Sky & Telescope March 2010

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OBSERVING the Heavens with ONLINE TELESCOPES p. 36

THE ESSENTIAL MAGAZINE OF ASTRONOMY

Did Dark Matter Power Early Superstars? p. 26 Deep-Sky Wonders in the Lair of the Lynx

FarOut

Planets? Large objects may be lurking unseen in distant regions of the solar system. p. 20

The Lion’s Feast of Double Stars p. 73 Amateurs Digitize a Century of Astro History

p. 30

Visit SkyandTelescope.com

p. 61

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March 2010 VOL. 119, NO. 3

On the cover: S&T illustrator Casey Reed depicts a planetsize body lurking within the frigid depths of the far outer solar system.

THI S M O N TH ’ S S K Y

42

Northern Hemisphere’s Sky

AL S O IN THI S I S S U E

6

By Fred Schaaf

43 45

By Robert Naeye

March’s Sky at a Glance

8

Binocular Highlight

8

By Gary Seronik

46

Spectrum Letters 50 & 25 Years Ago By Leif J. Robinson

Planetary Almanac

12

News Notes

Sun, Moon, and Planets

18

Cosmic Relief

FE ATURE S

48 20 What Else Is Out There? COVER STORY

Pla Planets and other large objects could be lurking far beyond cou Neptune, but they’ll be very Nep difficult to find. By David Jewitt

By Fred Schaaf

51

Exploring the Moon

By David Grinspoon

58

New Product Showcase

68

Telescope Workshop

By Charles A. Wood

55

Celestial Calendar

By Gary Seronik

By Alan MacRobert

26 Shedding Light

on Dark Stars Bizarre stars powered by dark matter may have been the first to form after the Big Bang. By Ker Than

61 66

70

Astro Q&A

By Sue French

76

Gallery

Going Deep

86

Focal Point

Deep-Sky Wonders

By Ken Hewitt-White

By Jacob Haqq-Misra & Seth D. Baum

30 Digitizing History Amateurs help scan a century of photographic plates. By Stephen Lieber

36 Observatories

on the Web You can rent time to observe from home with top-notch telescopes and CCD cameras around the world. How well does this work? By Andy Macica

and Around Leo The Lion is a treasure house of bright, rewarding visual binaries. By Richard Jaworski

36

LIGHTBUCKETS

73 Double Stars in

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.

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March 2010 sky & telescope

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

The Essential Magazine of Astronomy EDITORIAL

Bringing in More Women

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

In two recent Spectrum columns I tackled the issues of motivating

Editors Emeritus Richard T. Fienberg, Leif J. Robinson

more young people and ethnic minorities to become involved in amateur astronomy. This month I turn my attention to women. As I moved around the country over the years, I have belonged to about a dozen amateur astronomy clubs, all of which have had significant female membership. Women have regularly served as officers, including president. I usually see reasonable numbers of women at star parties and astronomy events. So women are not being excluded from amateur astronomy. Still, they are underrepresented, and our hobby will enjoy a healthier future if more women and girls become active participants. I have spoken to several women amateurs about what the community can do to engage and retain more females. Here are three themes that arose frequently in these discussions (I’m paraphrasing their comments): 1. Most male amateurs are consistently respectful toward women and cause no problems. But on occasion, one or two men at club meetings or star parties engage in boorish or predatory behavior that make women feel extremely uncomfortable or unwelcome, driving them away from the hobby. Astronomy events should not be treated as male social-fraternity outings, and clubs should try to identify problem members and make them aware that their actions are harmful to the organization. 2. Women with children often have difficulty attending club meetings or star parties because it can be a burden to find child care. If clubs provided activities for children, many mothers (and fathers) would find it much easier to attend meetings, and the activities themselves could spark an interest in astronomy for the kids. 3. At the request of Girl Scouts or other groups, women amateurs are sometimes asked to organize star parties or science fairs for girls or women only, not because they harbor prejudices toward males, but to provide a more relaxed environment for females. Men sometimes misinterpret the organizers’ intentions and react with hostility, creating an unpleasant experience that deters women from arranging future events. Female-only astronomy events are good things, and men shouldn’t feel threatened by them. With better and more affordable telescopes, the internet, CCDs, and other modern technologies, amateur astronomy has entered a Golden Age (except for light pollution). But let’s face it: amateur astronomers in many areas are predominantly middleaged and elderly white males (people like me), and many clubs are seeing membership decline. Amateur astronomy remains alive and well, but the future health of our hobby will depend on amateurs empathizing with underrepresented groups and actively reaching out to them. I encourage your comments on how to achieve these vital goals.

Editor in Chief 6 March 2010 sky & telescope worldmags

Senior Contributing Editors J. Kelly Beatty, Roger W. Sinnott Contributing Editors Edwin L. Aguirre, Greg Bryant, Paul Deans, Thomas A. Dobbins, David W. Dunham, Alan Dyer, Sue French, Paul J. Heafner, Ken HewittWhite, 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

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Letters

How To Attract Young Amateurs? In the December issue (“Missing Young Astronomers,” page 8), Robert Naeye writes about the paucity of new young amateurs and the general decline in the number of students entering science in the United States. As a former scientist and a devoted reader of your magazine, I share your concern. Dwindling enrollment in scientific curricula is a problem of national scope and urgency. Although political officials, including President Obama, have expressed concern about it, I see little evidence of effective action. This is lamentable, because steps to address the issue could be undertaken at small cost. For example, many years ago the Bell Telephone Company produced a series of remarkable science films. Aimed at elementary-school children, they were designed not just to inform, but to inspire future scientists. They succeeded admirably in both aims, thanks to impressive cinematic talent and artistry. I particularly remember a 1957 production called “The Strange Case of the Cosmic Rays.” Written and directed by Frank Capra, it portrayed the early history of particle physics, aptly enough, as a mystery. I can still remember the effect it had on my 10-year-old imagination; I decided to become a physicist that very night! Four years later, I was lucky enough

50 & 25 Years Ago

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March 2010 sky & telescope

A. J. Hill, M.D., Ph.D. Nederland, Colorado [email protected] I think we see so few young astronomers because kids get so turned off by science in school. After raising two children to college age, I can offer observations on why. With few exceptions, I’ve found that science is taught abysmally in elementary school. Few of my kids’ teachers were grounded in any aspect of it, and most limited their classes to rote memorization of science facts. So when my kids hit high school, the pace of their science education shifted too quickly into high gear. Their high school teachers, though far more educated and enthusiastic than their elementary school counterparts, too often

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.

introduced college-level materials that failed to bridge the gaps in most of the students’ previous education. By the time they graduated, the message most received was clear: science is hard, confusing, full of difficult tests, and neither fun nor terribly relevant. It’s not hard to see why so few young people show up at our star parties. Kevin Lindsey [email protected] Like a modern-day Paul Revere, Editor in Chief Robert Naeye gallops through the countryside sounding the alarm of the continuing decline of young people interested in astronomy. A lot of us have known this for some time, but like a person suffering from a drug or alcohol problem, denied or minimized it. Judging by my discussions with people from various scientific and educational fields, the main cause of this decline is plain economics. The economic policies of the past 30 years have crippled the middle class to the point where people no longer have the means to engage in anything more than day-to-day living, and this

Leif J. Robinson

March 1960 Oops! “At Sugar Grove, West Virginia, the U. S. Navy is building the world’s largest steerable radio telescope, having a paraboloidal antenna 600 feet in diameter, with a surface area of more than seven acres.” This project was canceled by the Secretary of Defense in 1962, in part due to escalating cost and design problems. Ninety-six million dollars had already been spent.

8

to attend a high school that offered MIT’s advance-placement physics course during its first year of distribution. Its innovative text and coordinated laboratory demonstrations were a radical departure from the standard approach to science instruction and gave students a taste of what modern physics was all about. Do programs like this exist now? If so, they’ve escaped my notice. Considering the resources and technology now available, it’s a shame that people of the caliber of Capra and Disney aren’t being asked to produce them or that schools and major media aren’t being enlisted to distribute them.

March 1985 Back to the Moon “A NASA-sponsored conference, Lunar Bases and Space Activities of the 21st Century [was] held in late October, 1984. . . . “NASA administrator James M. Beggs declared in Kennedyesque tones, ‘I believe it likely that before the first decade of the next century is out, we will, indeed, return to the Moon. . . .’ “NASA’s commitment to an orbiting space station in the 1990’s makes a lunar base seem all but inevitable; Beggs has already offered the

Moon base as a justification for building the space station.” NASA has planned a return to the Moon in a decade, and then it will go on to Mars in two to three decades. But in the wake of a recent report from a committee chaired by Norman Augustine, we would be wise to pay attention to reporter Mark Washburn’s level-headed conclusion on the matter: “Despite the enthusiasm and dedication in evidence at the conference, the road back to the Moon will be long and demanding.”

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Letters reflects in the values and priorities of the youth. It’s not that the youth of today don’t have an interest in astronomy; many do. When people have to work two or three low-wage jobs around the clock just to take care of basic necessities, there isn’t the time, energy, or money to devote to anything more than the basics, and that’s the message youth are growing up with today. Rudy Alfano York Haven, Pennsylvania [email protected] I think our problem is wanting to show off our glitzy new toys at star parties; this destroys the hopes of the kids who’ll never be able to afford them. Maybe we should have some star parties with nothing but equipment under $500 or home built. John Day [email protected] As an amateur active for 45 years, my interests have shifted in many directions over time. From constellations and binoculars as a kid, then a home-built, deep-cooled vacuum camera on a Schmidt with a 1-arcsecond electronic guider in the 1980s followed by thousands of observation hours, my attention has now shifted to things like the online Galaxy Zoo galaxy-classification project and telling others about stars and planets. And I read everything I come across. On really dark nights, I still visually observe. Basically, I do what my tutors and textbooks did for me: show people what we see and where it’s at, tell them what we think it is and why we think so, and encourage them to see and think for themselves. However, the sources of information have dramatically changed. We once relied on copied star-field pictures from the Palomar Sky Survey. We had too-simple star charts and too-opaque things such as Vehrenberg’s Falkauer Atlas. We had to build our own kit and we loved it. Now everybody has access to massive amounts of high-quality data online. Where is the guidance today on how to get knowledge out of information? The problem is lack of organization to find what you need at your own level — to build the overarching logical framework of astronomy, into which you can properly 10 worldmags

March 2010 sky & telescope

put information so it makes sense. In the old days a few standard books were all we had, and their authors knew it, so they did it well. Now kids are online in a vast, random flood. We need to get them connected to the right materials to create that framework, and to mentors in the community. Understandable astronomy brings great revelations, triggers questions, and connects astronomy to kids’ daily lives — rather than overwhelming them with “unformation.” Spike Wadman Waalre, The Netherlands I read your “Missing Young Astronomers: What Can We Do about It?” and had a compelling urge to write in. I am not going to major in astronomy or anything remotely related, but I crave knowledge about space. This brings me to what we can “do to help foster a deeper and sustained interest in astronomy.” For high school students, we could offer observational astronomy as an elective. If students have a chance to view things in space first hand, before they see pictures in a book, they may gain a deeper respect for our universe. If I had access to a good telescope, and someone nearby to explain what I was seeing and to answer my questions, my degree would have been in planetary astronomy or astrobiology. The 15-to-25 age bracket is a lost cause. It is just a matter of offering the right technology and people to as many students as possible. Matthew Hartenstein Brunswick, Georgia [email protected]

For the Record ✹ Due to an editor’s self-described “moment of brain death,” the December 2009 Sun, Moon, and Planets (page 49) said the Sun crosses the celestial equator on the December solstice. In fact, the Sun begins its six-month return northward on that date, after reaching its farthest point south. ✹ The URL published for Alan Dyer’s website in our special publication Beautiful Universe 2010 was incorrect. Dyer’s website is www.backyardastronomy.com.

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News Notes For astronomy news as it breaks, see SkyandTelescope.com/newsblog S ky .

Kepler’s First Exoplanet Haul Kepler 4b

Kepler 5b

Kepler 6b

Kepler 7b

Kepler 8b

–4 0 4 Hours from mid-transit

–4 0 4 Hours from mid-transit

–4 0 4 Hours from mid-transit

–4 0 4 Hours from mid-transit

–4 0 4 Hours from mid-transit

Orbital period

3.2 days

3.5 days

3.2 days

4.9 days

3.5 days

Diameter (Earths)

4.31

18.8

15.0

16.9

18.3

Sun

0.995 0.990

NASA’s Kepler spacecraft has been watching stars for exoplanet transits since last May, and its brightness-measuring instruments are matching or beating expectations. Mission scientists, however, have been holding Kepler’s candidate planet discoveries close to the vest for now so that they can be the ones to confirm them by radial-velocity studies from the ground. At the January American Astronomical Society (AAS) meeting, they announced their first five confirmed planets. These come from just the first 43 days of the spacecraft’s data, taken last May and June. Four are puffed-up hot Jupiters close to their stars, including two of the lowest-density planets yet discovered — with measured diameters and masses that yield average densities of 0.16 and 0.17 grams per cubic centimeter (compared to Saturn’s 0.69 and Earth’s 5.52). The fifth planet is a hot Neptune with about our own Neptune’s density — even though it orbits so close to its star that its surface layer should be roasted to 1,900°C. 12 March 2010 sky & telescope worldmags

All five host stars are somewhat larger and brighter than our Sun, with 1.4 to 2.0 times the Sun’s diameter. This is because the stars were chosen for follow-ups for showing many narrow spectral lines, good for radial-velocity measurements. Such large stars are not very common; this bodes well for greater numbers of planets to be found around smaller dwarf stars, which are much more abundant. Kepler is watching, nearly continuously, a selection of about 150,000 stars from 9th to 15th magnitude in a big square of sky in the Milky Way between Vega and Deneb. It should keep watching for at least 3½ years, in order to catch at least three transits of any luckily aligned planets that are in wide, Earth-like orbits around Sunlike stars. At the AAS meeting, Kepler’s handlers announced that it is achieving 1-part-in-40,000 brightness precision (0.000025 magnitude) for 12th-magnitude stars. That is good enough to find transits of worlds as small as Earth, as planned. Other news from the announcement:

• Kepler’s measurements are so precise that most “false positives” (such as an eclipsing binary star blended with the image of another star) can be weeded out upfront, without tedious and expensive radial-velocity measurements from the ground. Eclipsing binaries are the main source of false “transits.” • For a few stars, Kepler has measured surface oscillations like those on the Sun. These arise from low-frequency sound (pressure) waves resonating through a star’s body. These oscillations reveal a star’s size, mass, and state of evolution with very high precision — refining, in turn, the orbit, mass, diameter, and age of any planet. • Thousands of new variable stars are turning up, and Kepler’s extremely highprecision, near-continuous light curves offer rich material for new study. For instance, a third of the stars most similar to our Sun turn out to have tiny, shortterm variabilities greater than the Sun’s. • A star’s placement on the detector’s

S&T: CASEY REED, SOURCE: WILLIAM BORUCKI ET AL.

Relative brightness

1.000

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News Notes

J. LANGTON / PRINCIPIA COLLEGE

Abundant Super-Earths Meanwhile, ground-based planet hunts are keeping pace — at least for now. In December the radial-velocity team headed by Paul Butler and Steven Vogt announced three smallish worlds orbiting 61 Virginis, a near-twin of the Sun just 28 light-years away. They have minimum masses of 5, 18, and 24 Earths. At the same time the group announced an 8-Earth-mass world, and hints of two more, orbiting HD 1461, a close copy of the Sun 76 light-years away in Cetus. Butler says it increasingly appears that half of the nearest stars possess at least one detectable planet with Neptune’s mass (17 Earths) or less. This image is from a simulation of atmospheric flows on 61 Virginis b; it orbits so close to its star that jet streams carrying material from the day side to the night side should glow red hot. The planet’s sun has just set behind the left limb. In other exoplanet news, the very dim red dwarf GJ 1214 in Ophiuchus hosts the second super-Earth seen to transit its star. With about 6.5 Earth masses but 2.7 Earth diameters, it’s apparently a miniature “ice giant” with a deep atmosphere, like a baby Uranus or Neptune, rather than a rocky world like the first transiting super-Earth, Corot-7b, which is similar in mass but 14 worldmags

March 2010 sky & telescope

NASA / P. J. ARMITAGE / C. S. REYNOLDS

smaller in diameter (S&T: December 2009, page 14). Also, the Sun-like star 23 Librae seems to have a Jupiter-like planet in a circular orbit at a Jupiter-like distance — a sign that planetary systems similar to our own are beginning to reach detectability as technology improves and data timespans lengthen. Above is a computed-simulated image of material spiraling through the innermost accretion disk around a supermassive hole. The disk is tilted 10° from our line of sight. Its far side appears warped upward by gravitational bending as light rays pass over the hole. One side appears brighter because of Doppler-shift brightening and beaming; the material there is approaching us at a significant fraction of the speed of light.

