper, and it will follow a straight line. Now imagine an object inside the basin which could in some way pull the sheet of paper downwards (I admit that I do not see quite how this could be managed, but never mind). The marble will no longer roll straight; its path will be distorted. I know this is a poor analogy, but it is better than nothing. In space, the object at the bottom of the bowl represents our black hole. Black holes can therefore affect the paths of light-beams, and this is shown by the phenomenon of gravitational lensing (though other massive bodies can act similarly; large galaxies and clusters of galaxies, in particular). A good example of this is what is termed the Einstein Cross (because it was Einstein who realised that this sort of thing could occur). At a distance of 8,000 million light-years, we find a quasar, catalogued as Q2237 = 030; quasars, as we know, are the immensely luminous cores of active galaxies. En route to Earth the quasar’s light passes by the very massive galaxy called Huchra’s Lens. The light from the quasar is “bent”; we see four images of the background quasar, and you will agree that the effect is remarkably striking. Many other cases of gravitational lensing are known, though not many are as symmetrical as the Einstein Cross. I must not forget to say something about Hawking radiation, first proposed by the famous Cambridge cosmologist Stephen Hawking. What we call a vacuum is not actually empty; it is seething with “virtual particles” which appear in pairs, but vanish again so quickly that they are truly ghostlike. A particle and its antiparticle will annihilate each other – but if a pair appears at the extreme edge of a black hole, the so-called event horizon, one of the pair may enter the black hole, leaving its partner marooned outside. With no partner, the stranded member of the pair becomes a “real” particle, and the black hole is forced to emit a certain amount of radiation, which results in loss of mass. It has been suggested that the emission of enough Hawking radiation might finally make the black hole explode and destroy itself, but whether a major black hole has yet perished in this way seems somewhat uncertain…. Exotic theories about black holes are plentiful. They have been regarded as passages between our universe and a completely different universe, in a different dimension, with which we can normally have no contact whatsoever; on the “multiverse” picture, there may be many of these – perhaps an infinite number. Approaching a black hole in the hope of a free ticket to the universe next door would be rather hazardous, and there would be all manner of curious effects involving both space and time. Incidentally, what is the fate of a star which collapses to produce a black hole? Does it crush itself out of existence altogether, or does it turn up elsewhere, either in our universe or in another? Will we Earthmen ever be threatened by a maverick hole able to creep up and take us by surprise? At present these are the problems which we cannot solve. Perhaps we will find the answers eventually, but meantime it is not hard to see why some people still feel that there must be at least a tenuous link between black holes and black magic!

Chapter 27

Jodrell Bank: Fiftieth Anniversary

The Lovell Telescope (photo by Patrick Moore)

In October 2007, the great radio telescope at Jodrell Bank had been in action for half a century. Together with Chris Lintott, I went there and talked not only to Bernard Lovell but also to Bernard Baruch, Ian Morrison and Phil Diamond of the Jodrell Bank team. Bernard and I are very old friends. I remember thinking – would this be the last time we would meet face to face? Bernard, now 94, is totally fit in every way; thanks to the activities of our gallant German allies, long ago, I am not really mobile. We must see. Incidentally, both Bernard and I are cricket fanatics. He played to a really high standard; I did my best to spin my unorthodox leg-breaks. Sadly, we never actually took the field together, and now fear it is rather too late! Go to Jodrell Bank, near Macclesfield in Cheshire, and you will see the 250-ft Lovell radio telescope. In fact you cannot possibly miss it, because it dominates the entire landscape. It is a miracle of engineering even today and was even more so in P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_27, © Springer Science+Business Media, LLC 2010

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1957, when it first came into action. It was the brainchild of Professor Sir Bernard Lovell; but for him it would never have been built, and radio astronomy would not be so advanced as it actually is. Radio astronomy began in the 1930s, but was slow to develop because most astronomers were suspicious of it. Lovell was not; he could see the possibilities, and at the University of Manchester he began research as soon as he was free of his wartime work. Meteor trails, for example, could be studied by radar. Manchester was a hopeless site, because of pollution from electric trams and other sources. Lovell was given the use of a site well away from the city and was told that he would be allowed to stay there for 15 years. I well remember those early days. Jodrell Bank really was a grassy bank, and we lay there on our backs after dark plotting meteor trails. Then, thanks to Lovell, came the first radio “dish”; it was an improvement upon anything previously produced, and it was soon producing valuable results, but it could point only straight upward…. Lovell needed a steerable “dish,” and with engineer Charles Husband he planned one…. It was to be 250 ft in diameter and would stretch the powers of 1950s technology to its very limit – perhaps even beyond. The budget, rather grudgingly given, amounted to a million pounds. There were problems galore. Midway during the construction it was realised that the resistance to wind had been grossly underestimated, and this necessitated extensive redesigning, which cost a great deal. Government accountants, those sworn enemies of research, were always hovering like vultures, and on the fourth of October 1957 the situation was desperate. The telescope was not complete and the debt had spiralled to a quarter of a million pounds. To a colleague, Lovell said sombrely: “Only a miracle can save us.” Sputnik 1 was the miracle. The “bleep! bleep!” signals could be picked up easily, but the rocket launcher could not, and of course this launcher was the first Intercontinental Ballistic Missile (IBM). America panicked; outside the USSR only the Jodrell Bank telescope could track the rocket, and overnight Lovell was transformed from a reckless spendthrift into a national hero. Lord Nuffield paid the outstanding debts; the crisis was over and Jodrell Bank was safe. Since then research has been constant; the 250-ft dish is still the third largest in the world and arguably the best. Quasars, pulsars, gravitational lenses and other bizarre objects, unknown in 1987, have received particular attention. The telescope is never idle. It has been updated, and a new dish, made of galvanized steel, has been built on the site, notably the Mark 2 dish, the Jodrell Bank heads the MERLIN network of seven radio telescopes working together. Jodrell Bank has its place in history, and it will be in forefront of research for many years to come. I am proud to have been around to watch its development, and particularly proud to have been at its 50th anniversary with Bernard Lovell who, like his telescope, will never be forgotten.

Chapter 28

The Grand Collision

Andromeda (Credit: Robert Gendler)

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Look into the future, and you can visualise a collision which will be utterly ­devastating – far greater than a head-on clash between two planets, or two stars. Our Galaxy, with its hundred thousand million stars, will collide with an even larger system, the Andromeda Spiral. To talk about this coming cataclysm, I was joined by two regular and welcome guests, Professors Carlos Frenk and Derek Ward-Thompson, while in my observatory Chris Lintott and Nik Szymanek turned my 15-in. telescope towards Andromeda. Pegasus, the Flying Horse, is the main autumn constellation, but is still on view during evenings later in the year. Its four main stars make up a square, which is easy to locate even though maps tend to make it look smaller and brighter than it really is. The upper left-hand star of the square, Alpheratz, has for some illogical reason been transferred from Pegasus to the adjacent constellation of Andromedae, and has become Alpha Andromedae instead of Delta Pegasi. Andromeda is marked by a line of stars extending from Alpheratz in the direction of Capella. Not far from the second brightish star in the line, the orange Mirach, you will find the dim blur that marks the position of the Andromeda Galaxy, M31. It is just visible to the naked eye when the sky is really dark, and binoculars show it clearly, but photographic or electronic images obtained with adequate telescopes are needed to bring out details of its structure. It is in fact a spiral, much larger than the Milky Way Galaxy, and containing more than our quota of one hundred thousand million suns. It has been known since very early times and was the 31st object in Charles Messier’s catalogue of star-clusters and nebulae. It used to be popularly called the Andromeda Nebula, but Edwin Hubble’s work in the 1920s proved that it is an independent galaxy, far beyond ours. Its distance is now given as 2.6 million light-years, making it the most remote object distinctly visible without optical aid. Its distance was not easy to measure. Hubble made use of the stars known as Cepheid variables, some of which are to be found in M31. They do not shine steadily; they brighten and fade in short periods, generally a few days, and they are absolutely regular, so that we always know how they will behave. A Cepheid’s period is linked to its real luminosity; the longer the period, the more powerful the star – which means that we can find the luminosity of a Cepheid, and hence its ­distance, simply by watching it. Hubble’s original value for the distance of M31, 900,000 light-years, turned out to be too low, because Cepheids are more powerful than he had expected, but at least he had taken the essential leap. Our Galaxy is only one of many. Earlier, Vesto Slipher, at the Lowell Observatory in Arizona, had examined the spectra of galaxies and had found that almost all of them showed red shifts; the dark absorption lines were shifted over to the red or long-wave end of the background rainbow. This is the familiar Doppler effect; a red shift indicates a velocity of recession, and Hubble concluded, correctly, that the entire universe is expanding. Yet there are some exceptions. Galaxies tend to be gregarious, forming groups; the so-called Local Group, to which we belong, contains three large systems (the Milky Way, M31, and the Triangulum Spiral M33 – plus several of moderate size and more than two

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dozen dwarfs. These are not racing away from us. In fact, it is wrong to say that every galaxy is receding from every other galaxy – but it is true to say that the groups of galaxies are receding from the other groups. (Even this may be too sweeping, but it will suffice for now.) At the moment, M31 is 2.6 million light-years away, which works out to something like 16 million miles, but it hurtling towards us at almost 200 miles per second. Will this continue into the foreseeable future – and if so, will M31 eventually hit us? So far as we can tell the answers to these questions are “Yes” and “Yes.” But please do not be alarmed. The collision will not happen for at least a 1,000 million years, and probably longer than that; estimates range between 2,000 and 10,000 million years. By then the Earth will no longer exist, at least in its present form. The Sun will have evolved through hits red giant stage, and it is hardly likely that the Earth will survive. Even if it does, all life on it will long since have been wiped out. M31 will not rush straight towards our Galaxy and hit it, in the manner of two cars meeting head-on. They will first orbit each other and take part in what we may call a cosmic waltz; only then will they merge, and individual stars will seldom collide – after all, a star is a comparatively small target in the vastness of space. The situation may be likened to that of two orderly crowds passing through each other. But the material between the stars will be colliding all the time, and this will cause chaos, with energetic star formation triggered off. When the main encounter is over, after perhaps a 1,000 million years, the graceful spirals will have been destroyed, replaced by a single elliptical system. Galactic collisions are not so rare as we once thought, and neither are they so widely separated relative to their actual dimensions. Represent the Earth by a pinhead, and the nearest star, Proxima Centauri, will be another (even smaller) pinhead over four miles away. But is we represent the Milky Way Galaxy by a dinner-plate, Andromeda will be another plate on the far side of the dining-room table. We can see other encounters, too. Look at the Antennae Galaxies in Corvus (NGC4038-9) which are well within range of amateur owned telescopes; the images shown here tell the whole story, with the ejected gas and dust giving the appearance of insect antennae. The two systems passed through each other about 600 million years ago. Collisions between galaxies are by no means unusual today and were more frequent in the early history of the universe, when aggregations of galaxies were much closer together than they are now. It is only direct collisions between individual stars which are so rare. Quite apart from encounters between giant galaxies, we must also note that smaller systems will be absorbed; for example, our Galaxy is at present “swallowing” the Sagittarius dwarf, which will lose its identity long before the menacing swoop of Andromeda. In fact, large galaxies act as cannibals. I am particularly intrigued by the Mice (NGC 4676) where two huge galaxies are pulling each other apart; they have not yet merged, but it is only a matter of time, and the Hubble Space Telescope can show what is happening, even though the Mice are 3,000 million light-years away. The long streamers are due to the relative difference between the gravitational pulls on the near and far parts of each galaxy.

