Sky & Telescope April 2010

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Looking Down the Barrel: Finding Jets Aimed at Earth p. 70

THE ESSENTIAL MAGAZINE OF ASTRONOMY

S&T Test Report: “Do-It-All” Software for Observers p. 34 APRIL 2010

Hanging Balance

Could our solar system go haywire? p.26

Space Artists Envision Alien Worlds p. 56

See Mercury and Venus at Sunset p. 53

Black Hole Blowtorches p. 20 Visit SkyandTelescope.com

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"Apogee has a well-deserved reputation of being a leader in the field of CCD imaging technologies. The quality of their products is second to none, and I have been extremely pleased with their service." --Steve Cannistra

NGC2237-9 Image Courtesy Steve Cannistra Apogee Instruments Alta U16M camera Takahashi FSQ106 f/5 scope on Takahashi NJP mount AFW50 filter wheel with Baader SII, Ha, OIII filters

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April 2010 VOL. 119, NO. 4

On the cover: An orrery symbolizes the solar system’s stability. But modern computer models show we can’t take that for granted.

40

Northern Hemisphere’s Sky

43

April’s Sky at a Glance

45

Binocular Highlight

8 10

Letters 50 & 25 Years Ago By Leif J. Robinson

46

Planetary Almanac

12

News Notes

48

Sun, Moon, and Planets

18

Cosmic Relief

20 The Universal Jet Set

By David Grinspoon

By Fred Schaaf

50

Exploring the Moon By Charles A. Wood

53 26 Hanging in the Balance COVER STORY

Spectrum By Robert Naeye

By Gary Seronik

FE ATURE S

Wi Will the orbits of the planets ever go haywire? Mr. Newton, meet chaos theory. hay By Greg Laughlin

6

By Fred Schaaf

S&T: CASEY REED

Somehow, a wide variety of objects shoot out laser-like beams of matter, sometimes at near-light speed. By C. Renée James

AL S O IN THI S I S S U E

THI S M O N TH ’ S S K Y

65

38

New Product Showcase

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Telescope Workshop By Gary Seronik

Celestial Calendar By Alan MacRobert

76

Gallery

Deep-Sky Wonders

86

Focal Point

By Sue French

By Mark Stevenson

56 Imagining Other Worlds Space artists help us visualize planets and moons that humans have only glimpsed. By Michael Carroll

70 Blazar, Blazar,

Burning Bright These exotic galaxies are some of the most distant objects visible through backyard telescopes. By Steve Gottlieb

S &T TE S T R E P O R T

Skyhound’s SkyTools 3 From generating observing lists to logging your observations, this program promises to do it all. By Rod Mollise

36

Quick Look: Explore Scientific’s 14mm 100° Eyepiece By Dennis di Cicco

4 April 2010 sky & telescope worldmags

56 SKY & TELESCOPE (ISSN 0037-6604) is published monthly by Sky & Telescope Media, LLC, 90 Sherman St., Cambridge, MA 02140-3264, USA. Phone: 800-253-0245 (customer service/subscriptions), 888-253-0230 (product orders), 617-864-7360 (all other calls). Fax: 617-864-6117. Website: SkyandTelescope.com. © 2010 Sky & Telescope Media, LLC. All rights reserved. Periodicals postage paid at Boston, Massachusetts, and at additional mailing offices. Canada Post Publications Mail sales agreement #40029823. Canadian return address: 2744 Edna St., Windsor, ON, Canada N8Y 1V2. Canadian GST Reg. #R128921855. POSTMASTER: Send address changes to Sky & Telescope, PO Box 171, Winterset, IA 50273. Printed in the USA.

WALTER MYERS

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Robert Naeye Spectrum Founded in 1941 by Charles A. Federer, Jr. and Helen Spence Federer

The Essential Magazine of Astronomy

Astronomy’s Best-Kept Secret

EDITORIAL

Editor in Chief Robert Naeye Senior Editors Dennis di Cicco, Alan M. MacRobert Associate Editor Tony Flanders Imaging Editor Sean Walker Editorial Assistant Katherine L. Curtis Editors Emeritus Richard T. Fienberg, Leif J. Robinson Senior Contributing Editors J. Kelly Beatty, Roger W. Sinnott

CRISTIAN VALENZUELA

In early December I toured northern Chile for five days, my second trip to the South American nation. I visited several amateur and professional observatories, along with other tourist venues. The trip was a blast, and I came home thinking that many more astronomy aficionados from the Northern Hemisphere would enjoy visiting Chile. Here are some of the reasons why: 1. Chile is in the Southern Hemisphere. If you’re a deep-sky fanatic and haven’t seen 47 Tucanae, the Tarantula Nebula, or Eta Carinae, for example, you must travel south sometime in your life to see these treasures. I’m blown away by these objects, especially when I view them through large scopes. 2. In northern Chile, the skies are exceptionally dark and the seeing is usually very good. 3. Having a clear night sky at the astronomy sites in northern Chile is about as close as it gets to a “sure thing” in life. 4. During my two trips combined I have visited three amateur observatories: Observatorio Cerro Mamalluca (www.mamalluca.org/ Observatorio del Pangue, near Vicuña, ingles/inicio.htm), Observatorio del Pangue Chile, houses a 25-inch Obsession Dob (www.observatoriodelpangue.blogspot. and several other scopes. Posing left to com), and Observatorio Cruz del Sur (www. right are Carolina Medina of ProChile, observatoriocruzdelsur.cl). All three feature Cristóbal Benítez of Astronomica Chile, large telescopes that are staffed by expert and staff astronomer Cristian Valenzuela, friendly observers who can speak English. S&T Editor in Chief Robert Naeye, and Please make arrangements before your visit. staff astronomer Eric Escalera. 5. Chile has at least five world-class professional observatories, including Europe’s Very Large Telescope at Paranal and the U.S. site at Cerro Tololo. You’ll have to make prior arrangements for tours. 6. Since Chile is due south of the eastern U.S., North Americans can fly there with little or no jet lag. It’s also not a particularly expensive place to visit. 7. Chile is a relatively prosperous nation with a modern transportation infrastructure. Excellent food is in abundance. Chile is a politically stable democracy and crime is extremely rare in the areas of interest to astro-tourists. 8. Chile features beautiful natural scenery and interesting cultures. I particularly love the Valle de la Luna (Valley of the Moon) and the Valley de Marte (Valley of Mars) in the Atacama Desert. What names could be more astronomical? I plan to visit Chile again in the future, and I encourage you to do the same.

Contributing Editors Greg Bryant, Paul Deans, Thomas A. Dobbins, David W. Dunham, Alan Dyer, Sue French, Paul J. Heafner, Ken Hewitt-White, Johnny Horne, E. C. Krupp, Emily Lakdawalla, David H. Levy, Jonathan McDowell, Fred Schaaf, Govert Schilling, Ivan Semeniuk, Gary Seronik, William Sheehan, Mike Simmons, Charles A. Wood, Robert Zimmerman Contributing Photographers P. K. Chen, Akira Fujii, Robert Gendler, Tony & Daphne Hallas ART & DESIGN

Design Director Patricia Gillis-Coppola Illustration Director Gregg Dinderman Illustrator Casey Reed PUBLISHING

VP / Publishing Director Joel Toner Advertising Sales Director Peter D. Hardy, Jr. Advertising Services Manager Lester J. Stockman VP, Production & Technology Derek W. Corson Production Manager Michael J. Rueckwald Production Coordinator Kristin N. Beaudoin IT Manager Denise Donnarumma VP / Consumer Marketing Dennis O’Brien Consumer Marketing Nekeya Dancy, Hannah di Cicco, Beth Dunham, Christine Fadden, Jodi Lee, Adriana Maldonado, T.J. Montilli, Mike Valanzola Credit Manager Beatrice Kastner NEW TRACK MEDIA LLC

Chief Executive Officer Stephen J. Kent Executive Vice President / CFO Mark F. Arnett Corporate Controller Jordan Bohrer Office Administrator Laura Riggs Editorial Correspondence: Sky & Telescope, 90 Sherman St., Cambridge, MA 02140-3264, USA. Phone: 617-864-7360. Fax: 617-864-6117. E-mail: editors@ SkyandTelescope.com. Website: SkyandTelescope.com. Unsolicited proposals, manuscripts, photographs, and electronic images are welcome, but a stamped, self-addressed envelope must be provided to guarantee their return; see our guidelines for contributors at SkyandTelescope.com. Advertising Information: Peter D. Hardy, Jr., 617-864-7360, ext. 2133.

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Canada: $49.95 (including GST); all other countries: $61.95, by expedited delivery. All prices are in U.S. dollars. Newsstand and Retail Distribution: Curtis Circulation Co., 730 River Rd., New Milford, NJ 07646-3048, USA. Phone: 201-634-7400. No part of this publication may be reproduced by any mechanical, photographic, or electronic process, nor may it be stored in a retrieval system, transmitted, or otherwise copied (with the exception of one-time, noncommercial, personal use) without written permission from the publisher. For permission to make multiple photocopies of the same page or pages, contact the Copyright Clearance Center, 222 Rosewood Dr., Danvers, MA 01923, USA. Phone: 978-750-8400. Fax: 978-750-4470 Web: www.copyright.com. Specify ISSN 0037-6604. The following are registered trademarks of Sky & Telescope Media, LLC: Sky & Telescope and logo, Sky and Telescope, The Essential Magazine of Astronomy, Skyline, Sky Publications, SkyandTelescope.com, http://www.skypub.com/, SkyWatch, Scanning the Skies, Night Sky, and ESSCO.

Editor in Chief 6 April 2010 sky & telescope worldmags

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- Advanced Coma-Free™ Optics. ACF design produces a coma-free, flatter field of view with no diffraction spikes that equals traditional Ritchey Chrétien systems at a fraction of the cost. Combine this with Meade’s patented UHTC™ coatings that increase light transmission by 20% over standard coatings, for the sharpest, brightest images you can get.

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4 NEW! Series 5000 Auxiliary Equipment Mounting System. Machined aluminum dovetail plates, rings and counterweight systems (shown here with the Series 5000 102mm ED APO refractor) designed specifically for the Meade LX series of telescopes. They join seamlessly to create the ideal custom configuration. Available for 8", 10", 12", 14" and 16" LX scopes.

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Letters

I would love to share a photo of a work that might interest enthusiasts of telescopes and quilts alike: my quilt of the U.S. Naval Observatory’s 26-inch Alvan Clark refractor at the old Foggy Bottom site in Washington, D.C. The USNO’s 26-inch Great Equatorial Telescope, the world’s largest refractor for more than a decade, saw first light on November 20, 1873. Made by Alvan Clark & Sons of Cambridgeport, Massachusetts, the telescope has had a distinguished career. It was with this instrument that Asaph Hall discovered the two moons of Mars in August 1877. In 1893 the telescope was relocated from Foggy Bottom to its present site on Washington’s Observatory Hill. It is still in use for measuring double stars and positions of moons of the outer planets. The inspiration for my quilt was an old engraving from a newspaper story celebrating the work of the telescope. The engraving shows Superintendent Rear Admiral Benjamin F. Sands (standing) and astronomer Simon Newcomb in the dome with the brand new telescope in late fall of 1873. The quilt took me a year to make! It is machine pieced and appliquéd, and machine quilted. I used many reproduction 19th-century fabrics to give a period feel. The tube of the telescope and the astronomers’ garments are shaded by fabrics with stars. I took the quilt to Stellafane last summer and entered it in the homemade telescope competition. It took first place in the category of Telescopes-Mechanical / Special-Other. Sara J. Schechner Cambridge, Massachusetts

Tackling Diversity I question why you think the following quote from Dara J. Norman’s article 8 April 2010 sky & telescope worldmags

SARA J. SCHECHNER (2)

Quilted Wonders

(“Expanding Diversity in Professional Astronomy,” February issue, page 86) is true: “Quite simply, astronomers need to secure a diverse workforce in the field in order to insure that the best scientific research is accomplished.” Show me the proof that “diversity” of itself has actually achieved anything at all. What we do need is a better educational process, one that actually inspires all students in the sciences. I have had personal experience with a current crop of public school teachers and, frankly, I’m not impressed; it seems as though my own teachers in the 1950s did a better job! I recently had a high-school teacher with a master’s degree ask me what caused the auroras. No wonder our public schools aren’t turning out scientists…but it has nothing at all to do with diversity. Let’s encourage the best and brightest, no matter what color or gender. John Bartucci Cuyahoga Falls, Ohio I was extremely pleased to see Dara Norman’s Focal Point and the accompanying editorial by Robert Naeye (“Diversifying the Ranks,” page 6) in the February 2010 issue of Sky & Telescope.

Astronomy as a field has made great strides in some areas of diversity. The fraction of women in advanced academic and research positions is improving, albeit slowly, but the gradient is positive. That is not to say that there still is not a long way to go, but progress is being made. However, the field of astronomy has fared extremely poorly in attracting underrepresented minorities. Until recently, the number of astronomy doctorates awarded to minorities each year could be counted on the fingers of one hand. The American Astronomical Society (AAS) recognized this problem 20 years ago and created a standing Committee on the Status of Minorities in Astronomy whose charge is “to enhance the participation of underrepresented minorities in Astronomy and Astrophysics at all levels and experience.” The CSMA has been active in running workshops, it publishes a newsletter, Spectrum, it arranges mentoring, it helps arrange partnerships between historically black colleges and doctoral institutions, and it helps represent the society at meetings like that of the National Society of Black Physicists and the Society of Hispanic Professional Engineers. The AAS Council also has recently adopted a mission and goals statement that includes a statement on promoting diversity: “The Society supports and promotes increased participation of historically underrespresented groups in astronomy.” The AAS is acting by improving communications, by promoting family-friendly activities, and by promoting programs that train minority scientists. We care deeply about this issue and are committed to enhancing the participation of minorities in the field at all levels. John Huchra President, AAS Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts I commend Dara Norman and Robert Naeye for pointing out the benefits of diversity in astronomy. Having been active

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Letters

Sky & Tel called the AT106 “Too Good To Be True” at $1995.

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The headAT106LE line on the $1495 Sky & Tel cover said the $1995 Astro-Tech AT106 4.2” ED triplet refractor was “A Scope Too Good To Be True.” And the four-page review inside said the AT106 “provides all the benefits of a first-class 4-inch apo but without the premium price.”

And now, there’s a Limited Edition Astro-Tech AT106LE available with the same gorgeous f/6.5 FPL-53 triplet optics as the AT106 (simply fewer mechanical bells and whistles) for only $1495. An on-line comment called it “one of the best deals I have ever seen offered in over 2 decades of this hobby.” The production run of the AT106LE is strictly limited to 50 pieces at $1495. When they are gone, they are gone for good. Don’t miss out on this one.

Color-free scopes in glorious living Technicolor™! The Astro -Tech AT72ED 2.8” f/6 ED doublet reAT72ED fractor is a larger $379 aperture 2” dualspeed focuser version of the AT66ED, one of the most popular Astro -Tech scopes ever. The AT72ED was first available in black only. Then we started getting requests for the AT72ED body in color, the same way the AT66ED was once available. You spoke, we listened. The Astro-Tech AT72ED is now available in your choice of five tube colors: Celestron black, Meade blue, white, deep red, and forest green. You can now have great 72mm Astro-Tech ED optics, free from spurious color, in a glorious living Technicolor™ tube! Enjoy!

ASTRO-TECH from Astronomy Technologies 680 24th Avenue SW, Norman, OK 73069 Astro-Tech is available in the U. S. from these dealers:

astronomics.com ● highpointscientific.com auroraastro.com ● optcorp.com ● camerabug.com sunrivernaturecenter.org ● greatredspot.com apmamerica.com ● tetontelescopes.com In Canada, from: escience.ca ● astronomieplus.com a-p-o.ca In Europe, from: altairastro.com scopemania.eu In Asia, from: kkohki.com Dealer inquiries welcome: [email protected] Prices as of 1/1/10. All prices plus freight.

10 April 2010 sky & telescope worldmags

in international astronomy programs for several years, I have seen the enormous potential for contributions to astronomy from currently marginalized communities. As co-chair of the 100 Hours of Astronomy Cornerstone Project of the International Year of Astronomy 2009, I found that the most successful efforts were often in the countries with the least resources. It is the passion, determination, and abilities of individuals who make the difference and actually represent the most valuable resource for these efforts. But among these enthusiasts are many students who will never have the opportunity to employ those abilities at high levels of professional astronomy. As Dr. Norman points out, this represents incalculable loss to the world’s scientific community. The need to expand astronomy beyond academia and communicate with the public has been recognized for years, and that recognition and the ensuing effort led to the unprecedented IYA2009, in which 148 nations participated. That effort will expand further with the recent adoption

50 & 25 Years Ago

Write to Letters to the Editor, Sky & Telescope, 90 Sherman St., Cambridge, MA 02140-3264, or send e-mail to [email protected]. Please limit your comments to 250 words.

of the International Astronomical Union’s 10-year strategic plan, “Astronomy for the Developing World.” Adopted at the General Assembly in Rio de Janeiro in August 2009, the plan calls for the development of astronomy awareness, education, and professional development in countries that now lack adequate programs. A century ago, women were excluded from the male-dominated field of astronomy, and some Europeans saw the United States as little more than an upstart. Imagine the impact on astronomy if those prejudices had prevailed. The continued success of the pursuit of diversity will determine the future of the field. The untapped human resources yet to be discovered are to be ignored at our peril. Mike Simmons Agoura, California

Leif J. Robinson

April 1960 Hemisphere Imbalance “In his address . . . [Dirk] Brouwer discussed some consequences of the fact that the world’s observatories and astronomers are strongly concentrated in the Northern Hemisphere. This unbalance, which leaves the southern skies less well studied, is harmful to observational astronomy, and special measures are necessary to overcome it. . . . “Today the situation in Southern Hemisphere astrometry is alarming, for the Cape Observatory [in South Africa] is the only one below the equator now making fundamental determinations of star positions. This makes it practically impossible to provide adequate checks on possible systematic errors in the positions and proper motions of southern stars.” Brouwer’s specialty was the calculation of orbits, thus his emphasis on positional astronomy at the dawning of the Space Age.

April 1985 Hubble Heritage “Although U. S. officials rarely acknowledge the existence of photo-reconnaissance satellites, these ‘spies in the sky’ have played an indispensable role in military surveillance for more than two decades. Thus, a fair question might be whether NASA’s Hubble Space Telescope is simply an existing satellite redesigned to look up, not down. . . . “NASA and industrial managers [indicate] when interviewed that the Hubble telescope has little direct inheritance from past or current programs. . . . “But it has certainly drawn from state-ofthe-art military advances in detectors, control systems, data encoding, and data transmission — even the methods used to assemble spacecraft of this size.” So wrote space-exploration expert J. Kelly Beatty in an issue whose feature articles were largely devoted to the future Hubble telescope.

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News Notes

All News Note stories are presented in greater depth, with links to further inforgre mation, at SkyandTelescope.com; search ma for the keyword SkyTelApr10.

This artist’s concept shows the Epsilon Aurigae dust disk, with a single B star inside it, starting to cross the face of the F supergiant.

UV

VISIBLE

NEAR IR

MID-IR

NASA / JPL-CALTECH

Epsilon Aurigae Solved at Last?

FAR IR

1000

10

F Staar D. HOARD (SPITZER SPACE CENTER / CALTECH)

Relative brightness

100

1

Disk

0.1

B Star 0.01

0.1

1

10

100

Wavelength (microns) The entire observed energy output from the Epsilon Aurigae system, from the far ultraviolet to the far infrared (colored line and dots), is now fully accounted for by just three objects: the bright F supergiant star, a single hot B star about 1,000 times dimmer, and the enormous, warm dust disk glowing in the mid- and far infrared.