Imaging the Hole-y Grail A black hole is like a monster in a book with no pictures: vividly imagined but never seen. When astronomers talk of “seeing” a black hole, they’re referring to brilliant surroundings of hot material spiraling in. But with a good enough telescope, we could see the silhouette of the hole itself — a shadow of darkness against any bright material behind, distorted and enlarged by effects of general relativity. We’re nearing that capability. The two black holes with the largest known angular sizes in our sky are those at the centers of the Milky Way and the giant elliptical galaxy M87 in Virgo. The latter hole is 2,000 times farther away, but it’s nearly 2,000 times as massive and therefore nearly 2,000 times as wide. Their visible, distorted silhouettes should appear about 55 and 40 microarcseconds across, respectively. That’s 1,000 times finer than the resolution of Hubble, but it may soon be in range of millimeter-wave telescopes using very long baseline interferometry. VLBI involves two or more radio dishes spaced far across Earth and working at radio wavelengths as short as possible — nowadays, hardly more than a millimeter. The same individual waves arriving at the different antennas must be matched up, which requires millimeter distance precision across nearly the width of Earth — no small feat. Sheperd S. Doeleman (MIT) has been leading the charge to image these largest black holes. He and his colleagues say that progress in VLBI at ever-shorter wavelengths “has now made it extremely likely that this goal will be achieved within the next decade.” Already they’ve detected signs of structure at the scale of the Milky Way’s expected supermassive hole. Stay tuned.

First Super-Dupernova

NEARBY SUPERNOVA FACTORY

array of pixels yields its position to better than a thousandth of a pixel-width, or 4 milliarcseconds. This is how wobbling eclipsing binary stars are being weeded out. Such precision will provide the bestyet parallaxes (distances) for most of the faint stars in Kepler’s catalog, which will also help characterize any planets the stars are seen to have. • Slight, periodic variations can also reveal a star’s rotation rate, due to temporary starspots rotating in and out of view. In this way Kepler scientists expect to better calibrate the relation between a star’s rotation rate and its age and mass, the most widely useful way to assign ages to individual stars everywhere.

A new type of supernova, which physicists have predicted for decades and should be roughly 100 times more luminous than normal ones, has apparently been seen for the first time. A “pair-instability supernova,” like some of its lesser brethren, should happen when the core of a massive star no longer produces enough energy and pressure to hold back the inward pull of its gravity. But while a normal supernova happens to a dying star of perhaps 8 to 100 solar masses, a full-fledged pair-instability blast marks the death of a hypothetical superstar with perhaps 150 to 240 solar masses. In such cases, the star’s core should be squeezed to so high a temperature that it becomes very gamma-ray-hot, with a few of the gamma-ray photons being energetic enough to collide and turn into electronpositron pairs. When some of the gamma radiation vanishes this way, the star’s central pressure drops and the star collapses in on itself — a runaway process. The temperature leaps and nuclear reactions blow the entire star to smithereens. No compact remnant is left; no neutron star, no black hole. In April 2007 a supernova-

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PRICE NOTICE ED-APO Models Increase About 10% February 28, 2010

A LEADER IN DESIGN AND MANUFACTURE OF ED-APO SYSTEMS What is the most faithful imaging known to amateur astronomy worth? At some point, if you stay serious about the hobby, you too will come to the same realization as thousands of others before you that the APO experience, if not priceless, is indeed at least worth the cost of admission. During those cherished moments of transparent and stable air, the apochromatic refractor delivers the closest experience to being there human beings may ever know.

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SW P120 ED-APO OTA* SW AZ4 “THE ROCK” MOUNT *SW 120ED OTA and AZ4 Mount sold separately

“The Holy Grail of any refractor, and one expected of a scope carrying the apo moniker, is an in-focus star image free of false color fringes. The SW 120ED easily passed that test, but even when its images were slightly out of focus they remained free of obvious color fringing. As such, stars that danced around in turbulent seeing remained pure in color, which is not always the case for apos that are color free only when precisely focused.” Sky & Telescope, October 2009

WHAT WE LIKE: Excellent optics Handsome appearance WHAT WE DON’T LIKE: Nothing *October 2009

S&T SAYS: “Don’t be fooled by its modest cost; this 120-mm apo delivers images that are on par with premium-priced instruments.” “…its performance as a visual telescope was on par with similar-size apo refractors costing three times as much.” S&T October 2009

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S&T: CASEY REED

Comet Theory Faces Mammoth Confusion New research has confused the picture of what killed off the mammoths and other great mammals of North America around 12,900 years ago. Was it overhunting by newly arrived humans, or the rapidly changing climate at the time, or a comet impact as suggested in our September 2009 cover story? In a new paper published in Science, Jacquelyn Gill reports evidence that at least some populations of the big animals were in decline well before that date. On the other hand, a recent paper by Neal Woodman and others in Quaternary Research finds that a mastodon skeleton discovered in Indiana in 1976 was dated incorrectly; the creature was alive about 10,055 years ago, long after the impact. And the evidence for an impact has itself come under question; a team led by Francois Paquay (University of Hawaii) found none of the expected extraterrestrial debris in either land or marine sediments. So, ironically, the big-mammal extinction remains more confused than that of the dinosaurs 5,000 times farther back in time. That the dinosaurs (and much else) were wiped 65 million years ago by a globally devastating asteroid blow now seems quite clear.

The Discovery of Alcor B Add a new star to the Mizar-Alcor collection in the handle of the Big Dipper. Mizar and little Alcor next to it — the “Horse and Rider” — were a famous test of vision 16 March 2010 sky & telescope worldmags

in ancient times. Then Mizar became the first Alcor A telescopic double star discovered (by Benedetto CasAlcor B telli, a friend of Galileo’s; see S&T: July 2004, page 72). Some three centuries later, each of Mizar’s components turned out to be a spectroscopic binary too close to resolve, making it quadruple. Early reports that Alcor too was a spectroscopic binary proved spurious. Now it turns out that Alcor is a double star of a different kind. A team has been using the 5-meter Palomar Observatory telescope to hunt for faint objects near bright stars at infrared wavelengths. The project uses adaptive optics to steady the seeing and a coronagraph mask to block light from the stars. Next to Alcor the group detected a faint red dwarf star of spectral type M3 or M4. It’s 1.05 arcseconds south-southwest of type-A5 Alcor. The dwarf shares Alcor’s proper motion across the sky and its parallax motion as well. In the false-color infrared image above, the big messy blob is what’s left of Alcor’s light after most of it is blocked by the occulter in the coronagraph. The astronomers write that, just as Mizar and Alcor have been a test of naked-eye vision, “the Alcor binary system will be a convenient ‘vision test’ for the new generation of high-contrast imaging projects.”

Iapetus Solved? Ever since Giovanni Domenico Cassini discovered it in 1671, telescope users have marveled over Saturn’s large outer satellite Iapetus. It’s 10th magnitude when farthest west of Saturn but 12th when east of it. Its rotation is locked to its orbital period, so one side always faces forward in orbit and the other faces backward. The Voyager and Cassini spacecraft showed that the front side is covered with something that looks like very dark powdered chocolate, and the trailing side is covered with gray ice. Cassini’s high-resolution flyby revealed sharp-edged borders between the two substances even in the transition zones where

they intermingle, as in the landscapes below (S&T: June 2009, page 26). Two groups of planetologists now think they have Iapetus finally figured out. The front side of Iapetus sweeps up material from the huge, sparse, newly discovered dust ring that originates from tiny Phoebe farther out (January issue, page 18). Phoebe, and therefore the ring, revolve in the opposite direction from the other moons, so the ring material strikes Iapetus head on. This “chocolate dust” is only several meters deep, overlying ice. In addition, sunlight warms this material and drives off water to condense as frost on the trailing side — a process that explains the sharp borders and complex

NASA / JPL / SPACE SCIENCES INSTITUTE (2)

hunting group discovered a distant blast named SN 2007bi and quickly realized its unusual nature. It was much more luminous than most, took an unusually long 70 days to reach peak luminosity, and then faded slowly too. “Multiple lines of evidence lead to the conclusion for a huge helium core (about 100 solar masses),” says team member Alex Filippenko. Such super-blasts should have played a major role in shaping the early universe during the first generations of stars.

BEN OPPENHEIMER / PROJECT 1640 / AMNH

News Notes

patterns in the transition zones. This process is aided by the fact that Iapetus’s slow rotation allows warmer daytime temperatures to build up than on Saturn’s shorterperiod moons. The two frames above are each about 20 miles (30 km) tall.

WISE Launched On December 14th, after several delays, NASA’s Wide-field Infrared Survey Explorer (December issue, page 26) took off and successfully reached orbit. ✦

All News Note stories are presented in greater depth, with links to further information, at SkyandTelescope.com; search for the keyword SkyTelMar10.

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Cosmic Relief David Grinspoon

The Dream Is Coming Back Commercial spaceflight may renew our dreams of expanding into space. As a space-obsessed

MARK GREENBERG / VIRGIN GALACTIC

teenager in the ’70s, I was sure that I’d travel in space. My nerdy high school gang wore “L5 in 95” T-shirts, imagining we would help create permanent colonies at the Lagrangian points of Earth’s orbit. As children we had witnessed the Apollo landings and may have appreciated their mythical dimensions more vividly than the adults around us. We believed that the move into space would provide new arenas for human habitation and ensure the preservation of Earth’s environment and the long-term survival of all terrestrial life. I wanted to be Dave Bowman from the movie 2001, riding new spacecraft to “Jupiter and beyond the infinite.” These utopian visions crashed hard on the rocks of fiscal and geopolitical reality in the ’80s. When Apollo was cancelled we space geeks of a certain age felt that this decision, while shortsighted and naïve, was a bump in the road toward interplanetary civilization. It turned out we were the naïve ones, not understanding the central role of the Cold War in both starting and stopping the space race. Yet humanity, through our robot proxies, continued to explore, and some of us managed to fit our curiosity into these spindly little packages, finding desk jobs that allowed us to vicariously roam the solar system.

Virgin Galactic’s SpaceShipTwo (center craft) is mated to its mother ship, VMS Eve (WhiteKnightTwo), at the Mojave Spaceport in California last December.

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All this was on my mind on a Mars-cold evening last December when, with a few hundred other space enthusiasts gathered at the Mojave Spaceport in California, I witnessed the unveiling of Virgin Galactic’s SpaceShipTwo. At first we saw only a long, horizontal row of approaching strobe lights as the whining engines rose above the howling wind. The craft crawled out of the darkness, theatrically passing giant banners depicting iconic images of human flight, from Michelangelo’s winged contraptions to lunar landers and beyond. Suddenly the sleek three-hulled construction emerged into bright floodlights, turned slowly to the left, and rolled to a stop. The stunned crowd applauded and then the most enthusiastic of us sprinted across the tarmac. We engulfed the spacecraft and ran our hands along its smooth, carbon-composite skin, like those apes in 2001 touching the alien monolith. The surreal entrance, shiny nonmetallic curves, and jolly round windows all gave it the feel of a wondrous life-sized toy. But this (or just possibly the competition) will be the first reusable commercial craft to carry people into space. Tourism will initially drive this new space industry, but these flights will also enable new science. Frequent access to space will allow us to study microgravity, test instruments for other spacecraft, and probe the “ignorosphere” — the poorly studied region of the atmosphere 100 kilometers up, too high for aircraft and too low for satellites, where SpaceShipTwo will take its passengers. These flights also carry the potential to educate and inspire new generations of kids to form their own dreams of heading out beyond Earth. If the initial flights are successful, the price will come down, more craft will follow, and space exploration will become increasingly democratized. After these suborbital forays will come orbital craft, space hotels, and private expeditions to the Moon and beyond. Maybe I was too quick to shelve my personal vision of space travel, resigning myself to the more measured thrill of armchair and laptop exploration. The dormant dreams of my youth are stirring once again. ✦ 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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Outer Solar System

e

Planets and other large objects could be lurking far beyond Neptune, but they’ll be very difficult to find.

er

DAVID JEWITT

BEFORE GALILEO pointed his telescope skyward some 400 years ago, the solar system was a decidedly simple place. Apart from the Moon, the Sun, and the planets out to Saturn, only the occasional comet was seen by the unaided human eye. Things became more interesting as telescopes and their detectors improved. Major discoveries included Uranus and Neptune as well as new classes of objects, notably the main-belt asteroids between Mars and Jupiter and the icy bodies of the Kuiper Belt beyond Neptune. Remarkably, this phase of solar system discovery continues at an accelerated pace, as technological improvements allow us to peer ever more deeply into the abyss beyond the known planets. Steady observational progress and new speculations based on models together lead us to wonder what else might be found in the outer regions.

Plenty of Real Estate The most recently discovered solar system real estate is the Kuiper Belt. The belt extends at least to 1,000 20 worldmags

March 2010 sky & telescope

astronomical units (a.u.) and contains a rich abundance of primitive bodies that are, in part, leftovers from the planet-formation epoch. Astronomers have identified more than 1,000 Kuiper Belt objects (KBOs) since 1992, most larger than about 100 kilometers (60 miles) in diameter. A vast number of smaller objects await discovery: the Kuiper Belt holds perhaps 100 million icy bodies with diameters of 1 km or larger. Some of these bodies escape the belt and drift toward the Sun, where they vaporize and are seen as short-period comets. At the other extreme, KBOs are known to range in size up to Pluto and Eris, both about 2,300 km across. Neptune’s satellite Triton is almost certainly a captured KBO (S&T: September 2006, page 18) and is larger still, FAR-FLUNG PLANET Above: Given the solar system’s tumultuous early history, objects bigger than Earth could have been gravitationally flung into the outer reaches of the solar system. Such planets would be extremely faint and difficult to detect, and so for now we have only artist conceptions such as this.

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VACUUM CLEANER Jupiter has played a major role in clearing the solar system of debris. A small object hit Jupiter in July 2009, producing the dark spot. But for every object that hits Jupiter, many more are deflected. A small percentage end up in the Oort Cloud, but most are ejected from the solar system. NASA / ESA / HEIDI HAMMEL (SSI) / JUPITER IMPACT TEAM

S&T illustration by Casey Reed

at 2,700 km. But Triton is only 0.3% as massive as Earth. Could truly planetary-size objects lurk in the Kuiper Belt? The simple answer is an unqualified “yes.” The Kuiper Belt is enormous, providing lots of room in which to hide bodies the size of Earth or larger.

Consider a thought experiment in which an Earth twin is transported outward to ever-larger distances. At 5 a.u., the distance of Jupiter, this twin would appear at visual magnitude 2.6, comparable to one of the brighter stars in the sky. A telescope would reveal a disk 4 arcseconds across, about the same as the apparent diameter of Uranus. By 30 a.u., corresponding to Neptune’s orbit, the magnitude falls to 10.8 and the diameter to 0.6 arcsecond. At 600 a.u., much farther than any known planet but still well within the range of distances swept by known KBOs, Earth would appear near magnitude 24 and would have an angular diameter of only 30 milliarcseconds. It would be too faint to have been recorded in any all-sky survey conducted to date, and too small to be resolved even by the largest telescopes using adaptive optics. Neptune itself would appear at magnitude 24 if displaced to 1,200 a.u., and would go undetected in our surveys. Neither could we detect such bodies via their gravitational perturbations on the planets. Calculations show that Earth could be detected only to about 50 a.u. while Neptune’s pull would be immeasurable beyond about 130 a.u. So the vastness of the Kuiper Belt provides an enormous largely unexplored space where all sorts of interesting objects might lurk. KUIPER BELT OBJECTS Astronomers continue to find sizable objects in the Kuiper Belt. This illustration shows some of the largest known bodies, including Neptune’s captured moon Triton.