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Making forecasts is always dangerous, but so far as the future career of our Galaxy is concerned, we are confident that there is no major mistake. Go outdoors tonight, if the sky is clear, and seek out the innocent-looking smudge of light which marks the Andromeda spiral; it takes an effort of the imagination to accept that you are seeing a colossal star-system hurtling towards us at breakneck speed. It is certain to hit our Galaxy. The collision may happen in a 1,000 million years, 2,000 million year, 5,000 million years, perhaps not for 10,000 million years – but happen it will. There can be no final reprieve.

Chapter 29

Holmes’ Comet

Holmes’ Comet (Credit: Pete Lawrence)

We had actually recorded the December programme when Holmes’ Comet suddenly hit the headlines. We could not possibly ignore it, so we fixed a last-minute recording session. Fortunately, the sky was clear, and the comet shone down, blissfully ignorant of the fact that its abrupt flare-up had played havoc with our carefully planned broadcasting schedule. Comets are the most erratic members of the Solar System. We never quite know how they are going to behave, and one of them, known officially as Comet 17P/ Holmes, has given us a real surprise. Last October, it suddenly flared up from

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magnitude 17 to 2.5, and in less than 48 hours had brightened by a factor of over a million. Nothing quite like this had ever been seen before. The comet was originally discovered in 1892 by an English amateur, Edwin Holmes, who was casually scanning the region of the Andromeda Galaxy. It brightened up to the fringe of naked-eye visibility, and developed a short tail; it faded, brightened again and then became very dim. It proved to be a member of Jupiter’s comet family, with a period of 6.9 years; the distance from the Sun ranged from 2.05 astronomical units (191,000,000 miles) at perihelion out to 5.18 astronomical units (482,000,000 miles) at aphelion. The orbital eccentricity (0,43) and inclination (19.1°) were modest, and the comet could not make any close approaches to the Earth. It returned on schedule in 1899 and 1906, but was always faint, and caused no particular interest. It was not seen at the next few predicted returns, and was regarded as lost. But in 1964 E. Roemer, at the Lowell Observatory in Arizona, recovered it after its position had been determined by Brian Marsden, who makes a habit of locating long-lost comets. Since then, it has been observed at every return, but has been dim and unremarkable – until now. On 23 October 2007, J.A. Enriquez, in the Canary Islands, found that the comet was much brighter than expected. The outburst was violent, with material sent out from the tiny, icy, 2.2-mile nucleus so rapidly that by the 1st week of November the coma had expanded to become larger than the Sun. It lay in the constellation of Perseus, and completely altered the look of the whole of that part of the sky; with the naked eye it looked like a slightly fuzzy star, and on 25 October I estimated the magnitude to be 2.4, much brighter than Epsilon Persei. With binoculars it looked rather like a globular cluster, but telescopically it was clear that the brightest part of the huge coma was displaced from the centre. It was strange to realise that this flimsy object, of negligible mass, had become the largest member of the Solar System! What makes the event even more remarkable is that perihelion had been passed as long ago as 4 May, that the comet was receding from both the Sun and the Earth; at the time of the outburst it was more or less at opposition, so that when a definite tail developed it pointed away from us, and was so foreshortened that it was difficult to make out at all. Visually it was never conspicuous, but images from the Hubble Space Telescope in late November showed a bluish tail; at one stage the tail became disconnected, and there was also a section of material, which broke away from the coma itself. Evidently, there was considerable activity, and the magnitude fell surprisingly slowly (it was a pity that moonlight interfered with observations during a particularly interesting period). On 1 December, my estimated magnitude of the comet was 2.9, but I must add that seeing conditions were not very good. There does not seem to be anything very unusual in the comet’s composition, and the cause of the outburst is not entirely easy to explain. A collision with another body was suggested, but personally I do not believe than an impact was responsible, because of the previous outbursts in 1892. True, these were minor compared with that of 2007, but for the same comet to be struck three times would really be too much of a coincidence. Surely, the explosion must have been internal. Other comets have behaved in rather the same way, and it is worth recalling Comet

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P/Schwassmann-Wachmann (better known as Schwassmann-Wachmann 3) which has a period of 5.4 years, and has been seen regularly since discovered in 1930; at the return of 1995 it began to show obvious signs of breaking up. This has continued; fragments passed within eight million miles of us during the return of 2006, and in the foreseeable future the disintegration is likely to be complete. But Holmes shows no sign of breaking up completely, and all we can say is that very unusual activity is taking place. What next? Obviously it will be more difficult to follow events as the comet moves out beyond the asteroid belt toward the orbit of Jupiter, and what will happen to it before the next perihelion passage, in 2011, remains to be seen, but all observers, both amateur and professional, will watch it as closely as they can. It is certainly one of the weirdest things I have ever seen in the sky.

Chapter 30

Cosmic Debris

Encke’s Comet (Credit: Spitzer)

The year 2008 began in a rather unexpected way. A long-known comet, Holmes, surprised us all by suddenly flaring up to a million times its normal brightness, and so I thought that this would be a good moment to talk about cosmic debris – the “bits and pieces” of the Solar System. I was joined by two leading experts, Dr Simon Green and Dr. Richard Greenfield. P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_30, © Springer Science+Business Media, LLC 2010

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The Sun’s family is dominated by the eight planets, from Mercury out to Neptune, together with their satellites. But we must not forget that there are other members too; comets and asteroids, for example. There is also a vast amount of cosmic dust. We have just seen a comet take us by surprise, so let us begin with these strange, wraithlike objects, which can sometimes look so much more important than they really are. A comet is not a solid, substantial body similar to a planet. The only fairly substantial part is in fact the nucleus, seldom more than a few miles across, and made up of rocky particles and ice; the mass is very small compared with that of a planet or even a satellite, such as the Moon. When the comet moves in towards the Sun and is heated, it may develop a tail of either gas or dust; some comets may produce both. Tails always point away from the Sun. Gas-tails do this because the particles are driven out by what is called the solar wind and dust-tails because of the pressure of sunlight (and light does produce a pressure, albeit a very weak one). Most comets move in very eccentric orbits, and there are many with short periods, so that we always know when and where to expect them. Encke’s Comet has a period of only just over 3 years, so that it is an old friend. Like most short-period comets, it seldom becomes bright enough to be seen with the naked eye. The only bright comet which returns reasonably often is Halley’s, whose period is 76 years; it was last at perihelion in 1986 and is next due in 2061. Comets are generally named after their discoverers, but occasionally after the mathematicians who first computed their orbits, as with both Halley and Encke. Really spectacular comets have much longer periods, of centuries, millennia, or even millions of years, so they cannot be predicted. Thus, Hyakutake’s Comet of 1997 will be with us again about the year 14,000 ad. I wonder whether any astronomer of that time will remember to search for it as it draws inward? As a comet moves along, it leaves a “dusty” trail behind it. If Earth passes through such a trail, the tiny particles dash into the upper air, moving at relative speeds of up to 45  miles per second; they become heated by friction against the air-particles and burn away, producing what are termed meteors – more commonly called shooting-stars. We plough through a number of trails each year, and so there are a number of meteor showers, some rich and others sparse; there are also “sporadic” meteors, not connected with any particular showers and which may come from any direction at any moment. Because the meteors in a shower are travelling in parallel paths, they will all seem to come from one definite point in the sky, known as the radiant. Thus, the August meteors have their radiant in the constellation of Perseus, and we call them Perseids. Meteors are of sand-grain size, and burn out when they are at least forty miles above the ground, but we also encounter larger bodies, which are too big to burn away and land intact; these are called meteorites. Note that meteorites are not ­connected with comets, and have absolutely nothing to do with meteors; they come from the belt of asteroids, which are miniature planets moving between the orbits of Mars and Jupiter. Meteorites may produce craters, and they are fascinating places; the famous Meteor Crater in Arizona is a well-known tourist attraction. It was formed about 50,000 years ago, long before the area was inhabited – had the

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meteorite fallen upon a city, the death-roll would have been colossal. Many other impact craters are known, but there is no well-authenticated case of any human casualty, though several people have had narrow escapes. Could the Earth be hit by a missiles massive enough to do really serious damage to the world? The answer is: “Yes”. There is strong evidence that a major impact occurred about 65 million years ago, and resulted in a climate change which proved fatal to the dinosaurs. A similar impact may happen at any time – we can only hope that if so, we will cope with the situation better than the dinosaurs did! The chances of such a disaster in the near future are slight, but are not nil. Our Moon is crowded with impact craters, and so is the planet Mercury; both these worlds are airless, and so the craters remain, whereas most of Earth’s craters have been eroded away by the action of wind and water. Comets, then? The tails are so rarified that they are harmless, but it is true that a hit from an icy nucleus, several miles across, would cause wide devastation. Ancient people were terrified of comets, and believed them to be prophets of doom, which is not surprising – they can be remarkably spectacular. Great comets have been rare in recent years, but several were seen during the nineteenth century, and the comets of 1811, 1843 and 1882 were brilliant enough to cast shadows. Astronomers would give a warm welcome to a visitor of this kind, provided that it did not come too close. On June 30, 1908, there was a kind of explosion in the Tunguska region of Siberia which blew pine trees flat over a wide area. Nobody was hurt because the area was unpopulated, but if the explosions had happened at a slightly different era, it might have devastated the city of St. Petersburg. What was the body responsible? No fragments were found, and the body may have been a fragment of a comet which exploded well above ground. Another fall in Siberia occurred on 12 February 1947, in the Sikhote-Alin region. This was certainly a meteorite, because fragments of it were found, plus many small craters. Comets, meteors and meteorites are the stray members of the Solar System. They may be junior members of the Sun’s family – but there are few sights in nature equal to that of a great comet, with a gleaming head and a tail sweeping gracefully across the sky.