12 April 2010 sky & telescope worldmags

A group of astronomers claims a breakthrough in the long-standing mystery of Epsilon Aurigae. This 3rd-magnitude star, a type-F supergiant 130,000 times brighter than the Sun, loses half its light for almost two years every 27.1 years — when a nearly opaque dust disk, seen edge-on, slides across its face (S&T: May 2009, page 58). The problem is that the disk must have a massive body in its middle, but nothing is seen. Astronomers are quite sure that the disk’s central object is at least as massive as the F stars, so it ought to shine at least about as brightly. It can’t be totally hidden by the disk itself; the disk is open in the middle, like a flattened doughnut tilted slightly from edge on. We know this because around mid-eclipse, we see part of the F star through the opening. So what is this unseen thing in plain sight? Many ideas have been proposed and ruled out. (No, it can’t be a black hole.) The key that unlocks the mystery, says Donald Hoard of Caltech, is to not assume that the disk means Epsilon Aurigae is a young star system that’s still forming. If instead it’s nearing the end of its life, the bright star can have a much lower mass than has been presumed for it. Even a star with just 2 solar masses can shine with supergiant brilliance in its death throes. This would allow the disk’s central object to have only 6 solar masses, also much lower than formerly presumed. So it could be a normal, garden-variety type-B star with only a couple hundred times the Sun’s luminosity — bright by ordinary standards, but about 1,000 times dimmer than the supergiant and lost in its glare. Epsilon Aurigae began dimming again on schedule last August and reached its minimum brightness in December, where it will more or less remain until March 2011. The difference in Auriga’s familiar

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News Notes

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` Tauri Normally, Epsilon Aurigae is slightly the brightest of the three “Kids” stars south of Capella. But currently it’s only a match for Zeta (ζ) Aurigae, and the change is fairly plain to the eye. Stars are labeled with their visual magnitudes.

pattern (above) has become plain to careful skywatchers. NASA’s Spitzer Space Telescope has confirmed the presence and size of the warm dust disk: it’s 8 astronomical units wide. Far-ultraviolet satellites have found traces of B-star light coming from somewhere in the system. Hoard and his colleagues propose that the disk is material that the B star has gravitationally captured from the dying primary’s thick wind. “All of these intertwined parameters just sort of work out,” says Hoard. He estimates that the system is 10 million years old. If so, we’re catching it at a lucky time (which may be why it’s unique). Over the next thousands of years, the dying F star will puff off most of its remaining mass to form a planetary nebula. But the book is far from closed. Intensive observations continue worldwide, including by amateurs doing long-term photometry and spectroscopy.

Dark Energy News One of the biggest surprises in the history of astronomy was the discovery that, contrary to all expected physics, the expansion of the universe is speeding up. The unknown “dark energy” that’s caus14 April 2010 sky & telescope worldmags

ing this repulsion is strong enough that it amounts to about 74% of the entire matterand-energy budget of the universe (see the pie chart below). More evidence of the dark energy keeps showing up. An international team recently measured its effect right here in our Local Group of galaxies. The Local Group includes the Milky Way, the Andromeda Galaxy, M33, and about 50 dim dwarf galaxies identified so far. The team analyzed measurements of Local Group galaxy motions (radial velocities and distances) with respect to the group’s gravitational center. They found that a boundary exists where the Local Group’s gravity gives way to dark energy’s “antigravity” effect on larger scales. Dwarf galaxies that lie beyond this boundary are moving outward — cosmic acceleration in miniature. Says team member Gene Byrd (University of Alabama), “We found a dark-energy outflow repulsion consistent with that found from studying galaxies that are billions of light-years away.”

74% dark energy 22% dark matter 3.6% intergalactic gas 0.4% stars, etc.

Dark Matter News The mysterious dark matter, which amounts to another 22% or so of the cosmic matter-and-energy density, is also revealing itself more clearly. Astronomers have long known that large galaxies, such as our Milky Way, are centered in larger pools of dark matter, like patches of scum on invisible ponds. A group led by David Law (UCLA) now finds that the Milky Way’s dark-matter halo is not spherical but flattened in three directions into a triaxial shape, sort of like a squashed football. Surprisingly, the flattest side is perpendicular to the Milky’s Way’s starry disk of normal matter.

The team reached this conclusion by analyzing the motions of thousands of stars in the “Sagittarius stream,” a sparse filament that loops all the way around the Milky Way well outside the galaxy’s fringes. The stream is the far-flung remains of a dwarf galaxy that was pulled apart by the Milky Way’s tidal effect during a close encounter. The motions of stars in the different parts of the stream allowed the astronomers to map the gravitational fields exerted by different parts of our dark-matter halo.

Exoplanet News Roundup With more than 420 planets now known outside our solar system, and better instruments yielding ever-finer data, exoplanet specialists have lots of material to digest. Some recent news: Massive Host Stars. A group using the MMT Telescope in Arizona surveyed disks around big young stars that have 1.5 to 15 times the Sun’s mass. These will DAVID A. AGUILAR / CFA settle down to be hot shiners of spectral types F, A, and B when their birth processes are finished. The group found that many such stars have protoplanetary disks, and the disks often show infrared signs of gaps that planets have already cleared in them. Evidently, planet formation is a robust process that occurs around stars over essentially the whole range of stellar masses, from dim red M dwarfs to hot, blue-white B dazzlers. Super-Volcanic Planet From Hell. The only exoplanet known for sure to be rock and metal like Earth is Corot7b, a super-Earth that has Earth’s density and about 5 times Earth’s mass. It orbits so close to L. CALÇADA (ESO) its star, a yelloworange dwarf, that its surface should be roasted to molten-lava temperatures (S&T cover story, May 2009).

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News Notes

For astronomy news as it breaks, see SkyandTelescope.com/newsblog.

light. This discovery method, however, has one big advantage: it’s most sensitive to giant planets that are far from their stars, at roughly Jupiter’s and Saturn’s distance from the Sun. Looking at the statistics so far, a team led by Andy Gould (The Ohio State University) estimates that a third of stars host at least one giant planet in a distant orbit: a “cold Jupiter.” A sixth of stars may have multiple giant planets in distant orbits, as our solar system does. This is

NASA / JPL / UNIV. OF ARIZONA / DLR

good news for the possible formation and survival of terrestrial planets closer in. In related news, a group tracking stars’ radial-velocity wobbles has announced that the Sun-like star 23 Librae seems to have a Jupiter-like planet in a circular orbit at a Jupiter-like distance. Cold Jupiters are just beginning to reach detectability by the wobble method, as technology improves and the time span covered by radial-velocity monitoring lengthens. Planets Everywhere. As for smaller worlds? Exoplanet hunter Paul Butler now says that, based on statistics, it’s likely that half of nearby stars possess at least one detectable planet with Neptune’s mass (17 Earths) or less.

Sunglint from a Titan Lake

Millisecond-Pulsar GPS

NASA

In addition, says Rory Barnes of the University of Washington, it probably has strong internal heating as well, leading to extreme volcanism. The planet orbits its star so closely that if its orbit is even slightly elongated (quite likely, given the presence of a second planet nearby that should perturb it), then Corot-7b will be tidally squeezed and flexed once per orbit. Internal friction will dissipate some of this tidal energy, heating the planet’s interior. Jupiter’s moon Io is heated in a similar way, causing Io’s vigorous volcanism (page 30). But for Corot-7b the effect should be many times greater. Bare Core of a Gas Giant? Another group finds that Corot-7b could be boiling off half an Earth mass of its material every billion years under the heat of its star. Brian Jackson (NASA/Goddard Space Flight Center) concludes that the object may have started life as a gas giant, and that its hydrogen and helium were long ago driven off to leave the present rocky core behind. Water World? A different super-Earth has about the same mass but a larger diameter, as revealed by its transits across its star. GJ 1214b has an average density of only 1.9 grams per cubic centimeter. A good guess is that this planet is water almost all the way through, overlaid by a massive atmosphere. Even though deep planetary interiors are very hot, the high pressures there should force the water into solid form: a hot, dense phase of ice. Familiar Solar Systems. Only 10 exoplanets have been found by their “microlensing” of a distant background star’s

Pulsars are amazing enough; they’re like giant atomic nuclei with more than the Sun’s mass squeezed into a sphere about 20 kilometers (12 miles) wide. Even wilder are the millisecond pulsars, which spin several hundred times per second. Until recently, astronomers knew of only 60 of them floating loose in the Milky Way, but NASA’s Fermi Gamma-ray Space Telescope is providing a treasure map for finding more. Fermi’s first-year map of the high-energy gamma-ray sky recorded 1,451 discrete sources. Radio astronomers following up at these points have picked up signals from at least 17 previously unknown millisecond pulsars. Finding more of them matters. Millisecond pulsars are the most precise “clocks” in nature, matching or beating the best artificial atomic clocks. Enough of them could offer a sensitive, GPS-like timing grid to watch for gravitational waves — ripples in spacetime predicted by Einstein — passing Earth’s vicinity.

This picture of Saturn’s big, smog-covered moon Titan, recently returned by the Cassini probe, is surely destined to be a classic astro-image. Taken in haze-penetrating infrared light, it shows a patch of sunlight reflecting at a very low angle from one of Titan’s large northern lakes. The lakes are a mixture of methane and ethane, similar to liquefied natural gas (pure methane). The case for lakes on Titan was already pretty ironclad, but this certainly clinches it. The reflection is from Kraken Mare, an irregular lake or sea mapped by radar that covers about 400,000 square kilometers, larger than the Caspian Sea on Earth.

Saturn’s Weird Prometheus In nearly six years of orbiting Saturn, Cassini has flown by many of the planet’s 61 moons, no two quite alike. Prometheus, 74 miles (119 km) long and seen in new high resolution below, appears to be thickly mantled with dust from Saturn’s F ring, which it dips in and out of. Note how the craters are fi lled in. Before the first landings on Earth’s Moon in the 1960s, science-fiction writers sometimes set tales on the Moon involving seas of deep, treacherous, fluff y dust. Perhaps these stories will yet play out on a different moon. ✦

NASA / JPL / SPACE SCIENCE INST. / S. WALKER

16 April 2010 sky & telescope worldmags

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Cosmic Relief David Grinspoon

The Right Stuff? Our columnist reports on his harrowing round of astronaut training. Some things

ERIKA B. WAGNER / MIT

you can take for granted — such as gravity and air. Except when you can’t. I spent a couple January days learning how to deal with radical alterations in these basics as I prepared for an opportunity to briefly leave our familiar world and see things anew. I was fortunate to be invited to train for private suborbital spaceflight with the first class of scientist/astronauts. Five women and 7 men are planning to conduct experiments on these new spacecraft, possibly as early as 2011. The classroom was the easy part. After learning all that can go wrong in altitude training and the danger signs you can’t ignore (sharp tooth pains must be immediately reported because expanding air pockets can make your teeth explode!), we donned helmets and masks and entered a decompression chamber. After a half-hour of breathing pure oxygen to flush out nitrogen and avoid the bends, our trainers reduced the pressure. Lights were lowered to help us recognize the visual symptoms of hypoxia, and simulated altitudes were announced every thousand feet. At 18,000 feet we removed our masks. The idea is to purposefully bring on hypoxia in a controlled setting so

ASTRONAUT TRAINEE As the author experienced first hand, astronaut training is not exactly a casual stroll in the park.

18 April 2010 sky & telescope worldmags

we learn our reactions and limits. We performed various intellectual, mathematical, and mechanical tests and recorded our symptoms. One classmate slumped to the ground unconscious but was quickly revived when given oxygen. After 20 minutes I felt numb and drowsy. I thought I was performing well, but my final paper exercise — a maze — was an incoherent scrawl. The centrifuge offered a greater challenge. Our trainers explained techniques to avoid blacking out under increasing g-forces. But no matter how much they prepared us, I was a little freaked out when they sealed me in the chamber and began the countdown. I had sweaty palms and a racing heart. But I knew my image and voice were being webcast live to hundreds of people, including my colleagues in Denver, so I tried to keep it together. I was surprised by the intensity of the crushing, suffocating feeling when they whipped me up to 3.5 g’s (the maximum that shuttle astronauts encounter). When they accelerated me to 6 g’s (which SpaceShip2 will experience during re-entry), I had to quickly apply the anti-g straining maneuvers (clenching lower and upper body, pressured breathing) in order to keep my peripheral vision from closing in on me and to maintain consciousness. Our final centrifuge training was a full-up simulation of an entire trip on Virgin Galactic’s SpaceShip2. The surrounding visual projections simulated the changing horizon line, receding ground, and exterior views fore and aft. Despite the discomforts, the training was fun. As often occurs when experiencing new challenges in group situations, I quickly bonded with my fellow trainees. When one of us overcame difficulty, our personal triumphs became group successes. And on that final, full simulation, I was able to relax and enjoy the ride (except for the few moments of maximum g). The simulated views of Earth and space provided enough of a hint of the strangeness, beauty, and exhilaration of the real thing that I felt overcome with joy. “Normal” gravity and air pressure are overrated. There’s a universe out there waiting for us. Let’s go! ✦ Noted book author David Grinspoon is Curator of Astrobiology at the Denver Museum of Nature & Science. His website is www.funkyscience.net.

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Cosmic Blowtorches

the

universal jet set

c. renée james

RADIO: NSF / VLA / M. HARDCASTLE (UNIV. OF HERTFORDSHIRE) X-RAY: NASA / CXC / R. KRAFT (CFA) ET AL. OPTICAL: ESO / WFI / M. REJKUBA ET AL.

Somehow, a wide variety of objects shoot out laser-like beams of matter, sometimes at near-light speed.

20 April 2010 sky & telescope worldmags

COLLISION-INDUCED JETS Centaurus A (NGC 5128) is a classic example of a large elliptical galaxy cannibalizing a smaller spiral galaxy. This composite image includes a radio picture from the Very Large Array, an optical photo from a European 2.2-meter telescope, and a Chandra X-ray image. The spiral’s material feeds Cen A’s supermassive black hole, producing two powerful jets seen in radio and X-rays.

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It’s been over 90 years since Heber Curtis noticed something peculiar in M87. “A curious straight ray lies in the gap in the nebulosity in p.a. 20°, apparently connected to the nucleus by a thin line of matter,” he wrote of the unusual feature. Unaware of M87’s distance, Curtis had no idea of the true extent of that thin ray, nor could he have imagined the gargantuan power that lay behind its formation. A 5,000-light-year-long stream of high-energy particles racing from the galaxy’s heart at close to the speed of light, it was the first of many jets discovered peppering our universe. Some jets are ar measurable in mere astronomical units (a.u.), with ioni ionized gases flowing out at relatively modest speeds of a few hundred kilometers per second. Others stretch up to t 100 times the width of our Milky Way Galaxy, pourin pouring out 10 trillion Suns of energy. Some draw their power from fro young stars, dying stars, or pulsars, while others are ar powered by stellar-mass or supermassive black holes. Jets Jet are associated with an amazing range of objects, making makin them one of the most ubiquitous phenomena in our universe.

Cosmic Blow Blowtorches

ROBERT GENDLER

NASA / HUBBLE HERITAGE TEAM / STSCI / AURA

What unites all members of the universal jet set — objects that shoot forth matter in very tightly focused beams or cones — is that they embody a bizarre paradox. Members of the jet set pull matter inward, but they are also forced to spew narrow energetic streams of material outward. In extreme cases such as the “straight ray” emanating from the core of M87, these jets are some of the most violent and poorly understood objects in the universe. Even on

smaller scales, jet formation provides plenty of observational and theoretical challenges. “Picture Saturn with giant blowtorches pointing away from its north and south poles,” says David Thompson (NASA/Goddard Space Flight Center). Now increase the scale to the size of Jupiter’s orbit, with a ravenous 10-solarmass black hole in the center and a hot disk of material spiraling into the bottomless pit. Then increase the scale to 5 light-years, with the blowtorches ejecting material thousands or even millions of light-years at relativistic (near-light) speeds away from a supermassive black hole that resides inside M87’s active galactic nucleus (AGN). This is the image that NASA’s Chandra X-ray Observatory captured of Centaurus A (NGC 5128), a galaxy a “mere” 11 million light-years distant. Unlike other elliptical galaxies, Cen A is marred by a thick dust lane, a feature that indicates a relatively recent collision with another galaxy. Other than that curiosity, Cen A seems like a pretty quiet place, at least visibly. But when we look at the X-ray image, we see that Cen A is still reeling from that collision. Powered by a supermassive black hole that is voraciously consuming the abundant fresh gas and dust, two narrow jets extend some 13,000 light-years from Cen A’s center. The material racing from the heart of Cen A is traveling at least 10% the speed of light, and possibly as high as 45% light speed. Even more astounding, this activity should continue as long as Cen A’s black hole has a plentiful supply of gas and dust to feed upon. Jets on this scale affect the evolution of galaxies and the clusters in which they reside. Unfortunately, astronomers are still grappling with some of the fundamental questions of jet production, the

STRAIGHT RAY Heber Curtis first called attention to M87’s jet in 1918. The jet has been imaged innumerable times since, and appears prominent in an amateur shot (left) and in a picture taken by the Hubble Space Telescope (right). The jet extends for at least 5,000 light-years in optical wavelengths, but for 100,000 light-years in radio waves. North is to the upper right in both images.

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Cosmic Blowtorches

or supermassive black hole — a gravitating object will pull nearby available material toward it. But most of that mateMagnetic Jet rial won’t simply fall straight in. Instead, field lines it will tend to overshoot and go into orbit. Accretion disk In a friction-free environment, the material would blissfully orbit forever, but conditions near these accreting objects can get pretty crowded. Particles collide with one another and generate turbuTurbulence Turbul lenc lence, which causes their orbits to decay. Accreting The result is that the material collects in central Infalling material a great hot pancake (an accretion disk) Wind object swirling around the central object. Now the picture becomes more complicated. Disk material doesn’t JET PRODUCTION Disk material spirals inward due to turbulence. The turbulence simply swirl around forever. In order for and differential rotation twist magnetic-field lines, which wrap ever tighter near the that material to “land” on the accreting central object. The twisted magnetic field funnels hot plasma into jets. object, it has to lose even more angular momentum than the turbulence can remove (S&T: Janumost pressing of which is why an object that is accreting ary 2007, page 42). Otherwise, the disk would be like a matter equatorially should focus some of that matter, perpetually spinning ice skater, her hair and skirt flung along with prodigious amounts of energy, into narrow out for all eternity. Jets help with that problem. The only jets shooting from the poles. “That’s the big question that issue is figuring out exactly how and why they occur. everyone is trying to answer,” says AGN researcher Alan “Unfortunately, the study of accretion disks and jets Marscher (Boston University). is similar to where astronomers were 100 years ago with The Great Magnetic Squeezer the study of normal stars,” says former Cornell University astrophysicist David Rothstein, who has wrestled with To begin tackling this question, we need to look at how computer simulations of jet-producing environments. accretion occurs. No matter the scale — protostar, pulsar,

NRAO / AUI

NASA / JEFF HESTER (ARIZONA STATE UNIVERSITY)

S&T: CASEY REED

Creating an Astrophysical Jet

JETS ARE EVERYWHERE The sizes and speeds of jets differ considerably, but they appear in a wide variety of environments. Left: two radio jets shoot away for hundreds of thousands of light-years from a supermassive black hole in galaxy 3C 296. Right: Hubble captures a much shorter jet (arrowed) emanating from a young star in the Trifid Nebula. The counterjet is hidden by gas and dust.

22 April 2010 sky & telescope worldmags

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ANDREA CIARDI

Magnetic field lines

New bubble Foil

LABORATORY JET Physicists have recently reproduced jets in the lab, suggesting they are gaining a deeper understanding of the underlying formation mechanism. This experimental jet (right) is just a few inches long. It lasted less than a microsecond, but reached a temperature of 1 million degrees Celsius.

farther out. According to the magnetic model, this differential rotation twists the magnetic field so that it coils up along the poles. The coiled field guides charged particles so they shoot out along the poles. Magnetic pressure builds up so that it exceeds the pressure of the charged particles at the base of the jets. In the most extreme cases, usually around a rapidly spinning black hole, acceleration pushes the particles toward the speed of electromagnetic waves, which is the speed of light. A team led by Andrea Ciardi (École Normale Supérieure, France) in collaboration with Sergey Lebedev (Imperial College, UK) recently reproduced jet behavior with very-small-scale laboratory experiments using elec-

STSCI / NASA

X-RAY: NASA / CXC / J. HESTER (ARIZONA STATE UNIV.) ET AL. OPTICAL: NASA / HST / J. HESTER (ARIZONA STATE UNIV.)

Astronomers agree, however, that magnetic fields play a crucial role. In an accretion disk’s hot, turbulent environment, the revolving charged material generates strong magnetic fields. As the material spirals inward, so do the magnetic fields, but the turbulence twists and distorts them. We have first-hand experience with the consequences of twisted magnetic fields. The Sun periodically fires off coronal mass ejections (CMEs), huge blobs of plasma (partially ionized gas). The CME launch pad appears to be the distorted, pinched magnetic fields on the differentially rotating Sun. CMEs can launch material pretty much in any direction — and occasionally toward Earth. But for jet producers, the launch pad is always at the poles. For these accreting systems the poleward preference results from the disk’s rotation and the gradual constriction and strengthening of its magnetic fields. The result, according to Jonathan McKinney (Stanford University), “is like squeezing a tube of toothpaste.” The “squeezer” is a magnetic field that wraps ever tighter around a hot plasma of charged particles as they spiral inward. The toothpaste is the plasma, which is made of charged particles such as protons and electrons (or their antimatter counterparts). As the magnetic fields tighten, they squirt out material in the only direction available: the poles. And as long as material continues to spiral inward, there is a constant supply of “toothpaste” along with a perpetual “squeezer.” Following Kepler’s second law, the material near the central object is whirling around faster than material

UBIQUITOUS JETS Jets are also produced by dying and dead stars. Left: A Hubble Space Telescope near-infrared image shows multiple jet-like outflows shooting away from a dying star similar in mass to the Sun, helping to sculpt a planetary nebula known as the Egg Nebula. Right: A Chandra/Hubble composite image reveals a small jet blasting away from the pulsar at the center of the Crab Nebula.