Hydra Charon

Nix

Dysnomia

Hi'iaka Weywot

Quaoar

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Sedna

Haumea

Namaka

Makemake

Pluto

Eris

Triton

Sk yandTelescope.com

The Moon

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NASA / JPL / USGS

Outer Solar System

KUIPER BELT INTERLOPER Neptune’s large satellite Triton has a retrograde orbit, meaning it was captured from the Kuiper Belt. With a diameter of 2,700 kilometers, Triton is larger than any known Kuiper Belt object, a strong indication that sizable bodies remain undiscovered in the solar system’s outer reaches.

Kuiper Belt Planets?

NASA / JPL-CALTECH / MICHAEL BROWN

Whether large objects actually exist out there is a different matter. Our current understanding of planetary accretion indicates that it would be difficult for planets to form at Kuiper Belt distances. Smaller bodies must collide repeatedly in order to grow into larger objects and, in the rarified regions of the outer solar system, with slow orbital motions, the necessary collisions are expected to be very rare. In fact, modelers can’t even account for the formation of Uranus and Neptune at their current distances of “only” 19 a.u. and 30 a.u. But it’s conceivable that large objects might have formed close to the Sun and were then gravitationally scattered by planets to distant orbits in the Kuiper Belt. For example, some models suggest that Uranus and Neptune formed closer to the Sun and drifted outward due

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to tidal interactions with each other and with a long-gone massive precursor to the Kuiper Belt. Neptune’s radial migration, from about 20 a.u. to its current location near 30 a.u., would explain why so many Kuiper Belt objects occupy Pluto-like orbits in resonance with Neptune. Other evidence that planets can be thrown around comes from the highly elongated orbits of many known extrasolar planets, perhaps produced by close encounters with other planets. Alternatively, if the Sun formed in a dense star cluster, it might have grabbed objects formed around other stars into large, looping orbits far beyond the known planets. There are no known examples of such objects at present. Perhaps the closest analog is Sedna, whose perihelion distance of 76 a.u. lies more than twice as far from the Sun as Neptune. Sedna’s inclination, though, is a modest 12 degrees, suggesting that it originated in the Sun’s protoplanetary disk. Objects captured from other stars in a natal cluster would have large, even retrograde, inclinations far out of the ecliptic plane. The theoretical possibilities are essentially unbounded and all we can do is wait for future observations to show us what lurks in the Kuiper Belt. Spacecraft will probably not be useful in this regard — they’re good at making detailed observations of particular objects but not so useful for the surveys needed to explore the Kuiper Belt. The planned (but largely unfunded) Large Synoptic Survey Telescope, if built, will be more powerful (S&T: September 2008, page 30). With the ability to survey almost the entire sky to 24th magnitude, LSST could find planets in the Kuiper Belt’s outer reaches. DISTANT WANDERER The discovery of Sedna by Michael Brown’s team was yet another indication that interesting bodies lurk in the outer realm of the Kuiper Belt. Its elongated 12,000year orbit ranges from 76 to 975 astronomical units. These discovery images, taken over three hours on November 14, 2003 with the 48-inch telescope on Palomar Mountain, show Sedna’s slow orbital motion. Sedna is visible only because it’s near perihelion.

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Observations prove that the Kuiper Belt is real, but there is a structure at a much larger distance whose existence can only be inferred. The Oort Cloud is a roughly spherical swarm of comets about 100,000 a.u. in scale, with all of its members in orbit around the Sun. Dutch astronomer Jan Oort (1900–1992) inferred its existence in 1950, based on the observation that the orbits of long-period comets (those with periods greater than 200 years) are large and randomly oriented in the sky. Oort reasoned that these long-period comets must be falling into the planetary region from a vast, roughly spherical and unseen cloud surrounding the Sun. The first estimate of the number of Oort Cloud comets was 1012 (a trillion), while more recent work using improved measurements of the discovery rate of longperiod comets suggests that the number might be 10 times smaller. The Sun’s gravity is so weak at 100,000 a.u. that the gravitational tugs of passing stars and Milky Way tides together can destabilize the orbits of Oort Cloud comets. In fact, the cloud’s outer radius is set by the distance beyond which comets are ripped away from the Sun. Some Oort Cloud comets escape to interstellar space while others dip into the region of the planets and begin to vaporize in the Sun’s heat. The Oort Cloud has thus been steadily depleted since its formation. In the beginning, the cloud probably contained at least a few times more comets than it does now, and perhaps 10 times as many. The erosion is slower at smaller distances, lead-

O O R T CLO U D ’ S O U TE R E D GE The Oort Cloud’s outer boundary is probably about 100,000 a.u. from the Sun. That’s equivalent to about 1.5 light-years, or only about one-third of the distance to the nearest known star, Proxima Centauri.

ing to the idea of an inner Oort Cloud that might persist almost unaffected at 5,000 to 10,000 a.u. As far as we know, no comets formed in the Oort Cloud, since at these vast distances the density of any matter associated with the Sun’s protoplanetary disk must have been vanishingly small. Instead, we think the Oort Cloud comets were originally planetesimals formed between Jupiter and Neptune, and were then scattered outward by near-miss interactions with these growing planets. Most of the ejected planetesimals were launched above the Sun’s escape velocity and are now wandering the frigid depths of interstellar space. Perhaps 1% to 10% of the scattered objects were subsequently deflected by external forces into orbits weakly bound to the Sun. If true, Oort Cloud comets are samples of the Sun’s protoplanetary disk that have been expelled to great distances and stored in deep freeze (10 Kelvins) for the age of the solar system. The observational challenge posed in directly detecting Oort Cloud objects is daunting. At 100,000 a.u., the nucleus of Halley’s Comet would appear hopelessly faint at magnitude 64. Even at only 1,000 a.u. (and magnitude

Types of Orbits

INTERSTELLAR COMETS What happened to the comets that were ejected from the solar system as the Oort Cloud formed? They presumably float among the stars in interstellar space. If all stars lose 1012 to 1013 comets and there are about 1011 stars in our galaxy, the galaxy must hold 1023 or 1024 comets. Although numerous, the combined mass of comets is negligible compared to the mass in stars, dark matter, and interstellar clouds. Some interstellar comets should, by chance, wander into the solar system. Interstellar comets would follow distinctive, strongly hyperbolic paths relative to the Sun, quite unlike any comets observed

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to date (the orbits of all known comets are elliptical or parabolic). Although there have been a few claims of possible interstellar comets, none have shown hyperbolic orbits that are a prerequisite for interstellar origin. At best, the claims rely on measurements of “strange” composition, but “strange” is relative and there are other plausible explanations for such objects. But the galaxy’s huge size relative to the solar system means that we would expect visible interstellar comets to be rare, occurring at intervals from decades to centuries. No existing telescope would be

expected to have found one. Interstellar planets probably exist too, but these would be roughly a trillion times less common than interstellar comets. We would never expect to see one passing through our planetary region. Still, there is a small but real chance that the next generation of all-sky survey telescopes (Pan-STARRS or LSST) might detect an interstellar interloper. How fantastic would that be?

Sun

FPO

Elliptical orbit

COMET ORBITS Comets follow a wide variety of orbits. If a comet is ever found on a strongly hyperbolic trajectory, meaning it’s not gravitationally bound to the Sun, this would be a dead giveaway of an interstellar origin.

Parabolic orbit

Hyperbolic trajectory

Sk yandTelescope.com

S&T: GREGG DINDERMAN

The Outer Outer Limits

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Outer Solar System

For more information about the outer solar system, visit the author’s website at www2.ess.ucla.edu/~jewitt/.

Orbit of Neptune

Objects not to scale

50,000 a.u.

Objects not to scale

COMET RESERVOIRS The Kuiper Belt mainly contains bodies left over from the Sun’s protoplanetary disk; the Oort Cloud consists of objects ejected from the inner solar system. Both regions might contain large unseen bodies.

NEMESIS In the 1980s, reports of a 26-millionyear periodicity in Earth’s mass extinctions led some astronomers to infer that the Sun might have a distant binary companion. The hypothetical star — fittingly named Nemesis — would stir up the Oort Cloud, sending periodic, deadly comet showers into the planetary region. But evidence for the 26-million-year periodicity has not grown stronger with improved extinction data, and confidence in the Nemesis hypothesis has waned. A companion main-

sequence star would be optically bright and it should have already been recorded in our star catalogs. If the companion were instead a brown dwarf, it would be optically faint but bright in the infrared. NASA’s WISE spacecraft will easily detect its radiated heat (S&T: December 2009, page 26). The real trick will be to distinguish the companion from millions of stars of similar appearance. For example, WISE might detect the radiation but offer no way to measure the companion’s distinctive motion that would prove it to be gravitationally bound to the Sun.

SOLAR COMPANION? Some astronomers have suggested that the Sun might have a very distant binary companion, often referred to as Nemesis. There is no direct evidence that such an object exists. If it does, Nemesis is likely to be either a brown dwarf or a Jupiter-mass object.

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David Jewitt is a professor of planetary science at the University of California, Los Angeles. He is interested in the solar system’s small bodies, especially comets and Kuiper Belt objects, and in planetary formation processes. With Jane Luu, he codiscovered 1992 QB1, the first recognized Kuiper Belt object other than Pluto and its large moon Charon.

S&T: CASEY REED

Oort Cloud

20 a.u.

S&T: GREGG DINDERMAN

Kuiper Belt and outer KuiperSystem Belt planetary orbits Solar

43), it would be far beyond detection by any telescope yet built or imagined. Likewise, the heat radiated from comets in the cloud is too feeble to be detected against the lingering glow of the cosmic microwave background. Even stellar occultations will not cause noticeable dimming because the angular diameters of most comets at such vast distances are small compared to the angular diameters of the stars they block. Presumably, some very large objects, perhaps even planetary in size, were launched into the Oort Cloud, but these would be so rare and so distant that we cannot expect to find them. We may have to face the fact that direct measurements at these distances can be made only by going there with a spacecraft. But it will take a long time. Traveling outward at 4 a.u. per year, NASA’s New Horizons mission to Pluto is one of the fastest interplanetary craft ever flown. But it will take 25,000 years to reach 100,000 a.u. Patience, as they say, is a virtue. ✦

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Strange Denizens of the Early Universe

Shedding

LIGHTon Bizarre stars powered by dark matter may have been the first Ker Than to form after the Big Bang.

All Illustrations by S&T: Casey Reed

The scientific version of Genesis tells us that the universe sprang into being 13.7 billion years ago and that the first denizens of that new realm — stars — blazed into existence about 100 million years after the Big Bang. Even by stellar standards, the first stars were titans. They were bigger, brighter, and burned faster than any stars in existence today (S&T: May 2006, page 30). But if a new theory of star formation is correct, the stellar first born were even stranger beasts than scientists previously thought because of how they interacted with dark matter, the unseen “substance” that scientists think makes up more than 80% of the universe’s mass. Stars like our Sun rely on the fusion of light elements into heavier ones to counteract their own immense gravities and to keep them from imploding. But some of the most popular theories in physics suggest dark matter consists of particles that can act as their own antiparticles 26 worldmags

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(S&T: April 2009, page 22). This raises the intriguing possibility that the first stars were powered by the self-annihilation of concentrated dark matter in their cores. Such “dark stars” would have been cooler but more colossal than their fusion-driven brethren. “They’re still stars, made primarily of hydrogen and helium. Less than 1% of their mass is dark matter,” says Katherine Freese (University of Michigan). Freese, along with Paolo Gondolo (University of Utah) and Doug Spolyar (University of California, Santa Cruz), were the first to investigate dark stars in 2006. The team says that if dark stars existed, they could have altered the chemistry of the early universe by delaying the birth of “normal” first-generation stars — called Population III stars — by up to a billion years. Dark stars could also explain why supermassive black holes appear to have formed so soon after the Big Bang.

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Dark-Star Evolution In the aftermath of the Big Bang, the universe was a sea of smoothly distributed particles, featureless and dark. A smattering of the particles consisted of familiar, or baryonic, matter, but the vast bulk of it was dark matter. Over time, the dark-matter particles coalesced into a complex spider-web-like structure made up of filaments that intersected to form nodes, or halos. Baryonic matter flowed along the fi laments, drawn by gravity into the massive halos, where it assembled into gas clouds. The clouds collapsed gravitationally into luminous knots of gas, creating the first protostars. As the protostars grew in mass, they contracted in size until their cores reached a critical density and temperature that ignited nuclear fusion. In this standard scenario, dark-matter halos are stellar wombs where baryonic matter collected and matured into stars, but dark matter does not affect star formation directly. However, computer models by Freese and her colleagues challenge this idea. “In the standard picture, a protostellar cloud collapses until it’s small, dense, and hot enough to get fusion going,” says Freese. “We’re saying there’s an intermediate stage where it sits for a very long time with this dark-matter power instead.” In this revised stellar history, dark matter was not just the backdrop against which the lives of the first stars played out. Dark matter’s spatial density in the early universe was much higher than it is today because the universe — still in the early stages of expansion — was a much smaller place. The first stars were immersed in dark matter. Like a phantom wind, dark-matter particles blew through and around the first stars. The first protostars attracted dark-matter particles and concentrated

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them in their cores. If the protostar’s dark-matter density exceeded a certain threshold, the particles collided and self-annihilated in an energetic spray of photons, neutrinos, and electrons. During dark-matter self-annihilation, mass converts into energy much more efficiently than in nuclear reactions, so a small amount of dark matter can power an entire star. Importantly, the dark-matter-burning phase prevents further gravitational contraction of the protostar, essentially “freezing” it in an embryonic stage before its nuclear engine can ignite. As a result, dark stars would have been vastly larger and “fluffier” than normal Population III stars. They would have had diameters ranging from about 1 astronomical unit (the average distance between the Sun and Earth) to perhaps 30 a.u. — about Neptune’s distance from the Sun. And whereas a normal Population III star might contain 100 solar masses (S&T: May 2006, page 30), recent studies suggest the largest dark stars might have had masses between 1,000 and 10,000 Suns. Dark stars would have been yellow-orange like our Sun, but the largest ones might have shined a billion times brighter due to their huge surface areas.

STARS COMPARED The characteristics of stars are determined by their compositions, masses, and energy sources. Huge stars such as dark stars and red supergiants have powerful energy sources, which puff up their atmospheres, making their visible surfaces relatively cool. The name “dark star” is actually a misnomer. Due to their huge surface areas, they would have shined with the intensity of millions of Suns. Like dark stars, Population III stars existed only in the early universe, but they were powered by nuclear fusion rather than by dark-matter annihilation.

Star Comparisons A large Dark Star A standard Population III Star Red Supergiant (Betelgeuse)

Diameter = 30 a.u. Mass = 10,000 Suns Surface Temp = 5000K Luminosity = 1 billion Suns

Diameter = 10 a.u. Mass = 15 Suns Surface Temp = 3500K Luminosity = 100,000 Suns

Sun

Diameter = 0.1 a.u. Mass = 200 Suns Surface Temp = 100,000K Luminosity = 10 million Suns

Diameter = 0.009 a.u. Mass = 1 Sun Surface Temp = 5780K Luminosity = 1 Sun

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Life Cycle of Dark Stars 1 Dark matter in the early universe collected in long filaments.

2 Baryonic matter flowed along these filaments and coalesced gravitationally in large gas clouds.

3 Dark matter and baryonic matter collapse together in these clouds. The baryonic matter cools and pulls in dark matter.

Dark-Matter Annihilation Low-energy photons

Darkmatter particles

4 The gas clouds collapsed gravitationally to form the first stars.

Particles of familiar matter

Gamma rays

Some stars contained enough dark matter in their cores to be powered by dark-matter annihilations.