Chapter 31

Nearest Star

Stereo Mission Sun (Credit: NASA)

It was some time since “Sky at Night” had been devoted to the Sun, and it was the plan for April, but I could not ignore a vital news item. Mr. Gordon Brown’s Labour Government, always the enemy of anything that could not either be taxed or else turned to its own political advantage, was plotting to cut off funds to Jodrell Bank, our great radio astronomy observatory, and cripple al the projects associated with it. The loss would be irreparable, and something had to be done. There were protests not only from scientists, but also from the general public. Ever since it had been opened, in 1957, Jodrell Bank had led the way – and Bernard Lovell, who had created it, was still as active as ever. I wanted to play my part in the clamor, and I proposed going to Cambridge and talking to the Astronomer Royal. Permission was refused, “Sky at Night” was to remain apolitical. “All right. In this case, I will at once retire from the programme”. Reply: “Then someone else can go in your place”. “No; either I do it, or I stand down”. I meant it. To my immense relief, permission was then granted. P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_31, © Springer Science+Business Media, LLC 2010

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This was the first time I had put my foot down so firmly, and I imagine that it will also be the last. I went to Cambridge and talked to Lord Rees about theoutstanding Astronomer Royal who has done so much for British and world science. Well, Jodrell has been reprieved. Other important astronomical projects are threatened, but one battle has been won. I am not conceited enough to think that I could make any real contribution, but Martin Rees is a key figure, and at least “The Sky at Night” nailed its colors to the mast. The interview took up the first part of the program, after which we returned to the Sun. My guests were two leading experts, Dr. Tim Horbury and Dr. Chris Davis. There are two good reasons for choosing this month to discuss the Sun. First, the last solar cycle has come to its end, and the new cycle has just started. Second, there is news of the latest solar probes. Ulysses is finishing its immensely successful career; Stereo is starting a career, which we can hope will be equally fruitful. Ulysses is a box-shaped probe, 11 ft. high and spin-stabilized, carrying a variety of instruments. It was designed to study the poles of the Sun – which is not possible from Earth because we always view the globe reasonably broadside-on. Rather surprisingly, putting a space craft into a path, which takes it well away from the plane of the ecliptic, is not easy. Ulysses was launched with the Shuttle Discovery on December 6, 1990, and went out as far as Jupiter, so that it could use the gravitational pull of the Giant Planet to throw it into the required orbit. It functioned well until the late summer of 2008 – a total of more than 17 years, which is longer than a solar cycle. It surveyed the Sun’s north polar regions in 1994–1995, and the south pole in 2000–2001. Unexpectedly, it was found that the two poles are not alike, at least magnetically. The Sun is not a magnetic monopole, because the south magnetic pole is not a clear-cut point; it is decidedly diffuse. The average duration of a solar cycle is 11 years old. At maximum, the disk is very active with many sunspot-groups and faculae; near minimum there may be no spots at all for many successive days. The last maximum fell in late 2000, so that Ulysses was able to follow the Sun in all its moods. It also found that dust entering the Solar System from outer space is about 30 miles more time abundant than had been previously believed. Ulysses was able to make useful observations of Jupiter, and even found time to examine several comets. The two Stereo probes were launched from Cape Canaveral, on a Delta II rocket on October 26, 2006, and were fully operational by 2007. They were almost identical, but have different orbital periods, 347 days for the first vehicle (A) and 387 for the second (B); (A) moves in a heliocentric orbit inside that of Earth, while the orbit of (B) is outside ours. Because (A) is moving faster than (B), the two are separating at a rate of half a million miles per year, but the main observational programs were scheduled to last for a minimum of 2 years. Working together, the probes can ­provide stereoscopic results concerning the Sun – something which has never been previously achieved. Valuable data were soon received, notable with regard to the solar wind and to the violent outbursts known as Coronal Mass Ejections (CMEs). From the viewpoint of manned-space flight, in particular, we need to find out as

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much as we can about “space weather”. Travel beyond the atmosphere at the time of a major CME is emphatically not to be recommended. Comets have come under scrutiny, and a very bright visitor Comet McNaught, and its entry at just the right moment. Stereo also saw the tail of a familiar periodical comet, Encke’s, being literally torn off by the onslaught of a CME. Fortunately, the comet was quite unfazed, and promptly produced a new tail! Equipment carried by the Stereos makes it possible to study the region close to the Sun, between the Sun and the Earth. Here, we might well find “Vulcanoids”, asteroids moving in stable orbits. The name comes from Vulcan, the planet once thought to move in stable orbits. Vulcan does not exist, but tiny Vulcanoids may, and if so Stereo could well locate them. If so, I hereby promise that “The Sky at Night” will give a suitable prize to the discoverer of the first Vulcanoid! Time will tell.

Chapter 32

The Flight of the Phoenix

Phoenix Lander on Mars (Credit: NASA)

This was “a programme with a difference”. NASA’s Phoenix probe was scheduled to land on Mars on May 25, and clearly our followers expected us to cover it. In olden days, we would have put on a special programme, but this is impossible now. Also, our producer, Jane Fletcher, was on holiday somewhere in Scotland, and could not be contacted. We did not want to let our faithful viewers down, so we decided to do the programme ourselves and broadcast it on our web. P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_32, © Springer Science+Business Media, LLC 2010

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I must stress that Chris Lintott was the guiding spirit, acting as planner, organiser and figurehead. We enlisted the aid of Pete Lawrence (who else?) and Peter Grindrod, research Fellow at U.C.I., and converted my dining-room into a studio, which worked quite well. We had no producer (which did not matter), and no director (which mattered even less), but we had only one fixed camera; we took turns in “shooting”, and we could certainly have done with a mobile camera and an operator. Of course, NASA was doing a live programme and we were able to use it whenever we liked. We did what publicity we could, and at the appointed time we went on the air, heralded by the usual “Sky at Night” Sibelius music. Obviously, we were limited, but I think I can say that all went well – including our links with NASA. The programme was watched by many thousands of people, and reactions were very favourable. So the improvised programme was well worth doing, and we did not let our viewers down. We were all very aware of the importance of the missions. Phoenix was a new type of probe. By the start of 2000, there were several space craft studying the red planet, including the highly successful Mars Reconnaissance Orbitor (MRO) and the two amazing rovers, Spirit and Opportunity, which showed no signs of flagging even though they had been active for so much longer than their planners had dared to hope. Phoenix would not move around after arrival, and neither would it depend on airbags to cushion its landing – it was too massive for that. Instead it would use parachute braking and then retro-pockets, finally touching down gently in the Vastitas Borealis – the Martian Arctic. At the time of landing, that region was in constant sunlight; not until the following September would Phoenix see its first sunset. It could not expect to survive through the long, bitterly cold night, so that its active lifetime was bound to be limited. It would not last for more than 90 sols (92 Earth days, so the planners thought). The whole journey would cover over 420 million miles, between August 4, 2007, and May 25, 2008, but the last 7 min would be the most nerve-racking of all. Phoenix would plunge into the Martian atmosphere, and reduce its speed from 13,000 mph to virtually zero; for that vital 7 min all contact would be cut off. We at home would simply have to wait. Remember too, that at time it took radio signal 15 min to travel from Mars to Earth, so that we could not possibly receive a signal until a quarter of an hour after the actual touch-down. I think we were all tense as we assembled in the dining room – partly also because we had no real idea how successful our broadcast would be. We had announced it as part of the usual “Sky at Night” series, but it was completely unofficial. We hoped for the best. Chris opened – as I had been doing for over 50 years: “Good evening”. He introduced Peter Grindrod and me (it was Peter’s first appearance on “Sky at Night”, though it certainly will not be the last). We all made comments, and then we linked up to NASA. Phoenix was speeding towards Mars. When it entered the planet’s atmosphere, there would be an agonising 7 min of silence. NASA admitted that there was only a 50–50 chance of a safe landing. There was so much that could go wrong. This time there were no air bags, and the touch-down

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velocity had to be effectively zero – or at least below 6 mph. The stakes were high. Phoenix was not designed to search for actual life, but it was designed to search for subsurface water ice, and it carried a robotic arm to dig down to a depth of 50 cm – which ought to be sufficient. It was hoped that the landing site would be flat enough for the space-craft to stay upright, and the 2.35 m robotic arm to be deployed. If not – well, too bad. We linked with Mission Control; over a range of 171 million miles would take a radio signal 15 min to travel from Mars to Earth, so that at the time of our broadcast the landing – successful or otherwise – would actually have happened. We stayed with NASA as the entry into the atmosphere took place. Phoenix had to lose speed from 12,750  mph to just under 6  mph at touchdown, and during descent the heat shield would be subjected to a temperature of 2,000°F (1,420°C). Those 7 min of silence seemed to last for eternity. We made the occasional comment, but there was really nothing to do. Then, at last, came the voice of Dr. Fuk Li, NASA’s Mars Exploration Program Manager: “Phoenix has landed. Phoenix has landed. Welcome to the surface of Mars”. It was a great moment. Wild cheering from Mission Control, where everyone was ecstatic; the great gamble had paid off. It had cost about $340 million (230 million GBP), and this seems like a lot – until you equate it with a week’s operation in former U.S. President George Bush’s war in Iraq! One minute after arrival, Phoenix shut off communication to save battery power while it unfurled its solar panels, and there was another 15  min wait while the operation carried out – at a distance of 171 million miles from Earth. Again all went according to plan, and the situation was summed up by Barry Goldstein, NASA’s Phoenix project manager at J.P.L: “In all my dreams it couldn’t have gone more perfectly than it did”. And before long the first pictures came through. Thanks to our NASA link, they showed up perfectly in our dining room studio and we began to receive excited phone calls from our viewers. Phoenix landed in the Green Valley of the Vastitas Borealis, latitude 68° 21 min N., longitude 234° 23 min E. (the name the “Green Valley” was unofficial, and not particularly appropriate!). The surface was level, with only 0.3° tilt, and this was another relief, because there could have been no guarantee against coming down atop an inconvenient boulder. The visible surface was strewn with pebbles, and cut by small troughs into polygons about 15 ft. cross and 4 in. high. Large rocks and hills were absent, so the touchdown site had been well chosen. At midsummer, the Sun would rise to an elevation of 47° in the sky over Phoenix. We stayed on the air for another half-hour, and we were able to talk to some of the overjoyed technicians and astronomers at JPL. When we said “Good night” after our final summing up, we felt well satisfied. Of course, Phoenix had a long programme ahead before night overtook it, and we promised to keep viewers up to date. They were not disappointed – neither were we. The images obtained were invaluable as had been hoped, water ice was found below the surface and in September 2008 the first snowfall was recorded. Jim Whiteway, lead scientist for Phoenix’s Meteorological Station, said that Phoenix, “has detected snow falling from Martian clouds. The clouds are composed of ice crystals, and some of the crystals are large enough to fall through the atmosphere…

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we are going to watch very carefully for evidence that snow is actually landing on the surface. This is a very important factor in the hydrological cycle on Mars, with the exchange of water between the surface and the atmosphere”. In every way Phoenix has been a success, and I will always be glad that despite the BBC’s inability to cover the landing officially we were able to fill the gap. Will we be able to make a live broadcast of the discovery of Martian life? I hope so, even if we have to re-equip the dining room studio. I am becoming more and more confident that life will be found. It is such a pity that there are no Lowell-type Martians!

Chapter 33

Devil’s Advocate

(From left to right) Dr. Chris Lintott, Dr. Kate Land, myself and Dr. Gerry Gilmore (Credit: Chris Wheeler)

In May 2008, we came to Programme 666 in “The Sky at Night” series; we began in April 1957, and have not missed a month since (and there have been many extra programs for special events, such as the recovery of Haley’ Comet in 1984). Well, 666 is the number of the devil, so we decided upon dealing with problems that we have so far been quite unable to solve – possibly because we are prevented from doing so? We broadcast from the Farthings dark room, suitably darkened. Four of us sat round the table. I was in the Chair, acting as Devil’s Advocate and asking questions and being as awkward as I could. Being interrogated were Dr. Gerry Gilmore, Dr. Kate Land, and Dr. Chris Lintott. Did we get anywhere, or did we have to admit that, to use my own catchphrase: “We just don’t know”? Either way, I remember this as a particularly enjoyable programme. P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_33, © Springer Science+Business Media, LLC 2010

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As a start, let us look back at the origin of the Universe, which, we are now fairly sure dates back 13.7 thousand million years – but strictly speaking we are not talking about the origin of the Universe at all, we are discussing its evolution, which is by no means the same thing. When we go back to our starting point, we are faced with two choices – neither of which is understandable. Either (a) the Universe began at a definite moment in time, or else it did not; (b) if it began at a set moment as the Universe itself. The only alternative is to say that the Universe has always existed, so that there was no beginning. But we are no better off here because however far back we look there is always a “before”. I cannot understand either of these. Most astronomers go (a), but to me – “we just don’t know”. After the Big Bang, say the experts came the start of the expansion. If there were no initial “clumpiness”, and everything was completely smooth, galaxies and stars could never have been formed, and so it was a great relief to theorist when COBE, the Cosmic Background Explorer, detected slight temperature variations which showed that clumps – region of greater density – had indeed formed. But the cosmic microwave background was similar in all directions, and this indicated that the universe was once so small that all parts of it could be in touch with each other (if we see two galaxies, each 9,000 million light-years from us but in opposite directions, it would take a ray of light 18,000 million years to cross from one to the other, and the universe as we know it is not as old as that). So, say the cosmologists, there was a brief period of inflation, a millisecond after the Big Bang, when the universe was so small that all parts of it could be in touch with each other; there was a brief period of inflation, when the fledgling universe expanded a speed much greater than that, after which the rate of expansion slowed down its present value. “But nothing can exceed the speed of light. So how could the universe expand at that rate? Einstein said…” “Ah! Einstein said that nothing within our present universe can exceed the speed of light, but with inflation theory we are talking about the expansion of space itself, which is the same thing!”