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S&T: GREGG DINDERMAN

Cosmic Blowtorches

trically heated metal foils to create a hot plasma, which is collimated into a jet by magnetic fields. The tiny jets are relatively stable, even when the magnetic fields become a jumbled mess, providing a glimpse into how accretTHE R O LE O F S P IN ing objects can maintain A rapidly spinning central object rap such steady jets. Although is not required to produce jets, but it seems quite a leap from it can help. The fastest known jets, creating inch-long jets on a where material moves very close to time frame of microseconds the speed of light, seem to emanate from black holes. Evidence is accuto creating light-year-long mulating that at least some of these jets on a time frame of milblack holes are spinning very close to lennia, scaling the results their theoretical maximum velocity. upward seems to mimic observations of young stars. Recent computer simulations of accretion disks tend to show the same behavior, at least to some extent. But such complex and dynamic systems are gargantuan problems for modern computers to simulate, so astronomers have had to content themselves with brief simulated snapshots of magnetized accretion disks in action.

Jets at All Scales Then there’s the added complication of the sheer variety of jet-producing systems. If jets only came from supermassive black holes, astrophysicists might dismiss them as a consequence of bizarre relativistic effects. But jets seemingly show up wherever there’s a magnetic field and accretion, even if accretion is sporadic. This parallel has created an interesting crossover at recent professional

meetings, where high-energy AGN astrophysicists come together with astronomers from the comparatively calm field of young stars to work on the same problems. AGN astronomers can better measure the magnetic field strength in their jets, but it’s easier to measure parameters such as temperatures and densities in jets coming from young stars. Although not as flashy as their AGN kin, these observationally accessible young stars are still card-carrying members of the jet set. What’s more, jet production in this type of object is vital to our very existence. The Sun was once a youngster, and without jets to reduce the protoplanetary disk’s angular momentum, our forming star never would have accreted enough mass to turn on. “The Sun definitely would have gone through this phase or the planets wouldn’t be here,” says Tom Ray (Dublin Institute for Advanced Studies, Ireland). “If models are correct, jets launch 1 to 10% of the disk’s material, but carry away 100% of the angular momentum.” Jets from young stars remain active for up to a million years, ultimately sending material light-years away. The youngest of these objects — with ages of 100,000 years or so — are still embedded deeply in their molecular cloud nurseries, environments that are opaque to visible light. To study the earliest stages of jet formation, astronomers explore these objects in infrared light and radio waves, wavelengths that can penetrate the clouds. Astronomers recently discovered one of the record holders for jet production. Since even gas-giant-sized objects need to accrete matter to form, theorists have hypothesized that

Amateur Astronomers and the Case of the Missing Jets Hanging off the wing of Cygnus is a rather unassuming binary star that has tantalized amateur and professional astronomers for more than a century. The prototype of the class of stars that bears its name, the cataclysmic variable SS Cygni has been observed essentially nonstop since its discovery in 1896. So well known is this system that its distance (90 light-years), makeup (close red dwarf-white dwarf binary), and reasons behind its periodic outbursts (accretion of red dwarf gas onto the white dwarf) have been the subject of sci-fi novels. Given the constant scrutiny, it’s a wonder that SS Cygni was able to keep any secrets at all. But it baffled scientists for decades because in a system that involved accretion, nobody had ever observed jets. All that changed a few years ago when radio astronomers enlisted the help of the American Association of Variable Star Observers (AAVSO). With a worldwide network of enthusiastic amateurs constantly monitoring 10 dwarf novae

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NASA / CXC / UNA HWANG (GSFC) ET AL.

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SUPERNOVA–JET CONNECTION This Chandra X-ray image shows jet-like features in the supernova remnant Cassiopeia A. Both observational evidence and theoretical models strongly suggest that jets play a critical role in blowing up at least some massive stars. If the jets break through the star completely and are aimed toward Earth, we see the event as a gamma-ray burst.

giant planets, such as Jupiter, must produce jets at some point in their growth. The discovery of jet outflows in a flyweight 24-Jupiter-mass brown dwarf prompted Ray’s collaborator Emma Whelan to suggest that “it may even be feasible for young giant planets with accretion disks to drive outflows.” Not all jets are sustained over long periods of time,

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though, nor are they all associated with a growing object. The essential recipe for a jet is differentially twisting magnetic fields, conditions that exist in some of the most destructive places in the universe: core-collapse supernovae. It has not been proven definitively that jets are the driving force behind these explosions, but leading theorists have proposed that the collapsing stellar core — a rapidly rotating ball of neutrons possessing an intense magnetic field — creates colossally energetic jets that play a major role in blowing up massive stars (S&T: January 2002, page 40). The smoking gun that at least some supernovae involve jets was found in the decades-long gamma-raybursts (GRB) mystery. Several long-duration GRBs, which involve high-speed jets, have been linked directly to supernovae (S&T: August 2006, page 30), leading Craig Wheeler (University of Texas at Austin) to state, “There is little doubt in the community that these standard gammaray bursts are formed in the collapse of massive stars.” Violent galactic eating machines, the gradual formation of giant planets, even the explosive deaths of massive stars. They comprise a huge array of phenomena, but the same thin line of matter first observed by Heber Curtis ties them all together into the universal jet set. ✦ C. Renée James is an astronomer at Sam Houston State University in Huntsville, Texas. She was awarded the 2008 Popular Writing Award by the American Astronomical Society’s Solar Physics Division for her article “Storm Watch,” which appeared in the July 2007 issue of S&T

modest-sized telescope. During its outburst phase, which happens on average every month or two, it flares up to magnitude 8.3. But the outbursts are unpredictable, and radio astronomers had always, in the immortal words of Maxwell Smart, “missed it by that much.” “Radio emission is most prominent during the beginning of the outburst,” explains Körding. As such, radio astronomers needed instantaneous knowledge of the nascent outburst in order to catch the jet. This tall order was met by nearly 700 observers who dutifully kept a close eye on SS Cygni and the other nine dwarf novae. On April 24, 2007, Polish amateur Stanislaw Swierczynski first reported a magnitude of 11.5, alerting variable-star observers around the globe to turn their telescopes toward SS Cygni and verify the outburst. Once confirmed, AAVSO members and radio astronomers began coordinating their observations, and the elusive radio jets were finally discovered. As Körding says, “The observations of amateur astronomers have and will be of great value to anyone studying SS Cygni.”

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The Stability of the Solar System

Hanging

R. CUMMING / STOCKHOLM UNIV.

in the Balance

Will the orbits of the planets ever go haywire? Mr. Newton, meet chaos theory.

greg laughlin daunting problems — climate change, recession, reality TV shows — but by “world,” we usually mean the fi lm of life coating its surface, not the planet itself. We take for granted the clockwork stability of planetary orbits. Nobody worries that Mercury will run rampant in the inner solar system. There’s no serious concern that Mars will smash into Earth. After all, the planets have been stably circling the Sun for the last 4.54 billion years. If anything could go wrong, you’d think it already would have. Nevertheless, an ironclad “proof” of the solar system’s stability has been one of the longest-standing and most vexing problems in astronomy. The discovery of hundreds of extrasolar planets has raised new interest in the question. Many exoplanets follow highly elongated (eccentric) orbits, hinting that they are the survivors of past episodes of planetary chaos. In some systems that have two or

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more known planets, we see clear evidence that largescale orbital instabilities have indeed occurred among them. In the three-planet Upsilon Andromedae system, for instance, the outer two have eccentric orbits whose shapes and alignments can be understood as resulting from the ejection of a fourth planet when the system was young. Even after 2.5 billion years (Upsilon Andromedae’s estimated age), the signature of that ejection is clearly preserved; every 8,000 years the system returns to the eccentricity configuration that existed just after the disaster.

Not So Simple Isaac Newton was the first to understand the physics of planetary orbits. His law of universal gravitation — the formula telling how every mass attracts every other mass, depending on their separation — beautifully explained the solar system’s marching orders. By applying Newton’s

S&T ILLUSTRATION: CASEY REED

The world faces

NASA / JPL / CALTECH

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FELIX HENRI GIACOMOTTI / BRIDGEMAN ART LIBRARY

POSTHUMOUS PORTRAIT BY MADAME FEYTAUD

formula, a planet’s future path can be told from its present position and velocity and all the gravitational pulls that it experiences. The Sun contains 99.8% of the solar system’s mass, so to an excellent approximation, each planet’s orbit can be described independently as a simple ellipse with the Sun at one focus. If the Sun were really all that mattered, each planet’s orbit would remain exactly the same forever. But the planets exert tiny gravitational pulls on one another too. It turns out that these small effects need not always remain small. THE END OF PERFECT PREDICTABILITY Left: Pierre-Simon de Laplace (1749–1827), an extraorGiven enough time, they can add up in dinary mathematical genius, solved the mystery of Jupiter’s and Saturn’s slight, slow orbital drifts. complex and unexpected ways to produce This triumph helped give rise to “Laplacian determinism”: the idea that if you knew the present state effects that become overwhelming. of every particle in the universe, you could completely predict the future forever. Even in Newton’s day, observations Center: Urbain J. J. Le Verrier (1811–77), the pre-eminent mathematical genius of his own time, was of the planets’ movements had been the first to find signs of trouble in the idea of perfect orbital determinism. elevated to a highly refined art. Kepler Right: Henri Poincaré (1854–1912) proved that the planets’ positions in the very far future cannot had shown that the planets’ quirky paths predicted at all. Even microscopic uncertainties in their present orbits will eventually mushroom, by on Earth’s sky could be explained as what’s now called a butterfly effect, into overwhelming unpredictabilites. simple, elliptical orbits in three-dimensional space. But by Newton’s time, his theory to explain what was happening. The mathematthree generations later, astronomers had determined the ics were simply too daunting. In a letter, he implicitly trajectories of the planets with enough precision to reveal conceded defeat: “…to consider simultaneously all these deviations from perfect ellipses. causes of [planetary] motion and to define these motions by Newton knew that the planets’ tugs on one another exact laws admitting of easy calculation exceeds, if I am not would deform their orbits, and he was particularly keen to mistaken, the force of any human mind.” see whether he could account for a pronounced peculiarity Newton’s failure to explain the errant paths of Jupiter in the orbits of Jupiter and Saturn. All through the 16th and Saturn provided tremendous motivation to the elite and 17th centuries, astronomers could see that Jupiter mathematicians of the 18th century. The problem, the was slowly spiraling inward by a trace, while Saturn was “Grande Inegalité” as it came to be known, was cracked in gradually drifting outward. If that trend were to continue 1776 by Pierre-Simon de Laplace. He showed that Jupiter for tens of thousands of years, the whole system would be and Saturn experience thousand-year-long orbital oscilimperiled. Despite great efforts, Newton was unable to use lations around a mean, arising because Jupiter circles the Sun very nearly five times for every two orbits of Saturn. This commensurability, or “resonance,” allows the perturbations that the two planets exert on each other to add constructively for centuries on end. A seemingly negligible series of tugs, correctly timed, produces a very tangible long-term effect. Having devised his theory, Laplace could effectively run the solar system’s clock backward to predict the sky locations of the planets during antiquity. He obtained a stunning match with a 2,000-year-old WORST CASE If Mercury ever falls into just the right resonance with Jupiter in the next 6 billion years, Mercury’s orbit could eventually become elongated enough to cross the orbit of Venus — and then Mercury could be thrown practically anywhere, including a possible collision with Earth. But the chance of Mercury getting loose before the Sun dies is only about 1%.

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The Stability of the Solar System

Babylonian observation, which (by his interpretation) stated that “on March 1, 228 B.C., at 4:23 in the morning (mean Paris time), Saturn was observed to lie two fingers beneath the star Gamma Virginis.’’ His success in pinpointing the position of Saturn across the millennia gave him a supreme confidence that his theory was correct, and no doubt served to usher in the concept that came to be known as Laplacian determinism: The entire future would be known precisely if one knew the present positions and velocities of all the particles in the universe.

The Dream of Predictability In Laplace’s set of formulae, the solar system is completely stable. His mathematical framework explicitly disallows any evolution of the planetary periods over the very long term, and Laplace thought that he had proved that planetary orbits are inviolate. By the mid-1800s, however, cracks began to appear in the celestial clockwork. It became clear that the approximations underpinning Laplace’s theory implied that it could not be used with confidence for time intervals longer than several thousand years. Urbain J. J. Le Verrier (who accurately predicted the existence of Neptune based on its perturbations of Uranus) sounded the alarm that the solar system might not be subject to the lockstep certainty promoted by Laplace. Within decades, the problem had become pressing enough that a high-profile international contest was staged, in which the first person to prove the stability of the planetary orbits would receive 2,500 crowns and a gold medal from King Oskar of Sweden. Frustratingly, the eventual winning entry, submitted by Henri Poincaré, was a proof that the problem could not be solved. Poincaré showed that even a simple system that contains a star and two planets is “non-integrable,” meaning that one cannot write down a formula that will give the positions of the planets forever — or a yes/no answer regarding their longterm orbital stability. Poincaré’s work was nearly a century ahead of its time; it provided the first inkling of chaos theory and the now-familiar “butterfly effect,” a term describing any system in which a tiny cause leads to an overwhelming effect. (The term came from the apparent finding, in atmospheric modeling, that even a butterfly flapping a wing in Brazil should change all the weather worldwide just months ahead.) Poincaré’s 28 April 2010 sky & telescope worldmags

work established that a definitive trajectory for the solar system cannot be told indefinitely far ahead, and that any statements about the fate of the planet’s orbits must be expressed in the language of probabilities.

The Brute-Force Solution In modern times, three events have revitalized the oncearcane discipline of celestial mechanics. Spaceflight demands planetary positions and spacecraft trajectories of extraordinary accuracy. Powerful computers enable brute-force numerical simulations that can carry accurate planetary motions quite far into the future, by calculating and re-calculating the planets’ positions and motions in vast numbers of small steps along the way. And third, the discovery of extrasolar planets, including multi-planet systems with orbital resonances and signs of past chaos, spurred renewed interest in the solar system’s own fate. In the 1980s, a number of

S&T ILLUSTRATION: CASEY REED

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S&T: GREGG DINDERMAN. DATA: E. ASPHAUG, C. B. AGNOR, Q. WILLIAMS.

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NEAR MISS A near-collision of planets could be as bad as a smash. Computer simulations like this show that if Mars were to swing close enough past Earth, tidal forces would radically distort the smaller planet, spin it up, and pull off much of its mantle as a massive streamer of asteroid-size rocks and debris — some of which Earth would collect, with catastrophic effects. Earth is shown here unrealistically as a simple sphere. In reality it too would be temporarily distorted. In fact, a very close Mars-Earth encounter would dissipate enough tidal energy in Earth’s interior to melt the planet completely. Earth would become a globe of lava, even with no contact between worlds.

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showed no signs whatever of instability. (We now think they would be stable for quadrillions of years, all else being equal.) But the terrestrial planets exhibited subtly chaotic disturbances and orbital drifts, with Mercury in particular hinting that it might eventually come unhinged. Laskar thus conducted an experiment to see whether Mercury could be “guided” toward the exit. To do this, he examined the results of his half-billion year calculation

NASA / JHUAPL / CARNEGIE INST. OF WASHINGTON

astronomers used supercomputers to probe the subtleties of solar-system dynamics. One fruit of these calculations was explicit demonstration that the solar system is indeed chaotic, and, in particular, that the timescale over which orbital predictions are bound to deteriorate can be measured in millions of years — much less than the solar system’s age. As an example: even if the present-day positions of the planets could be determined to a precision of less than the width of an atom, it still becomes impossible to make any concrete statement about where the planets will be in 100 million years. We have no way of knowing whether January 1, 100,000,000 AD will occur in winter or summer, or even, with certainty, whether Earth will be orbiting the Sun at all on that far distant New Year’s day. In 1995 Jacques Laskar, who is LeVerrier’s intellectual successor at Paris Observatory, published the results of an interesting numerical experiment. With the aid of computer algebra, he developed a sophisticated approximate method for marching the positions of the planets forward in time. The computer program that implemented his scheme contains more than 150,000 terms that account for the subtle gravitational interactions between the planets, allowing him to move the solar system forward in big, roughly 200-year steps. He was thus able, for the first time, to study the solar system’s many possible courses of evolution over billions of years. Is there any indication that the planets might fail to hew to their well-worn tracks? When pushed out for a half billion years, Laskar’s program displayed no overt tendencies toward disaster. The giant planets, Jupiter, Saturn, Uranus, and Neptune,

THE BLACK SHEEP Innocent-looking Mercury turns out to be the only significant pathway to future solar-system craziness.

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The Stability of the Solar System

and identified the moment when the ellipse of Mercury’s orbit reached its maximum eccentricity (elongation). He then used the configuration at this moment as the starting point for four near-identical solar-system models that differed only by imperceptible (and utterly unobservable) changes to Earth’s orbit. As he marched the four copies forward in time, they at first traced one another in lockstep, but as millions of simulated years elapsed,

the models began to drift inevitably apart as the butterfly effect exerted its influence. After each of the four versions had run through a half billion years, Laskar again examined the resulting trajectories and again identified when Mercury had achieved its highest eccentricity. He then used this confi guration as the starting point for a further branching of four simulations, and repeated the procedure.

NASA / JPL

The Instability of Jupiter’s Moons

BY LANDON CURT NOLL In 1771 Pierre-Simon de Laplace realized that three of Jupiter’s four big moons have an intimate relationship. In the time it takes Ganymede to orbit Jupiter once, Europa orbits Jupiter twice and Io orbits four times. Astronomers honored Laplace by naming any orbital resonance among three or more bodies a Laplace resonance. Io, Europa, and Ganymede form the only known example in our solar system. One consequence of their 4:2:1 resonance is that their mutual gravitational perturbations help prevent them from settling into exactly circular orbits. In the case of Io, closest to Jupiter, its slightly elongated orbit contributes to its famous tidal flexing, which heats Io’s interior to make it the most volcanically active body in the solar system. In the 42 hours Io takes to revolve around Jupiter, parts of its rocky surface rise and fall by perhaps as much as 100 meters (330 feet)! By comparison, the Moon raises “Earth tides” in our planet less than 1 meter high.

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Sulfurous, fuming Io draws its extraordinary internal heat from tidal flexing that drains orbital and rotational energy from elsewhere in the Jupiter system. At top is an active volcanic plume.

Recently, in a paper published in Nature for June 18, 2009, Valéry Lainey, Jean-Eudes Arlot, Özgür Karatekin, and Tim Van Hoolst calculated that Io’s tidal flexing pumps heat into its interior at a rate of 90,000 gigawatts, more than 5 times the capacity of all electric power plants on Earth. Io’s extraordinary tidal heating creates an average surface heat flux almost 25 times greater than Earth’s. These calculations agree with infrared telescopic measurements of heat from Io, which also suggest that Io’s interior is in thermal equilibrium — and thus that Io’s heat comes from tidal flexing rather than, for instance, radioactive decay at its core or residual heat left over from its formation. Some dynamicists had assumed that Io drew its energy from

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After more than a dozen such branchings, yielding numerous possible outcomes, Laskar discovered that in some of them Mercury’s orbit can become so eccentric that it is in danger of crossing the orbit of Venus. Orbit crossings generally lead to disasters: collisions, nearmisses that tidally shred one or both planets (see the illustration on page 29), or the eventual ejection of a planet from the solar system completely.

The consequences for Earth would range from more frequent asteroid impacts to the planet’s direct destruction.

the other Galilean moons, thus maintaining the 4:2:1 resonance as all their orbits shrank. Instead, Lainey and his colleagues, using 116 years of positional observations of Jupiter’s moons, determined that the Laplace resonance is slowly breaking. They found that since 1891, Io’s orbit has shifted 55 km (34 miles) toward Jupiter, while Europa and Ganymede edged 125 and 365 km away, respectively. The diagrams below show just two of the several significant forces acting on Io. Lainey and his colleagues demonstrated that the inward force illustrated in the right panel dominates over the outward force in the left panel, resulting in a net shift of Io toward Jupiter. A similar pair of forces act on Europa and Ganymede, except that in these cases the outward force dominates, shifting them away from Jupiter. It came as a surprise to many that the Galilean moons are slowing leaving their Laplace resonance. Lainey and his colleagues make no prediction as to when the resonance will be broken. But when it does happen, Io’s orbit will become more circular, the tidal flexing will greatly diminish, and Io’s

volcanoes will cease their activity and grow cold. And beyond that? To predict the far fate of the Galilean moons will require better data and new insights. Perhaps when the Laplace resonance is broken, the forces resulting from Jupiter’s tides will drive Io outward again, and Io, Europa, and Ganymede will re-enter another resonance, leading to a reawaking of Io’s volcanoes. Might this have happened already, perhaps several times? We can’t trace the Galilean moons indefinitely far back any better than we can trace them indefinitely far ahead. For example, it’s unclear whether outer Callisto ever joins the resonances of the other three. One thing we do know is that we are fortunate to be living during such an exciting period of Galilean history!