5a The largest dark stars ultimately collapsed into heavy black holes, which could be the seeds of supermassive black holes in galaxy centers.

5b Smaller dark stars eventually ran out of dark matter, and were then powered by nuclear fusion.

7 Some of these supernovae could have left behind stellar-mass black holes.

6 When the nuclear fuel ran out, the stars exploded as standard core-collapse supernovae.

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“Standard Population III stars were hotter and bluer by comparison,” says Freese. Computer simulations predict that dark stars can survive so long as the surrounding dark-matter density remains high. At a minimum, dark stars should have survived for about a million years, and perhaps even billions of years if the dark-matter halo is very large or if there is an influx of dark-matter particles from outside sources. It’s possible that some primordial dark stars might have survived to the present day. “We might find these first stars still shining. That would be tremendous,” says Igor Moskalenko (Stanford University).

Cosmic Consequences

changed things. “The early universe would have looked quite different because these stars would have been a much longer-lived source of radiation than if they were to die after only a million years or so,” he says. Hernquist adds, however, that while dark stars are interesting, they are still fairly speculative, “because the modeling used by the scientists makes several assumptions and their calculations are fairly simple.” For example, says Avi Loeb (Harvard-Smithsonian Center for Astrophysics), it’s possible that the dense central regions of dark-matter halos — called cusps — were fragile and easily disrupted by interactions with baryonic matter. “Until the existence of such cusps is demonstrated to be a robust result based on three-dimensional numerical simulations, I would not be convinced that dark stars could exist in reality,” Loeb says.

The fate of dark stars once they run out of dark-matter fuel depends upon their mass. Dark stars with only a few hundred solar masses could become “unfrozen” after Finding Dark Stars exhausting their dark-matter reserves. They would revert to normal fusion-driven stars and live for another million The first evidence for dark stars might come not from years or so before exploding as supernovae and seeding computer models, but from astronomers. Fabio Iocco the universe with their heavy elements. (Paris Institute of Astrophysics, France) reasons that dark But a return to normal stellar life would be out of the stars should postpone the supernovae of standard Populaquestion for the most-massive dark stars. Their incredible tion III stars by tens to hundreds of millions of years. mass would cause them to collapse directly into black holes. “The best signature we might have is a delay in PopulaDark stars could thus explain how quasars — bright galax- tion III supernovae by a certain time due to the dark-star ies with supermassive black holes at their centers — existed mechanism,” Iocco says. Scientists speculate that if the only a few hundred million years after the Big Bang, sooner delay is sufficiently long, the first supernovae could be than most current theories predict. “There’s just not enough observed by future space telescopes. time in the current theories without dark stars for black Next-generation satellites might also be powerful holes with only a few solar masses to come together and enough to detect ancient light emitted by primordial dark form the million-solar-mass black holes that are required to stars that disappeared long ago. Theories predict that the explain quasars,” says Gondolo. light from early dark stars should Dark stars may also have played a be shifted to far-infrared waveWHAT IS DARK MAT TER? role in ending the cosmic dark ages, lengths by the time they reach us. a period of total darkness after the “We were hoping for an infrared Scientists have yet to identify the Big Bang when newly formed hydrodetection with the James Webb nature of dark-matter particles, but many physicists think they are weakly gen and helium atoms absorbed all Space Telescope, but our dark stars interacting massive particles, or of the universe’s light. According to turn out to be just slightly too dim WIMPs. These wispy particles are standard theory, the ultraviolet light for it,” says Gondolo. “We’re explorpredicted by supersymmetry, a theory of several generations of stars and ing other ways.” that postulates that all the known galaxies was required to break apart, Alternatively, space missions particles have heavy partners, most of which have decayed since the Big Bang. or ionize, the atoms and make the might detect frozen dark stars that Because the surviving WIMPs interact universe transparent again. But dark have managed to survive to the with familiar matter only through the stars should have given rise to larger present epoch. Mass and chemical weak nuclear force and gravity, nature’s and more energetic fusion-driven compositions being equal, dark two weakest forces, these particles are stars, and this could have sped up the stars should be bigger and colder exceedingly difficult to detect. reionization of the universe. Freese than fusion-driven stars. They says dark stars could also have should also be similar in temperadelayed reionization by delaying the formation of standard ture to our Sun, but about a million times brighter. If Population III stars. “I’m hedging on that one,” she says. astronomers ever find a star with these peculiar proper“Dark stars are going to affect reionization, but we don’t ties, it could be evidence that some astral relics from the know in what direction yet.” dawn of time are still with us. ✦ Lars Hernquist (Harvard-Smithsonian Center for Astrophysics) says dark stars would definitely have Ker Than is a science journalist living in New York City.

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COLLEG CO LLLEGE EG GE O OBBSE SERV SERV RVAATTO ORRRYY

BBO OYD YDEN EN STATI TAATION TTIION ON, N, PPEERU RU

BACKGROUND PHOTOS: HARVARD COLLEGE OBSERVATORY, INSETS: STEPHEN LIEBER

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Pro-Am Collaboration

Digitizing stephen lieber Bringing 100 years of photographic plates into the 21st century.

In a crowded basement at the Harvard College Observatory (HCO) archives, a group of amateur astronomers and observatory staff members is digitizing the world’s largest collection of astronomical glass plates. These photographs, totaling about 525,000, were part of a long-term, full-sky survey of stellar magnitudes and positions that took place over more than a century, from 1885 to 1989. For most of that period, glass photographic plates were the primary research tool in many fields of astronomy. But when digital detectors were invented, astronomers soon lost interest in the older, more cumbersome technology. Today, workers at observatories around the world are attempting to digitize these older images and make them available for modern computer analysis. Harvard is leading this effort with its Digital Access to a Sky Century @ Harvard (DASCH) project under the direction of Jonathan Grindlay.

100 years of History Over the duration of the Harvard survey, approximately 50 different instruments were used to photograph the sky from various locations around the world, including Massachusetts, California, South Africa, New Zealand, and Peru. The astronomers who took these images experienced many hardships during their work. For example, Solon Bailey and his coworkers experienced altitude sickness at the research station at Arequipa, Peru. When a civil war caused fighting to break out near the facility in 1893, Bailey had to bury the telescope’s objective lens

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under the observatory’s floorboards for safekeeping. Bringing the plates back to Harvard was often a difficult job; some had to be ferried down from remote observatories by mule teams. After they arrived at HCO, many were discarded because of exposure problems and other errors that made them useless. Others have been broken, lost, or stolen. And during the middle to late 1950s, HCO Director Donald Menzel interrupted the plate taking, producing the “Menzel gap” in an otherwise unbroken full-sky record. One shipping story that stands out is that of the freighter SS Robin Goodfellow. On July 25, 1944, while carrying a shipment of plates from South Africa, it was torpedoed and sunk by the German submarine U-862 in the South Atlantic. Ironically, the U-862 was transporting valuable cargo to the Japanese, including a shipment of optical glass. But despite these losses, the surviving collection at Harvard is still a quarter of the world’s entire inventory of approximately 2 million plates.

A Collaboration is Born In the late 1980s, during the early years of CCDs, Grindlay had outlined the possibility of digitizing Harvard’s plate archives, but the technology available at the time was still in its infancy. He revisited the idea in 2001, enlisting archives curator Alison Doane and Doug Mink to investigate new commercial scanners. They tested and rejected two machines, one of which took 20 minutes to digitize a single plate. At 8 hours per day, that scanner would have

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STEPHEN LIEBER

taken 60 years to complete the entire project. Doane outlined the problem at a 2002 meeting of the Amateur Telescope Makers of Boston (ATMoB). DASCH would require a specialized scanner with high positional accuracy, speed, and dynamic range, in order to yield accurate data on stellar magnitudes and positions. It would need about 10-micron resolution to capture every detail in the images, and require high-speed data transfer to process such a huge number of plates in the 3-to-5-year goal set for full production scanning. The scanner also had to handle glass plates with uneven edges, varying thickness, or that were broken and pieced together. Doane’s presentation caught the interest of Robert Simcoe, a longtime ATMoB member and electrical engineer. He quickly realized that a scanner with the required speed and resolution could be derived from those developed for flat-panel LCD inspection. Simcoe did a preliminary design employing a commercial scanner made by Aerotech Inc., and Grindlay submitted a proposal for grant funding to the National Science Foundation, which supported development of the world’s fastest plate scanner as well as initial software to analyze the images. The completed DASCH scanner is built around a liquid cooled, 45-millimeter-square 16-megapixel CCD camera with 11-micron pixels donated by Salvador Imaging. Its base is a 2,200-pound polished granite table that rests on the 5-foot-thick cement basement floor of the HCO archives. Pneumatic supports isolate it from outside vibrations. There’s no door to the outside, so the base also had to be brought in through a window. Even walking down to the room is difficult; the only access for staff is by a nar-

Amateur Telescope Makers of Boston member Ed Los places two 8 × 10-inch glass plates onto the DASCH scanner plate loader. The loader is attached to an X-Y platform that “floats” on air bearings and moves the plate into its scanning positions.

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HARVARD COLLEGE OBSERVATORY

Pro-Am Collaboration

With its archive of more than 500,000 images spanning more than 100 years, Harvard College Observatory is home to the largest collection of astronomical glass plates in the world. The Digital Access to a Sky Century @ Harvard (DASCH) project will allow astronomers to perform computer analysis on this treasure-trove of data for the first time.

row, steep, spiral staircase. The plate loader rests on an X-Y platform that glides on air bearings with precision scales for 0.1-micron positional accuracy. Students from Worchester Polytechnic Institute helped design and manufacture its plate holding fi xtures. Unlike conventional scanners, the DASCH scanner photographs one section of the plate, then moves the X-Y platform sequentially until the entire plate is completed. Each scan frame overlaps by 50% to ensure accurate alignment when all the pieces are assembled into a single image. Using this system, a single 8-by-10-inch (200 × 250 mm) plate produces 100 scans. It takes about 80 seconds to image two plates simultaneously. These pieces are then automatically stitched together using software custom-written by ATMoB member Edward Los. A single 8-by-10 plate produces a 700-megabyte, 12-bit grayscale image. “Our ultimate goal is to record every bit of information in each photograph,” says Los. Ultimately, the entire DASCH collection will amount to nearly 2,000 terabytes of digital information. Los has also developed software that can analyze and remove imperfections in the resulting scans. Some plates

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were exposed with a prism known as a Pickering wedge, which produced secondary stellar images for bright stars, in order to improve magnitude estimates (at a time when women had to work using their eyes and magnifying glasses, and bright stars were especially difficult to measure). The wedge produced spurious reflections that can be digitally removed from the scan, restoring the image to what it would look like if the prism was never used.

Top: HCO Archive Curator Alison Doane examines and cleans plates before moving them on to the DASCH scanner. Often they need to be cleaned of chemical residue leftover from the developing process. Bottom: Cracked or broken specimens such as this photograph of the Small Magellanic Cloud can be reassembled by HCO staff, and accommodated by the flexible design of the plate loader.

A Window into the Past As part of the DASCH project at Harvard, volunteers from the American Museum of Natural History in New York City are busy converting all 1,200 logbooks of the photographs into digital format. These logs document important facts about every photograph such as right ascension, declination, exposure time, and duration. Each logbook contains up to 250 pages of information, handwritten and often in hard-to-read 19th-century cursive script. One HCO volunteer (and ATMoB member), George Champine, has photographed every page of the logs with a simple digital camera, producing some 80,000 images. Holly Barton, Supervisor of Explainer Programs at the Museum, has organized a team to transcribe these

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HARVARD COLLEGE OBSERVATORY

After scanning is completed, Harvard astronomers use a standard photometry program, SExtractor (http://sourceforge.net/projects/sextractor), to derive precise stellar position and magnitude measurements. Extensive photometry analysis is then performed using the thousands of Hubble Guide Star catalog stars found on each plate, correcting for image distortions and blending effects. This data analysis pipeline, developed initially by Silas Laycock and now greatly extended by graduate student Sumin Tang, examines variations between each exposure by comparing thousands of stars on that plate and others of the same field to average out differences due to atmospheric seeing, exposure times, and other conditions. This process yields precise measurements to 0.1 magnitude and positional measurements for each star. The resulting analysis of the typical 500 to 2,000 plates of any given field then yields light curves and proper motions for every star scanned. One of the first regions scanned was of the open cluster M44 (the Beehive), chosen because it provides a well-studied and calibrated field. Each DASCH plate is centered on an object or region of interest, but given the plate sizes, they typically include the surrounding area extending over some 20 to 40 degrees. Hundreds of newly discovered variables were found in this first field. A discovery by Tang, soon to be published in the Astrophysical Journal, reveals a previously unknown type of variability in K giant stars, not readily explained by current stellar evolution models.

STEPHEN LIEBER (4)

Old Data Yield New Discoveries

photos. They usually work at home over the internet and carefully input the data to an online spreadsheet. Later, Barton will proof any areas that were difficult to read. The volunteers examining these books have a unique window into the bygone world of the remote HCO observers. They see the dedication of the many astronomers who worked hard in order to produce the plates. Barton notes, “They were out there on December 24 and Christmas day, knowing that they wouldn’t see the results of their work.” The images would be analyzed by others, and over time would be used by future generations of astronomers. The Harvard staff must also be able to correctly identify where the various telescopes were pointed for each plate. While most of the later logbooks contain very specific data, the earlier books are more difficult because the astronomer at the telescope would often write down only the facts he thought were important — often not in a standardized format, or even accurately. The time might have been recorded using Universal Time, Local Sk yandTelescope.com

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Pro-Am Collaboration

HARVARD COLLEGE OBSERVATORY

Custom software can remove flaws such as the scratches on this plate of Baade’s Window. More information, including a searchable index of the complete plate logbooks, is available at http://hea-www.harvard.edu/ DASCH/index.php.

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Time, or Local Sidereal Time. Los says of one set of notes, “If we interpret these literally, then the image must have been taken in the middle of the day. On others, the entry implies that the telescope was pointed at the ground.” Fortunately, an online computer program at www. astrometry.net can analyze astrophotos to provide positional data. This service identifies the coordinates of any image regardless of scale or orientation, even if the image is mirror-reversed. Los has incorporated Astrometry.net into the DASCH pipeline for an initial coordinate determination for each plate and a check on its recorded exposure time. Finer coordinates are then derived for each scanned image (using software from Doug Mink), which remove plate distortion effects, and allow stars found with SExtractor to be matched to known stars. Astrometry.net was originally produced to solve for coordinates for some “lost” Sloan Digital Sky Survey images. It’s now so accurate that the authors claim close to a 100% success rate in recovering positional data. Soon amateurs will also be able to use this free service, opening many collections of astrophotos to researchers worldwide. New York University professor David W. Hogg, one of the project’s developers, explains, “We have only one sky: this makes our project possible. We have only a brief period of time in which we have been observing it. This makes our project necessary.” With NSF support, DASCH is in the fi nal stages of software and hardware development. Thus far, only 1.5% of the Harvard plates have been scanned. The full project will require a staff of 6 to 8 operators and software engineers. Once DASCH is completed it will affect virtually every field of study within astronomy. Having access to a century of data allows entirely new types of research to be done on poorly explored time scales, relevant, for example, to the masses of black holes in distant quasars or to the orbits of nearby asteroids. DASCH will make its scans and derived light curves available on the web for ready access to images or even movies of the temporal universe. It will take another 90 years before modern sky surveys have the duration of coverage of the Harvard Surveys. Thanks to the help of these generous amateurs and volunteers contributing to DASCH, researchers will soon have a massive photographic database available to them that has been digitally generated from some of the oldest images in astronomy. ✦ Stephen Lieber is a member of the Astronomical Society of Long Island and observes with his 17.5-inch reflector.