All this sounds suspiciously like fudge, so let me turn to an unmistakable fudge introduced by Einstein himself. We know that the universe is expanding, with each group of galaxies racing away from all other groups; the further apart they are, the faster they are separating. Gravitational influence should make the rate of expansion slow down with age – but it does not. In the remote reaches of the universe the rate of expansion is increasing, not decreasing. I asked; “Why?” Einstein’s original equations did not give him the static universe that he wanted, i.e. either expanding or shrinking, so he introduced the “cosmological constant”, a force acting against gravitation. The result did provide a static universe, but using the cosmological constant meant that Einstein missed predicting the fact that the universe is expanding; he later called this his “greatest blunder”. Now we know that we need it after all, in modified form, to explain why the rate of expansion has been accelerating for the last few million years. But what exactly is it? Here, we enter the mysterious realm of dark matter and dark energy.

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The idea of dark matter was originally due to an eccentric Swiss astronomer, Fritz Zwicky, who spent most of his life in America. “Eccentric” is certainly a mild term. He used to describe his colleagues as spherical bastards, because they were bastards no matter from which direction you looked at them. He realised that the individual galaxies of a group would fly apart unless something was “glueing” them together, and also that spiral galaxies, such as ours, were not rotating as they would do if the main mass were concentrated in the centre. They did not obey Kepler’s Laws. Remember that in the Solar System, well more than 99% of the total mass is concentrated in this central body, the Sun. There had to be a vast amount of missing mass in the shape of invisible matter and it now seems that this invisible matter is responsible for more than 90% of the total mass. But what is it? The next question I put to the experts. Well, as a start it is not dark, so that name is misleading. If it were dark, it would blot out objects beyond it, and we would be able to track it, just as we do with dark nebulae. It must therefore be transparent. It sends out no radiation at any wavelength, but it does have gravitational effects. Over to the particle physicists: when faced with a knotty problem, their usual recipe is to invent a new particle. WIMPS have been postulated – Weakly Interacting Massive Particles. Nobody has managed to detect them, so if they exist we have to ask whether they are baryonic, i.e. made up of matter of a type we can understand, or whether they are totally alien. These are how things rest at the present. We are confident that dark matter does exist, but we have not the faintest idea what it is like. “And what about the acceleration of the universe?” Answer: “This is due to dark energy, which acts in opposition to gravity”. Gravity weakens with increasing distance, whereas dark energy strengthens. In effect, we are back to Einstein’s cosmological constant, which he abandoned as a fudge. Unless all our observational results are wrong, the acceleration is real, so that some kind of force must be responsible – but if dark matter is mysterious, dark energy is even more so. We do not have any idea of how to investigate it, and we have run up against a scientific brick wall. We must just keep trying. There are other fundamental problems, and I could not resist bringing up one of them. “Is there intelligent life elsewhere in the universe, or are we unique? And if intelligent life does exist, what will it be like?” The response was exactly what I expected. Our Earth is a very ordinary planet, orbiting a very ordinary star. There are 100,000 million stars in our galaxy, many of them attended by planets; there are many thousands of millions of galaxies, so that the number of worlds suitable for life must be staggeringly great. But if life COULD appear, WILL it? We cannot be sure, and as yet we have not detected life except on Earth. Until we do, we cannot hope to answer either of my questions. Time and time again we come to a point where we have to admit that. “We just don’t know”. Will we ever knows? Or will something forever top us? 666…

Chapter 34

Galaxy Zoo

Chris Lintott (Credit: Robin Rees)

We know that our Sun is one of the 100 thousand million suns in our star-system or galaxy. We also know that our galaxy is not the only one. There are countless millions of others, a few of which, such as M.31 in Andromeda, are visible with the naked eye. Some are graceful spirals, like Catherine wheels. Some are “barred wheels” with arms issuing from the ends of a bar through the major axis of the system. Some are elliptical, some are spherical and some are irregular. Astronomers are very anxious to find out the relative numbers of the various forms, but a full analysis is difficult simply because of the sheer quantity of galaxies available. During a “star party” at my observatory, Chris Lintott had a brainwave. He discussed it with Professor Bob Nichol, who was with us, and the “Galaxy Zoo” project was born. It was soon in full swing, and by August 2008 we were ready to present a program about it. With us was another enthusiast, Dr. Kate Land. Surveying a few hundred galaxies, or even a few thousand, is all very well, but to tackle millions is too much for any astronomer, or any ordinary team, and various telescopic surveys, notably what was known as the Sloan Digital Survey, had P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_34, © Springer Science+Business Media, LLC 2010

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recorded vast numbers – as tiny images. But which were spirals, which were ellipticals, which was irregular? Sloan and the other telescopic surveys could not say. Chris Lintott’s idea was staggeringly simple and yet staggeringly logical; Bring in the amateurs. The Sloan images could be made available on a website set up purely for the purpose. The volunteer helpers (mainly amateur) would select a galaxy, obtain its image and answer a few definite questions about it. What type was it – if spiral, did it seem to be rotating clockwise (arms trailing) or anti-clockwise (arms leading)? Obviously one could not see a galaxy move (!) but the arrangement of the arms would indicate the direction of spin. This was not as easy as might be thought. The images were very small, and tricky to interpret, so that, for example, it was only too easy to confuse an elliptical with a spiral seen almost edge-wise on. I soon found this out. I am an observer of the Moon rather than galaxies, but I joined the project immediately. I passed a preliminary test to show that I was competent, and began work. The test involved classifying twenty objects whose forms were known. It must be said that one volunteer who was a professional astronomer failed; I do not know who it was – the organisers keep his identity strictly secret! I found that to classify a galaxy took me between 2 and 3 min, but in some cases much longer. Occasionally, I had to admit that I could not decide. When Chris and co-organisers began work, they had absolutely no idea of how viewers would react. Replies came in not in dribs and drabs, but in thousands. The website was swamped, and within a few weeks the volunteers numbered 160,000. More than a million galaxies had been surveyed, many by up to 60 different observers. Professionals, at first rather dubious, soon realised how valuable the project was. Generally speaking the observers agreed with each other very well. All this showed that the level of popular interest in astronomy really was surprisingly high, and also that to carry out surveys of this kind amateurs are just as reliable as professionals. Since they are more used to actually looking through telescopes, they may even be better. One of the most intriguing aspects of the Zoo is that one may at any one time happen upon something really weird. A Dutch amateur, Henny van Arkle, did so when she found an object which defied classification. Sensibly she at once notified the project leaders, and before long some large professional telescopes were turned towards the “Voorwerp”, as it was nicknamed (Voorwerp is Dutch for “unknown”). Learned papers were published. We still do not know what it is. I have looked at it very carefully, and I am baffled. Chris Lintott thinks that it may be a cloud of gas that has been affected by a nearby galaxy which used to be much more active than it is now – but what is the origin of the original cloud? Apparently, the Voorwerp contains no stars at all. No other Voorwerps have been found, but it is surely unlikely that Henny van Arkle’s discovery is unique. Interesting facts have emerged from the survey. In general, spirals tend to be dominated by hot young blue stars, ellipticals by stars which are old and red, but the Zoo results show quite considerable numbers of “red” spirals and “blue” ellipticals. The spin directions of the spirals have led to much discussion. Much depends upon the angles from which we view them, but the numbers of clockwise and anti-clockwise

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spinners do not seem to be quite equal, for reasons which are still unclear. Further researches are needed. The project planned by Chris and Bob at my observatory that night has been wildly successful, and it is being continued. If you are interested in helping, you will find all details on the Galaxy Zoo website [http://www.galaxyzoo.org/]. Such a comprehensive survey could not have been carried out in any other way – how else could you muster, and organise, over a 150,000 observers? New projects along similar lines are now being worked out! During the August program, I brought up one further point. People who live in or near cities seldom see the sky; this is too much glare, and trying to use a telescope is hopeless, so that the would-be observer can do virtually nothing. Galaxy Zoo changes all this. Using the Internet, our town-dweller can join in, and be just as useful as his country cousin. So keep watching our website – and good luck to you. Who know, you may even find a new Voorwerp!

Chapter 35

Four Hundred Years of the Telescope

Allan Chapman and myself on 15 February 2008 (Credit: Patrick Moore)

For the first week of the New Year, several programmes on BBC2 were to ­commemorate the 400th anniversary of the first astronomical observations made with telescopes. The first of these programmes was the “Sky at Night”. We decided to look back at some of the telescopes we had visited since that first programme, way back in 1957. Various people were shown – in various locations – and we used extracts from the actual interviews. The earliest, I think, was with George Hole, for the 50th programme. We were down at Brighton, with George’s fine 24-in. reflector, hoping to give direct views of Jupiter and Saturn. Of course, it was “live” – everything was, in those days – so that we were at the mercy of the clouds. Five minutes before transmission, and 5  min late, the sky was brilliantly clear, but during the actual transmission cloud-cover was complete. As George said: “Totally obscured!”