The Picture Today Laskar’s 1994 results provided the first concrete demonstration that, even with no outside influences, orbital chaos can arise during the Sun’s remaining 6-billion-year lifetime as

Landon Curt Noll is a computer security specialist for Cisco Systems and a member of the American Astronomical Society. He enjoys giving talks at Fremont Peak Observatory (www.fpoa .net) and adding new research results to his astronomy page (www.isthe.com/astro).

Two Competing Tidal Effects Io’s orbit without effect

Io’s orbit with effect

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S&T: GREGG DINDERMAN

Jupiter’s 10-hour rotation

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Left: Gravity from Io raises slight tides in the body of Jupiter. Jupiter’s 10-hour rotation (faster than Io’s 42-hour orbit) carries these tidal bulges ahead of the line between the two bodies. The pull from the leading bulge tugs Io forward, speeding it up and thereby slinging it a little farther away from Jupiter. Right: Jupiter raises tidal bulges in Io too. Like Earth’s Moon, Io always presents the same face to Jupiter, but not quite. Io’s orbit is an ellipse — so its motion speeds up once per orbit as it approaches its closest point to Jupiter. During this time its rotation lags a little behind the direction toward the planet. When the rotation lags, Jupiter’s gravity pulls on Io’s tidal budge to speed up Io’s rotation. The energy of that speedup comes from Io’s orbital energy, so Io settles closer to Jupiter. This effect dominates the one described above.

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The Stability of the Solar System

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ROAD TO DISASTER Mercury has a modestly eccentric orbit. Jupiter’s orbit (outside the frames) is also eccentric, though less so. Each orbit’s long axis, called the line of apsides, is slowly precessing counterclockwise (blue arrow), and at a different rate. If these rates ever fall into lockstep, as shown here, Mercury’s orbit becomes more and more eccentric until it grows so long that it crosses the orbit of Venus. At that point, close encounters between the two planets could fling them every which way, spreading chaos throughout the inner solar system.

a hydrogen-burning star. Several important questions were left unanswered, however. It was unclear how much “help” was given by repeatedly selecting the seemingly least-stable trajectories for exploration. How long would the solar system last if one were to make a single end-to-end simulation? What is the underlying mechanism or influence that destabilizes Mercury’s orbit? And finally, would there be any difference if the subtle effects of general relativity were included in the calculation? All these questions have recently been answered. As a

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result of simulations carried out independently by several groups, the solar system’s Achilles heel — the mechanism that gets Mercury into trouble — has been identified. Mercury is at risk because of Jupiter’s gravitational influence. Ongoing tugs between the planets incite a whole range of deviations from pure ellipses. Prominent among these disturbances are orbital precessions. When an orbit precesses, the long axis of its ellipse shifts direction, so that the point where the planet is closest from the Sun slowly but steadily drifts around, either clockwise or counterclockwise. In our solar system, planetary precession rates are all moderately slow. Mercury’s orbit is currently precessing by 0.16° per year, and Jupiter’s is precessing by 0.23° per year. But simulations show that over the very long term, gravitational influences can lead to significant excursions in Mercury’s precession rate. Most dramatically, if Mercury’s precession rate approaches that of Jupiter, it can become caught in a so-called secular resonance (“secular” meaning long-term), in which the orbit of tiny Mercury becomes compelled to precess in synch with its huge Jovian brother (see the illustration above). The development of a secular resonance spells trouble. Over millions of years, Jupiter steadily drains angular momentum from Mercury’s orbit. The effect on massive MODELING MERCURY Top: In most simulations of Mercury’s long-term future, nothing much happens. This typical run shows Mercury’s orbital eccentricity, beginning from a present-day starting point, doing nothing radical in 20 billion years. (An eccentricity of zero means a circular orbit centered on the Sun. Eccentricity 1 refers to an ellipse so narrow that it looks like a single straight line with the Sun at one end. Mercury’s eccentricity today is 0.21.) Bottom: In a few cases, however, Mercury goes crazy. In this run, the author picked a time when Mercury reached a high eccentricity and used this as a “branching point” for starting four new runs. When one of these runs reached another high eccentricity, he branched it again, and again. Occasionally a future turns up that wrecks the inner solar system.

S&T: GREGG DINDERMAN. DATA: GREG LAUGHLIN

Orbit crossing!

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Jupiter is virtually nil, but Mercury sees its eccentricity climb to a level that precipitates disaster. Computers have now reached the point where it’s possible to carry out thousands of solar-system simulations, each without approximation, and including the subtle modifications provided by general relativity and by secondary bodies such as the asteroid Ceres and Earth’s Moon. The biggest study by far was released last summer, in which Laskar and collaborator Mickael Gastineau reported results from 2,501 solar-system simulations. The simulations contain a trove of detail. They indicate, for example, that we are lucky Einstein was right. The effects of general relativity famously modify Mercury’s precession rate by a tiny 0.43 arcsecond per year. This shift places Mercury’s orbit in a regime where it is much more difficult for it to wander into the dangerous secular resonance with Jupiter. Were it not for general relativity, the chance of Mercury becoming destabilized would be measured in tens of percent. With general relativity exerting its hand, the odds that the solar system will go haywire before the Sun’s death are only about 1%. While small, a 1% probability is nonetheless non-negligible. Laskar and Gastineau computed several possible future trajectories for the solar system in which Earth

itself does not fare well. In one particularly dramatic case, Earth takes a devastating direct hit from Mars. In another, Mars passes just a few hundred kilometers from Earth’s surface. In this case, a miss is by no means as good as a mile. The tidal stretching and squeezing during the close approach would heat Earth’s interior enough to completely melt the planet’s mantle and crust. Earth’s oceans would become a crushing atmosphere of steam above a global sea of glowing lava. I prefer to see the glass 99% full rather The author frequently blogs than 1% empty. We now have a definitive about exoplanets and his work with them at www.oklo.org. probabilistic answer to the centuries-old problem of solar-system stability. There is no chance of anything going wrong within the next 50 million years, and the odds are truly excellent that the planets will all be present, and orbits accounted for, when the Sun faces its denouement some 6 billion years from now. ✦ Gregory Laughlin is an astronomy professor at the University of California, Santa Cruz, where his primary research focuses on extrasolar planets and their discovery. Laughlin also coordinates the Transitsearch.org planet-hunting project for advanced amateur observers.

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S & T Test Report

Rod Mollise

Skyhound’s SkyTools 3 From generating observing lists to logging your observations, this program promises to do it all. WHAT WE LIKE:

SkyTools 3 Pro Edition US price: $179.95 (the standard edition, with smaller databases and telescope control available as on option, costs $99.95) Skyhound P.O. Box 1182, Cloudcroft, NM 88317 575-446-1221; skyhound.com

One program that “does it all” for observers Powerful tools for generating observing lists Easy-to-use system for logging your observations

WHAT WE DON’T LIKE: Non-standard user interface takes time to learn No printed or online user’s manual

Today’s amateur astronomers, whether observing alone or in groups such as the one pictured here at last year’s Stellafane gathering in Springfield, Vermont, are seeking out many out-of-the-way objects, often with the help of observing-planning software.

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When most of us

think astronomy software, we think planetarium programs — applications that paint a simulated night sky on the computer screen. There is, however, another genre of astro-ware, the planner, which may be even more useful for observers. Most planners can draw star charts, but they also have tools to help telescope users build lists of sky objects to observe (or image) on any given evening. One of the premier planners, SkyTools, is now in its third release, and it brings new and innovative features to the table. The professional edition of the program, which is the one I tested, adds many more star clusters, nebulae, and galaxies (a whopping total of 1 million galaxies!) to the standard edition’s already impressive databases. It also makes some formerly optional features standard, such as telescope control. Despite its huge number of objects, SkyTools 3 ships on just two disks, a program CD-ROM and a data DVDROM. Installation is straightforward; all I had to do was insert Disk One into my CD-ROM drive, follow the onscreen prompts, and the software installed without complaint on both my Windows XP laptop and my Windows Vista desktop computers (the program is compatible with the 32- and 64-bit versions of these operating

SkyTools 3 opens with a list of celestial objects culled from the program’s internal databases that meet criteria you select. These criteria can be customized for your observing equipment and conditions, and they take into account such factors as sky brightness, moonlight, and object altitude.

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SYSTEM REQUIREMENTS PC: Windows 7, Vista, XP, 2000, NT4, or 98, 233-MHz Pentium II processor (Pentium 4 recommended), 512 megabytes or better of RAM, CD-ROM drive, minimum 20 megabytes disk space (650 megabytes for full install), DVDROM drive and 4.8 gigabytes of disk space for the extended database of the professional edition. Mac: Macintosh running a Windows emulator, other requirements as above.

systems). The only minor irritation is that the program doesn’t come with installation instructions. Yes, it was obvious I should insert Disk One to begin, but the more computer-shy folks among us might like a little handholding when we’re getting started. When all systems were go, I was presented with the screen shown at lower left. Since I’m often all thumbs when it comes to computers, I knew beforehand that I’d need help getting the program configured. SkyTools 3 doesn’t come with a manual, printed or otherwise, but I found I could get by without one. It was easy for me to click the “How To” icon and “Getting Started” and be presented with comprehensive instructions for entering my latitude, longitude, time zone, and the other preliminaries that astronomy programs typically require. Once SkyTools 3 is configured, it’s time to build an observing list. Not sure what should go in it? The program can automatically produce lists tailored to specific observing equipment, dates, and conditions. Click an icon, indicate general preferences, which can range from “showpiece objects” to “off the beaten path,” and SkyTools 3 will spit out a ready-made assortment of galaxies, nebulae, star clusters, asteroids, comets, and planets. You can also use “Designation Search” to add individual objects to a list. Particularly noteworthy here is that the program didn’t care what I typed. I could key in “NGC 7331,” “NGC7331,” or just “7331” and it always returned data for the correct galaxy. How do you know if a faint fuzzy is good enough to deserve a look? Maybe it’s a little low or the Moon is in the sky. SkyTools 3 can tell you about object visibility. Click “more object information” in the search window and select the “Visual Synopsis” tab. Doing that for NGC 7331 elicited the following and more: “On this night NGC 7331 is best visible between 18:32 and 21:30, with the optimum view at 19:44. Look for it in Pegasus, high in the sky in moonlight. It is challenging

Sk yandTelescope.com April 2010 35

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S&T Test Report

Left: SkyTools 3 can generate conventional star charts that include extensive customization options. Right: The program can also generate “Visual Sky Simulation” charts that are tailored for your telescope, eyepiece, and observing conditions. The one here has a mirror-reversed view to match the author’s 11-inch Celestron Schmidt-Cassegrain telescope fitted with a star diagonal. The circle represents the field of view with his Tele Vue 13-mm Ethos eyepiece, and the arrow shows the direction that the sky appears to drift, allowing quick visual orientation with a non-tracking telescope.

visually in the Celestron Nexstar 11. Use the Panoptic 35mm for optimum visual detection.” The equipment recommendations are based on the gear I own and entered into the program’s database.

“Power Search” retrieves a series of objects from the database — all the galaxies in Virgo, for example. Types of objects, constellations, magnitudes, and other variables can be specified. You can then

send candidate objects found by the search to an observing list by highlighting them and clicking “add to list.” Once a list is done, it can be printed, but these days most of us carry a laptop

company to jump on the 100° bandwagon, announcing 14-, 9-, and 20-mm eyepieces in quick succession. And recently TMB Optical and Zhumell have each announced 16- and 9-mm models. Last fall and winter I tested the Explore Scientific 14mm 100° Series Nitrogen-Purged Waterproof Eyepiece. While the name is a bit of a mouthful, it accurately describes two features that set the ocular apart from all other astronomical eyepieces, not just 100° models — its waterproof design and nitrogen-filled body, which are said to eliminate internal fogging of the lenses. Except for a youthful acquaintance of mine who tried to clean a set of eyepieces by running them through a dishwasher (true story!), I’ve never heard of water damage to the inside of an eyepiece. Nevertheless, both features are good things, especially for those of us who observe in dewy conditions and/or use liquid lens cleaners.

As with the other 100° eyepieces announced by Explore Scientific, the 14-mm model fits only 2-inch focusers, which are pretty much standard fare on today’s telescopes. The barrel is threaded for standard 2-inch filters, and it has a large, tapered “safety” groove, which allows it to be securely gripped in any holder that has thumb-screw locks or a compressionring clamp. Furthermore, the tapered design prevents the groove from snagging a compression ring and being difficult to remove from a holder, as sometimes happens with eyepieces having sharp-edged safety grooves. The only noteworthy mechanical aspect of the Explore Scientific 14-mm eyepiece that might be considered a downside is its weight. At 31 ounces (0.88 kg), the eyepiece is heavy, and it’s 11 ounces (55%) heavier than Tele Vue’s 13-mm Ethos. This was enough to upset the balance of my 12-inch Dobsonian, forcing me to tighten the friction clamp on the

Quick Look

Explore Scientific’s 14mm 100° Eyepiece US price: $499 ($399 introductory price still in effect at press time) Explore Scientific 7401 Katelyn Ct., Suite A, San Diego, CA 92120 888-599-7597; explorescientific.com

No product in recent memory has received more universal acclaim from the observing community than Tele Vue’s 13-mm Ethos eyepiece introduced in mid-2007 — the first astronomical eyepiece offering a 100° apparent field of view. With such rave reviews, it’s not surprising that a year and a half later there are more than a dozen 100° eyepieces on the market. What is surprising, however, is that there are now four companies offering them. Newcomer Explore Scientific was the next

36 April 2010 sky & telescope worldmags

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into the field for use at the telescope. That telescope doesn’t have to be the latest Go To wonder, though. I found the program just as useful with my “push to” Dobsonian reflector, especially when I used the star-hopping method to hunt for faint targets. SkyTools 3’s charts, accessed by right-clicking any object in a list, are extremely detailed and display more stars and deep-sky objects than any printed atlas. These sky maps are attractive and almost infinitely customizable. SkyTools 3 can also display a second type of chart, called “Sky Simulation,” which is automatically configured for a selected telescope and eyepiece. When hunting difficult deep-sky denizens such as dim galaxies, I fi nd it helpful to have actual images on hand. SkyTools 3 can download photographs of deep-sky objects from the Digital Sky Survey and superimpose them on charts if desired. If an internet connection is not available at an observing site, pictures can be saved beforehand for later use. Not everybody likes to star-hop. I, for

WHAT WE LIKE: Excellent image quality Top-notch construction

WHAT WE DON’T LIKE: Significantly heavier than competing eyepieces

one, have been spoiled by Go To technology, and SkyTools 3 is easy to use with a computerized telescope. The program’s Real Time tab handles Go To operations. Here, the telescope is connected to the computer with a few mouse clicks, and Go To commands are initiated with the “Slew To” button. Since SkyTools 3 uses the (free) ASCOM platform for communicating with Go To telescopes, nearly any model of telescope old or new is supported. All done observing? Why not preserve your records? SkyTools 3 includes an elegant, easy-to-use logging system that has space for extensive notes. It can be set to automatically enter a lot of observing information, including location and sky conditions, which is a real time-saver. So, is SkyTools 3 perfect? That’s not really a fair question, since no computer program is or ever will be perfect. Nevertheless, I did have a couple of nits to pick with SkyTools 3. While the star charts are beautiful and highly detailed, they are a bit of a chore to configure. That isn’t because of a lack of options but, con-

versely, because there are so many. Almost everything can be customized, and that sometimes led to confusion. Then there’s the program’s User Interface. Don’t expect the familiar Windows File, Edit, etc. menus; instead, the software’s author, Greg Crinklaw, uses a mix of icons, tabs, and hyperlinks. The interface works, and works well, but it does take a little learning. Once you catch on to the SkyTools 3 way of doing things, you’ll like it, but expect to spend some time getting comfortable with the program. The good news is that taking the time to learn SkyTools 3 is amply rewarded. This software is a powerful program for observers and astrophotographers. I have little doubt I could erase every other astronomy program from my hard drive and get along fine with just SkyTools 3. ✦

altitude axis more than I like for optimal “feel.” The solution, of course, would be to have an adjustable counterweight on the scope, and I would certainly consider adding one if I owned the eyepiece. This minor issue, however, was quickly forgotten the moment I looked through the eyepiece. The view was everything one would expect from a premium eyepiece — crisp, contrasty views with round, pinpoint stars across a field so big that I had to roll my eye around to see it all. There is a very slight pincushion distortion at the edge of the field, which I only noticed when I was sweeping large, “solid” objects such as the Moon in and out of the field. As long as I kept my eye centered in the eyepiece’s exit pupil, there were no visible color fringes even on the Moon’s brilliant, high-contrast limb. The times when I did note a thread of green along the limb served as a reminder that my eye wasn’t centered properly.

I tried the eyepiece on a variety of telescopes, ranging from the 12-inch Dob down to a 92mm apo refractor, all with excellent results. Perhaps the most demanding test came with the eyepiece fitted to a 4-inch, flat-field apo. Under critical examination I could detect a slightly different focus position for stars at the center and edge of the field, indicating the eyepiece has a very mildly curved focal surface. This focus shift was tiny, however, and I suspect much of the reason I could see it at all is because my eyes have lost virtually all of their focus accommodation as I’ve grown older. Observers with accommodating eyes will likely see perfectly sharp stars when they concentrate on the center and edge of the field without adjusting the focus. Just about any way you look at and through it, the Explore Scientific 14mm 100° eyepiece is a winner. — Dennis di Cicco

Rod Mollise, known to many in the amateur community as “Uncle Rod,” lives in Mobile, Alabama, and maintains an entertaining website at skywatch.brainiac.com/astroland.

S&T: DENNIS DI CICCO

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New Product Showcase PANEL Alnitak Astrosystems announces the Flat-Man ($299), a flat-field illumination source for mid-size telescopes. The Flat-Man employs an electroluminescent panel to provide a uniform light source in front of your telescope objective to produce high-quality flat-field frames necessary for serious astrophotography and photometric work. A simple Windows interface controls the brightness of the Flat-Man via a single USB cable, which also provides the operating power. Simply point your telescope at the zenith and place the unit directly on the front aperture. Flat-Man will evenly illuminate telescopes with tubes or dew shields of up to 7 1/8-inches (180 mm) diameter. Alnitak Astrosystems P.O. Box 936, Rockport, ME 04856 www.alnitakastro.com

S&T: SEAN WALKER

◀ CALIBRATION

▾ MEGA

DOBS What dedicated deep-sky observer hasn’t dreamed of owning a gigantic telescope? Orion Telescopes & Binoculars can make your wish come true with its new series of Orion Monster Dobsonians (starting at $55,600 for a 36-inch f/4 model). These behemoths feature low-expansion-glass primary mirrors of 36-, 40-, and 50-inch apertures with enhanced aluminum coatings. These massive mirrors are produced by master optician Normand Fullum and are honeycombed to reduce mass and weight. The Dobsonian rocker box is constructed of furniturequality Russian birch and laminated with aluminum plate for extra stability. Its 8 trusses are manufactured from carbon graphite composites with stainless-steel hardware connections. Each Orion Monster Dobsonian comes with ServoCAT tracking Go To and Argo-Navis digital setting circles to automatically locate and track more than 29,000 celestial targets. Orders require a 75% deposit. See Orion’s website for additional details.