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the growing cadre of observers working with high-end telescopes to measure the brightnesses of st stars for the American Association of Variable Star Observers. But only recently has this 55-year-old labeled himself an amateur astronomer. For more than 20 years Mogul worked as a flight attendant, mainly covering northern routes between the U.S. and Europe. His interest in astronomy was inspired by occasional work breaks when he’d marvel at the Milky Way and aurorae through cockpit windows. Mogul’s initiation as a “real” amateur happened barely two years ago, after he suffered a disabling accident that left him bedridden about 20 hours a day. Mogul says that astronomy has saved his life intellectually; that alone makes his story fascinating. But it’s even more so when you learn that this talented observer doesn’t own a telescope. Instead, he rents telescope time at web-based observatories around the world, planning and executing all of his observations from a home computer. 36 worldmags

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LIGHTBUCKETS

Ken Mogul of Newnan, Georg Georgia, is among

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A web-based observatory (WBO) is an internet tool that makes high-end observing equipment available to the public. Whether you are a beginner, a seasoned astrophotographer, a science teacher, or a researcher, there are WBO services available for your needs. WBOs are the logical melding of today’s astro-imaging technology and widespread high-speed internet access. Computer-controlled CCD cameras entered the amateur scene about 20 years ago, followed soon after by computerized Go To telescope mounts. By the turn of the century software developers had created the necessary automation for observers to set up high-end observatories that could be remotely operated over the internet. WBOs make this technology available, for a modest fee, to any computer user with internet access. WBOs offer lots of benefits. Like me, many amateurs live in light-polluted suburban areas. I image from my backyard, but my best work is done by transporting my equipment to locations away from city lights. The WBOs I sampled for this story are in the kinds of locations most of us only dream about. They tend to be at higher elevations, very far from city lights, and experience good year-round weather. Some have telescopes in the Southern Hemisphere, giving me a chance to image many fascinating objects that can’t be seen from my home in California. And I can do it with premium equipment. On those occasions when I’ve traveled south of the equator, I’ve been limited to carrying little more than a small telescope or a good pair of binoculars. With WBOs, there’s no equipment to transport or set up, and weather is only an issue for time-sensitive observations. But given the geographic distribution of the telescopes, it might be possible to have at least one under a clear sky at the right time. Indeed, some WBOs legitimately claim to have 24/7 dark-sky access, as well as policies that allow users to work around poor weather conditions without incurring extra costs. WBOs offer a bridge for beginner and intermediate observers by making high-quality equipment available without the risk of a substantial investment. Beginners can start with easy imaging modes that produce good results, and then transition to more advanced imaging as they develop the necessary skills. The experience can be far less frustrating than starting out with a lot of new gear that you have to set up and master on your own. There’s also an advantage for those of us who are already seasoned astro-imagers and want to try our skills on very high-end equipment. This reflects on my own experience, since I’ve often wondered what images I could produce with a top-notch telescope at a premier

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site. WBOs provide that opportunity. They don’t replace my telescopes, but they put another tool in my toolkit, while also extending my reach to celestial objects located anywhere in the sky. The cost varies according to what you want to do, and there are a variety of payment plans. Some services require an annual fee. Others have you purchase points that are used to schedule observations. In some cases you request that an image be made with parameters you select, but the WBO maintains the freedom to queue your observation to its own schedule. And there are WBOs that allow direct, real-time control of the telescope and imaging equipment. What follows is an overview of four WBOs based on my own experiences using them.

Slooh Mike Paolucci, an experienced internet entrepreneur, founded Slooh in 2002 with the idea of creating a userfriendly observatory that anyone with web access could use. It’s an affordable service with a simple user interface that’s particularly well suited for beginning astro-imagers.

SLOOH

Web-Based Observatories

You can hear more about Mogul’s story in an interview he did with astronomer Doug Welsh, available as a Slacker Astronomy podcast at www.slackerastronomy.org/shows/081224-sa.mp3.

Current web-based observatories are located under skies that most amateur astronomers only dream about. These domes for Slooh’s telescopes in the Canary Islands share the same sky as adjacent world-class professional observatories.

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March 2010 37

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Remote Astronomy

It’s also a good service for children, and Slooh has been focusing it efforts on attracting a youthful audience with its “Slooh Kids” program. It provides online tutorials aimed at stimulating a child’s interest in and understanding of astronomy. Combined with live access to the observatories, Slooh is an excellent introductory experience. For about $15 you can purchase 100 minutes of access time, or there’s an unlimited annual subscription available for about $50. Slooh has four observatories. Two are in the Canary Islands off the northwest coast of Africa; the others are at Mount Dehesa in Chile and the Macedon Ranges in southern Australia. The available telescopes range from a 77-mm apochromatic refractor for wide-field imaging to a 20-inch Dall-Kirkham Cassegrain for deep-sky work. Although Slooh doesn’t give you exclusive access to an observatory, it’s a “live” experience. Users can access any observatory that is online and imaging. You can follow the progress of the images as they are acquired and save them in your own gallery or download them to your own computer.

Slooh refers to its imaging sessions as missions, and you can browse through the website’s Mission Schedule to see if there’s already a plan to observe an object you’d like to image. If there is, then you simply need to be at your computer at the appropriate time to be part of that mission. When you’re online with an observatory you have no indication if the telescope is being shared simultaneously by others. If your object of interest isn’t already on the schedule, or if you want to image it at a different time, then you use the website’s Reserve Mission page to schedule your own time slot. Other pages provide a real-time day/night map showing the observatories and their weather conditions. You can cancel a reserved mission if the weather doesn’t look favorable. Slooh’s observing method works because most of the imaging details are handled by the observatory. You select only the object, time, and high or low magnification for your observation. The observatory controls the exposure time (maximum is 5 minutes) and whether the image will be color or monochrome.

LightBuckets

ANDY MACICA

Steve Cullen, founder and CEO of LightBuckets, retired to the small town of Rodeo, New Mexico, after a successful technology career in California. Far from city lights and at an elevation of 4,000 feet, Rodeo was an ideal location for Cullen to build a personal observatory for his 24-inch Ritchey-Chrétien reflector. As the telescope was being hoisted into the dome, Steve thought to himself, “Wouldn’t it be cool if other people could use a telescope like this?” Thus the inspiration for LightBuckets was born. This WBO currently has five telescopes available. In addition to the 24-inch, users can access a 12½-inch Ritchey-Chrétien and an 8-inch wide-field Newtonian in Rodeo and 14½- and 16-inch Ritchey-Chrétien telescopes in Australia. There are plans to bring more scopes online in the Northern and Southern Hemispheres. The LightBuckets home page provides details on all of its equipment. Navigating LightBuckets’ recently redesigned website is very straightforward, and the Support page provides detailed help if you

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March 2010 sky & telescope

Observing with Slooh’s telescopes is a “live” experience; users can log onto any telescope currently operating and follow the progress of images as they are captured. The observatory maintains a detailed schedule of upcoming imaging “missions,” and users can participate in those scheduled by others as well as ones they plan themselves. At left is the author’s Slooh image of the nebulous complex NGC 3324 deep in the southern constellation Carina.

JIM WOOD AND EMANUELE COLOGNATO

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The LightBuckets user interface has star charts that aid in setting up images. This narrowband view of Crescent Nebula, NGC 6888, was captured with the scope pictured below.

need it. You begin by submitting an observing plan, and LightBuckets responds with e-mail status reports telling you when the plan is started, when it’s completed, if it needs to be rescheduled, and when your images are available for downloading. You pay for the observations with points purchased at the website. For beginners, there’s LightBuckets Easy Imaging. You specify a target, whether the image is to be color or monochrome, and the amount of detail recorded (based on a

scale of 0 to 10, with 10 requiring the longest exposures). Before you submit the plan, you’re given an estimate of the exposure time and the number of points deducted from your account. For these simple plans, LightBuckets handles the technical details of which telescope and what specific imaging parameters are used. For experienced astro-imagers, there’s the Use Telescopes option that gives you more control of the imaging session. You get to select the telescope, whether you or the observatory queues the observation to a particular time, and the exposures parameters, including duration, filter, binning, and number of images to make in a sequence. There’s even a star chart displayed for your object showing the CCD camera’s field of view to aid in framing and selecting a guide star. You get immediate feedback on the points that will be deducted from your account. Once the plan is submitted, you can monitor its status on the website.

LIGHTBUCKETS

Global Rent-A-Scope

The largest LightBuckets instrument currently online is this RCOS 24-inch f/8 Ritchey-Chrétien reflector in New Mexico, fitted with a large-format CCD camera.

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Arnie Rosner, the founder of Global Rent-A-Scope (GRAS), lives near Los Angeles, California, where observing conditions make it difficult to pursue a passion for astronomy. Others with this problem have built their own remotely operated observatories. But rather than an individual incurring the expense of a remote setup, Rosner envisioned an astronomers’ cooperative that would pool resources and share expenses. This was the motivation behind GRAS, which currently has 13 telescopes online. Sk yandTelescope.com

March 2010 39

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GLOBAL RENT-A-SCOPE

Remote Astronomy

In addition to its 14½-inch Ritchey-Chrétien reflector (right), Cherry Mountian Observatory maintains two 10-inch Schmidt-Cassegrain telescopes for video and webcam imaging. The Horsehead Nebula in Orion was captured with one of the observatory’s refractors.

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March 2010 sky & telescope

always controls the schedule for the imaging session. The website provides current weather information at the observatories as well as telescope status and availability. For the novice astro-imager there’s One Click Image. With this mode you’re presented a list of currently visible objects and their details, including their current elevations above the horizon. You simply pick an object from the list and the telescope slews to it and takes a 5-minute exposure. There are more advanced modes that let you specify details such as exposure duration, fi lter, and camera binning. In all cases you are able to monitor the real-time status of the exposure and see the image as soon as it’s finished. For seasoned astro-imagers and researchers, there are three GRAS modes of operation that I’ll cover briefly. One is to submit a plan that you prepare with the Astronomer’s Control Panel (ACP) scripting language. The plan

CHERRY MOUNTIAN OBSERVATORY

DAVID PLESKO AND WARREN KELLER / CHERRY MOUNTAIN OBSERVATORY

Seven are in Moorook, Australia, and another six are in Mayhill, New Mexico. They range from 16-inch Ritchey-Chrétien and 12-inch Dall-Kirkham reflectors to 4.2-inch refractors for wide-field imaging. Users set up an account with GRAS and purchase points on an as-needed basis or with a monthly subscription plan. The website makes it easy to understand how many points per hour are required for each telescope, as well as how much time you’d have available on a particular instrument based on your current account balance. GRAS provides many modes of operation. You can go live to any available telescope, make a reservation to go live at some later time, or submit a plan that will execute automatically at a specific time in the future. The user

JOHN GLEASON

This menagerie of telescopes in New Mexico is only part of the selection available from Global Rent-A-Scope. In addition to narrowband filters used to make the image of the Large Magellanic Cloud at right, this observatory also has setups for UBVRI photometric observations, complete with integrated analysis software.

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Web-based Observatories Compared For more information about the online observatories mentioned in this article, you can visit their websites: slooh.com, lightbuckets.com, global-rent-a-scope.com, and cherrymountainobservatory.com.

Slooh

LightBuckets

Global Rent-A-Scope

Cherry Mt. Obs.

Telescopes 10-inch and larger

4

4

8

3

Wide-field telescopes

4

1

5

2

Northern-Hemisphere sites

1

1

2

1

Southern-Hemisphere sites

2

2

1

0

can be executed immediately (if the Easy mode Yes Yes Yes No telescope is available), or run at a Advanced mode No Yes Yes Yes specified time in the future. ScriptDirect control No No Yes Yes ing makes it easy to image multiple objects in a single session. Schedule for later (unattended) No Yes Yes Yes Another mode of operation Live monitoring Yes Yes Yes Yes lets you make detailed brightness measurements with telescopes at Color imaging Yes Yes Yes Yes both GRAS observatories that are Monochrome imaging Yes Yes Yes Yes equipped with special UBVRI fi lters. The photometry analysis is done with Narrowband imaging No Yes Yes Yes Photometrica, software developed Photometry No V filter UBVRI filters No by Geir Klingenberg of Norway. A Exclusive ownership of data No Yes Yes Yes researcher submits a scripted plan, and the images are automatically Data formats BMP, JPEG, FITS, FITS, JPEG, FITS, calibrated with bias, dark, and flatPNG FITS calibration FITS calibration FITS calibration field images before being uploaded Approximate cost $50/year $35/hour* $37/hour Negotiated to a Photometrica FTP site. The (12- to 15-inch telescope) researcher can then activate the pro*Promotional discount rates are in effect in early 2010; check website for details. gram to generate light curves for the objects of interest. GRAS also offers Direct Control, which lets you slew the telescope, focus the camera, set apart from the other WBOs. A video session can be broadup autoguiding, and have full control of the CCD camcast to a web service for sharing with multiple users. era. Reserving a telescope for direct control needs to be The observatory primarily caters to intermediate coordinated with the observatory staff in advance. When and advanced users, as well as researchers. While the you’re operating a telescope with Direct Control, your website has detailed information about the equipment computer screen looks very much like what you’d see at available, all plans for using it are negotiated via e-mail the telescope, with desktop icons for applications such and/or telephone. It’s an iterative process. You work with as Diff raction Limited’s MaximDL, Software Bisque’s the observatory staff to define your imaging goals, and TheSky, and FocusMax. You simply launch these applica- the staff responds with a proposed plan tailored to your tions and use them to operate the telescope. needs. This process is free. When everyone agrees to the plan, you pay for its execution through a PayPal account. Cherry Mountain Observatory The observatory staff then schedules and executes the plan and sends you an e-mail with details for downloadDavid Plesko founded Cherry Mountain Observatory in ing the image data from a private FTP site. Fredericksburg, Texas, after a successful 20-year busiWhether you simply want to dabble, shoot astrophotos ness in computer technology. The dark skies coupled with for fun, or gather data for advanced research projects, Plesko’s childhood passion for astronomy and science there are telescopes available for online rental that can were driving forces behind the project, and he subsehelp you out. Your personal window on the universe is quently expanded his goals to make the observatory open just a few mouse clicks away. ✦ to the public. Cherry Mountain Observatory has five telescopes ranging from a 14½-inch Ritchey-Chrétien reflector to a 4-inch Observer and astro-imager Andy Macica is an engineer workrefractor. It also has two 10-inch Schmidt-Cassegrain ing on machine-vision systems. He frequently volunteers at reflectors equipped with video and webcams, which sets it Lick Observatory near his home in San Jose, California.

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Sk yandTelescope.com

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Fred Schaaf Northern Hemisphere’s Sky

The Sky Above Us It’s time to celebrate the tent that encompasses all humanity. Last month here, I mentioned my idea for an

AKIRA FUJII

International Decade of the Sky: 2011–2020. There are several ways to explain what this event might be like. Let’s start by comparing it to 2009’s International Year of Astronomy (IYA). A year of astronomy to a decade of sky. We all hope that the phenomenally successful IYA programs will continue through 2010. But don’t we need some coordinated planning to guarantee that they will go on for many years to come? We could extend and expand some of the IYA’s good programs and ideas by bringing them under the umbrella of a formalized, structured — and highly publicized — International Decade of the Sky. I also see some marvelous differences between IYA and the Decade of the Sky. Most amateur astronomers find the science of astronomy enthralling — and science goes with observation as the mind goes with the eye. Still, a Decade of the Sky could be more largely dedicated than IYA was to seeing and experiencing. The science of astronomy concentrates on understanding the universe, but the sky

The five central stars of the Big Dipper are the core of the Ursa Major Group. It’s the closest true physical star grouping to Earth, but it doesn’t quite qualify as a gravitationally bound cluster.