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I introduced the programme from my observatory at Selsey. Among astronomers shown were Allan Chapman, Howard Bond, Kim Hermann, Peter Wehringer, Roger Angel, Pete Lawrence, Michael Barstow, Jeff Hoffman, Geoff Marcy, John Culshaw, Michelle Dougherty, Richard Ellis, and of course, Chris Lintott. Quite a galaxy – but it was a pity about those clouds… Who invented the telescope – and who first turned a telescope skyward? Most people would say “Galileo”, but they would be wrong. The first telescope about which we have definite information was made by a Dutchman, Lippershey, in 1608. Earlier reports coming from England are interesting, but not conclusive. Unfortunately for himself, Lippershey did not take prompt steps to establish priority, and other telescopes quickly appeared over Europe. Galileo obtained one during 1609, and “sparing neither trouble nor expanse”, as he put it, made one for himself. On July 26, 1609, came the first known astronomical observation made with a telescope; Thomas Harriot, one-time tutor to Sir Walter Raleigh, used his tiny “Dutch tube” to look at the crescent Moon and to marvel at the mountains, the valley, the craters, and the grey plains we still miss-call “seas”. Within a year or two, he had constructed a remarkably good map of the Moon. It was far better than any of Galileo’s lunar work, but he did little else astronomically, and it is Galileo who is rightly called the first true telescope observer. From January 1610, he made a series of spectacular discoveries, notably the four main satellites of Jupiter, the phases of Venus, spots on the Sun, and the “myriad stars” of the Milky Way. He even saw that there was something strange about the appearance of Saturn, though he could not make out its true nature. Galileo’s most powerful telescope magnified a mere 30 times, and was nothing like so effective as a pair of modern binoculars, quite apart from the fact that it had inconveniently small field of view. Its object-glass is convex, and the eyepiece lens is concave; a “Galilean” is bound to give a great deal of false colour. It was some time before this problem could be tackled, and although it is true to say that modern lenses give very little false colour, it would be wrong to claim that they give none at all. Isaac Newton never did solve the problem, which was one reason why he abandoned refractors altogether and turned his attention to reflectors, building the first “Newtonian” 60 years after Galileo’s pioneering work. This certainly eliminated false colour, and a mirror is much easier to make thank a lens, but of course they have their disadvantages too. Reflectors can be temperamental, and requite regular servicing, which a refractor does not. For an early programme I did show Galileo’s telescope, and also Newton’s, but let me move on to the largest nineteenth century, the 72-in. reflector at Birr Castle, in Southern Ireland. It was homemade by the third Earl of Rosse, who had a lively interest in astronomy and is the supreme example of what my old friend Dr. Allan Chapman called a “grand amateur”. Lord Rosse wanted to build a telescope larger than any of its predecessors (at that time the record holder was Sir William Herschel’s 49-in. reflector) and, amazingly, he succeeded even though he had to

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make his own equipment and cast the huge metal mirror, an alloy of copper and tin – the casting process, vividly described by an onlooker, must have resembled a major display of pyrotechnics. The only assistants came from the Earl’s, and were workers trained by Lord Rosse specially for the purpose. The telescope was unwieldy and difficult to handle but it worked well, and was used to show the spiral structures we now know to be galaxies. It was, for some time, in a class of its own, but later in the century was overtaken by the new large refractors. For many years, it was out of action, but thankfully is now fully operational again (I am proud to say that I had something to do with this). It remains unique in the history of science. Refractors were in vogue near the end of Victorian times, and almost all the largest telescopes of this kind were built before 1900 – notably the largest of all, the 40-in. at the Yerkes Observatory. This may be the useful limit, because an object-glass has to be supported round its edge, and if too heavy will distort under its own weight. A 49-in. was once made, but was a total failure, so that for Earthbased telescopes, at any rate, the Yerkes 40-in. is not likely to be surpassed. I admit that my own favourite is the 24-in. of the Lowell Observatory in Arizona, which I used a great deal in my pre-Apollo Moon-mapping days. There is one branch of observational amateur for which a refractor is far more suited than a reflector: solar work. Turn a Newtonian toward the Sun, and you are likely to cook your secondary. Heat is bad for mirrors, and also for eyepieces. Much the best way to study the solar surface is to use a refractor, and project the image on to a screen fixed behind the eye-end of the telescope. Moreover, adding H-alpha equipment is relatively easy with a refractor, the main problem being finance. Come back now to our historical story. After the large refractors we reach the twentieth century, and the dominance of single-mirrors. Glass, coated with a thin layer of silver or copper, took over from metal, and progress was amazingly rapid, due largely to George Ellery Hale, in America. Hale’s constant call was for “More light!” and he master-minded first a 60-in. and then, in 1917, a 100  in. both of which were set up on Mount Wilson in California. Hale was well aware of choosing sites with the best available seeing conditions, and this meant high altitude, above the thickest part of the Earth’s atmosphere. For three decades, the 100-in. reflector was in a class of its own, “spiral nebulae”, measuring their distances and proving the spirals were separate galaxies, far beyond our Milky Way. No other telescope of the time had sufficient power to make observations as delicate as this. The 100-in. remained the largest until 1948, with the completion of the 200-in. on Palomar Mountain (again planned by Hale, though sadly, he did not live to see it finished). The 200-in. was supreme for a while, and in 1952 enabled Walter Baade to show that the observable universe was twice as large as had been believed. But two major developments lay ahead. The larger mirror, the more difficult it is to make. Quite apart from this, these is the problem of our unsteady atmosphere. By the end of the war virtually all astronomical research was carried out photographically, so that images were blurred. New techniques, known as active optics and adaptive optics, reduced these effects very significantly. But even more important was the rise of electronics, and well

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before the end of the twentieth century electronic devices had taken over from sensitive plates, just as photography had superseded visual observations a 100 years earlier. On my study wall, I have an image of Saturn taken with my 15-in. reflector a few weeks ago. It is far better than anything which could have been produced by the best professional observatory as recently as 1990. Electronic aids have made all the difference. The Palomar reflector is no longer the world’s largest, and is not even in the “top twenty”. Atop Mauna Kea in Hawaii, 14,000 ft above sea-level, you will find the Keck I and Keck II telescopes, each with a 100-m (387-in.) mirror and capable of working together. On Cerro Paranal, in the Atacama Desert of Northern Chile, is the VLT or Very Large Telescope, where each of the four components has an 8-m (630 in.) mirror. Together, they can pick up the light of the objects over 13,000 million light-years away – and remember, the universe as we know it is no more than 13.7 thousand million years old. These huge mirrors are not single, but segmented, i.e. made up of hundreds of individual parts fitted together to form the correct optical curve. There are of course space telescopes orbiting the Earth, so that seeing condition are perfect all the time, and no incoming radiations are blocked out by the Earth’s atmosphere. The 94-in. Hubble Space Telescope, launched by NASA in 1990, was the first; others have followed and have provided data impossible to obtain from ground level. We have indeed come a long way since Harriot had that first view of the crescent Moon through his time “Dutch tube”, 400 years ago. How far will we go during the next 400 years? Your guess is as good as mine!

Chapter 36

The Merry Dancers

Aurora (Credit: Peter Lawrence)

Polar lights – Aurora Borealis in the northern hemisphere, Aurora Australis in the southern – have been known since early times; in Scotland, they were called the “Merry Dancers”, supernatural beings enjoying themselves in the heavens. To Eskimos, they represented a game of football played by spirits using a walrus-head as a ball. From England, they are not often seen really well; from higher latitudes, they are more frequent, and can be breathtakingly beautiful. For this programme Chris Lintott and Pete Lawrence went to Tromso in North Norway, and were rewarded with a brilliant display. Sadly, I could not go (I love Tromso), but back in Selsey I was joined by two researchers deeply involved in this work; Dr. Chris David, from the team STEREO (Solar Terrestrial Relations Observatory) and Professor Tony van Aiken, former Director of EISCAT (European Incoherent Scatter Scientific Association), which uses three radar systems in

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Scandinavia to study interactions between the Sun and the Earth as revealed by disturbances in the ionosphere and the magnetosphere. I first saw the Northern Lights in 1938 – not from Norway, but from my then home time, East Grinstead in Sussex. It was a beautifully clear winter evening and the whole sky was glowing a brilliant red. I wondered whether there could be a huge fire somewhere in Ashdown Forest, and it took me several minutes to realise that I was being treated to a brilliant display of aurora. After all, a Roman emperor, the much-maligned Tiberius, once made the same mistake when he sent his firefighters to quench what he thought was a huge blaze in the port of Ostia. After that display, I began to look up old stories and legends about the Lights. I found plenty of them. The nickname “Merrie Dancers” is Scottish; supernatural beings were cavorting about in the heavens – not always peacefully, because a red aurora showed that blood had been spilt. From Scotland aurorae are more frequent than they are south of the border. To some of the Eskimos, an aurora indicated a game of football played by spirits using a walrus-head as a ball (perhaps Reykjavik United versus Longyearbyen Town?) but in Siberia the tables were turned, where the walruses were the players and the ball was the human head. In Russia, the Lights were associated with the fire dragon Ognenniy Zmey, who approached women and seduced them while their husbands were away. There are legends everywhere. The Greenlanders believed that people who had passed on to the next stage of existence were signalling to their kinsfolk who were still on Earth. The Faroe Islanders kept their offspring indoors during displays, in case the Lights came down and singed their children’s hair, while in Estonia the aurorae were down virmalised, spirits from higher planes, sometimes friendly and sometimes not. To the Inuit of Alaska the Lights are people who have gone to the sky and are dancing to remind their loved ones that they are still around. The Finnish name for aurorae is revontulet, or sparks whisked upward when the Lapland foxes wagged their tails. The Sami people believed that the Lights (guovssahasat) could be dangerous, and might even descend and kill anyone who made fun of them. And in parts of Scandinavia it was said that the Lights were warlike Valkyries, “mounted upon horses and armed with helmets and spears…When they ride forth…their armour sheds a strange flickering light, making what men call the “aurora borealis (Thomas Bullfinch, 1855)”. There were more scientific explanations too. In Denmark and Sweden, it was believed that aurorae were due to volcanoes in the far north, put there to provide mankind with light and heat. The Inuit of Hudson’s Bay thought that the sky was a solid dome, and that the stars were holes letting through light from a shining background. But my favourite explanation is Norwegian; the Northern Lights are reflections in the sky cast of swarms of presumably luminous herrings swimming happily in the Arctic Ocean! Early astronomers had their own ideas. The Greek philosopher Anaxgoras (c. 500–428 bc) knew about aurorae, even though they are seldom seen from Greece, and attributed them to fiery vapour poured down in to the clouds above, while the Roman writer Se eca (5 bc–ad 65) put them down to currents of boiling at very high altitudes. Because the stars moved so quickly, they could emit enough

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heat to set them alight. The term “aurora” was coined by the French astronomer P. Gassendi in 1621, and the first scientifically accurate account was written in 1650 by K. Gesner of Zurich. It is not true that aurorae are the best seen from the North Pole – far from it. The electrified particles from the Sun do make for the north magnetic pole, but are captured by the Earth’s magnetic field, and the most favourable observing site are in the “auroral oval”, a belt centred on the magnetic pole. Generally, the Oval remains north of England and brushes Scotland, but during a solar storm it may broaden sufficiently to cover the whole of the British Isles. I have hunted aurorae in Hudson’s Bay, Alaska, Finland and Norway, but I have had my best views from Tromso in North Norway, which is why I took “Sky at Night” viewers on trips there, though I admit that I was influenced by the fact.