Orion Telescopes & Binoculars 89 Hangar Way, Watsonville, CA 95076; 800-447-1001 www.oriontelescopes.com

ORION TELESCOPES & BINOCULARS

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DIAGONAL Refractor and Cassegrain telescope owners considering an upgrade for their star diagonals should take a long look at the Astro-Tech one-piece machined 2-inch diagonal ($249). Its housing is machined from a single block of aluminum, to guarantee perfect alignment. The unit features a 1/ 10 -wave-or-better quartz mirror with 99% reflective dielectric mirror coatings. It weighs 14¼ ounces (404 grams). The Astro-Tech one-piece machined 2-inch diagonal uses non-marring compression rings to hold your eyepieces securely in both the 2-inch eyepiece holder and in the included 2-to-1¼-inch eyepiece adapter as well. Both the 2-inch focuser barrel and 1¼-inch adapter are threaded to accept standard 2-inch filters. Dust covers and plugs are included with each purchase. Astronomy Technologies P.O. Box 720013, Norman, OK 73070 www.astronomytechnologies.com

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S&T: SEAN WALKER

◀ SHOOTING

STAR CHRONICLES Meteorite collectors should enjoy The Fallen Sky: An Intimate History of Shooting Stars by Christopher Cokinos (hardcover, $27.95). The author weaves together natural history, memoirs, and his own research to piece together the story of our understanding of meteorites. Cokinos takes the reader from the birth of our solar system to the icy wastes of Antarctica, retelling the stories of scientists and meteorite hunters who risked their lives and reputations in the search for these bits of fallen sky. 517 pages, ISBN 978-1-58542-720-8. The Penguin Group 212-366-2000, http://us.penguingroup.com

▶ SELF-ALIGNING

GO TO Meade Instruments rolls out its second addition to the groundbreaking LightSwitch series of self-aligning Go To telescopes with the ETX-LS SC 8-inch LightSwitch ($1,799). This 8-inch f/10 Schmidt-Cassegrain telescope uses GPS technology combined with Meade’s Level North Technology and its built-in ECLIPS CCD camera to automatically align the telescope within minutes of turning the system on. After that, simply use the telescope’s AutoStar III computer to slew to more than 100,000 celestial objects in its database. In addition, the system includes Meade’s Astronomer Inside software, which incorporates more than 4 hours of audio content describing hundreds of objects visible in the telescope that you can hear through a built-in speaker. An optional LCD monitor is also available to display 75 onboard animated videos. The ETX-LS SC 8-inch LightSwitch comes with an adjustable-height tripod, a red dot finder, a 90° 1¼-inch star diagonal, and a 26mm Meade Super Plössl eyepiece. Meade Instruments 27 Hubble, Irvine, CA 92618 800-626-3233; www.meade.com

ATIK CAMERAS

MEADE INSTRUMENTS

◀ CRIMSON IMAGER Atik Cameras introduces its new 383L+ CCD camera ($1,814) for deep-sky enthusiasts. This imager features the Kodak KAF-8300 monochrome CCD sensor, which boasts an 8.3-megapixel array of 5.4-micron-square pixels measuring approximately 18 by 14 millimeters. Its regulated dual-stage thermoelectric cooling is capable of stable temperatures down to 40°C (72°F) below ambient. Full-frame images download to your computer in 10½ seconds via a USB 2.0 interface. The Atik 383L+ is powered by a 12-volt DC cigarette lighter cable and comes with a T-thread-to-2-inch nosepiece adapter, a 10-foot USB cable, a CD-ROM with camera drivers, camera-control software, and a PDF user manual. The Atik 383L+ is also available with a color matrix CCD detector. ATIK-USA 5108 Pegasus Ct., Suite M, Frederick, MD 21704 877-284-5226; www.atik-usa.com

New Product Showcase is a reader service featuring innovative equipment and software of interest to amateur astronomers. The descriptions are based largely on information supplied by the manufacturers or distributors. Sky & Telescope assumes no responsibility for the accuracy of vendors’ statements. For further information contact the manufacturer or distributor. Announcements should be sent to [email protected]. Not all announcements can be listed.

Sk yandTelescope.com April 2010 39

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Fred Schaaf Northern Hemisphere’s Sky

Return of the Leo Hour Every sidereal time has its own unique look and feel.

These past few months I’ve been writing

instance, he called sidereal 0h the Andromeda Hour after the constellation that’s most prominent on the meridian at that time. Why names? Well, names are usually more vivid than numbers. And, says Ottewell, a term like the Andromeda Hour refers to and reminds us of a whole “state of the sky.” The sky at the Leo Hour. Let’s take a quick look at the state of the sky portrayed on our current all-sky map, at sidereal hour 10. We will call this the Leo Hour, because the 10h line of right ascension cuts right through the Sickle (the front part of Leo), passing just west of 1st-magnitude Regulus. At the Leo Hour, Sirius, Orion, Aldebaran, the Pleiades, and Algol are all still visible but only 10° to 20° high in a span southwest to northwest, and within an hour or two of setting. But Vega is just rising in in the northeast. As Earth goes around the Sun Su during the course of a year, 10h sidereal time —the Leo Hour — will come at a differH ent en clock time. The Leo Hour occurs at dawn in November, oc midnight in February, nightfall m in April, and noon in late summer. m But it is always the time when wh Leo’s Sickle is highest in the south, Orion is about to start st setting in the west, Arcturus is one-third of the way up tu the eastern sky, and Cepheus is th at its lowest in the north. And note, for our International Decade of the Sky, that tio a “state of the sky” such as the Leo Le Hour is not something you can ca just see. It’s something to experience, something you must be in. ✦ m

here about a proposed International Decade of the Sky (2011–2020). The principal goal of this 10-year event would be to get people outside and looking at the sky. Actually, just looking isn’t enough. We can, after all, see impressive representations of celestial objects on a computer monitor. We need to go out and experience the sky — not just the sights but also the sounds and other sensations that occur around us and to us. And not just parts of the sky but its entirety — along with the landscape, the weather, and the human circumstances. The Heavens by Hours. More than 17 years ago, when I started writing this column, my mandate was to discuss not just what could be seen in the night sky but what could be experienced in the observations. One way I did this in the first few years was by adapting an idea of astronomy writer Guy Ottewell — one that I called the “Heavens by Hours.” It’s now time to bring it back. The “Heavens by Hours” was originally presented by Ottewell in 1976 in the cover essay of his then-young Astronomical Calendar. He described the 24 views of the whole starry sky that are visible at each of the sidereal hours. The sidereal time is determined by the right ascension of the objects that lie on the meridian, the line that stretches from the north celestial pole through the zenith and down to the southern horizon. If you look at our all-sky chart, you will find that the line marked 10h ends right above the label Facing South, so this chart shows the sky at sidereal hour 10. Guy Ottewell’s classic Astronomical Calendar, a masOttewell’s innovation was to terpiece of illustration, information, and inspiration, is turn numbers into names. For available from ShopatSky.com. 40 worldmags

April 2010

sky & telescope

Fred Schaaf welcomes your comments at [email protected].

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April 2010 April 2010

Sky at a Glance

Mar. 31 EVENING: This is the last good chance –Apr. 15 in 2010 to see the evening zodiacal light

MOON PHASES SUN

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at mid-northern latitudes. From a dark site, look westward for a tall, leftwardslanting triangle of light as the last of evening twilight fades away. Its base is centered on Venus, and it reaches up between the Hyades and Pleiades.

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1–15 DUSK: Mercury is more than 10° above the western horizon a half hour after sunset, to the lower right of much brighter Venus. See page 53.

3 DAWN: Look for Antares just 1° below the Moon an hour before sunrise in North America, as shown on page 49.

PLANET VISIBILITY ◀ SUNSET

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6 LAST-QUARTER MOON (5:37 a.m. EDT). SUNRISE ▶

13–20 EVENING: Mars and the Beehive Cluster

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(M44) fit together within a 2° field of view, a fine sight through binoculars.

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11, 12 DAWN: The waning crescent Moon is about 5° above Jupiter on the 11th and 11° left of Jupiter on the 12th (seen from North America).

Visible March 23 through April 17

14 NEW MOON (8:29 a.m. EDT).

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PLANET VISIBILITY SHOWN FOR LATITUDE 40o NORTH AT MID-MONTH.

15 DUSK TO EVENING: Bring binoculars to a location with an unobstructed western horizon and, starting a half hour after sunset, look for Mercury and the very thin crescent Moon 7° lower right of Venus, as shown on page 48. If your site is far from light pollution, the zodiacal light will appear as Mercury and the Moon set.

16 EARLY EVENING: The thin crescent Moon IMAGE BY ROBERT GENDLER

is roughly 8° above Venus. And as the sky grows dark, the Pleiades glimmer into view just above the Moon.

21 FIRST-QUARTER MOON occurs at 2:20 p.m. EDT. Later, in the evening, Mars will appear 5° above the Moon.

23–25 EARLY EVENING: Venus and the Pleiades fit within a 5° field of view — a fine sight to the unaided eye and even better through binoculars.

24, 25 EVENING AND NIGHT: The Moon is lower right of Saturn on the 24th and lower left of the planet on the 25th.

28 FULL MOON (8:18 a.m EDT).

Messier 44, the Bee Beehive, is notable for its pairings of colorful stars.

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Mars pays this cluster a visit in the second and third full weeks of April.

See SkyandTelescope.com/ataglance for details on each week’s celestial events.

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Facing North

Northern Hemisphere Sky Chart

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Using the Map

Binocular Highlight:

WHEN

Disparate Dipper Duo

Late February

Midnight

Early March

11 p.m.

Late March

11 p.m. *

Early April

10 p.m.*

Late April

Dusk

N

W

*Daylight-saving time.

h

Hya

Q

A

ERID ANUS

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n bara trix Bella G

L

K

A

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OR ION

Go outside within an hour or so of a time listed above. Hold the map out in front of you and turn it around so the yellow label for the direction you’re facing (such as west or southeast) is at the bottom, right-side up. The curved edge is the horizon, and the stars above it on the map now match the stars in front of you in the sky. The map’s center is the zenith, the point overhead. Example: Rotate the map so that “Facing East” is at the bottom. Nearly halfway from there to the map’s center is bright, yelloworange Arcturus. Go out, face east, and look halfway up the sky. There’s Arcturus! Note: The map is plotted for 40° north latitude (for example, Denver, New York, Madrid). If you’re far south of there, stars in the southern part of the sky will be higher and stars in the north lower. Far north of 40° the reverse is true. The planets are positioned for mid-April.

L

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Facing West

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Two challenging Messier objects lie in the same binocular field as 2.3-magnitude Merak (β Ursae Majoris), the more southerly of the Dipper’s two pointer stars. Here you’ll find M97, the Owl Nebula, and neighboring oddball galaxy M108. Both objects are situated near a hockeystick-shaped asterism southeast of Merak. But despite their apparent proximity, the only thing these two objects have in common is that they’re tough binocular finds. The Owl, named for its owlish appearance in large telescopes, is one of only four planetary nebulae in the entire Messier catalog. Searching the field with my 15×45 imagestabilized binoculars, I spotted M97 near the hockey stick’s blade. The nebula appears as a small, perfectly round haze that needs averted vision (looking slightly away) to be seen with confidence. This isn’t surprising considering that it’s variously listed as glowing from magnitude 9.9 to 12.0. However, the view in my binos suggests that the Owl is closer to the bright end of that range. Once spotted in the 15×45s, I was able to claim it with my mounted 10×50s too. If you can see M97, try for neighboring M108. This galaxy is a slightly tougher find even though it’s similarly bright (visual magnitude 10.2). In my 15×45s M108 is an elongated smudge midway down the shaft of the hockey stick. I never did see it for certain with 10×50s, though I expect it’s possible to do so under skies darker than those in my semi-rural backyard. If you manage to find both objects, you can experience an astonishing sense of distance. Consider that M97 is in our cosmic backyard, only about 2,600 light-years away. M108, on the other hand, hangs in the background perhaps as distant as 45 million light-years. Talk about depth of field! ✦ — Gary Seronik

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Galaxy

B Hockey Stick

Double star

M97

Variable star

iew

n

M108

Open cluster Diffuse nebula Globular cluster Planetary nebula

rv

ci Fa

You can make a sky chart customized for your location at any time at SkyandTelescope.com/ skychart.

URSA MAJOR

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SW

IS N OR J A

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Sk yandTelescope.com April 2010 45

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Planetary Almanac

Sun and Planets, April 2010

Mercury

April

11

Apr 1

21

Sun

30

Right Ascension

Declination

Elongation

Magnitude

Diameter

Illumination

Distance

h

m

+4° 22′

––

–26.8

32′ 01″

––

0.999

h

m

+14° 38′

––

–26.8

31′ 46″

––

1.007

1

h

1 39.6

m

+11° 51′

16° Ev

–0.9

6.2″

70%

1.085

11

2h 25.7m

+17° 29′

19° Ev

+0.3

8.1″

33%

0.828

21

2h 35.3m

1

0 40.5

30

Venus Mercury

1

30

16

2 28.1

+17° 58′

12° Ev

+3.1

10.6″

7%

0.633

h

m

+14° 31′

2° Mo

––

11.9″

0%

0.563

1

h

1 53.1

m

+11° 03′

19° Ev

–3.9

10.5″

95%

1.587

11

2h 40.3m

+15° 30′

22° Ev

–3.9

10.8″

93%

1.550

21

3h 29.1m

30

Mars Venus

1

16

30

Jupiter

2 18.9

+19° 18′

24° Ev

–3.9

11.1″

91%

1.509

h

m

+22° 00′

26° Ev

–3.9

11.4″

89%

1.467

1

h

8 22.6

m

+22° 23′

112° Ev

+0.2

9.2″

92%

1.015

16

8h 39.5m

+20° 56′

101° Ev

+0.5

8.1″

90%

1.150

30

9h 00.1m

30 Mars

Jupiter

16

Saturn

Saturn Uranus

4 14.5

+19° 13′

93° Ev

+0.7

7.3″

90%

1.277

h

m

–5° 59′

24° Mo

–2.0

33.5″

100%

5.881

30

h

23 37.5

m

–3° 34′

46° Mo

–2.1

35.0″

99%

5.625

1

12h 05.4m

+2° 13′

169° Ev

+0.6

19.5″

100%

8.519

30

11h 58.4m

1

23 14.1

16

+2° 56′

139° Ev

+0.8

19.0″

100%

8.728

h

m

–1° 26′

28° Mo

+5.9

3.4″

100%

20.978

h

m

23 54.1

Neptune

16

22 01.3

–12° 35′

58° Mo

+7.9

2.2″

100%

30.545

Pluto

16

18h 22.0m

–18° 12′ 110° Mo

+14.0

0.1″

100%

31.454

16 The table above gives each object’s right ascension and declination (equinox 2000.0) at 0h Universal Time on selected dates, and its elongation from the Sun in the morning (Mo) or evening (Ev) sky. Next are the visual magnitude and equatorial diameter. (Saturn’s ring extent is 2.27 times its equatorial diameter.) Last are the percentage of a planet’s disk illuminated by the Sun and the distance from Earth in astronomical units. (Based on the mean Earth–Sun distance, 1 a.u. is 149,597,871 kilometers, or 92,955,807 international miles.) For other dates, see SkyandTelescope.com/almanac.

Uranus Neptune 10"

22h

0h

+40°

20 h

A QU AR IU S

C A P RI C ORNUS –30° –40°

VIRGO

Fomalhaut

10 am

8 am

6 SAGITTARIUS 6 am

CANCER Regulus

Saturn

EC

LIBRA

Pluto

Neptune

–20°

4h AURIGA

8h 6h RIGHT ASCENSION

Mars

LEO

AQU ILA

9

CETUS

10 h

Castor Pollux

T LIP

23 IC

Pleiades

CORVUS

21

ORION Betelgeuse

+20°

Venus TA U R U S

Procyon

0°

E Q U AT O R Rigel

Sirius

ER I D AN US

H Y D R A

CANIS MAJOR

3 SCORPIUS 2 am 4 am

+30°

Mercury

Spica

April 27–28

2h ARIES

18

GEMINI

OPHIUCHUS

Uranus Jupiter

12h

Arcturus

HERCULES

PISCES

14 h BOÖTES

CYGNUS PEGASUS

+20°

–10°

16 h

18h Vega

+30°

0°

Planet disks at left have south up, to match the view in many telescopes. Blue ticks show the pole tilted toward Earth.

LOCAL TIME OF TRANSIT Midnight 8 pm 10 pm

6 pm

4 pm

2 pm

DECLINATION

Pluto

–10° –20° –30° –40°

The Sun and planets are positioned for mid-April; the colored arrows show the motion of each during the month. The Moon is plotted for evening dates (in April) in the Americas when the Moon is waxing (right side illuminated) or full, and for morning dates when it’s waning (left side). “Local time of transit” tells when (in Local Mean Time) objects cross the meridian — that is, when they appear due south and at their highest — at mid-month. Transits occur an hour later on the 1st, and an hour earlier at month’s end.

46 April 2010 sky & telescope worldmags

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Saturn’s Moons Apr 16 0h UT

Apr 1 2

EAST

WEST

3 4

Rhea

5 6 7

Tethys

8 9 10 11 12 13 14 15 16 17

Titan

18 19

Enceladus

20 21 22 23 24 25 26 27 28

Dione

29 30 May 1 The wavy lines represent five Saturnian satellites; the central vertical bands are Saturn and its rings. Each gray or black horizontal band is one day, from 0 h (upper edge of band) to 24h UT (GMT). The ellipses at top show the actual apparent orbits; the satellites are usually a little north or south of the ring extensions.

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Fred Schaaf Sun, Moon, and Planets

A Procession of Planets Each of the bright planets makes an appearance over the course of an April night. Mercury is

unusually high at dusk in the first half of April, floating lower right of brilliant Venus. Fading Mars hangs very high in the south at nightfall all month. Saturn is highest later in the evening, and Jupiter doesn’t appear until dawn.

DUSK Mercury puts on its best evening display of 2010 (for mid-northern latitudes) in the first half of April. From April 1st to 15th the flighty planet is at least 10° above the westnorthwest horizon for observers looking a half-hour after sunset. Note, however, that it fades eight-fold in those two weeks, from magnitude –0.9 to +1.4, so it will be difficult to spot without binoculars by mid-April. Mercury shines at magnitude +0.1

Dusk, April 15 –17 1 hour after sunset

Moon April 17

on April 8th, the day it reaches greatest elongation from the Sun. Telescopes then show its tiny disk 40% lit and less than 8″ wide. The planet sets more than 1½ hours after the Sun during the first half of April, lingering above the horizon just after the end of astronomical twilight (at 40° north latitude) for the only time this year. Venus is the planet you’ll see low in the west well before Mercury. It flames at magnitude –3.9, providing a handy guide for locating Mercury to its lower right. The minimum separation between Venus and Mercury occurs on April 4th, when the two are 3° apart. This is what Belgian calculator Jean Meeus has dubbed a “quasi-conjunction”: when two bodies come within 5° of each other without ever sharing the same right ascension or ecliptic longitude. It’s the first quasi-conjunction between bright planets since 2006. By April 15th, when the lunar crescent hangs just above greatly dimmed Mercury, the separation between Venus and Mer-

To see what the sky looks like at any given place, date, and time, go to SkyandTelescope.com/skychart.

cury has grown to 7°. On April 24th and 25th, wait at least an hour after sunset to see the Pleiades poised beautifully about 3½° right or upper right of Venus (binoculars help). Aldebaran and the Hyades are somewhat farther to the upper left or left of Venus on those nights. Venus remains small and roundish in telescopes this month. But from early April until early September, Venus will be at least 10° above the horizon 45 minutes after sunset (though never very high), and during that period we will see its disk grow and enter its crescent phase.

EVENING AND NIGHT Mars, in Cancer, is highest in the south during evening twilight and remains

10°

April 20 –22

Aldebaran

Shortly after dark Pleiades

Hyades Moon April 16

Sickle of LEO Regulus Castor Mars

Venus

Moon April 15 Mercury

Looking West-Northwest

48 April 2010 sky & telescope worldmags

Moon April 22

Beehive Cluster Moon April 21

Looking High in the Southwest

Pollux Moon April 20

These scenes are drawn for near the middle of North America (latitude 40° north, longitude 90° west); European observers should move each Moon symbol a quarter of the way toward the one for the previous date. In the Far East, move the Moon halfway. For clarity, the Moon is shown three times its actual apparent size. The visibility of objects in bright twilight is exaggerated. The 10° scale is about the width of your fist at arm’s length.

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December solstice

Venus

Mars Mercury

March equinox

Sept. equinox

Sun

Earth June solstice

high enough for good telescopic viewing all evening. On the other hand, Mars continues to fade and shrink as it falls far behind speedier Earth in its orbit. Another month, another halving in brilliance: in April it falls from magnitude +0.2 to +0.7. The Martian globe shrinks from 9″ to 7″, too small to show surface features in most telescopes. But the eastward motion of Mars carries it just 1° north of the center of Messier 44, the Beehive Star Cluster, from April 16th through 18th, providing pretty sights for telescopes, binoculars, and unaided eyes. Saturn was at opposition on the night of March 21–22, so it’s visible just about all night in April. It’s not very high in the east-southeast at dusk, so wait until later in the evening to study its 19″-wide globe and very thin rings. Late last month, when Saturn was closest to Earth and the rings were tilted more than 3° from edgewise, Saturn shone at magnitude +0.5. Saturn fades slightly in April as it moves farther

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FPO Saturn

Neptune Pluto

ORBIT S OF THE PL ANE T S

from Earth and the rings tilt narrower (toward their minimum of 1.7° from edgewise in late May). But the planet still outshines both Regulus and Spica, the bright stars that bracket the large swath of the zodiac that Saturn has passed through for the last two years. Saturn now floats just above the celestial equator and the ecliptic, in the head of Virgo, not far from the richest region of the Virgo Galaxy Cluster.