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March 2010 sky & telescope

is the wonder filled with wonders that we can all experience first-hand. Science can always use help. But in an age when light pollution separates people from the stars, and social and entertainment media lure many people — especially young ones — away from interacting with nature, a decade-long movement to bring folks back to the sky is desperately needed. I also see the International Decade of the Sky as the perfect opportunity for amateur astronomers to join together with two other huge groups who are devoted to the sky: birders and weather watchers. And even they are only a small part of the vast audience (or, to coin a word, a vidience, meaning a body of watchers) that could benefit from a connection with the sky and its inspiration. Open season on open clusters. What uplifting astronomical sights are offered by the sky of March evenings? For just a little longer, winter’s fantastic richness of open clusters is available to us — plus a few huge naked-eye open clusters of spring. It’s well-known among amateur astronomers that winter’s mostly dim ribbon of Milky Way is richly loaded with open clusters. But have you ever noticed that four of the five clusters closest to Earth are located to either side of winter Milky Way? The Pleiades and Hyades are on the west side of the band, while the Ursa Major Group and the Beehive Cluster (M44) are on the east. On March evenings, the fifth of the close groupings — the Coma Star Cluster in Coma Berenices — is also looming into view a third of the way up the eastern sky. The new season of galaxies galore. What’s arriving to take the place of all the departing winter clusters? Something the winter constellations largely lack: galaxies. The queen of galaxies, the Great Galaxy in Andromeda (M31), is about to set in the northwest at the time of our map. But in replacement comes a throng of galaxies ascending in the east. Leo and Ursa Major offer several groups of galaxies, but the most amazingly rich cluster of all is below them. It speckles parts of Coma Berenices and the northwestern region of Virgo with what telescopes show as a veritable blizzard — a spring blizzard — of glowing wisps and swirls of light. ✦ Fred Schaaf welcomes your comments at [email protected].

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Sky at a Glance

March 2010 MOON PHASES SUN

MON

TUE

WED

1

THU

FRI

SAT

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

2–17

Mercury

W

Venus

W

Mars

E

DAWN: Spica is 4° to 6° above the Moon (for North America).

7

DAWN: Antares is 4° to 6° right of the Moon; see page 48.

SUNRISE ▶

14

DAYLIGHT-SAVING TIME begins at 2 a.m. for most of the U.S. and Canada.

15

NEW MOON (5:01 p.m. EDT).

Visible March 23 through April 17

E

16, 17

NW Visible starting March 26

Jupiter Saturn

LAST-QUARTER MOON (10:42 a.m. EST).

MIDNIGHT

S

EVENING: This is a good time to view the zodiacal light from dark sites at midnorthern latitudes. A tall, tilted pyramid of pearly light should appear above the fading western twilight. Start looking about 80 minutes after sunset.

3

PLANET VISIBILITY ◀ SUNSET

EVENING: Saturn is 8° left of the rising, just-past-full Moon for observers in North America.

S

E W

20

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

DUSK: A very thin crescent Moon should be visible a half hour after sunset in North America 6° or 7° lower right of Venus on the 16th, and 10° above Venus on the 17th, as shown on page 48. SPRING BEGINS in the Northern Hemisphere at the equinox, 1:32 p.m. EDT. EVENING: The waxing crescent Moon is very close to the Pleiades. It passes through the southernmost fringe of the cluster starting around 9 p.m. EDT for observers in the eastern U.S., and covers some of the bright Pleiads for parts of Latin America. See page 56 for more information.

21–22

ALL NIGHT: Saturn is at opposition, rising around sunset and setting around sunrise.

23

FIRST-QUARTER MOON (7:00 a.m. EDT).

23–25

EVENING: The Moon passes beneath the arc formed high in the south by Mars, Pollux, and Castor (left to right).

29

FULL MOON (10:25 p.m EDT).

Mar 30 DUSK: Mercury is easy to see 30 to 45 –April 6 minutes after sunset. Look low in the west, 3° to 4° lower right of Venus.

Venus appeared low at dusk in March 2009, as it will again this

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

year. Note the zodiacal light reaching up slightly left of the Pleiades. IMAGE BY TUNÇ TEZEL

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March 2010 43

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Facing North

Northern Hemisphere Sky Chart

20h G

+60°

h

M

23

B

A

E Z

D

D

M

31

A

B

SS

c Fa L

E

H

B

A

U

in

S

+80° G

G

G

D

Polaris

E

B

URSA MINOR

A

Th

uba

n

A

C

G

B

S

Al

A

ard

T E

O

R

R V

D

U

R

in

0 1 2 3 Star 4 magnitudes

44 March 2010 sky & telescope

AN

PYXI S TL IA

LU

B

M

G

U NG

M

ol

A

RI

R E P E

Z

s

B

42

B

B

el

g

Ri

K M

A

A

M41 D

B

B

P LE

S NI CA JOR E M A

CO

B

P

–40°

8h

Facing South

TAU RU S

es Hyad

A

R

H

Z

Pleiade

Z

aran Aldeb

Z

O

U E Q

D

M

A

VEL A

E

5

Be

G

N

Sirius

–20°

S

c Fa

A

g tel

IO

K

M46

A

e

A

M47

Y

A

s eu

M50

M48

ph

M93

11h

M3

NGC 2244

x

tri

lla

Be

X

A

A

B

7 M3

7

C1

L

EROS MONOC

R

C

H

Alg

U Q

e

E

2 H C

M G

C A N I SR MINO

M6

Z

I

X LYN

A

kl

N

B

E

S ella B

6 A M3 38 M H

GA RI AU

Cap

+60° I

M

B

E

D

+20°

CE R

I

cyon 0° Pro

A

S

B

Y

B

T

G

M81 M82

G

c A Si LEO MINOR G s ulu O Reg LE

G

X

A

P

A

D

N

4

IN

M GE

G

SE

ELO

B Di ig pp er

U M R A SA JO R

A

COMA BERENICES

VIRGO

M4

A

E

CAM

+80°

LIS

E

ARD A

Z M & izar Alc or

1

M5

CAN ES V E N ATI CI

B

A E

S

B

D

Moon Mar 26

Moon Mar 29

34

H

le ub er Do lust C

G

M3

T

CA N

G

A

llux

Po

Mars

A

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CA

C

Z

M5 2

A

R

Ö H

Saturn

–1

EI

E

B

BO TE S

E A

s

E

E

n Moo 22 Mar

tor

Ca

I

Z

Q

g

IO P

H

O AC DR

D

CE PH EU S

17 h

g

N E urus

Arct

h

14

Facing East

D

B

Zenith

PUPPIS

LU B

M A

U

BA

S

5h

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N

in

g

c Fa

Using the Map

Binocular Highlight:

WHEN

Circumpolar Messiers

Late January

Midnight

Early February

11 p.m.

Late February

10 p.m.

Early March

9 p.m.

Late March

Dusk

W

D

R

O

M

These are standard times.

B

G

ES ARI A

A

ES SC I P

3 M3

B

A

N

HOW

h

2

S

R

ER ID

G

AN

D

U

E

O AT

CETU S

A

G

O

X

Facing West

on Mo r 19 a M C T I P L I E C

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 a little so that “Facing SW” is at the bottom. Nearly halfway from there to the map’s center is the constellation Orion. Go out, face southwest, and look halfway up the sky. There’s Orion! 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. Saturn and Mars are positioned for mid-March.

The most northerly objects in the Messier catalog are M81 and M82 in Ursa Major. With declinations of 69° 04′ and 69° 41′ respectively, these galaxies are circumpolar objects (visible any time of night throughout the year) for observers throughout Canada, Europe, and the United States. And in addition to being readily available, the duo forms one of the most interesting and attractive galaxy pairings in the sky. M81 and 82 are situated in a fairly barren patch of sky, some 10° from the nearest bright star. The simplest way to locate them is to use Alpha (α) and Gamma (γ) Ursae Majoris in the bowl of the Dipper as pointer stars. To find the target field, draw a diagonal line from Gamma to Alpha and extend that line the distance between those stars. The galaxies are separated by only ½°, and their apparent proximity is no illusion. They are gravitationally linked and reside together some 12 million light-years from Earth. Under suburban skies, I can see only 7.3-magnitude M81 in my 7×50s. The higher magnification of 10×50s adds 8.9-magnitude M82 to the picture, though with some difficulty. Under darker skies, though, both galaxies are readily apparent even in 7×50s as small, soft glows. Anyone who has seen photographs of these galaxies knows that they’re very different from each other. While M81 is an elegant spiral, M82 is an irregular, elongated object. Surprisingly, their general shapes can be discerned in binoculars. You’ll need mounted (or image-stabilized) binos that magnify 10× to 15×, but under good conditions, you can tell which galaxy is which by its appearance. And that’s pretty cool at any time of the year. ✦ — Gary Seronik

DRACO L

M82

g

SW

M81

ci Fa

n

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Galaxy

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

5°

binocular view

Double star Variable star Open cluster Diffuse nebula Globular cluster

A URSA MAJOR

Planetary nebula

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March 2010 45

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Planetary Almanac

Planetary Almanac, March 2010

Mercury

March

11

Mar 1

21

31

Sun

1

31

16

Mars

Magnitude

Diameter

Illumination

Distance

–7° 46′

—

–26.8

32′ 17″

—

0.991

+3° 58′

—

–26.8

32′ 02″

—

0.999

–13° 52′

11° Mo

–0.7

4.9″

95%

1.358

23h 14.6m

–6° 52′

4° Mo

–1.6

4.9″

99%

1.369

0h 25.0m

m

h

m

h

m

11 21

0 36.9 22 07.2

1

+1° 58′

6° Ev

–1.6

5.2″

97%

1.299

h

m

+11° 03′

16° Ev

–1.0

6.1″

74%

1.110

h

m

–4° 33′

12° Ev

–3.9

10.0″

98%

1.668

11

0h 17.3m

+0° 34′

14° Ev

–3.9

10.1″

97%

1.647

21

1h 02.6m

31 Venus

1

16

31

Jupiter

1 33.4

23 31.8

1

+5° 41′

17° Ev

–3.9

10.3″

96%

1.621

h

m

+10° 35′

19° Ev

–3.9

10.5″

95%

1.590

1

h

8 15.6

m

+23° 52′

140° Ev

–0.6

12.1″

96%

0.773

16

8h 13.2m

+23° 27′

125° Ev

–0.2

10.6″

94%

0.881

31

8h 21.7m

31 Mars

Jupiter

16

Saturn

Saturn Uranus

Declination

22 46.7

31 Mercury

Elongation

h

1

Venus

Right Ascension

1 48.4

+22° 28′

112° Ev

+0.1

9.3″

92%

1.006

h

m

–8° 47′

1° Mo

–2.0

33.0″

100%

5.981

31

h

23 13.2

m

–6° 05′

23° Mo

–2.0

33.5″

100%

5.887

1

12h 14.0m

+1° 14′

157° Mo

+0.6

19.4″

100%

8.571

31

12h 05.7m

1

22 46.5

16

+2° 11′

170° Ev

+0.6

19.5″

100%

8.517

h

m

–2° 06′

1° Ev

+5.9

3.3″

100%

21.090

h

m

23 47.8

Neptune

16

21 57.8

–12° 53′

28° Mo

+8.0

2.2″

100%

30.896

Pluto

16

18h 21.6m

–18° 14′

80° Mo

+14.0

0.1″

100%

31.958

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

+40°

Planet disks at left have south up, to match the view in many telescopes. The blue ticks indicate the pole currently tilted toward Earth.

10"

22h

20 h

16 h

18h Vega

+30° +20°

CYGNUS

12h

10 h

Mars 25

LEO

A QUILA

+10°

OPHIUCHUS

VIRGO

8h 6h RIGHT ASCENSION Castor Pollux

Arcturus

HERCULES

PEGASUS

14 h BOÖTES

Saturn

Regulus

2h

4h

22

ECL

CANCER

ARIES

19

Pleiades

GEMINI

+20°

IPT

IC

–10°

10

–20°

–40°

10 am

LIBRA

Spica

7 SAGITTARIUS 8 am

4 am

2 am

Venus Mercury

Rigel Sirius

E RIDA N US

H Y D R A CANIS MAJOR

Antares

SCORPIUS 6 am

Mar 29–30 CORVUS

4

CAPRICORNUS –30° Fomalhaut

E Q U AT O R

ORION

Pluto

+10°

TA U R U S

Betelgeuse Procyon

Jupiter AQUARIUS Neptune

0h +30°

LOCAL TIME OF TRANSIT Midnight 10 pm

8 pm

6 pm

4 pm

2 pm

DECLINATION

Pluto

–10° –20° –30° –40°

The Sun and planets are positioned for mid-March; the colored arrows show the motion of each during the month. The Moon is plotted for evening dates in the Americas when it’s 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 March 2010 sky & telescope worldmags

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FOCUS ON

Saturn’s Moons

KOHL Observatory — Lakewood, NY The ASH-DOME pictured is an 18’6”-diameter, electronically operated unit. The observatory dome shelters a 20-inch DFM computer-controlled telescope. The observatory is used for personal observing and by many local grade school, high school, college, and amateur astronomy groups.

Mar 16 0h UT

Mar 1 2

EAST

WEST

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29 30 31 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 0h (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

Saturn Parades, Mars Fades Four bright planets are visible at nightfall by the end of March. Venus shines low in the west at dusk at the beginning of March, creeping a little higher each evening. Mars dims a lot during the course of the month, but even at the end of March it’s still the brightest “star” high in the southeast as twilight fades. Saturn is visible all night long for most of the month, and Mercury peeps into sight below Venus in the west in the last week of March.

DUSK Venus starts March only 12° from the Sun. But the steep angle of the ecliptic during late-winter sunsets places Venus 5° above the western horizon a half hour after sundown for observers around latitude 40° north. All month Venus shines at the same brightness, magnitude –3.9, but it’s climbing slowly into better view. By the end of March it’s 12° high a half hour after

sunset. Telescopically, Venus is boring this month — a 10″-wide shaky round dot. On the evening of March 3rd, Uranus is less than 1° upper right of Venus, but it’s invisible in such a bright sky. Mercury passes through superior conjunction with the Sun on March 14th. By the final days of March, Mercury has climbed high enough to appear about 10° above the west horizon a half hour after sunset. On March 31st Mercury, shining at magnitude –0.9, has pulled to within 3½° lower right of Venus, and the two planets will get even closer in early April.

EVENING AND NIGHT Mars loiters in western Cancer, forming a crooked line with Gemini’s Castor and Pollux but hugely outshining them. Observers at mid-northern latitudes see the orange-yellow world high in the east

Dawn, March 6 –10

or southeast at dusk in early March, and very high in the south a little later in the evening. That’s a good thing for telescopic observers, because Mars was at opposition back on January 29th, and its disk is now dwindling as Earth leaves it behind. Mars shrinks in March from 12″ to 9″ wide, but a good telescope can still show surface features on such a small disk when it’s high and seen through a minimum of atmospheric turbulence. Mars fades by ¾ magnitude in March. But even at month’s end it shines at magnitude +0.1, matching Capella in radiance. Mars halts its retrograde (westward) motion through the stars on March 11th. It

Dusk, March 16-17

1 hour before sunrise

30 minutes after sunset Moon March 6

Moon March 7

Moon March 8 10o

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

Moon March 17

Antares

Moon March 9

SCORPIUS

Moon March 10

Venus

Cat’s Eyes

Moon March 16

S A G I T TA R I U S

Looking Southeast

Looking South

Looking West

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.

48 March 2010 sky & telescope worldmags

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December solstice

Mars

Venus March equinox

Earth Sun

Sept. equinox

Mercury

June solstice

then slowly gathers speed as it moves back eastward towards the center of Cancer and the Beehive Star Cluster (M44). On March 30th, Mars is at the aphelion (far point from the Sun) of its lopsided orbit. Saturn rises at the end of twilight as March begins. It shines high in the southeast, in the dim head of Virgo, by late evening. The ringed wonder reaches opposition to the Sun on March 21st, rising then around sunset. Opposition is about when a superior planet reaches its maximum apparent size and brightness. At this opposition Saturn is magnitude +0.5, about midway in brightness between brighter Arcturus far to Saturn’s lower left and dimmer Spica below the planet. Saturn shines highest in the middle of the night, so this is the best time to examine its 19.5″-wide globe and narrowing rings. The rings are tilted 4° from our line of sight at the start of March and 3° at month’s end. Against the background stars Saturn is retrograding slowly westward, away from Eta Virginis (Zaniah) and towards Beta Virginis (Zavijava).