Chapter 37

The Fountains of Enceladus

Fountains of Enceladus (Credit: NASA)

At the time of this programme, Saturn was in Leo at opposition and thus well place observation. The rings were edgewise-on, so that the planet was temporarily shorn of its beauty, but to make up for this, there was a great opportunity to watch the satellites. Two were very much in the news: Enceladus. With its icy fountains, and Titan, with its chemical lakes. The Huygens space craft, still orbiting Saturn and

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sending back a stream of data, had now proved that the lakes were liquid, and made up of ethane with other hydrocarbons. For this programme, I was joined by two very special friends of “The Sky at Night”, Professors Michelle Dougherty and John Zarnecki. Saturn has wealth of satellites. More than 60 are known by now, but only one of these, Titan, is larger than our Moon. Before the start of the Space Age, nine had been discovered. The rest are tiny and probably asteroidal. The two closest-in of the main satellites are Mimas and Enceladus, both discovered in 1789 by William Herschel with his 49-in. reflector (one of the few achievements of this great telescope). Both are small, Enceladus 320  miles in diameter and Mimas only 260; before the Huygens mission, both were expected to be icy, inert and cratered. This is true for Mimas, but Enceladus has proved to be a remarkable little world. Huygens took close-range photographs of both satellites. Part of Enceladus was speckled with rather small craters, but there were also wide areas which seemed to be more or less crater-free and gave the impression that they had been re-surfaced in the fairly recent past. This was odd enough, but later discoveries made the situation even odder. Near the south pole there were streaky features nicknamed “tiger stripes”, which turned out to be deep surface cracks, and there were indications of an atmosphere. It was extremely thin, but it was a major surprise. The gravitational pull of Enceladus is so weak that it would not be expected to hold down any atmosphere at all. Michelle Dougherty had designed an instrument to study Saturn’s magnetic field. As Huygens flew past Enceladus, the instrument showed disturbances which could well be due to salty liquid. Intrigued, Michelle persuaded the controllers to make a still closer pass of the satellite. It was well worth while. The atmosphere really existed, and from the south polar vents there gushed geysers of ice crystals. This meant that we were dealing with an active world, presumably with an underground ocean – but in view of Enceladus small size and low mass, this seemed to be impossible. Two other points struck me immediately. First, why should Enceladus be so unlike Mimas, which is ice-coated everywhere, and which has one immense crater. It is totally inert, with no trace of atmosphere. Second, as Enceladus has geysers now, they must have been active for a very long time. We can hardly believe that they have been turned on specially for us, just as we have developed equipment capable of observing them. The particles gushed are certainly responsible for the existence of the E ring, which is incredibly tenuous but which extends from the orbit of Enceladus out to well beyond the orbit of Dione, the fourth of Saturn’s principal satellites. Moreover, the geysers must be “feeding” the ring all the time. The vents from which the geysers issue are not large, and in size are comparable with football fields. They have been called “hot”; at a temperature of 9–90°C, this does not sound inviting, but the general temperature of the surface is a chilling −200°C. There are no observed geysers or tiger stripes away from the south polar region, and spectroscopic analysis show that, as expected, the crystals are of

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o­ rdinary water ice. There is no escape from the conclusion that the sub-crystal sea must be warm enough for the water to remain liquid. What can be the cause of this internal store of heat? Tidal effects have been proposed, and they certainly work for Jupiter’s satellite Europa, but there are ­difficulties here, one of which is the inertness of Mimas. It has also been suggested that Dione, much larger and more massive than Enceladus, might be involved in some way, but this appears to be even less probable. Huygens has told us a great deal, and it is still being helpful. For instance, the geyser activity varies considerably from one pass to another. But for real progress we may have to wait for the next Saturn mission, tentatively scheduled for launch in 2021. For the moment we have to confess that we are completely baffled, and that Enceladus has defeated us. Its underground sea and its ice fountains simply cannot exist. But…they do!

Chapter 38

The Herschel Telescope

The Herschel Telescope (Credit: Arianespace ESA)

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Following the successful launch of the Keper mission, two more major missions were planned: Herschel and Planck. For our April programme, we concentrated on Herschel, and we were joined by Dr. Thomas Passvogel, from Holland, Professors Matt Grifflin, and Seb Oliver, with me in Selsey, and Dr. Allan Chapman, with Chris Lintott in my observatory dome. We had decided to try something. Four of Saturn’s satellites – Dione, Enceladus, Tethys, and Rhea – were due to transit the planet at the same time. Quadruple transits were very rare – I have never seen one! – and in the dome of my 15 in. reflector, Pete Lawrence prepared to take photographs and Paul Abel to make sketches. Alas, for once the Selsey weather let us down, and we were clouded out. But you cannot be lucky every time! This was Jane Fletcher’s last programme as producer. After 6 years with us, she was retiring. It was sad to say farewell. She has been a tower of strength. Visual light makes up only a tiny part of the whole range of wavelengths. Beyond the short-wave end of the visual range, we have ultra-violet, X-rays and gamma-rays. Beyond the long-wave end, we have infra-red, microwaves and radio waves. Today, we have instruments to study all these, and they make use of spacecraft because these frequencies are blocked by our atmosphere. Infra-red studies are of vital importance to astronomers, because it means that we can “see” through dust – and there is a great deal of dust in space. It also means that we can examine very cool objects, not able to show visually. It is easy to show this. Switch on an electric fire and you will feel the infra-red as heat. Well before the bars become hot enough to glow. Serious infra-red astronomy really began in 1983 with IRAS, the Infra-Red Astronomical Satellite. It functioned for less than a year, but it discovered a large number of new discrete sources, plus a huge cloud of cool, probably planetforming material round Vega. Other infra-red missions have followed, notably the immensely successful Spitzer Space Telescope, and now we have Herschel, built in Holland by the European Space Agency and launched from Kourou in South America. Its 3.5 m mirror – which is single, not segmented – is the largest ever launched, much larger than Hubble. The whole probe weighs 3.3 tons. It is named after William Herschel, who is best remembered for his discovery of Uranus in 1781, but who carried out work in all fields of astronomy. In 1800, he was studying the spectrum of the Sun, and realised that there were radiations beyond the red end of the rainbow band. He called them “black light.” We know them as infra-red. Stars are born in dusty regions, so that the actual processes of star formation are hidden in visual light. Infra-red comes to the rescue, and Herschel will be particularly valuable because it will look into the far infra-red beyond the range of its predecessors. To quote Dr. Poglitsch, one of the main investigators: “With the help of Herschel we will be able to see even small gas clusters masses down to 1/10 of the Sun’s mass. We will check if these stars-in-the-making already show the same mass-distribution as adult stars.” It should also be possible to obtain high-quality images of very remote, numbingly cold objects.

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The whole equipment will itself have to be chilled, and this is done by using liquid helium. This means that the telescope must have a limited lifetime, because the liquid helium will be exhausted in less than 5 years and the thin mirror, with its f/0.5 focal ratio, will become too warm to operate. The obvious question is: Why not re-fill the liquid helium tank? Answer: Because Herschel will be too far away. Unlike Hubble, it is not orbiting the Earth, but is orbiting the Sun at what is called the L2 lr Second Lagrangian Point, a stable point beyond the Earth’s orbit where a body will have the same orbital period as the Earth. The main advantage of the L2 point is that it is isolated, and therefore not affected by radiations from Earth, either natural or man-made. Herschel did not start his journey alone. With it was Planck, designed to study the CMB or Cosmic Microwave Background – the aftermath of the Big Bang, 13.7  thousand million years ago. Once they separated, safely away from Earth, Herschel and Planck said good-bye rather than adieu, because they will never meet again. By 2013, both will have ended their active careers, but they will have given us new insight into the nature of the great universe around us.

Chapter 39

Onward to the Moon

With Neil Armstrong; photo with my film camera!

Man reached the Moon in July 1969; for the 40th anniversary, we obviously had to look back at it. Accordingly, we dealt with lunar mapping in June and the Apollo 11 mission in July. In June, I was joined by Pete Lawrence, Allan Chapman, Chris Lintott and Ian Crawford. In July, also by Chris Riley, John Davies, Katherine Joy, Jon Culshaw, Gerry Gilmore, Buzz Aldrin, Colin Pilinger, Gene Cernan and (recorded earlier) Neil Armstrong. Quite a galaxy of astronautical stars... I hope we presented a fairly comprehensive programme, and viewers seemed to like it, even though (as usual) our faithful TV scheduling friend, Mr. Dixon, put us “on air” at a time when more people retired for the night. After all, why should he regard a mere Moon landing as more significant than a soap opera or a quiz? P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_39, © Springer Science+Business Media, LLC 2010

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Nobody who has ever looked at the Moon can have failed to see the dark patches once believed to be oceans. No doubt sketches of them were made in very early times, but no Greek or Egyptian lunar drawings have come down to us, and the first known map of the Moon goes back only to the late seventeenth century. It was the work of William Gilbert, the pioneer researcher of magnetic phenomena, also physician to Queen Elizabeth I. This was before telescopes became available, so that Gilbert had to depend upon naked-eye work. His map was published in 1651, but it must have been completed before the end of 1603, for the excellent reason that this was the year in which Gilbert died. It shows several of the “seas” in ­recognisable form, so that it did at least make a start in lunar cartography. Then came the invention of the telescope, by Dutch optical workers – not by Galileo, as is popularly believed. Neither was Galileo first to turn a telescope Moonward. That distinction goes to the English mathematician Thomas Harriot, one-time associate of Sir Walter Raleigh, in the summer of 1609. Harriot obtained a telescope from Holland, and used it well. His map of the Moon was much better than Galileo’s, as well as having been drawn 6 months earlier, but he never publicised it and never followed it up, probably because some of his Court friends were out of  favour. Raleigh was executed – Harriot was no doubt wise to keep out of the limelight! Galileo did produce a map, and by measuring shadow lengths was able to estimate the heights of some of the lunar mountains. He believed them to be higher than they actually are, but he was not too wide of the mark. The next major advance in lunar mapping was made by Giovanni Riccioli, and Italian Jesuit, who drew a map in 1651 and introduced the system of naming important craters after famous early astronomers. Because Riccioli named all the major craters, later astronomers had to have their names assigned to much less prominent formations. The first really great lunar observer was a German, Johann Hieronymus Schfoter, who in 1777 set up a private observatory at Lilienthal, near Bremen, and equipped it with the best telescopes available, including one made by William Herschel. He was tireless worker, and made many hundreds of drawing which formed the basis of later observations – but sadly, his observatory and unpublished records were destroyed in 1813 by invading French troops. Even his telescopes were lost, because they were brass-tubed, and the French soldiers believed them to be made of gold. The mantle of Schfoter fell upon two of his countrymen, Wilhelm Beer and Johann Madler. They began lunar work in 1830, and 9 years later, they published a map which was incredibly good even though they used only a small telescope, the 3/4 in. refractor in Beer’s observatory. The map was accompanied by a book, “Der Mond,” containing a description of every named formation. Amazingly, it has never been translated into English. I only wish I could speak German. Any volunteers? Not much more was done for some time, because it was widely believed that Beer and Madler had achieved everything that observers could manage. There was one observer who kept on studying the Moon. This was Julius Schmidt, also German but who became Director of the Athens Observatory in Greece. In 1866, he made a startling announcement, an indication of change on the lunar surface. In the plain of the Sea of Serenity (Mare Serenitatis), Beer and Madler had drawn a small but conspicuous crater, named Linne. Schmidt re-observed