Dawn, April 2–5 1 hour before sunrise Moon April 5

Moon April 4

Moon April 3

Moon April 2 Antares

SCORPIUS S A G I T TA R I U S

Uranus Jupiter

Cat’s Eyes

Looking South

The curved arrows show each planet’s movement during April. The outer planets don’t change position enough in a month to notice at this scale.

DAWN Neptune and Pluto are high enough to observe as morning twilight starts but will be better positioned for viewing this summer. Jupiter shines at magnitude –2 but is quite low in the east at dawn. It comes up about an hour before the Sun at the start of April, about 2 hours by month’s end. Uranus was at conjunction with the Sun on March 17th, so it’s hard to observe in the dawn glow even by the end of April.

MOON ENCOUNTERS The Moon is gibbous at dawn on April 3rd, when it’s only about 1° from Antares for North America. At dusk on April 15th, a sliver of lunar crescent floats about 1° above or right of Mercury — though both will be difficult to see without binoculars. On the 16th the Moon is well above Venus but just below the Pleiades (use binoculars). And on April 17th, it’s well to the upper right of Aldebaran. ✦ Sk yandTelescope.com April 2010 49

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Charles A. Wood Exploring the Moon

Lessons in Basinology The youngest lunar impact basin can teach us much about older impacts. Most observers interested in the Moon have seen the amazing spacecraft images of Mare Orientale on the western limb. Dating back 3.8 billion years, it is thought to be the last large basin to form. Only a small amount of mare lava fills Orientale’s interior, making it a good model for how other, more heavily modified basins may have appeared originally.

Montes C ord il

ler a

Outer R oo k Ro

M ou

ok

M

s ain nt

Inner

n ou NASA / USGS

s tain

50 April 2010 sky & telescope worldmags

Orientale is a multi-ring basin with three well-defined rings, creating an obvious bull’s-eye pattern. With a diameter of about 920 kilometers (570 miles), Montes Cordillera (Cordillera Mountains) defines the basin’s outer rim. These ridges have a scarp facing the center of the basin and gently declining elevations on the opposite side. Two rings of different character lie inward from the Cordillera. Montes Rook consists of two separate mountain ranges not recognized as such until the era of lunar exploration. The 620-km-diameter outer Rook Mountains look something like Montes Cordillera, with a scarp on the inward side and a gently sloped outer side. The inner Rook Mountains are made of more-isolated mountains — called massifs — in a ring 480 km in diameter. Inside the inner Rooks, an ill-defined 320-km-diameter ring forms Mare Orientale’s edge. We can apply our view of a little-modified basin interior to understand older lunar basins, but there are uncertainties simply because older basins have been altered by later impacts and lava flooding that hide original features. Consider Mare Crisium. Many observers see the wide expanse of Crisium lavas but don’t recognize the underlying impact-basin structure. The boundary of Crisium’s mare lavas is pronounced, being defi ned by rather abrupt massifs that oddly have never received a formal name. Because lunar mountain ranges are named for terrestrial chains, I informally call them the Wasatch Mountains, named after a range in Utah. Inside that well-defined 570-km-diameter ring is a less-obvious ring only seen a few days after new and full Moon. At these times the Wasatch reveals itself as a circular pattern of low ridges roughly 375 km across. Two more rings exist around Crisium but require additional detective work and a wider field to see. The easiest ring is noticeable fi rst as a difference in the texture of the lunar surface. North of Crisium near the crater Geminus is a curved boundary that has smooth plains inside it, and a more typical hilly and cratered highlands surface beyond. A low scarp is visible toward Mare Orientale is barely visible from Earth due to its location on the Moon’s western limb. It’s perhaps the Moon’s youngest large impact basin, and the only one not completely filled by mare lavas.

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The Moon • April 2010 Geminus

Cleomedes

Highlighted feature

Size

Description of Feature

A Montes Cordillera

930 miles

Outer ring of the Orientale Basin

B Mare Crisium

350 miles

Mare-filled impact basin

C Geminus

52 miles

Terraced crater with central peak

D Firmicus

34 miles

Mare-filled crater 26

Phases

Macrobius

27

Last quarter

April 6, 9:37 UT

New Moon

April 14, 12:29 UT

First quarter

April 21, 18:20 UT

Full Moon

April 28, 12:18 UT

C B

Ridge ring

D

Distances April 9, 3h UT diam. 29′ 25″

Perigee 228,130 miles

April 24, 21h UT diam. 32′ 56

A

Librations Wasatch Mountains

Bailly (crater)

April 11

Shi Shen (crater)

April 26

S&T: SEAN WALKER

Belkovich (Walled Plain) April 27

April 11 For key dates, yellow dots on the map indicate what part of the Moon’s limb is tipped the most toward Earth by libration under favorable illumination.

Firmicus

Mare Crisium on the eastern side of the Moon displays many of the same structures visible in the Orientale Basin, though it takes a keen eye to pick them all out.

the limb from Geminus, revealing that the plains’ material is lower than the highlands beyond. The final ring is harder to see but is also recognizable by a difference in surface materials. Between Macrobius and Cleomedes, and continuing on toward the limb, there is a less-regular boundary with dark mare lava near the Wasatch Mountains. This “Cleomedes ring” has a diameter of about 635 km, and the Geminus ring is 1,075 km. For reasons poorly understood, these two rings are not well expressed on the south side of Crisium, but the area where they should be is low and filled with Mare Undarum and lava-filled craters such as Firmicus. How do these rings compare with Orientale’s? Let’s start with the outer ring and move inward. Both Montes Cordillera and the Cleomedes ring are scarps with lower, smooth material inward and rougher terrain beyond; both are probably faults. The Cleomedes ring at Crisium is in nearly the same position as the outer Rooks at Orientale, but the latter is well-developed, whereas the Cleomedes ring is weak. Scientists interpret the outer Rooks as the

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actual rim of the Orientale impact, the edge of the excavated hole. The better-developed Wasatch Mountains may be Crisium’s excavation rim. Finally, the Crisium wrinkle ridge may be what Orientale’s inner ring would look like if that basin’s entire floor were covered by lava. Identifying these old rings is fun detective work, but there’s more significance than just mapping rings. Scientists want to know what the lunar mantle is made of, and huge basins are the only features big enough to have penetrated the lunar crust that deep. If the Cordillera ring of Orientale is the original rim of the crater, than the impact would have excavated into the lunar mantle. Unfortunately, geologic evidence suggests that Orientale’s real diameter is probably the outer Rook Mountains, too small to have reached the mantle. These large-scale structural features are the framework for understanding why the Moon looks as it does. Have fun discovering them! ✦ To get a daily lunar fix, visit contributing editor Charles Wood’s website: lpod.wikispaces.com. Sk yandTelescope.com April 2010 51

S&T: DENNIS DI CICCO

Apogee 251,656 miles

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DECEMBER 13 – 23, 2010

w w w. I n S i g h t C r u i s e s. c o m / S k y CURIOUS ABOUT THE BEAUTY OF THE NIGHT SKY AT SEA? Game to explore facets of the moon, then take in a total lunar eclipse in the company of kindred spirits? Gather astronomy knowledge on a new wavelength aboard Cosmic Trails, December 13–23, 2010, on Holland America Line’s m.s. Zuiderdam. Journey with Sky & Telescope into the Panama Canal, whose engineering is the product of an historic struggle against Nature and skepticism. You’ll get a behind-the-scenes look at the Apollo program; explore the road less traveled in the winter sky; see beyond the obvious, into the mysteries of the Moon; bring home an insider’s techniques, tips, and tricks for getting the most out of lunar observation; and learn astrophotography details from basic to cutting edge. While you’re in balmy tropical climes, kayak with your companion through crystal blue Aruban waters and venture into Costa Rica’s rainforests, surrounded by the sounds of birds and the colors of flora and fauna. Indulge your thirst for knowledge. Sail with Sky & Telescope and indulge your thirst for knowledge. Relax with a friend; enjoy fun and camaraderie with fellow astronomers; rekindle a longdormant fascination with the cosmos. Visit www.InSightCruises.com or call Neil or Theresa at 650-787-5665 to get all the details, and then enrich your astronomy routine with an intellectual adventure with the Sky & Telescope community. As we sail away from Fort Lauderdale, Florida, we’ll kick off Cosmic Trails with observation of the GEMINIDS METEOR SHOWER.

© Wally Pacholka / AstroPics.com

Listed is a sampling of the 19 sessions you can participate in while we’re at sea. For a full listing visit

www.InSightCruises.com/Sky-talks

During Our Trip: TOTAL LUNAR ECLIPSE Tuesday, December 21, 2010

Capturing the Light: The Night Sky — In this session we’ll cover all the basic techniques in capturing the night sky: cameras, lenses, exposure times, and camera setting as well as Landscape Astrophotography equipment that is good, better, and best for the budget imager or cutting-edge imager. By then end of this talk you’ll understand the difference between what the eye sees and what the camera sees — and how to use this knowledge to make great photos. Speaker: Walter Pacholka

Viewing and Understanding the Moon — When is the best time to view the Moon? What kinds of features can I see? Where is the best place to look? These are just some of the questions answered in this talk. But perhaps most rewarding is developing an understanding of what it is you’re seeing in your telescope. How did this crater Origin of the Moon — Although there are many form? Why does it look this way? Why are some parts of ideas for how our Moon came to exist, only one makes the Moon bright, and others dull? Why are some smooth, sense chemically and physically: The Moon came from a while other regions a jumble of craters? Equipped with a Big Splash, the molten and vaporized rock that is ejected telescope and armed with the information presented in during a giant impact on Earth by a body about the size this talk, you can explore the Moon like a lunar geologist. of Mars. I will describe how this not only explains the Speaker: Gary Seronik Moon but also sets the stage for all of subsequent Earth evolution. Speaker: David Stevenson, Ph.D. Telescopes for Stargazing — A backyard telescope is a wonderful thing. But with the bewildering variety of Naked-Eye Astronomy — Contrary to popular equipment available today, it’s difficult for the budding opinion, you can enjoy a lifetime of astronomy with little astronomer to know what best suits his or her needs. A or no equipment other than your unaided eye. Learn to lot can be done at modest expense, while some fairly explore the constellations and see colors in the stars. Find expensive telescopes can be quite frustrating. Learn out how to spot the International Space Station passing about the different types of telescopes, and what they are across your sky or watch the brilliant flash of an Iridium best suited for. Find out what accessories are essential, satellite. Know when to look for gatherings of the Moon and which can wait. Discover how you can test drive and planets. Look for Sun dogs, Sun pillars, and radiant telescopes and some of the equipment that goes along crepuscular rays. These and many more celestial wonders with them, as well as how to look for help when you need can be viewed by those who know where and when to it. Speaker: Sue French look. Speaker: Sue French Winter-Sky Wonders — For many of us, this is the Exploring the Night Sky with Binoculars — Just coldest time of the year — but it also harbors the most about every one associates stargazing with telescopes brilliant stars and some of the most spectacular wonders — but even the most experienced backyard astronomer of the deep-sky. They include nebulae, clouds of gas and owns binoculars. But not all binoculars are created dust either glowing by their own light or reflecting the equal. In this talk Gary will tell you how to choose and light of nearby stars; clusters of stars, both old and young; use binoculars specifically for viewing the night sky. He galaxies far beyond our own; multiple stars; and variable also describes tips and tricks to help you get the most stars. And if that’s not enough, we also have intricate out of your viewing experiences. Finally, Gary lists the Jupiter in our evening sky and awe-inspiring Saturn in the Top 10 binocular sights you can view while on our cruise. morning! Speaker: Sue French Speaker: Gary Seronik Apollo Astronaut Experience — Only 24 men have America the Beautiful at Night — It’s truly amazing been to the moon. While researching his landmark book, results one can achieve with Landscape Astrophotography A Man on the Moon, Andrew Chaikin spent more than 150 using just a tripod and 35mm camera with a standard hours interviewing 23 of the 24 Apollo lunar astronauts lens. Whether you are a novice astrophotographer or an about every aspect of their incredible journeys. Chaikin advanced imager, you will be amazed at the simplicity will share anecdotes and insights from this extraordinary and beauty that you can obtain using basic equipment handful of men, the only humans to visit another world. and a little know how. Speaker: Walter Pacholka Speaker: Andrew Chaikin

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Alan MacRobert Celestial Calendar

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Mercury Takes the Spotlight The innermost planet has its best apparition of the year — close to Venus! Did Copernicus really lament on his deathbed that he’d never seen Mercury, as the story goes? It might seem plausible. Sun-hugging Mercury is the most elusive of the five classical planets. To puzzle out their Sun-centered orbits, Copernicus worked mostly from others’ measurements of their positions; he made few observations himself. He lived at north latitude 54°, where Mercury appears especially low during its poorer apparitions. And he often complained about the local mists and fogs that obscured his views. But this age-old legend comes from an old misreading. Copernicus did complain in his great book, De revolutionibus orbium coelestium, that he was unable to observe Mercury during its poor apparitions. These happen only in late summer and early fall at dusk, and only in late winter and early spring at dawn, when a Northern Hemisphere observer sees the ecliptic lying at its lowest angle to the horizon. Copernicus’s complaint was misstated by Alex-

ander von Humboldt in his book Kosmos, hugely popular in the mid-19th century, and the legend has been unkillable ever since, despite repeated debunkings.

Best apparition This month most S&T readers can spot Mercury plain as day. In late March and early April the little planet will be as obvious as it ever becomes for mid-northern observers. And Venus will be a bright marker pointing the way. The two planets remain less than 5° apart from March 28th to April 12th, though Mercury fades during this time from magnitude –1.1 to +0.7, a loss of four-fifths of its light. They appear closest, 3.0° apart, on the evenings of April 3rd and 4th for North America. The diagram below shows the scene. Venus and Mercury are plotted in bright twilight for viewers near latitude 40° north. For your date, draw a pencil line between the two planets’ curves to set the scene.

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On the diagram, the planets are shown with their correct shapes and relative sizes as seen in a telescope at medium-high power. Venus is an almost full disk 10″ or 11″ wide. Mercury is smaller and dimmer but more interesting. It wanes rapidly from gibbous to crescent, while enlarging from 5″ to 10″ across, from March 22nd to April 16th. The best time to examine these planets telescopically is in the afternoon while they’re still high in a clear blue sky. To

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The positions, phases, and relative sizes of Mercury and Venus are shown every five days (evening dates for North America). Their altitudes (scale at right) are for a half hour after sunset if you live at latitude 40° north (for example, Denver, New York, Madrid). If you live much farther south, the line from Venus to Mercury on any given day will point lower than it does when you draw the line here. If you live far north of 40°, the line from Venus to Mercury will be oriented higher than it is here. Your latitude difference from 40° tells by how much.

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Celestial Calendar

Oct. 2

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Messenger Sept. 29

Contrast enhanced...

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Boudreau Oct. 2

...then blurred

avoid the risk that you’ll accidently sweep up the Sun and burn your eye, set up your telescope in the shadow of a building where the sinking Sun will stay behind the building and not surprise you. Look for Venus as a tiny white dot in your finderscope about 20° above the Sun and somewhat to the left. Once you’ve got Venus, use the diagram on the previous page to judge Mer-

Lyrid Meteors The Lyrid meteor shower should be active in the early morning hours of April 22nd and 23rd. The shower is normally weak, but surprises can occur. The waxing gibbous Moon sets about 2 and 1½ hours, respectively, before dawn’s first light on those mornings.

Mercury imager John Boudreau captured Mercury last October as it waxed in phase and shrank from 7.8″ to 6.0″ wide. He took these images well after sunrise, using an 11-inch Schmidt-Cassegrain scope at f/18 to f/22 with a DMK21AF04.AS video camera and a red or near-infrared filter. South is up. Boudreau compares his October 2nd image of Mercury to a view from nearly the same angle taken by NASA’s Messenger spacecraft. For a good comparison, Boudreau boosted the contrast of the Messenger image and then blurred it to approximate the blurring of his backyard image. Clearly, the main features he recorded are real.

cury’s distance and direction from it. A degree scale is on the right edge. You may have to switch to your main telescope (at lowest power) to sweep up dim Mercury. Venus in daylight looks like brightly polished silver compared to Mercury’s dull lead. Most telescope users will be doing well just to get a good look at Mercury’s phase. But switch to high power, and keep watching. Can you make out any hint of surface markings? Are you sure? Before the space age, visual observations of Mercury’s markings were so vague and unreliable that astronomers failed to determine Mercury’s correct rotation period. But now that we have closeups of its gray lava plains and bright ray craters, a few of the old visual features seem to have been real. In particular, observers sometimes report that near Mercury’s dichotomy (halfMoon phase), its southern cusp appears

Bright Asteroid Occultation! The bright star Zeta Ophiuchi, magnitude 2.5, should be occulted early on the morning of April 6th by the small, invisibly faint asteroid 824 Anastasia along a narrow track from southern California through Idaho. The asteroid will be moving slowly, so the occultation should last for up to 9 seconds. See maps and details at www.asteroidoccultation.com/ 2010_04/0406_824_20757.htm. For timing methods, see iota.jhuapl.edu/timng920.htm.

54 April 2010 sky & telescope worldmags

FILTE R S IN DAY LI GHT For observing planets in the daytime, an orange or red filter dims the sky’s blue light while dimming the planet a bit less, improving contrast a trace. Test this out on the daytime Moon.

slightly blunter than the northern one. Spacecraft imagery shows that Mercury’s north polar area is indeed slightly brighter (and thus more distinct through a daytime sky) due to a large, relatively young impact crater and its rays. The comparative blunting of the southern cusp is often cited as Mercury’s most detectable visual feature (S&T: October 2009, page 72). Nowadays, stacked-video imaging rules ground-based planetary astronomy. This technique shows features on planets much more clearly than the eye sees through the same telescope. Add a red or infrared fi lter to penetrate the daytime sky, and amateurs have been achieving almost unbelievable results, as shown at left. Comparisons with views from the Mariner 10 and Messenger spacecraft show that many of the amateur-imaged features on Mercury are real, not artifacts from overprocessing as some skeptics have suggested. John Boudreau describes his methods and results with Mercury in last October’s issue, page 70. But even if you’re just watching by eye for a trace of something to sketch, don’t let this opportunity slip by. ✦

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Space Art Today

56 April 2010 sky & telescope worldmags

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Imagining Other Worlds

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michael carroll

Space artists help us visualize planets and moons that humans have only glimpsed. A GUST OF WIND scatters grit across the rim of an ancient crater. In the distance, a dust devil reaches into a pink sky. The robotic rovers on Mars aren’t there to witness the event, because the Red Planet is a hundred million kilometers away. This scene instead unfolds in Death Valley, California, before the eyes of a group of space artists. In our modern age of robotic probes and orbiting observatories, we’re constantly bombarded by fabulous images of alien worlds in our own solar system. In the midst of these electronic vistas, is there still room for space art? The answer is yes. Space artists can take us to vistas unseen by spacecraft or telescope, and can show us — on a human scale — what is only glimpsed by these spacecraft at ranges of hundreds or thousands of miles. In addition, artists translate non-visual science (radar imagery, magnetosphere measurements, and gravity fields) into a popular form that viewers can understand.

Observation Informs Imagination Space art has its roots in early painting movements such as the Hudson River School, where artists rendered fairly accurate images of natural landscapes. Painters Albert Bierstadt, Thomas Moran, and others traveled with surveying expeditions into the vast “unexplored” western regions of North America during the mid-19th century. Paintings by these artists helped convince Congress to establish the first national parks at Yellowstone and Yosemite. Bierstadt’s and Moran’s paintings of the new Walter Myers envisions a variety of exotic flora and fauna dominating the landscape of a hypothetical life-bearing planet. He drew inspiration from Earth’s crinoids (sea animals that resemble plants) and armored dinosaurs.