DAWN Neptune and Pluto are above the horizon at dawn, but they will be much easier to observe in a few months. Jupiter passes through conjunction with the Sun on February 28th. It emerges into view extremely low in bright dawn toward the end of March; use binoculars to scan for it just above the eastern horizon 20 or 30 minutes before sunrise.

MOON PA SSAGES The Moon, just past full, rises on March 1st about 8° to the right of Saturn in early evening in the Americas. New Moon

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FPO Saturn

Uranus Jupiter Neptune Pluto

ORB IT S OF THE PL ANE T S The curved arrows show each planet’s movement during March. The outer planets don’t change position enough in a month to notice at this scale.

occurs on March 15th, and a very thin crescent is visible shortly after sunset on the 16th about 7° lower right of Venus, as shown on the facing page. On the 17th a slightly fatter crescent hovers about 10° above Venus. Early on the evening of March 20th, the thickening crescent Moon passes just left of the Pleiades as seen from much of the Americas. It occults some of the cluster’s bright stars in parts of South America and some of the faint, outlying stars in the U.S. and Canada (see page 56). On the evening of March 24th the Moon, just past first quarter, forms a roughly 8°-wide equilateral triangle with Mars and Pollux.

March 18 – 21

Moon March 21

Around 9:30 pm

Aldebaran

Hyades

Pleiades

Moon March 20

Moon March 19

ARIES

THE SUN The Sun arrives at the equinox on March 20th at 1:32 p.m. EDT, crossing the celestial equator heading north for the year. This event inaugurates spring in the Northern Hemisphere and autumn in the Southern Hemisphere. ✦

Moon March 18

Looking West Sk yandTelescope.com

March 2010 49

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Charles A. Wood Exploring the Moon

Lunar Transient Phenomena Japan’s Kaguya orbiter sheds new light on some old LTPs. On the evening of November 3, 1973, the devoted lunar observer James Bartlett noticed a feeble glow on a narrow swath of the floor of the crater Ptolemaeus, which was otherwise in complete shadow. His report ultimately ended up in a catalog of approximately 2,250 lunar transient phenomena (LTP). LTP’s have a long and controversial heritage. One of the earliest telescopic observations came from 18th-century astronomer William Herschel, who had earlier discovered Uranus. He observed an unusual brightening of the crater Aristarchus on the night of April 19, 1787. The idea of LTPs is captivating because most of the reported phenomena are brightenings or obscurations that could be manifestations of volcanism, outgassing, or other geologic processes that would imply that the Moon is not geologically dead. Confirmation of recent lunar geologic activity would force a major re-examination of our understanding of the Moon. All of the samples brought back by Apollo astronauts show that lunar volcanism was extensive about 3½ billion years ago, and died off during the next billion years. Although we have no samples from northwestern Oceanus Procellarum or Mare Smythii,

estimates of their ages based on crater counts indicates that small volcanic eruptions may have occurred in those locations as recently as 1 billion years ago. But even if there was residual activity then, scientists think the Moon has cooled so thoroughly that its mantle is now solid rock, unable to melt and feed volcanic activity. Most lunar scientists are skeptical of LTPs because the majority were visual observations by single amateurs, and can’t be confirmed by later observations. Despite 400 years of searching, there has never been a confirmed observable change on the lunar surface. There are two scientific approaches to testing the reality of LTPs. Columbia University astronomer Arlin Crotts has assembled an autonomous robotic telescope system that searches for newly occurring LTPs using video cameras. This instrument is designed to document even faint changes of surface brightness in near real time. If this system detects anything, it will be the strongest evidence yet for their reality. A second approach attempts to determine the causes of reported past LTPs. Raffaello Lena of the Geologic Lunar Research group, with the help of Anthony Cook of the

24 miles

Bright crater

B Ptolemaeus

93 miles

Flooded crater

C Oceanus Procellarum

Mare

D Mare Smythii

Mare

Phases

Distances March 7, 15:42 UT

New Moon

March 15, 21:01 UT

First quarter

March 23, 11:00 UT

Full Moon

March 30, 2:25 UT

ru

m

Mare Smythii

C B

A

D

Apogee March 12, 10h UT 252,282 miles diam. 29′ 39″ Perigee March 28, 5h UT 224,859 miles diam. 33′ 4″

S&T: DENNIS DI CICCO

Last quarter

ce

A Aristarchus

sP ro

Description anu

Size

la

Oce

Highlighted feature

l

The Moon • March 2010

Librations There are no favorable librations in March

Sk yandTelescope.com

March 2010 51

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THE NEXT GENERATION OF

ASTRONOMY

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8

British Astronomical Association, have tabulated the exact observing conditions for some of the most highly regarded LTPs. In 2003 Lena reported re-observations of the unusual brightening of the floor of Ptolemaeus, similar to Bartlett’s 1973 observation. His visual and photographic observations documented that small swaths of the floor of Ptolemaeus are illuminated temporarily while the rest remain in shadow. These results suggest that this LTP may be a rare, though predictable, lighting of the crater floor when the Sun is shining from precisely the right direction. Low gaps in crater rims, or high spots on crater floors, permit sunlight to reach the floor only at precise times in the Moon’s 18-year cycle. This was masterful detective work, showing that this LTP was totally unrelated to any geologic activity within the Moon. But it would be extremely time consuming to re-observe each of the 2,250 entries in the LTP catalog because exactly the right illumination conditions occur very infrequently. Fortunately, modern technology can now provide an easy way to re-create LTP

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52 worldmags

March 2010 sky & telescope

RAFFAELLO LENA

1/4“ CCD (60FPS) 1/3“ CCD (30FPS) 1/2“ CCD (15FPS)

LTVT Simulation

Intrepid observer Raffaello Lena used the free software Lunar Terminator Visualization Tool (LTVT), which now incorporates JAXA’s Kaguya laser altimeter measurements, enabling him to re-create the exact observing geometry for James Bartlett’s 1973 LTP observation in Ptolemaeus. At top is Lena’s drawing, compared to the simulation generated with LTVT at bottom.

S&T: SEAN WALKER

Exploring the Moon

Nearly a third of all LTP’s have been reported in the general vicinity of the crater Aristarchus at right, including one by astronaut Neil Armstrong while in lunar orbit aboard Apollo 11.

observations. The Japanese lunar orbiter Kaguya carried a laser altimeter that made more than 6 million point elevation measurements of the lunar surface. These data have been combined to create a highresolution digital elevation model (DEM) that displays the height of any spot on the lunar surface for the first time. Amateur astronomer Jim Mosher has incorporated the Kaguya DEM into his Lunar Terminator Visualization Tool (http://ltvt.wikispaces. com/LTVT) to create a three-dimensional map of the Moon that shows exactly which hills cast shadows and which low spots allow sunlight to pass unimpeded to illuminate parts of crater floors. Using LTVT, Lena has re-created the precise lighting conditions for the Ptolemaeus LTP he previously had studied at the telescope. These simulated images show the same lighting anomaly that was previously considered a LTP. Using this new technique, it’s now possible to re-create all LTP observations to see which result from normal play of sunlight over lunar terrain, and which must have other explanations. Finally, Bartlett’s observations have been proven accurate. Perhaps other LTP observations may tell us more about the great skill of observers than about volcanic processes on the Moon. ✦ To get a daily lunar fix, visit contributing editor Charles Wood’s Lunar Photo of the Day website: lpod.wikispaces.com.

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www.InSightCruises.com/Sky-talks Capturing the Light: The Night Sky — In this

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.

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

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 Byline.column Rubric Calendar Celestial

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Lunar Occultations in 2010 The fastest action in astronomy happens often on the Moon’s edge.

The Moon, in its monthly travels around the sky, often passes in front of moderately bright stars. These lunar occultations are fascinating to watch in a telescope. But if you want really bright examples, the pickings this year are slim. No 1st-magnitude star is occulted over land anywhere in the world from February through December, and in North America the next chance for a star that bright will be with Spica in 2013. Mars is the only planet occulted for North America this year — very deep in sunset on December 6th for a narrow band from Manitoba to the Carolinas. The two brightest stars that are occulted for our continent, both magnitude 2.9, will be Alcyone (Eta Tauri, the brightest of the Pleiades) on the evening of March 20th,

visible only from Mexico; and the red giant Mu Geminorum, on the morning of November 24th from the U.S. and Canada. But don’t be daunted. Hundreds of fainter events await, listed in the resources at the end of this article. Using these you can plan when to watch — or learn more about an occultation you just happened to luck into, when you noticed a star waiting off the Moon’s eastern side. In the tables here, the Moon’s phase is given as the percentage of the lunar disk that’s sunlit, followed by “+” for waxing and “–” for waning. Stars disappear on the Moon’s dark limb when the Moon is waxing, and reappear on the dark limb when the Moon is waning. The opposite events occur on the bright limb, where the glare of the

Major Planets Occulted in 2010 Approx. Date (UT) time (UT)

Planet

Mag.

Moon Phase

Where it is visible

May 16

12h

Venus

– 3.9

7+

n. Africa, s. Eurasia

Sept. 11

14h

Venus

–4.7

14+

e. Brazil, s. Africa (daytime)

Venus

–4.2

1–

s. Africa, w. Australia (daytime)

Mars

+1.5

1+

Manitoba to Carolinas & Cuba

Nov. 5

7

Dec. 6

h

23

h

Sigma Scorpii Occultations (close binary) Approx. Date (UT) time (UT) Feb. 7 Mar. 6

Hawaii, Mexico, s.e. U.S. (daylight)

21

57–

s. Asia; Japan (daylight)

h

80 –

e. N. America (graze: NB – n. FL)

94–

n.e. Asia, Japan

h

100

w. Europe

h

95+

n.w. North America (graze: OR – MT)

h

81+

s.w. Siberia, Mongolia

6

16h

July 21 PHIL CULHANE

34–

h

14

Apr. 3

June 24

Where it is visible

h

Apr. 30 May 28

Moon phase

1

9

14

Left: The crescent Moon was approaching a Pleiades occultation on March 22, 2007, when an airplane sliced across it — a few seconds before Phil Culhane of Kanata, Ontario, pressed the shutter to start this 2-second exposure.

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March 2010 55

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Celestial Calendar

Sky & Telescope That’s what Sky & Tel said in their 4-page review last December of the Astro-Tech AT8IN imaging Newtonian and AT6RC and AT8RC Ritchey-Chrétien astrographs.

Sky & Tel said “Astro-Tech has done a great job of balancing performance and price on all three of these imaging telescopes. By optimizing them for use with the cameras that many beginning and intermediate-level astrophotographers are using, the company has created affordable instruments that can produce stunning images. It’s an exciting time to be entering the field of deep-sky astrophotography.” AT8IN Of the Astro-Tech AT8IN 8” f/4 imaging $449 Newtonian, right, Sky & Tel said “while all three of the Astro-Tech scopes represent excellent value, the AT8IN, with its 8-inch aperture and $449 price tag, wins the biggest-bang-for-the-buck award.”

AT6RC

And Sky & Tel said the AstroTech AT6RC 6” f/9 RitcheyChrétien, a Sky & Tel Hot Product for 2009 , left, was “a superb match” to the APS-C size imaging chips used in many DSLR cameras.

About the Astro-Tech AT8RC 8” f/8 Ritchey-Chrétien, below (A Sky & Tel Hot Product for 2010, along with the $2695 10” f/8 AT10RC), Sky & Tel said “of the three scopes, I liked this one the most. Its advanced features . . . carbon fiber tube, quartz optics, and dual mounting rails (Losmandy- and Vixenstyle dovetails) . . . were part of the reason. But it was how nicely this scope is matched to APS-C and 35-mm formats that really wowed me . . . what’s not to like?”

$795

But don’t take our word for it. Ask Sky & Telescope. Remember what they said? That these “affordable” Astro-Tech astrographs, optimized exclusively for digital imaging, truly do make this “an exciting time to be entering the field of deep-sky astrophotography.”

AT8RC

$1395

ASTRO-TECH from Astronomy Technologies

Other Binaries Occulted for N. America Approx. Date (UT) time (UT)

Star

Moon Phase

Mar. 20

4

h

ε Ari

17+

s.w. U.S. (graze: OR – CO)

Apr. 16

3h

μ Ari

3+

w. N. America (graze: AB, SK)

July 7

10h

ε Ari

23 –

s. Mexico, s. FL (graze: FL)

Aug. 3

11h

μ Ari

48 –

n.w. U.S. (graze: s. BC)

Where it is visible

sunlit lunar surface overwhelms all but the brightest stars. Note that a star’s disappearance or reappearance can occur up to three hours from the approximate hour listed, depending on your location.

The Pleiades on March 20th Friday, March 20th, deserves a mark on your calendar. That evening the waxing crescent Moon will perform the last Pleiades occultation visible from North America until 2023. The waxing crescent will miss the brightest stars for most of the continent, but several outlying 5th- and 6th-magnitude Pleiads will be occulted for much of the U.S. and Canada. Some

Minima of Algol Feb.

UT

Mar.

UT

2

9:07

3

1:20

5

5:56

5

22:10

8

2:45

8

18:59

10

23:35

11

15:48

13

20:24

14

12:38

16

17:14

17

9:27

19

14:03

20

6:17

22

10:52

23

3:06

25

7:42

25

23:55

28

4:31

28

20:44

31

17:34

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 riders.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 11/1/09. All prices plus freight.

56 worldmags

March 2010 sky & telescope

These geocentric predictions are from the new heliocentric elements Min. = JD 2452253.559 + 2.867362E, where E is any integer. Derived by Gerry Samolyk (AAVSO Eclipsing Binary Section), they reflect a slight lengthening in the star’s period that seems to have occurred in early 2000. For more about this star and its eclipses, visit SkyandTelescope.com/algol.

of these will have grazing occultations along the Moon’s dark northern limb. For example, a graze of 6.2-magnitude ZC 564 will be visible from a line passing near Calgary, Minneapolis, Milwaukee, Cleveland, Pittsburgh, and Baltimore. You’re invited to join observing expeditions by the International Occultation Timing Association that will probably be held for this event near most of these cities.

For Complete Information • Timetables: Many more occultation predictions for less-bright stars, with times for when they should disappear and reappear on the Moon’s edge as seen from your location, are at the International Occultation Timing Association’s site, www.lunar-occultations.com/iota. There you can download the free Occult program to create full, detailed predictions for your exact location. • Grazing-occultation maps: Go to iota.jhuapl.edu/grazemap.htm. Detailed interactive maps of some of the better North American graze paths are at Brad Timerson’s site, www.timerson.net/IOTA. • Asteroid occultations: The main page (with links to predictions, observing methods, reporting, and past results) is at www .asteroidoccultation.com/observations. • Timing methods: Go to iota.jhuapl .edu/timng920.htm. • Online book: Lots about observing occultations of every type is in Chasing the Shadow: The IOTA Occultation Observer’s Manual, available free at www.poyntsource .com/IOTAmanual/Preview.htm. • E-mail alerts: To receive Sky & Telescope’s AstroAlerts for important occultations, both lunar and asteroidal, sign up at SkyandTelescope.com/AstroAlert. — David W. Dunham

S&T: DENNIS DICICCO

“. . . ideal for today’s digital astrophotographers.”

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Sirius B Continues To Widen x 2025 x x 2020

2030

North

2035

6˝

4˝

Orbit of Sirius B 2015

East

Sirius and its faint but famous whitedwarf companion are now 9.1˝ apart, compared to 8.2˝ two years ago — still a very tough telescopic challenge. Sirius B is now exactly east of Sirius A. To try to detect it through the primary’s overwhelming glare, seize upon a night of excellent seeing, try when Sirius is highest in the south, turn your scope so that any diffraction spikes are off the east-west direction, and beware of internal eyepiece reflections. Practice on Rigel, which has an easier companion at the same distance (to its south-southwest). For more, see the February 2008 issue, page 33.