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the area, and found that Linne no longer existed as a crater, but had been replaced by a small white spot. This caused intense interest had been replaced by a small white spot. This caused interest everywhere, and telescopes all over the world were swung back to the Moon. Had there been any real change? The answer, surely, must be “no.” The appearance of Linne does change strikingly according to the angle of solar illumination. I have made many observations myself and I have found that there are occasions when Linne does look like a crater, while at other times it is no more than a white spot. The final clue came much later, when spacecraft had been sent passed the Moon, and sent back very detailed images. Linne is in fact a small, perfectly normal crater, surrounded by a white nimbus. This means that Beer and Madler were wrong, but this is quite understandable because, as noted, they used a small telescope. Any major surface changes on the Moon date back at least 2,000 million years, and the main features were formed long before that. There was an argument about the origin of the craters. Were they volcanic, or were they produced by meteorites hitting the Moon – a cosmic bombardment? The argument began in the eighteenth century, and was only finally settled in recent years. I admit that I was on the wrong side. I was convinced that the craters were of volcanic origin, but it is now quite definite that they are impact structures. Photography began to play a major role in lunar work during the latter part of the nineteenth century. Then, after the 1890s, photographic lunar atlases were produced, and we began to realise that we had a really good working knowledge of the whole of that part of the Moon which we can see from Earth. The Moon rotates in the same time that it takes to complete one orbit of the Earth. There is no mystery about this. Tidal forces over the ages have been the cause. However, it means that part of the Moon is always turned away from us, and before the Space Age we knew nothing definite about it. The edges of the Earth-turned hemisphere are so foreshortened that they are difficult to map accurately, and it is not easy to tell a crater from a ridge. When I began observing the Moon, when I was still in my teens, I did my best to map these foreshortened areas. Because the Moon’s path round the Earth is not quite circular, there is a slight “wobbling” which means that small parts of the far side are brought in and out of view. This effect is known as libration. Altogether we can see 58% at any one time. There were all sorts of theories about the permanently averted regions, but we had to wait for the arrival of spacecraft. The idea of sending rocket to the Moon seemed pure science fiction well into the twentieth century. Then, however, came the breakthrough. In 1957, the Russians sent up the first artificial satellite, Sputnik 1, and ushered in the Space Age. Only 4 years later, the astronaut made a flight around the Earth – Yuri Gagarin – whom I had the honour of meeting on several occasions, but even before that a Soviet spacecraft, Lunik 3, had been right around the Moon and sent back the first pictures of the far side. The Russians had actually sent for my own drawings of the libration areas, so I did pay a part. I was a minor member of a very large team of observers. During the early 1960s, spacecraft from both Russian and America went passed the Moon and sent back photographs which made all earlier maps obsolete. Moreover, spacecrafts were actually landed on the lunar surface, and made one very

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important discovery. There had been suggestions that parts of the surface were covered with deep dust drifts, so that any spacecraft landing there would promptly sink out of sight. If this theory had been correct, then travel to the Moon would have been impossible, but the fact that automatic vehicles landed safely shoed that this was not the case. Men really could go to the Moon. In 1961, President Kennedy of the USA announced plans for sending the first astronaut to the Moon before 1970. At the time I thought that this was being widely optimistic, and I said so! I was wrong. The Apollo programme was under way, and as we all know, the first landing was made in 1969 by Neil Armstrong and Buzz Aldrin in Apollo 11. Do you remember where you were when the first landing was made? I know exactly where I was – in Studio 7 at the BBC Television Centre, carrying out a live commentary. Believe me, the atmosphere was tense. There was so much that could go wrong – and if the astronauts had made a faulty landing they would have been doomed. There was provision for rescue, so when I heard Neil’s voice; “The Eagle has landed!” I felt a sense of immense relief, shared by viewers all over the world. For our programme in July 2009, the 40th anniversary, I was able to broadcast an interview I had made with Neil Armstrong, and I was honoured when Buzz Aldrin also joined me. Later astronauts knew what to expect. Neil and Buzz did not, and were literally “going where no men had been before.” They were great pioneers. All in all, I think that it is fair to say that the Moon turned out to be very much as expected. The gravity is only 1/6th as strong as that of the Earth, and the lunar atmosphere is so thin that to all intense and purposes it can be forgotten. Neil and Buzz had no difficulty in walking around the Moon, and they were able to bring samples of Moon rock back for analysis in our laboratories. The rocks were purely volcanic, but there is no active vulcanism on the Moon now. The dinosaurs could have seen the Moon looking almost the same as it does today – though it is hardly likely that they bothered to look! Other explanations followed. Apollo’s 12, 14, 15, 16 and 17 made successful landing, and our knowledge of the Moon was improved beyond all recognition. Equipment was left on the surface, and sent back data long after the astronauts themselves had departed. What next? Well, there is every prospect of establishing a base on the Moon, and this will be of the utmost value to mankind. To give just one example, a lunar base would be major centre for medical research. There will be a physical laboratory, and of course an astronomical observatory, where conditions of seeing will be perfect all the time. Also, the Moon is the first step towards sending a manned rocket to Mars. On the other hand, we must recognise that a Martian journey is quite different from a lunar journey, and there are several major problems, which we cannot appreciate. One of these is dangerous radiation from the Sun and space. Of course, this applies equally to the airless Moon, but it will be possible to build radiation-proof centres there, and a journey to the Moon takes only a day or two as against several months of Mars. However, all this talk of reaching Mars lies well in the future yet. It has been claimed that the first trips there will take place within the next few decades, but I admit to being rather sceptical.

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One thing must also be borne in mind. If we are to go to the Moon, it must be a programme involving all nations, and not only a few. Until recently manned space research was confined to America and Russia, but other nations have now joined in, and both China and Japan have expressed tremendous interest. Let us hope we can work together, and that a lunar base will be truly international. That is the situation now, 40 years after Apollo 11. It is difficult to say what will happen during the next 40 years. One thing, however, is certain; it all began with Armstrong and Aldrin touching down on the bleak rocks of the lunar Sea of Tranquility, and they will be remembered as long as civilisation lasts. I have lived all through the Space Age, and the Sky at Night programme actually started before Sputnik 1. Also, I can claim to be one of the very few people who have met the first airman, (Orville Wright), the first space man (Yuri Gagarin) and the first men on the Moon (Neil Armstrong and Buzz Aldrin). It is possible that the first man on Mars has already been born, but he will certainly be very young, and as I am now 86 it is not very likely that I shall meet him. But I hope that when the first Martian journey takes place the Sky at Night will still be being broadcast once every month. I feel that for me it is a great honour for me to have initiated it. My best wishes to all Sky at Night viewers and to those who have read this book.

Chapter 40

Forty Years on

2008 TC3 trail (Credit: Mohamed Elhassan Abdelatif Mahir (Noub NGO), Dr Muawia H. Shaddad (Univ. Khartoum), Dr Peter Jenniskens (SETI Institute/NASA Ames))

In July 1969, the first men reached the Moon. They did go “where no men had been before,” and on a programme four decades later, I talked to Neil Armstrong and Buzz Aldrin. Apollo 11 seems long, long ago, but the memory of it will never fade. It is now four decades since men first landed on the Moon, and therefore a good moment to look back and sum up just what this mission signified. I have vivid memories of it, because as one of NASA’s Moon mappers I had the privilege of knowing all the lunar astronauts, and during the whole Apollo programme I was commenting on BBC Television. I did go over to Cape Canaveral for the launch of Apollo 17, last in the series, and believe me, it was a never-to-be-forgotten experience.

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Apollo 11 was particularly important because if it had failed, the whole American space programme would have been thrown into chaos, and there would have been strident calls for its total abolition. Moreover, there were still qualms about the stability of the Moon’s surface. The once-popular theory of deep dustdrifts had been disproved, thanks to the unmanned landers, but there could well be unsafe areas here and there, and as Neil Armstrong and Buzz Aldrin came down my main feeling was one of anxiety. If for any reason the landing were faulty, there could be no second change – and there was no provision for rescue. When Neil’s voice was heard saying “The Eagle has landed,” I think my feeling of relief was shared by the whole world. Remember too that the later astronauts had a very good idea of what to expect. Neil and Buzz did not. The second moment of crisis came when it was time to take off, blasting away to re-join Michael Collins in orbit. The Eagle’s single ascent engine had to work properly, first time. Mercifully, there were no problems, but all in all I feel that it was wise to end the series with No. 17. Site for Apollos 18–21 had been chosen, but would probably not have added a great deal to what had been already learned, and sooner or later something would have gone wrong. Next time men go there, rescue missions will be available. Some people maintain that reaching the Moon is a waste of time and money, but by national standards the cost is not exorbitant, and the cost of the wars since the invasion of Iraq would pay for the entire space programme well into the twentysecond century. A Lunar Base will be of immense value (for example, consider its value to medical researchers), and if all goes well it will be truly international. Space is no longer dominated by America and Russia, and China, Japan and India have already joined in the programme. I may be accused of being starry-eyed, but genuinely believe that space research may give us the best hope of uniting the Earth. Forty years ago we did not know what lay ahead, and indeed we still do not. But July 1959 marked the real beginning of a new era. Neil Armstrong’s “one small step” will be remembered for all time.

Chapter 41

Impact!

Can the Earth ever be hit by an asteroid? Yes – and on 7 October 2008 we were. Dr. Alan Fitzsimmons joined me to talk about it. On 6 October 2008, Richard Kowalski of the Catalina Sky Survey, working with the 1.5 m telescope at Mount Lemmon, north of Tucson in Arizona, discovered a small asteroid. It was catalogued as 2008 TC3, and from its distance and brightness it was thought to be between 7 and 16 feet in diameter – perhaps 10 feet would be a good estimate. Any body as small as that would have to be very close – an NEA (Near-Earth Asteroid) – and observers of the Spaceguard programme were called in. It soon became clear that instead of swooping past us, as most NEAs do, 2008 TC3 was on a collision course. Interest was immense, and observations came in from professionals and amateurs all over the world. Almost 600 photometric measurements from 27 separate localities, and spectra were obtained from the William Herschel Telescope on La Palma, indicating that the asteroid was of type C or M. This continued for 19 h – and then, at 02.46 GMT on 7 October, the end came. Asteroid 2008 TC3 entered the Earth’s atmosphere, and broke up. According to US Government sources, satellites were able to follow the course of events. The doomed asteroid was first detected at 02.45 GMT at an altitude of 35.5 miles (65.4 km) above the ground, but by then the break-up had started. The main impact followed less than a minute later, with position latitude 20.8°N, long 32.2°E, in Northern Sudan, fortunately an uninhabited area. The final explosion had happened at an altitude of 23 miles (37 km). The explosion was probably about as powerful as from 1 to 2 kilotons of TNT, and caused a brilliant fireball in the sky over the Nubian Desert, though very few people were around to see it. A low-resolution image of the explosion was obtained by the Meteosat 8 weather satellite, and the infra-red detector arrays in Kenya recorded a sound wave. Obviously, it was important to collect fragments, and this has started on 8 December. Altogether 280 were found, with a total weight of 8.7 pounds (3.9 kg). They are known collectively as Almahata Sitta, which is Arabic means “Station Six.” The asteroid

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seems to have been an anomalous ultra-fine grained porous polymict ureilite achondrite, with large carbonaceous grains; the fragile material of this class links it to anomalous dark carbon-rich ureilites. This is the first time that fragments have been found from an object previously tracked in outer space. Small though it was, it could have caused damage if it had hit a city centre. No, we are not immune!

Chapter 42

Life?