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Space Art Today

frontier have a direct parallel to the work of modern-day astronomical artists. While these past artists traveled with pack mule and Conestoga wagon, today’s explorers are outfitted with circuit boards and solar panels. Robotic probes continue to return travelers’ tales to a waiting world from a far more distant frontier. Perhaps humans will again do the same, as they did in the glory days of the Apollo lunar landings. While the first space art can be found in ancient petroglyphs from the Americas to Australia, it wasn’t until Galileo drew the Moon’s surprisingly rugged surface that the seeds of modern space art were first planted. Before he trained his telescope heavenward, the lunar surface was thought to be a pristine sphere, reflecting the structure of the universe in harmony. Galileo’s magnified views of the Moon we were the earliest examples of space art that th was informed and inspired by telescopic observations. The cratered tele wasteland Galileo depicted across wa PHOTO OF DAVID A. HARDY BY FRANK HETTICK

58 April 2010 sky & telescope worldmags

Above: This original sketch by David A. Hardy shows a rift valley (graben) in Iceland where the Eurasian and North American tectonic plates are gradually pulling apart. Below: Similar graben are found on Mars, so Hardy later developed the Iceland sketch into this painting of a Martian scene, complete with a robotic exploration rover and looming dust storm.

his pages sent ripples through religious and scientific circles, forever changing our perception of the universe. In the early 20th century, the French astronomer Lucien Rudaux foreshadowed the era of modern space art. Rudaux, an accomplished oil painter, attempted some of the first landscapes of other worlds. As the director of the Meudon Observatory outside of Paris, he had access to some of the best celestial views of the time. In the early 1900s, Rudaux painted remarkably realistic scenes of the Moon, Mars, and other planets, based on his observations at the eyepiece. They were among the first paintings to depict what it might be like to see these alien landscapes from their surfaces, putting the viewer directly on these strange worlds. They hold up well, even today. The true father of modern space art, Chesley Bonestell, worked with rocket scientist Wernher von Braun to paint realistic scenes of people on other planets. His work for the book The Exploration of Mars (1956) depicted blue-skied Martian landscapes looking very much like the desert Southwest of the U.S., and eerily similar to the first images returned from NASA’s Viking landers 20 years later. Bonestell’s meticulous attention to detail and pursuit of realism in his art inspired the generation of scientists and engineers who made space exploration happen. Like Galileo’s early Moon drawings, space art today actively challenges scientific paradigms while also reflecting today’s scientific thinking.

GAVIN MUNDY

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Above: This location in Death Valley, California, was dubbed Mars Hill by members of the International Association of Astronomical Artists due to its resemblance to the Viking 1 landing site.

One powerful tool available to astronomical artists is the study of planetary analogs. Like Bierstadt and Moran, today’s space artists travel to remote sites across the globe — from Iceland to Death Valley — to study terrestrial landscapes that are geologically similar to those of other planets and moons. These travels not only inspire wellinformed and convincing art, but also high adventures. “Since we can’t visit the places we paint,” says British artist David Hardy, “this is the next best thing.” Some of the best planetary analogs stretch across Earth’s deserts and arctic regions. NASA’s Phoenix Mars mission recently returned images of polygonal ground patterns at its landing site in the northern arctic plains. This alien vista bears a striking resemblance to areas in Alaska and Siberia, where subsurface ice takes a geologic toll on tundra landscapes. Other places on the Red Planet, recently imaged by NASA’s Mars Reconnaissance Orbiter, appear to contain rock glaciers similar to those found in the San Juan Mountains of Colorado. Images of shifting sand dunes returned from Mars resemble the landscapes of the Sahara Desert in Northern Africa. Terrestrial volcanic landscapes find their brethren on Venus, Mars, and even Jupiter’s erupting moon Io. As we venture farther into the outer solar system, ices become the dominant material, making ice analogs on

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BOTTOM: MICHAEL CARROLL; TOP: NASA / JPL / CALTECH

Space on Earth

Top: The Mars rover Opportunity captured this grayscale image of hematite globules called “blueberries” embedded in martian rock. Above: Similar water-related processes on Earth formed these hematite spheres in Utah, known as Moqui Marbles.

Sk yandTelescope.com April 2010 59

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Space Art Today

60 April 2010 sky & telescope worldmags

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Earth more important. Glacial flows, sea ice, and icerelated geology all inform the space artist in renderings of distant moons and the frozen denizens of the Kuiper Belt. Some of the finest Mars analogs are found in Iceland — the land of fire and ice. This island nation’s unique geology is born of interactions between volcanism and glaciers. Some researchers propose that Martian volcanoes once erupted under thick ice sheets, giving rise to structures similar to the table mountains of Iceland. Iceland has much more to offer the space artist. Its fresh volcanic structures find cousins on other terrestrial worlds. In addition to Mars’s towering volcanoes, fully 90% of the surface features on Venus are volcanically related. NASA’s Messenger spacecraft continues to return fresh data from Mercury, where lava flows appear to lap against some crater walls, and where potential volcanic vents have been recently identified. Earth’s own Moon endured a volcanic era early in its evolution, blanketing vast regions under magma seas. Iceland’s cinder cones

Pixel Painting The digital realm has enhanced astronomical art in many ways. Much of the data from spacecraft is non-visual, but can be translated into visual scenes by the use of software. An example is NASA’s Cassini mission, which is currently revealing the surface of Saturn’s moon Titan with the use of infrared and radar systems. Artists interpret radar images, consulting with scientists, and transform Cassini data into a bit map. This artistically enhanced radar data can be fed directly into software programs such as Terragen (www.planetside.co.uk), a fractal landscape program. Armed with this data, Terragen can generate accurate shorelines or mountain ranges. It is then up to the artist to create an accurate, convincing environment, complete with methane rains and liquid ethane ponds. Illustration by Steven Hobbs.

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Texas artist Pat Rawlings envisions a martian landscape reminiscent of the desert buttes in the American Southwest. A massive dust storm and towering dust devils greet this fictional visitor from Earth. To see more inspiring imagery from these and other space artists, visit the International Association of sp Astronomical Artists website at http://iaaa.org. As

and lava fields played host to Apollo astronauts who trained there in preparation for the first Moon landings. Geysers in Iceland and Yellowstone Park also have counterparts in the outer solar system. Though the mechanisms for these formations are different, their appearance may be quite similar on human scales. If humans can somehow survive Jupiter’s radiation belts, travelers to Io will undoubtedly find familiar landscapes. On location, space artists use a variety of reference materials. Cameras are a must, but sketching in nature provides many insights that photography cannot. The subtle play of light, the shifting of texture, and the visual impact of an environment can often be captured by the human eye more fully than by photographic means. These observations are put down in sketches and notes that will later inform the final artwork. Astronomer/ artist William K. Hartmann paints his sketches in acrylics, while Hardy and Pamela Lee use pastels. Artists Joel Hagen and Marilynn Flynn often render information in colored pencil. Anil Rao and Paul Hoff man have embraced the age of digital technology and take laptop computers into the field, sketching in pixels. Some environments provide quite specific lessons for the observer. A band of space artists recently journeyed to Utah’s Escalante region in search of what the local population calls “Moqui Marbles,” or Shaman Stones. These concretions are made of hematite, an iron-rich mineral usually formed in water. NASA sent the Mars Exploration Rover Opportunity to the Meridiani Plains to search for Sk yandTelescope.com April 2010 61

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MICHAEL CARROLL

Space Art Today

The volcanic region of Mývatn in Iceland served as the model for this view of Jupiter seen from it’s geologically active moon Io. From the moon’s surface, Jupiter would appear as large as 39 Moons in Earth’s sky.

water’s telltale signs, precisely because orbiters had detected hematite there. Sure enough, Opportunity found what mission planners have dubbed “blueberries,” spheres of hematite eroding out of the rocks. Many geologists think that Escalante’s Moqui Marbles represent a terrestrial parallel.

Painting in the field gives the space artist tools with which to render convincing — and accurate — landscapes of other worlds. Planetary orbiters and landers are designed to record scientific data to help us understand these enigmatic locales. Space artists put the viewer on the surfaces of distant worlds only hinted at

in mountains of data. The imagery they produce can inspire the next great push for human space exploration. ✦ Science journalist, book author, and space artist Michael Carroll has a painting on the surface of Mars — in digital form — aboard the Phoenix Mars spacecraft.

Art at the Telescope The Moon is a fine subject for the fledgling space artist. At full phase, gray maria yield subtle tans and blues to the careful observer. As the Moon moves through its phases, the terminator provides the artist with a rich canvas of textures. Drawing the Moon through a small telescope or even good binoculars will teach you to see small-scale details often overlooked in a casual glance, and it will help inform your imagination. 62 April 2010 sky & telescope worldmags

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Sue French Deep-Sky Wonders

Between the Bears The area north of the Great Bear is worthy of study but often neglected. Here the huge Snake in many a volume glides, Winds like a stream, and either Bear divides. — Virgil, Georgics, Book I

Parting the constellations

BRIAN LULA

of Ursa Major and Ursa Minor is the tail of Draco, the serpentine Dragon of the sky. The region between the Bears owns no particularly bright stars, but it does possess a memorable assortment of deep-sky wonders. Let’s begin our journey at 4th-magnitude Kappa (κ) Draconis. As plotted on the all-sky chart at the center of

this magazine, it’s the second star from the tip of Draco’s tail and makes a readily recognizable triangle with Megrez (δ) and Dubhe (α) in the Big Dipper. Kappa is unevenly bracketed by a pair of 5th-magnitude attendants that share a low-power telescopic field of view. They make a colorful stellar trio shining orange, blue-white, and gold, from south to north. The barred spiral galaxy NGC 4236 lies 1.5° west and a bit south of Kappa. With a total integrated magnitude of 9.6, this is the brightest galaxy in the area. In other words, NGC 4236 would shine as brightly as a 9.6-magnitude star if all its light were gathered into a single point. However,

NGC 4236 is a barred spiral galaxy with unusually prominent star-forming regions. The brightest of these is designated VII Zw 446.

Sk yandTelescope.com April 2010 65

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Deep-Sky Wonders

this light is actually smeared over an oval roughly 22′ minutes long and 7′ wide, so it’s highly attenuated. The galaxy’s average magnitude per square arcminute, known as surface brightness, is only 15.0. Seeing a tiny galaxy with such a low surface brightness would be a hopeless task with a small telescope, but our eyes are better at detecting dim objects when they’re large. Another factor in our favor is that the light of NGC 4236 isn’t evenly spread. The galaxy is brighter than average, and therefore easier to see, across a large portion of its interior. In my semirural skies, I notice NGC 4236 easily through my 105-mm refractor at 47×. Its oval form leans north-northwest and is sheltered by a distinctive pattern of stars that helps pinpoint its exact position. The galaxy 14h

13h

12h

11h

10h

32 IC 3568

CAMELOPARDALIS

+80°

HD 106112 Group

Star magnitudes

+75°

3 4 5 6 7 8

DRACO

4589

4750

+70° 6

h

g

4236 4

9

7 3

RY 8

4125 4121

66 April 2010 sky & telescope worldmags

2

+65°

is lovely at 87× and shows a fair amount of detail. NGC 4236 appears large in our sky because it’s relatively nearby — only 14 million light-years away. Its proximity allows observers with large telescopes to glimpse the star-forming regions that spangle its disk. A bright but tiny spot 4.5′ south-southeast of the galaxy’s center bears the designation VII Zw 446, signifying its place in a catalog of compact galaxies by Fritz and Margrit Zwicky. But in deep, color images of NGC 4236, this spot appears to be a region of ionized hydrogen, and it stands out better when using a narrowband nebula filter with my 14.5-inch scope at 100×. Nebula fi lters may also tease out other H II regions within the galaxy. Let’s compare NGC 4236 with the elliptical galaxy NGC 4125, located 4.4° south-southwest, where it sits sentinel at the border of Ursa Major. At magnitude 9.7, NGC 4125 has nearly the same total brightness as NGC 4236, but its light is concentrated into a much smaller area. Its 6′ × 3′ oval averages magnitude 12.9 per square arcminute, a much higher surface brightness than its large neighbor has. As a result, NGC 4125 is significantly easier to spot. Through my 105mm refractor at 47×, NGC 4125 is a moderately bright oval tipped a bit north of east. It grows considerably brighter toward the center, and a 10th-magnitude star embosses its eastern edge. The tiny companion galaxy NGC 4121 rests 3.8′ south-southwest and is visible most of the time with averted vision. I can hold NGC 4121 steadily in view at 87×. The galaxy marks the southern corner of a right triangle that it makes with the star and the center of NGC 4125. At this magnification, I estimate NGC 4125’s visible size as 3¼′ × 1½′. NGC 4125 is about 75 million light-years away. If placed at the same distance as NGC 4236, it would appear one-third again as large as NGC 4236 and shine at 6th magnitude. Sweeping 5° eastward we find the carbon star RY Draconis along the eastern side of an isosceles triangle made by the 5th-magnitude stars 7, 8, and 9 Draconis. RY is a semiregular variable with poorly known periodicity. It appears to have long, superimposed cycles that undergo slow changes. The star is generally found between magnitude 6 and 8 and is an impressively deep reddish orange when seen through my 130-mm refractor. It nicely contrasts with the triangle stars, of which the northern two glow yellow-orange and the southern one white. Draco isn’t the only constellation between the Bears. The head of Camelopardalis, the Giraffe, also divides them. With unaided eyes, I see a little fuzzy patch in Camelopardalis that lies about one-third of the way from Kappa Draconis to Polaris. The two stars at the end of the Little Dipper’s bowl roughly point toward it. Aiming my 130-mm scope toward this smudge at low power, I discovered an eye-catching little asterism. Two slightly

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12h 40m

12h 20m

12h 00m

6

g 4

Star magnitudes

(S&T: April 1991, page 380). For example, the three stars in the triangle bearing RY Draconis have Flamsteed numbers. But if you look at a star chart that labels numbered stars, you’ll find that 32 Cam is completely out of order in the eastward progression of Flamsteed numbers across the constellation. That’s because the number did not come from Flamsteed’s catalog, but rather from Prodromus Astronomiae, the 1690 catalog of Johannes Hevelius. Most Hevelius numbers have fallen by the wayside, but 32 Cam lingers on many star charts, to the recurrent puzzlement of stargazers. Telescopically, 32 Cam is a nearly matched pair of white suns with the companion star northwest of its primary. With a generous separation of 21″, the stars are easily split at low power. The planetary nebula IC 3568 sits 1° south-southwest of 32 Camelopardalis. It has been called the Lemon Slice because of the radial structure and yellow color displayed in its 1997 Hubble Space Telescope image. Amateur astronomer Jay McNeil nicknamed it the Baby Eskimo for its resemblance to the Eskimo Nebula (NGC 2392). IC 3568 is fairly bright through my 130-mm refractor at 63×. It could be mistaken for a star at first glance, but it doesn’t look as sharp as a star and shows a decidedly non-stellar, bluish gray hue. I see a very bright center surrounded by a faint, bluish fringe at 102×, while at 164× the fringe loses its color but the core becomes slightly uneven in brightness. With my 10-inch scope at high power, I see a 13th-magnitude star nuzzling the planetary’s western edge. My 15-inch reflector helps bring out details in the brilliant core and the elusive star cloaked in its bright center. With its patterned core and fainter fringe, IC 3568 truly does look like a miniature of the Eskimo Nebula. ✦

+70°

4236

+68°

4 5 6 7 8 9 10

DRACO

+66°

4125 4121

diverging arcs of three stars each are nested one beside the other and topped by a 5th-magnitude star. The arc stars are magnitude 6.8 to 9.7, and the southernmost star in the western arc gleams yellow. Sure that others must have noticed this asterism, I looked it up in the Deep Sky Hunters (a Yahoo group) database, where the asterism is listed as the HD 106112 Group. The designation stands for the brightest star’s Henry Draper Catalogue number. The 5th-magnitude star 32 Camelopardalis dwells 6° north of HD 106112. Similar designations for most of the bright northern stars represent their number in the 1721, unauthorized version of John Flamsteed’s star catalogue

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Sue French welcomes your comments at scfrench@nycap.

Deep-Sky Treats in Draco and Camelopardalis Object

Type

Magnitude

Size/Sep.

RA

Dec.

NGC 4236

Galaxy

9.6

21.9′ × 7.2′

12h 16.7m

+69° 28′

NGC 4125

Galaxy

9.7

5.8′ × 3.2′

12h 08.1m

+65° 10′

NGC 4121

Galaxy

13.5

0.6′ × 0.6′

12h 07.9m

+65° 07′

RY Draconis

Carbon star

6–8

—

12h 56.4m

+66° 00′

HD 106112 Group

Asterism

4.7

17′

12h 11.3m

+77° 29′

32 Camelopardalis

Double star

5.3, 5.7

21″″

12h 49.2m

+83° 25′

IC 3568

Planetary nebula

10.6

18″″

12h 33.1m

+82° 34′

This 1997 Hubble photo gave the planetary nebula IC 3568 its nickname the Lemon Slice.

Angular sizes and separations are from recent catalogs. Visually, an object’s size is often smaller than the cataloged value and varies according to the aperture and magnification of the viewing instrument. Right ascension and declination are for equinox 2000.0.

Sk yandTelescope.com April 2010 67

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Gary Seronik Telescope Workshop

Apartment ATMing Telescope making doesn’t require a fully equipped home workshop. I have a confession — I was a closet mirror

JASON ABBOTT

maker. Literally. When I lived in Vancouver years ago, my apartment had a walk-in closet where I set up my mirrorgrinding operation. And to paraphrase the song, if I can make it there, I can make it anywhere. But pushing glass is one thing, what about actually making an entire Dobsonian telescope in an apartment? Easily do-able if you know a few tricks and have access to some basic tools. Obviously, tackling a telescope project without a dedicated workshop requires some adjustments. The dust, noise, and smells that go along with telescope making don’t lend themselves to apartment living. And it’s likely you’ll have to work with a limited selection of tools. But none of these problems is insurmountable. Cutting the main plywood parts for a Dobsonian is surprisingly easy. Get someone else to do it. Who? The store that sold you the wood. Home-improvement stores such as Home Depot will do it. Usually you get several cuts for free, and additional ones for a minimal charge. The key to using this strategy successfully is to know exactly what you want ahead of time. Have your cut list ready and, if possible, a layout diagram showing the placement of each part on a plywood sheet. It also helps if you show up when the store isn’t too busy. There is a catch, however. Stores will only make straight cuts. When it comes to cutting curves, you’re on your own. If there’s one piece of gear that every apartment-based telescope maker should own, it’s a jigsaw. This handy tool will cut virtually any shape and even do long, straight rips. You can buy a perfectly serviceable jigsaw for about $50. Many include a circle-cutting attachment, but you may be surprised at how accurately you can cut circles freehand. For long, straight cuts, tack a ruler to 68 April 2010 sky & telescope worldmags

the work piece as a guide for the edge of the jigsaw. These saws aren’t terribly noisy, so your neighbors won’t complain unless inspiration strikes in the wee hours of the morning! An equally important tool for telescope making is an electric drill. You can usually buy one along with a decent set of drill bits for less than $50. For those times when you wish you had a drill press, you can purchase a tabletop device that essentially turns your hand drill into one. Another useful product for drilling accurate holes is a drill-guide attachment. It will set you back only $30 or so, so it’s money well spent. Few hardware stores seem to stock them, but they’re readily available from online sources. When it comes to painting your scope, avoiding paint fumes is the name of the game. Luckily, there are many odor-free options for apartment dwellers. Indoor/outdoor latex paints are a good choice, but if you prefer to retain the wood’s natural looks, consider Minwax paste finishing wax or similar products. Your local paint supply store will probably have lots of good suggestions. For protecting cardboard tubing, I like to use MonoKote, which you can buy at any hobby store that specializes in model airplanes. MonoKote works like shrink-wrap and the finish is beautiful — much better than anything I can get with a paint brush. And it’s completely odorless. Although you do have to take a little care to avoid making a serious mess, and likely sacrifice a good deal of convenience, there’s no reason you can’t make just as good a telescope in your apartment as you can in a well-equipped workshop. Just be sure you have some drop cloths and a good vacuum cleaner handy. ✦ Contributing editor Gary Seronik builds scopes and observes at his home in Victoria, British Columbia, Canada. He can be contacted through his website, www.garyseronik.com.

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FOCUS ON

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Observing Variable Galaxies

116h Mrk 501

+40°

144h

BÖÖTES

CANES VENATICI

12h Mrk 421

URSA MAJOR

HER

W Comae +20° Arcturus

LEO Denebola

0°

VIRGO

OPH LIBRA

–20° AP Librae Antares

Star magnitudes 1 2 3 4 5

70 April 2010 sky & telescope worldmags

Th exotic galaxies are some of These the th most distant objects visible through backyard telescopes. ba

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STEVE GOTTLIEB Galaxies all shine with a constant luminosity, right? That assumption was shown to be false in 1965 when California Institute of Technology astronomer Fritz Zwicky discovered an unusual, variable object on plates from Palomar Mountain’s 48-inch Schmidt telescope. On dozens of plates taken over a 30-year period, this slightly fuzzy “star” varied from magnitude 16 to 18. At first, astronomers thought it might be a variable star superimposed on a distant galaxy. But a spectrum revealed that Zwicky had stumbled on a Seyfert galaxy more than 1 billion light-years distant with the first known variable nucleus. By 1971 astronomers were scrutinizing the General Catalogue of Variable Stars in search of additional variable galaxies, and several entries were found to coincide with extragalactic radio sources — including BW Tauri (3C 120), BL Lacertae (VRO 42.22.01), AP Librae (PKS 1514-24), and W Comae (ON 231). Astronomers now classify these objects as blazars, a term coined in 1978 by Columbia University astronomer Edward Spiegel to encompass two classes of objects: Optically Violently Variable quasars and BL Lacertae objects. Blazars are members of a larger group, galaxies with active galactic nuclei (AGNs) powered by actively feeding black holes. As heated material spirals down the accretion disk surrounding an AGN, an intense magnetic field helps produce high-energy, relativistic plasma jets (see page 20). What makes a blazar special is that one of its beams happens to point directly toward us. From our head-on perspective looking down the throat of its jet, a blazar appears much brighter than it normally would. Changes in the jet result in variability in radio, infrared, optical, X-ray, and gamma–ray wavelengths. In some cases, short-term outbursts of several magnitudes have been recorded over just a few days. I have observed a number of blazars through my 18-inch Dobsonian telescope at dark sites in northern California. I will describe here four that are visible in the Northern Hemisphere’s spring sky, and four more for the rest of the year.