Ptolemy, my beloved cat (Patrick Moore)

For our hour-long “special” we decided to discuss Life in all its aspects; Where did it start? How did it develop? And most important – can it exist on worlds in the universe? During the programme I was joined by Dr. Pete Lawrence, Paul Able, Dr. Allan Chapman, Dr. Lewis Dartnell, and Dr. Giovanna Tinetti; in America, Chris Lintott talked to Dr. Jill Tarter; and Dr. Bill Barucki; on film, recordings of Dr. Frank Drake, Dr. Paul Davies, Dr. John Cockell, and the late Professor Sam Tolansky, Arthur C. Clarke and Michael Bentine. There was, however, another participant. I began the programme by showing three objects. The first was a stone, totally lifeless. The second was a lemon, which is certainly living, but has no consciousness. I then wanted an example of intelligent life, so I introduced my beloved black cat Ptolemy, who, I assure you is very intelligent indeed. Following the programme, Ptolemy had several letters from viewers who were attracted by his appearance, his behaviour and his friendly purr! P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_42, © Springer Science+Business Media, LLC 2010

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In our programme, we had several guests, but they agreed upon three vital points. First, we do not know the secret of what we may call “the spark of life,” i.e. why the lemon is alive and the stone is not. It would be easy enough for a chemist to construct an artificial lemon, made up of the same materials as the real one and looking very much the same, but it would be as inert as the stone. We cannot create life, though, sadly we can kill it with alarming ease. Second, we do not know how life began. Some people believe that the first living molecules built up from what was really a kind of chemical “soup” on the surface of the young Earth; others that is originated in the fiercely hot thermal vents we now find far below the ocean surface. There is also “panspermia theory,” according to which life on Earth did not originate here at all; but was brought to our world by a comet or an asteroid. Third, we do not yet have the slightest evidence of any life except on Earth. The Moon, the only world close enough to be studied in real detail with our groundbased telescopes, is quite definitely sterile, and our spacecraft searching for traces of life on less unpromising targets, notably Mars, have had no luck at all – leading some authorities to believe that our part in the universe, at least, is devoid not only of intelligent life, but also of life of any kind – even microbial. Let us try to speculate about numbers. Our Galaxy contains about 100,000 million stars, many of them attended by planets. We can see at least 100,000 galaxies, but even this accounts for no more than a very small part of the universe. The number of planets must be staggeringly large, and it is reasonable to assume that many of these planets must be Earthlike. It follows that there must presumably be intelligent Earthlike life. But – wait! My first guest was Dr. Lewis Dartnell, who is well known as an astrobiologist. He did not dispute the likelihood of life elsewhere, but intelligent life requires a special set of circumstances – so special, in fact, that civilisations must be very rare indeed. Round every star there must be what is commonly known as an ecosphere or “Goldilocks zone,” where other things being equal, the temperature is neither too hot nor too cold for the existence of complex life-forms (this really means, between the freezing and the boiling points of water at normal pressure). In the Solar System torrid Venus orbits just inside the Zone, chilly Mars just outside and the Earth comfortably in the middle. If we want to find an extra-solar civilisation, we should therefore try to locate an Earth-sized planet orbiting permanently inside the Goldilocks zone of a Sunlike star. The planet must have an adequate supply of water and all the elements we need to produce and sustain advanced life. Lewis maintains this combination of factors is so unlikely that in all probability our civilisation is the only one in the entire Galaxy. Time must also be taken into account. Low-type life appeared here and surprisingly soon after the Earth cooled down sufficiently following its condensation from the solar nebula, but sentient life took much longer, with Man a very late arrival on the scene. On some planets the parent star may well have changed its output before advanced life had time to develop, but we must remember that there is no proof that low-type life-forms will evolve into intelligent beings. It has happened here, but this is as much as we can say. Searches are going on apace. The recently launched Kepler satellite has been designed specially to detect Earth-sized planets – not by seeing them directly, but

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by measuring the drop in brightness of the parent star as the planet passes in front of it, i.e. transits. This has been done before, but most of the planets so far found have been “hot jupiters” – gas-giants very close-in. All this is linked with SETI, the Search for Extraterrestrial Intelligence. The SETI leaders, such as Giovanna Tinetti and Jill Tarter, hold views very different from Lewis Dartnell’s. They believe not only those civilisations exist, but if we continue to hunt will probably make contact in the foreseeable future. There are several possible ways of doing so, the most promising being radio, and the first attempt here was made as long ago as 1965 by Dr. Frank Drake and his team, who used the radio telescope at Green Bank, West Virginia, to see if they could pick up any sort of signal from the two nearest Sun-like stars, Tau Ceti and Epsilon Eridani, both of which are less than a dozen light-years away. The results were negative. Any signal would be mathematical, which applies to the whole universe (as I have said, we did not invent mathematics; we merely discovered it.) We now know that Tau Ceti is a disappointment, because there is no sign of a planet – merely a cloud of debris. Epsilon Eridani does have a planet, but so far the Eridaneans (if they exist!) have remained obstinately silent. One other point is worth making here. If we did pick up a signal from a planet of Epsilon Eridani, it would not prove that a civilisation exists there now – only that it did, a dozen years ago; radio waves travel at the same speed as light. So far we know, nothing can flash along faster than that. Possibly, the Kepler probe’s best hope is to pick up a beacon set up by an alien race. We have already done this unintentionally. Serious broadcasting began around 1920, and many of these ­programmes have “leaked” into space, so that they could be picked up by any ­suitably equipped operator within 90 light-years of us (I am writing these words in March 2010). Thus to an operator on a planet orbiting Pollux (34 light-years away), we are “radio noisy,” but to a world moving round Arcturus (115 light years away) we are still “radio quiet.” If aliens exist, will they resemble us, or will they be quite different? We have to admit that we do not have the faintest idea. However, we do know that life is amazingly versatile. There is not much outward resemblance between a man and a jellyfish, but they are made of carbon. We have found life in the Dry Valleys of Antarctica, the undersea thermal vents and even inside rocks; these so-called extremophiles seem to be able to survive almost anywhere. If we manage to collect samples which are unquestionably Martian, and not Earth contamination, we can search for life-forms. If we find any, we may be confident that life will arise wherever conditions for it are tolerable. How long a civilisation lasts is another question which we cannot yet answer. It will be around a 1,000 million years before our Sun becomes too hot for us to endure, but whether Mankind will survive until then is another matter. The Earth might, for example, be devastated by the impact of a comet or an asteroid, or a gamma-ray burster might explode inconveniently close to us; the chances of this are low, but not nil. Probably, the worst danger comes from ourselves. A nuclear war could easily render the Earth uninhabitable, and with world leaders of the type spawned during the last and present centuries it certainly cannot be ruled out. At the moment, this is really about as far as we can go. If other civilisations exist, sooner or later we may contact them. I will be quite frank – I hope this will happen. Time will tell.

Index

A Alpha Centauri, 14, 34, 71 Andromeda Galaxy, 110, 114 Antares, 96, 97 Antennae galaxies, 111 Apps, K., 40 Arrhenius, Svante, 65 Ashen Light, 66 B Baily’s Beads, 26, 27, 42 Beagle, 78 Beta Scorpii, 96 Betelgeux, 31, 71, 96 Black holes, 30, 50, 54, 55, 103–105 C Carrington, 7 Cassini space-craft, 82 Cepheid variables, 110 Ceres, 35, 57, 62, 63 Charon, 34, 59, 62 Chiron, 34 Chromosphere, solar, 7 Colshaw, 88, 138, 153 Comet Arend-Roland Holmes, 113–115, 117 Schwassmann-Wachann, 114 Shoemaker-Levy, 2 Swift-Tuttle, 100, 102 Tempel, 2, 9, 10, 34 Crab Nebula, 32, 50, 54, 104 D Deep impact space-craft, 10, 34 Deimos, 78, 79

Delta Scorpii, 96 Diamond ring, 42 E Eclipse of 2005, 25 of 1961, 41 Einstein, Albert, 51, 105, 130, 131 Enceladus, 14, 22, 23, 47, 48, 82, 85, 145–147, 150 Enriquez, J.C., 114 Epimetheus, 47 Epsilon Eridani, 15, 39, 92, 93, 165 Eris, 18, 33, 35, 58, 59, 62, 63 Eta Carinae, 30, 31 Europa, 14, 20, 35, 147 F Face on Mars, 79 Fomalhaut, 39, 93 G Gagarin, Yuri, 2, 73, 155, 157 Galaxy collisions, 111 Galaxy, rotation, 50 Gamma-ray bursters, 53–55, 165 Gamma-rays, 54, 55, 150 Gliese, 40, 92, 93 Globular clusters, 97, 114 H Halley’s Comet, 10, 88, 100, 118 Halley’s Comet society, 88 Hawaii, 2, 37, 38, 140 Hawking radiation, 105 Helioseismology, 70

P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0, © Springer Science+Business Media, LLC 2010

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168 Hubble Space Telescope, 1, 3, 30, 38, 46, 59, 63, 74, 111, 114, 140 Huygens probe, 82 Hydra, 59, 63 Hyperion, 21, 47, 48 I Iapetus, 21, 22, 47, 48, 83–85 Iota Herculis, 93 J James Webb Space Telescope, 3, 74 Janus, 47 Jodrell Bank, 107–108, 121 Jupiter Red Spots, 57 K Keck telescopes, 40 Kuiper Belt, 18, 21, 33, 34, 57–59, 62, 92 KY Cygni, 31 L Lake Vostok, 14 Life elsewhere, 13–16, 131, 164 Lovell, Sir Bernard, 107, 108, 121 Lunar base, 75, 88, 156, 157, 160 M M4, 97 M6, 97 M7, 97 Marcy, G., 40, 138 Mars probes, 14 Marsden, B., 114 Mauna Kea, 37–40, 140 May, Dr. Brian, 88 Mercury, 14, 43, 50, 57, 63, 67, 118, 119 Meteors, 34, 99–102, 108, 118, 119 Michell, J., 104 Moon, the shadow of, 26, 42 Mu Cephei, 31 N Neptune, 14, 33, 40, 57–59, 61–63, 84, 93, 118

Index Neutron stars, 30, 32, 55 New Horizons space-craft, 34, 63 Nix, 59, 63 O Oort Cloud, 34, 59 Opportunity space rover, 20, 78, 126 Orientale, Mare, 27 Orion, 31, 43, 71, 95, 96 Orion Nebula, 38 Oschin Telescope, 18 P Palomar telescope, 10, 18 Pandora, 47 Pegasus, 39, 110 Perseid meteors, 99, 100, 101, 118 Planets of other stars, 92 Pluto, 2, 18, 20, 33–35, 57, 61–63, 89 Porco, 20, 22 Prometheus, 47 Proxima Centauri, 6, 111 Ptolemy, 18, 95, 97, 163 Pulsars, 104, 108 Q Quetelet, A., 100 R R Doradus, 31 Rosette space-craft, 11 S Santorini, 26 Saturn, 2, 14, 18, 21, 22, 34, 45–48, 58, 82–85, 137, 138, 140, 145–147, 150 Scorpius, 95–98 Scuba, 39, 40 Sedna, 18, 34, 59 Sellers, Piers, 73 Slipher, V., 110 SMART, 20 SOHO space-craft, 8 Solar cycle, 7, 42, 122 Solar system, origin, 10 Spirit rover, 20 Squyres, Dr. S., 20, 77, 78 Star maps, 18

Index Stars, evolution of formation of, 40, 111, 150 twinkling of, 29 Sunspots, 6, 42, 70, 122 Sun, the energy of, 6, 96 Supernovae, 18, 50, 51, 53, 54 SuperWASP, 90–93 Swift, Lewis, 100

169 V Venus, 14, 20, 26, 43, 58, 65–67, 78, 89, 93, 138, 164 Venus Express, 65–67 Very Large Telescope (VLT), 2, 140

T Tau Ceti, 39, 92, 165 Titan, 14, 21, 22, 45, 46, 48, 81–86, 145, 146 Tombaugh, C., 61 T Tauri stars, 58 Tuttle, Horace, 100

W Weakly Interacting Massive Particles (WIMPS), 50, 131 Wheeler, 104 White dwarfs, 30–32, 50, 59, 104 WIMPS. See Weakly Interacting Massive Particles

U UK Infra-Red telescope (UKIRT), 38, 39 Uranus, 18, 34, 58, 61, 84, 150

Z Zero gravity, 74 Zwicky, F., 49, 50