Markarian 421

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Star magnitudes 5 6 7 8 9 10

Vmag 12.0–14.4, Size 0.8′ × 0.6′ 11h 10m

11h 05m

11h 00m

10h 55m

47 +40°

URSA MAJOR 49 +39°

51 +38°

Mrk 421

Markarian 421 is a relatively nearby BL Lacertae object (400 million light-years) and is one of the brightest gamma-ray sources in the sky. It has displayed rapid, violent variations over a period of hours to days along with longer periodic fluctuations of roughly 23 years. Using 220× in my 18-inch scope, Markarian 421 appeared similar to a 12.7-magnitude star, though I glimpsed a small, fuzzy halo at 300×. This blazar is very easy to locate just 2′ south-southwest of 6.0-magnitude 51 Ursa Majoris. Use high power, and keep the bright star off the edge of the field so its glare doesn’t overpower the faint blazar.

Steve Gottlieb has observed almost all of the NGC and much of the IC through his Dobsonian telescopes. All the photos in this article are from POSS-II red plates in the Digitized Sky Survey (stdatu.stsci.edu/cgi-bin/dss_form), courtesy Caltech and Palomar Observatory. The first four objects have charts deep enough to show at least one star in the corresponding photo. You may need a detailed star atlas or a computerized planetarium program to locate the last four objects.

Spring

RA 11h 04.46m, Dec. +38° 12.5′

Mrk 421

′

field 10 wide

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Observing Variable Galaxies

W Comae Berenices

Spring

Star magnitudes

RA 12h 21.53m, Dec. +28° 14.0′ Bmag 13–17.5

5 6 7 8 9 10

4245

4274

COMA BERENICES 4495

4310

4286

15h 20m

G

10

W Comae 4408 4393

4475

Star magnitudes

15h 15m

5 6 7 8 9 10

15h 10m

5903 5898

–24°

4185

AP Librae

4196 IC 777 4211

4295 9

4251

LIBRA +28°

–25°

S

23

4275

14

IC 3376 12h 30m

–26°

+27° 16 12h 25m

12h 20m

12h 15m

German astronomer Max Wolf discovered variable star W Comae Berenices based on observations at HeidelbergKönigstuhl State Observatory from 1892 to 1916. In 1971 the radio source ON+231 was found to coincide with W Com. This distant blazar (1.3 billion light-years) has varied by 4 magnitudes over the past century. In June of 2009, I saw W Com as a 14.7-magnitude stellar object at 325×. To find it, locate the 14thmagnitude galaxy NGC 4295 on the northwest side of the Coma Berenices Star Cluster. Shift your position 6′ northeast to a 12th-magnitude star and look for the blazar 1′ north-northwest of that.

In 1942 Harvard College Observatory astronomer Martha Ashbrook listed AP Librae as one of 74 new variable stars she found on plates taken since 1935. Nearly 30 years later, Howard Bond noticed its equivalence with the extragalactic radio source PKS 1514–24. AP Librae displays a nearly three-magnitude optical variation with occasional shortterm oscillations of over ½ magnitude in just 5 hours. I picked up this compact galaxy in my 18-inch at 225×, though the view improved after upping the magnification to 375×. At this power it appeared as an extremely faint patch just 6″ across punctuated by a dim stellar nucleus. AP Lib resides just north of a neat semicircular asterism.

W Comae

AP Librae 4295

′

field 15 wide

72 April 2010 sky & telescope worldmags

15h 05m

+29°

4338 4375

Spring

4283 4278

4448

AP Librae

RA 15h 17.70m, Dec. –24° 22.3′ Bmag 14 –16.7, Size 0.5′ × 0.4′

′

field 10 wide

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Markarian 501

Spring

Star magnitudes

RA 16h 53.87m, Dec. +39° 45.6′ Vmag 13.5–14.0, Size 1.1′ × 0.9′ 16h 55m

16h 50m

5 6 7 8 9 10

16h 45m

16h 40m

+40°

Mrk 501

6212

HERCULES

6257

+39°

H

+38°

Markarian 501 is one of the brightest and closest blazars in the sky, at a distance of 460 million light-years. The NASA-IPAC Extragalactic Database lists 689 references to this object in journal articles and 63 aliases based on its inclusion in numerous radio, X-ray, ultraviolet, infrared, and quasar catalogs. Viewing Markarian 501 through my 18-inch telescope at 283×, the galaxy appeared as a 14th-magnitude knot just 10″ in diameter, though with averted vision the halo doubled in size. With direct vision a sharp, stellar nucleus appeared and the halo nearly disappeared. See if you can detect this blinking effect.

Research Opportunities Visual observers can follow blazar fluctuations through the eyepieces of their telescopes. And amateurs with even modest CCD setups have participated in cutting-edge astronomical research involving blazars and other objects with active galactic nuclei. In 2003 the American Association of Variable Star Observers (AAVSO) partnered with the Global Telescope Network to help establish baseline activity of several blazars prior to the 2008 launch of NASA’s Fermi Gamma-ray Space Telescope. Currently the AAVSO has a program to follow the visual behavior of several blazars that are being monitored at higher energies by VERITAS (Very Energetic Radiation Imaging Telescope Array System), a ground-based gamma-ray observatory in Arizona that works in conjunction with ESA’s XMM-Newton X-ray satellite.

STEVE CRISWELL / VERITAS

Mrk 501

′

field 20 wide

VERITAS is an array of four optical telescopes with segmented 12meter mirrors. They look for Cherenkov radiation from the showers of charged particles produced when highly energetic gamma rays strike Earth’s upper atmosphere. The stereoscopic view from multiple scopes helps pinpoint the gamma rays’ trajectories.

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Observing Variable Galaxies

3C 371 h

m

RA 18 06.84 , Dec +69° 49.5′

Late Spring to Early Autumn Vmag 13.5–15.0, Size 0.15′

BL Lacertae RA 22h 02.72m, Dec. +42° 16.7′

Late Summer / Autumn Vmag 12.7–16.0

3c 371 BL Lac

′

′

field 10 wide

The radio source 3C 371 was first identified as a galaxy in 1966. A year later Allan Sandage measured a redshift of z = 0.05, corresponding to a distance of nearly 700 million light-years. Various studies have revealed long-term optical variations of 1.5 magnitudes along with spikes of 0.1 or 0.2 magnitude over several hours. The Hubble Space Telescope revealed an optical jet in 1999. I picked up 3C 371 easily at 175× as a faint, quasi-stellar object that appeared softer than similar field stars. Upping the magnification to 300×, I resolved a compact 10″ knot containing a 15th-magnitude stellar nucleus.

3C 66A RA 2h 22.66m, Dec. +43° 02.1′

field 20 wide

German astronomer Cuno Hoffmeister discovered BL Lacertae in 1929 on photographic plates. In 1968 John Schmitt of David Dunlap Observatory noted its equivalence with the radio source VRO 42.22.01. BL Lac is the prototype of a class of AGNs with a nearly featureless spectrum displaying very weak absorption and emission lines. It exhibits a slow, irregular variation from magnitude 12.7 to 16.0 with brief onemagnitude flares. It is 900 million light-years away. At 280× I was able to identify a 15.5-magnitude stellar object just 25″ west of a 13th-magnitude star. At moments BL Lac seemed slightly fuzzy, with a tiny 2″ or 3″ envelope.

BW Tauri

Autumn / Early Winter Vmag 13.5–15.6

RA 4h 33.19m, Dec. +5° 21.3′

Late Autumn / Winter Vmag 13.5–15.5, Size 0.8′×0.6′

UGC 1832

3C 66A BW Tauri UGC 1841

UGC 1841

′

field 15 wide

In 1974 Texas astronomers Beverley and Derek Wills identified the radio source 3C 66A as a high-redshift quasar (z = 0.44, distance 4.6 billion light-years). This blazar shows rapid fluctuations as well as long-term changes from magnitude 13.5 to 15.6. 3C 66A appeared as a 14th-magnitude star when I observed it in July 2007, so it was probably near its maximum brightness. Coincidentally, 3C 66A lies behind the rich galaxy cluster AGC 347 in Andromeda and shares a field with three foreground cluster galaxies (circled above). 74 April 2010 sky & telescope worldmags

′

field 20 wide

Harvard astronomers Harlow Shapley and Catherine Hanley discovered BW Tauri in 1940 during a photographic search for new Cepheid variable stars. In 1968 Michael Penston (Royal Greenwich Observatory) discovered that BW Tauri is a compact galaxy coinciding with the variable radio source 3C 120. This blazar varies from magnitude 13.5 to 15.5 and lies at a distance of 450 million light-years. Through my 18-inch scope, BW Tauri appears as a fuzzy 14th-magnitude star (the nucleus of the galaxy) encased in a low-surface-brightness halo about 20″ across. ✦

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Astronomy Workshop on Astronomical Research Techniques in the Introductory Laboratory PROJECT CLEA (Contemporary Laboratory Experiences in Astronomy) announces a summer 2010 workshop on Astronomical Research Techniques in the Introductory Laboratory. Targeted primarily at faculty who teach undergraduate college courses and who do not themselves have graduate specialization in astronomy or astrophysics. The workshop will introduce modern techniques of observation and data analysis with an emphasis on the introductory laboratory. Hands-on observing with CCD’s, as well as an intensive introduction to the CLEA simulations and other computer resources will be featured. Centered at the beautiful Gettysburg Campus, the week will include workshops on observing techniques, hands-on experience with all CLEA exercises, evening observing sessions at the Gettysburg College Observatory, and an observing trip to the National Radio Astronomy Observatory in Green Bank, WV. Dates for the workshop are June 17 - June 26, 2010. Room and board will be provided to the applicants selected. Registration deadline is April 3, 2010. For information and registration write: PROJECT CLEA Physics Department, Box 405 Gettysburg College Gettysburg, PA 17325

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April 2010

75

Sean Walker Gallery

76 April 2010 sky & telescope worldmags

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EARTHSHINE AT DAWN Miguel Claro An old crescent Moon greeted Portuguese amateur Miguel Claro after a long night of watching the Geminid meteor shower last December. Details: Canon 400D DSLR camera with a 20-mm lens at f/5.6, 2½ -second exposure.

◀ NEBULAE IN THE UNICORN Pan Weike This wide-field image of northern Monoceros includes the Cone Nebula, Hubble’s Variable Nebula, and the open cluster Trumpler 5 at right. Details: Takahashi FSQ-106ED refractor with an SBIG STL-11000M CCD camera. Total exposure was 4⅔ hours. ▶ SPIRAL NEIGHBOR David Plesko and Warren A. Keller Camelopardalis contains many interesting galaxies, including the beautiful face-on spiral NGC 2403. Details: 14½-inch RCOS Ritchey-Chrétien telescope with an SBIG STL-11000M CCD camera. Multiple exposures totaling 35 hours through Astrodon color filters.

Sk yandTelescope.com April 2010 77

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Gallery

▴ STINGERS AND PAWS Jérôme Astreoud The Stinger stars in the tail of Scorpius (bottom center) lead observers to a cascade of Milky Way objects. The open cluster M6 is at the top, followed by the reddish-emission nebulae NGC 6357 (middle right) and NGC 6334, the Cat’s Paw Nebula. Details: Modified Canon EOS 5D DSLR camera with a 200-mm lens. Total exposure was 30 minutes. ▶ FERTILE GROUND Jim Janusz The gaseous cloud IC 410 is being slowly evaporated from within by the open star cluster NGC 1893. Details: Astro-Physics 180EDT refractor with an Apogee U16M CCD camera. Total exposure was 14 hours through Astrodon color filters. ✦

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Meade (Pages 7, 17) Meade.com 800-919-4047 | 949-451-1450 Orion (Page 9) OrionTelescopes.com 800-447-1001 | 831-763-7000 Sky-Watcher USA (Page 5) SkyWatcherUSA.com 888-880-0485 Tele Vue (Page 2) TeleVue.com 845-469-4551 TMB Optical (Pages 10, 63) Astronomics.com 800-422-7876 | 405-364-0858 VERNONScope (Page 80) VernonScope.com 607-659-7000

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Index to Advertisers Adirondack Astronomy . . . . . . . . . . . . . . . . . 81

Northeast Astronomy Forum . . . . . . . . . . . . 83

ADM Accessories . . . . . . . . . . . . . . . . . . . . . 79

Oberwerk Corp. . . . . . . . . . . . . . . . . . . . . . . . 80

Adorama . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Observa-Dome Laboratories . . . . . . . . . . . . 75

Apogee Instruments . . . . . . . . . . . . . . . . . . . . 3

Obsession Telescopes . . . . . . . . . . . . . . . . . 62

Ash Manufacturing Co., Inc. . . . . . . . . . . . . 69

Oceanside Photo & Telescope . . . . . . . . . . . 75

Astro-Physics, Inc.. . . . . . . . . . . . . . . . . . . . . 83

Officina Stellare s.r.l. . . . . . . . . . . . . . . . . . . . 33

Astrobooks. . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Orion Telescopes & Binoculars . . . . . . . . . . . 9

Astrodon . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

Peterson Engineering Corp. . . . . . . . . . . . . . 80

Astronomical Tours. . . . . . . . . . . . . . . . . . . . 42 Astronomics . . . . . . . . . . . . . . . . . . . . . . . . . 63 Astronomy Technologies . . . . . . . . . . . . . . . 10 Atik Cameras . . . . . . . . . . . . . . . . . . . . . . . . . 13 Beta Electronics, Inc. . . . . . . . . . . . . . . . . . . 79 Bob’s Knobs . . . . . . . . . . . . . . . . . . . . . . . . . 80 Celestron . . . . . . . . . . . . . . . . . . . . . .19, 64, 88

IN THE NEXT ISSUE

Pier-Tech . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 PlaneWave Instruments . . . . . . . . . . . . . . . . 82 PreciseParts . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Project CLEA . . . . . . . . . . . . . . . . . . . . . . . . . 75 ProtoStar . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Take Back the Night!

Quantum Scientific Imaging, Inc. . . . . . . . . 81

The fight against light pollution is now in high gear.

Rainbow Optics. . . . . . . . . . . . . . . . . . . . . . . 79

One Eye Versus Two

CNC Parts Supply, Inc. . . . . . . . . . . . . . . . . . 79 Riverside Telescope Makers Conference . . .75

How do 70-mm binoculars stack up against telescopes with similar apertures?

Dream Cellular, LLC . . . . . . . . . . . . . . . . . . . 81 ScopeStuff . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Explore Scientific LLC . . . . . . . . . . . . . . . . . . 11 SCS Astro. . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Fishcamp Engineering . . . . . . . . . . . . . . . . . 81

The Biggest, Baddest Stars

Sky-Watcher USA. . . . . . . . . . . . . . . . . . . . . . . 5 Foster Systems, LLC . . . . . . . . . . . . . . . . . . . 79

Hands On Optics . . . . . . . . . . . . . . . . . .69, 82 High Point Scientific . . . . . . . . . . . . . . . . . . . 33 Hotech Corp. . . . . . . . . . . . . . . . . . . . . . . . . . 80 Hubble Optics Sales . . . . . . . . . . . . . . . . . . . 79 In Sight Cruises . . . . . . . . . . . . . . . . . . . . . . . 52 Into the Wind . . . . . . . . . . . . . . . . . . . . . . . . 81

Skyhound . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Society for Astronomical Sciences. . . . . . . . 64 Software Bisque. . . . . . . . . . . . . . . . . . . . . . . 87 Stellarvue . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Technical Innovations . . . . . . . . . . . . . . . . . . 64 Tele Vue Optics, Inc. . . . . . . . . . . . . . . . . . . . . 2 Texas Nautical Repair . . . . . . . . . . . . . . . . . . 82

iOptron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

The Observatory, Inc. . . . . . . . . . . . . . . . . . . 82

JMI Telescopes . . . . . . . . . . . . . . . . . . . . . . . 47

The Teaching Company . . . . . . . . . . . . . . . . 41

Khan Scope Centre . . . . . . . . . . . . . . . . . . . . 82

TravelQuest International . . . . . . . . . . . . . . . 83

Knightware. . . . . . . . . . . . . . . . . . . . . . . . . . . 81

University Optics, Inc. . . . . . . . . . . . . . . . . . 79

Lumicon International . . . . . . . . . . . . . . . . . 79

VERNONscope . . . . . . . . . . . . . . . . . . . . . . . 80

Meade Instruments Corp. . . . . . . . . . . . .7, 17

William Optics Co., Ltd. . . . . . . . . . . . . . . . . 82

Metamorphosis Jewelry Design . . . . . . . . . . 81

Willmann-Bell, Inc. . . . . . . . . . . . . . . . . . . . . 81

North Star Systems. . . . . . . . . . . . . . . . . . . . 81

Woodland Hills Telescopes . . . . . . . . . . . . . 69

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BOTTOM: JON MORSE / NASA; TOP: C. MAYHEW / R. SIMMON (NASA/GSFC) / NOAA / NGDC / DMSP DIGITAL ARCHIVE

Glatter Instruments . . . . . . . . . . . . . . . . . . . 80

Researchers are trying to identify the most massive star in our galaxy.

Digging Out the Details A novel deconvolution technique helps you sharpen your astrophotos without adding noise

SkyandTelescope.com 800-253-0245

On newsstands March 30th! Sk yandTelescope.com April 2010 85

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Focal Point

Mark Stephenson

Reasons for Not Choosing Astronomy A whimsical look at why amateur astronomy might not be good for your health.

I’m sure most S&T readers, like me, love amateur astronomy and enjoy sharing their enthusiasm with others. In our zeal to proselytize, we may fail to tell people the pitfalls of our hobby. Specifically, we owe it to potential newbies to warn them they run the risk of becoming an astrogeek. Here’s my Top 10 list of ways to tell if you’re an astro-geek: 10. You not only know what a Schiefspiegler is, but how to spell it. 9. The main criterion for purchasing a car is whether your telescope will fit inside. 8. You own more than one telescope. 7. Your idea of a great holiday present is a Barlowed laser collimator. 6. Your telescope is worth more than your car. 5. You feel passionately about whether Pluto is a planet or a dwarf planet. 4. Your wristwatch is set to Universal Time. 3. You’ve replaced the interior lights in your car with red light bulbs. 2. Your pets are named after lunar craters. 1. You’ve asked a date if she (or he) wanted to go for a drive in the country

to look at the stars… and you actually looked at the stars. We should tell the potential newbie about the health risks of our hobby, and I’m not talking about aperture fever. It almost goes without saying that most astro-geeks are sleep deprived. That pasty complexion may be symptomatic of a far more serious problem: anemia. On those warm summer nights, while engrossed at the eyepiece, mosquitoes may be sucking out one’s lifeblood. Observers in Minnesota must be particularly alert to this threat. Speaking of Minnesota, hypothermia can be a real problem for those who observe during winter. If you don’t care what you look like, it’s possible to dress in enough layers to maintain your core body temperature. This won’t be a problem for you, but it can be a real issue for the newbie. Then there are the risks of broken bones from falling off a ladder or tripping over a tripod, as well as the risk of back injury from lifting heavy equipment. Let’s face it; if we had strength, coordination, and balance, we’d be out playing sports. Many of us have developed “telescope envy.” Sure, for some, a telescope is just

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as darker and darker skies to get his or her “kicks.” The astroholic becomes increasingly irritable and depressed when bad weather keeps him or her away from the eyepiece. But even the average astro-geek runs the risk of depression. Those who have experienced clouds the night of the great Leonid meteor storm, or just before totality, know what I mean. If, after cautioning the newbie about the pitfalls of amateur astronomy, our advice falls upon deaf ears, we can console our new comrade with one undeniable truth: astro-geeks make great friends! ✦ Despite the pitfalls described in this article, Mark Stephenson has been an avid amateur astronomer for 50 years, and remains active despite being legally blind for the past decade. He can still observe because of reasonably normal peripheral vision.

ELWOOD SMITH (3)

86 April 2010 sky & telescope

a telescope, but others secretly long for a bigger instrument. Unfortunately, as the size of the telescope goes up, cost goes up, well, astronomically. Left untreated, the astro-geek with telescope envy may become an astroholic. The astroholic needs bigger and bigger telescopes, as well

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worldmags

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