2˝

2012 2010 10˝

Sirius A 8˝

2009 2008 2007 2006

6˝

4˝

2˝ 2˝

2004 2002

2000

1998

4˝

An Asteroid Occultation for Binoculars On Tuesday night, February 2–3 (when most readers will have this issue), select viewers can watch the 6.3-magnitude star 14 Tauri near the Pleiades blink out in a black sky for up to 4 seconds, as the invisibly faint little asteroid 1248 Jugurtha passes in front of it. The 25-mile-wide occultation path should run roughly from Wichita, Kansas, through the Chicago area, northern Michigan, Labrador, England, Belgium, and Germany. The event happens in early evening for

North America and the middle of the night for Europe. Path maps and other details are available at www.AsteroidOccultation.com; scroll down to Feb. 3, Jugurtha, and click the “details” column. IOTA seeks timings of this and other asteroidal occultations, primarily to determine the sizes and shapes of the asteroids by reconstructing the silhouettes of their shadows. ✦

Pleiades

14 Tauri

AKIRA FUJII

Hyades

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Aldebaran

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March 2010 57

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New Product Showcase

WHEEL Every amateur astronomer inevitably is asked why the Moon is sometimes visible in daylight or why it’s not visible at night. Now there’s a clever tool by author Bob Crelin to help introduce the uninitiated to the phases of our Moon: the Moon Gazers’ Wheel ($4.95). This handy field guide teaches users how to identify the Moon’s phase by matching its appearance to the illustration on the wheel. When the phases match, the Moon Gazers’ Wheel also tells you when the Moon rises and sets, its position in its orbit around Earth, and the day of the lunar month. Charlesbridge Publishing www.charlesbridge.com

S &T : SE

AN

WA LK

ER

▾ MOON

S&T: SEAN WALKER

▴ EXOPLANET FILTER Amateur astronomers are increasingly becoming involved with the exciting field of exoplanet research. The new XOP-BB filter ($175) can help. It is a joint creation of Adirondack Astronomy and Astrodon filters, with input from exoplanet hunter Bruce Gary. The filter transmits light from 490 nanometers through the near infrared with transmission of over 90%, allowing users to better monitor stars throughout an entire evening to record the minute dimming of the star’s light as a large planet moves across its face. By blocking the blue end of the spectrum below 490 nanometers, the filter can minimize photometric problems associated with short spectral wavelengths such as atmospheric extinction near the horizon. The XOP-BB filter is ideal for planet hunters using red-biased, high-quantumefficiency CCD cameras such as those manufactured with Kodak detectors. Adirondack Astronomy 72 Harrison Ave., Hudson Falls, NY 12839 877-348-8433 www.astrovid.com

S&

D T:

EN

S NI

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 nps@ SkyandTelescope.com. Not all announcements can be listed.

58 March 2010 sky & telescope worldmags

DI

CI

CC

O

◀ GIANT BINOCULARS APM America now carries the APM 150mm 45º Binocular ($3,875). This beefy pair of optics feature 150-millimeter f/5.5 triplet objectives with BaK 4 prisms that will treat observers to sharp views of the universe. The unit’s 2-inch helical focusers utilize twist-lock compression-ring eyepiece holders, allowing the use of most 1¼- and 2-inch eyepieces. Weighing 46 pounds, the APM 150mm 45º Binocular measures 29½-inches long with dew shields retracted. Each purchase includes an aluminum carrying case. Complete packages including eyepieces, fork mount, and tripod are also available on APM America’s website. APM America P.O. Box 247, Hawthorne, NJ 07507 973-406-4060; www.apmamerica.com

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▶ EXOPLANET OBSERVING Bruce L. Gary, who helped develop the XOP-BB Exoplanet Transit Filter described on the facing page, introduces amateurs to the exciting field of exoplanet research in his book Exoplanet Observing for Amateurs —Second Edition ($39.95). Gary discusses the latest techniques and equipment available to amateurs who want to monitor known stars during transits, and explains how to set up amateur surveys with the goal of discovering new systems. Gary also describes how to prepare your observations for submission to the Exoplanet Transit Database (ETD), where it can be downloaded by other ADIRONDACK ASTRONOMY amateur and professional researchers. Adirondack Astronomy 72 Harrison Ave., Hudson Falls, NY 12839 ◀ 8.3-MEGAPIXEL MADNESS Orion Telescopes 877-348-8433 pes & Binoculars expands its line of aff ordable imaging ng equipment www.astrovid.com with the introduction of its most advanced CCD camera yet — the Orion Parsec 8300C Astronomical Imaging Camera ($2,499.95). This new deep-sky imager features the Kodak KAF-8300 CCD colormatrix sensor, which boasts an 8.3-megapixel array of 5.4-micronsquare pixels measuring approximately 18 by 14 millimeters. Its regulated dual-stage thermoelectric cooling is capable of stable temperatures down to 40°C (70°F) below ambient. The unit’s compact housing measures 4 inches square and 3 inches deep, and weighs 2 pounds. It has standard T-threads on the camera body and a removable 2-inch nosepiece adapter threaded to accept 2-inch filters. The Parsec communicates with your computer via a USB 2.0 interface, compatible with Windows XP, Vista, and Windows 7 operating systems. Each purchase includes a 10-foot USB cable, a 10-foot, 12-volt DC cigarette-lighter power cable, a hard protective case, and a 60-day trial version of MaxIm DL Pro, plus a $100 discount off of purchase of the software. A monochrome version of the camera is also available for $2,599.95. Orion Telescopes & Binoculars 89 Hangar Way, Watsonville, CA 95076 800-447-1001; www.oriontelescopes.com

▶ IPHONE ASTRONOMY Users of the Apple iPhone or iTouch should check out SkyVoyager ($14.99). This planetarium app from Carina Software includes a database of 300,000 stars down to 10th magnitude, 30,000 deep sky-objects, including the entire NGC and IC catalogs, and it renders the Moon and planets in detail. SkyVoyager accurately shows the sky from any location on Earth, at any time up to 100 years in the past or future. Users of the iPhone 3GS with built-in compass can display the sky in the same direction that you’re holding your phone. Tilting your iPhone also shows the sky at the same altitude angle that you’re holding your phone. The app also includes a new time-flow animation feature, and WiFi telescope control with the additional purchase of a WiFi-to-serial adapter. See Carina Software’s website for a complete list of features.

CARINA SOFTWARE

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Sk yandTelescope.com

March 2010 59

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Astro-Tech 1.25” Paradigm eyepieces have two ED lenses in their six-lens optics for excellent color correction and flat 60° fields to get the most out of a dielectric diagonal’s 99% reflectivity. In 5, 8, 12, 15, 18, and 25mm for only $60 each.

More betterest? My grammar may not be perfect, but you Meade ETX-LS6 ACF get the idea. Accessories can really spiffy up a scope. And StarBound makes many a Meade “easy-to-use” is an understatement. You get totally handsmore comfortable . . . A StarBound obfree /eyes-closed sky alignment with Meade LightSwitch serving chair lets you observe in comfort Technology. Just turn on your 6” Meade ETX-LS and walk with an ETX-LS or any scope. No aching away. Your ETX-LS lines up on the night sky all by itself! back from bending over a too-low eyepiece, You can choose time-tested Schmidt-Cassegrain (SCT) no crick in the neck, just a cushioned seat or new Advanced Coma-Free (ACF) optics. ACF optics have that adjusts in seconds to put you at the the same coma-free views as a Ritchey-Chrétien telescope, right height for observing for only $159. but without an R-C’s high price. A 640 x 480 pixel CCD camera under the optical tube takes and stores 8° Every scope deserves a Hot Product TMB 100° wide field deep space images on an optional SD card. eyepiece to make astonishment affordable. Unique Astronomer-Inside software and a built-in speaker take you on guided tours of the heavens. Add an optional $99 LCD color monitor and see the tours. Until now, the immersive, jaw-dropping, “picture window The Hot Product for 2010 Meade ETX-LS. Astronomy made easy. on deep space” views of a quality 100° eyepiece have been priced out of the reach of many backyard astronomers. But Protect your Meade from dust and sun . . . TeleGizmos TMB Optical® asks “Why so pricey?” scope covers protect your Meade (or any scope) from occasional The TMB 100® 2” 9mm and 16mm 100° eyepieces (Sky & exposure to dust, dew, and the sun (at star parties or in your own Tel Hot Products for 2010) make astonishment affordable. $299 backyard). Prices start at only $29. Full-time protection 24/7/365 For $299, you’ll feel like you’re gazing out a picture window each covers start at $39. onto space instead of squinting through an eyepiece. What’s not to love?

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Hot Product optics on a Hot Product mount. What more do you need? The Celestron CGEM is a high precision/heavy-duty go-to German equatorial mount with a 40 lb. payload capacity. A Sky & Tel Hot Product for 2010, the CGEM is a highly accurate and very stable mount that’s ideal for imaging. Celestron CGEM EdgeHD scopes use unique new comafree flat-field Hot Product for 2010 EdgeHD optics optimized by Celestron for DSLR and CCD digital astrophotography. CGEM 800 HD, 8” EdgeHD optics, CGEM mount ...... $2399 CGEM 925 HD, 9¼” EdgeHD optics, CGEM mount ..... 3099 CGEM 1100 HD, 11” EdgeHD optics, CGEM mount .... 3499 Also available are CGEM SCT scopes that use the famous Schmidt-Cassegrain optics that Celestron introduced to amateur astronomy in 1970 and has been perfecting for decades. CGEM 800, 8” SCT optics, CGEM mount .................. $2099 CGEM 925, 9¼” SCT optics, CGEM mount ................. 2699 CGEM 1100, 11” SCT optics, CGEM mount ................ 2999

Three Astro-Tech Ritchey-Chrétiens . . . each one named a Hot Product. The $795 Sky & Tel Hot Product for 2009 6” f/9 AstroTech AT6RC, called a “superb match” for the APS-C size chips used in DSLR cameras by Sky & Tel, was conceived and introduced by Astro-Tech. Others have copied the AT6RC, but Astro-Tech AT8RC $1395 why settle for a copy when you can have the original? The 8” f/8 Astro-Tech AT8RC astrograph has premium features competitors don’t offer – quartz mirrors and a carbon fiber body; 99% reflectivity dielectric mirror coatings; two dovetails; and more. The $1395 AT8RC was the first sensibly-priced 8” Ritchey-Chrétien in the U. S. and it’s still the best. At $2695, the new Astro-Tech AT10RC is priced nearly $4000 less than the formerly least-expensive 10” f/8 Ritchey-Chrétien. Quartz mirrors, 99% reflectivity dielectric coatings. With all you get, for the little you pay, it’s easy to see why the 8” and 10” Astro-Tech R-Cs are Sky & Tel Hot Products for 2010.

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Sue French Deep-Sky Wonders

Keeper of Secrets Little-known Lynx hosts some exotic deep-sky objects. To some native North Americans, the lynx was a

DOUG MATTHEWS / ADAM BLOCK / NOAO / AURA / NSF

totem animal regarded as a keeper of secrets. This is an apt description for the constellation Lynx, which bears no star brighter than 3rd magnitude and no deep-sky object that immediately springs to mind for the casual observer. Lynx was devised by Johannes Hevelius and depicted in his 1687 atlas Firmamentum Sobiescianum. In her monumental work on celestial cartography, The Sky Explored, Deborah Jean Warner writes, “Lynx stands as a reminder of Hevelius’ distrust of telescopic sights for stellar observations: to see the stars as a constellation, he wrote, you must be as sharp-sighted as a lynx.” Since Lynx isn’t easy to pick out in the sky, let’s start

our tour of deep-sky wonders in nearby Cancer. Cancer is also a faint constellation, but it enjoys the advantage of having a distinctive, upside-down Y shape lodged between the bright patterns of Gemini and Leo. Iota (ι) Cancri, which marks the base of the Y, is a beautiful double star. Its deep yellow primary and white companion are easily visible through any telescope at low power. Some observers see the companion star as bluish, a color-contrast illusion. Using enough magnification to put lots of space between the components will help you discern the true colors. Working our way toward the border of Lynx, we find the triple star 57 Cancri at the end of a curvy line of

The edge-on spiral NGC 2683 is the most spectacular galaxy in Lynx.

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March 2010 61

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Deep-Sky Wonders

7th- to 9th-magnitude stars trending northeast from Iota. The primary is a deep-yellow, 6th-magnitude star. Low power shows a 9th-magnitude attendant a roomy 55″ to the south-southwest. But you will need additional magnification to separate the primary from a companion barely fainter than itself. Through my 105-mm (4.1-inch) refractor, the pair is elongated at 87×, kissing at 122×, split by a hair at 153×, and well split at 203×. The companion cuddles up northwest of its primary and gleams with a yellow-orange hue. From 57 Cancri, hop 2° north to Sigma1 (σ1) Cancri and then 1° farther to Lynx’s brightest galaxy. The elongated smudge of NGC 2683 hangs out with the four members of the Sigma Cancri gang through my little

10h 00m

9h 00m

8h 00m

Q 2841

URSA MAJOR

2681

I 2776

36

22

2500

K 35

28 66

10 UMa

2782

Inchworm

2424

LYNX

Star magnitudes

2 3 4 5 6

A

1 3 S S4 S

T

See us at:

NEAF NORTHEAST ASTRONOMY FORUM

Suffern, NY / April 17-18

62 worldmags

57

P

CANCER

J

Pollux

31″

8h 46.7m

+28° 46′

6.1, 6.4, 9.2

1.5″, 55″

8h 54.2m

+30° 35′

9.8

9.3′ × 2.1′

8h 52.7m

+33° 25′

Inchworm

Asterism

4.3

46′

9h 05.9m

+38° 16′

AUR

NGC 2782

Tidal-tail galaxy

11.6

3.5′ × 2.6′

9h 14.1m

+40° 07′

+40o

NGC 2419

Globular cluster

10.4

5.5′

7h 38.1m

+38° 53′

NGC 2424

Flat galaxy

12.6

3.8′ × 0.5′

7h 40.7m

+39° 14′

NGC 2537

Dwarf galaxy

11.7

1.7′ × 1.5′

8h 13.2m

+45° 59′

NGC 2537A

Face-on galaxy

15.4

0.6′

8h 13.7m

+46° 00′

IC 2233

Flat galaxy

12.6

4.7′ × 0.5′

8h 14.0m

+45° 45′

JnEr 1

Planetary nebula

12.1

6.8′ × 6.0′

7h 57.9m

+53° 25′

63

+30o 2371-2

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.

New Mexico Skies Where the “Seeing” is Believing, day and night! The world's finest amateur astronomy community. Famous for our dark night skies.

March 2010 sky & telescope

4.1, 6.0

Spindle galaxy

O A Castor

B

Dec.

NGC 2683

2419

GEMINI

RA

Triple star

65

S 2 2683

Size/Sep.

57 Cancri

38 2859

Magnitude

Double star

IC 2233 31

Type

ι Cancri

21

26

2537 34

Object +50o

2541

In the Lair of the Lynx

7h 00m

JnEr 1

27

refractor at 17×. NGC 2683, Sigma1, and Sigma2 mark the corners of an equilateral triangle, and a trapezium of four faint stars dangles 12′ south of the galaxy. At 87× NGC 2683 is a 6′ × 1½′ spindle, tilted to the northeast, that harbors a 3′-long core. A faint star lies off the galaxy’s southeastern flank, and a very faint star sparkles on the galaxy’s northern edge. The core looks mottled at 127×. In my 10-inch reflector at 213×, NGC 2683 is very pretty. The halo spans 7½′, and the textured core grows more intense toward a very small, bright nucleus. NGC 2683 is a spiral galaxy seen nearly on edge. Relatively nearby at 23 million-light years, this metropolis of stars presents us with such a striking profi le that some folks call it the UFO Galaxy.

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+54o JnEr 1

+52o 27 2500 +50o

2552 2541

26

+48o

25 2537A

2537 +46o

Star magnitudes

Puttering around in Lynx with my 4.1-inch scope at 17×, I happened upon a cute asterism, which I’ve christened the Inchworm. It’s found 3° northwest of 38 Lyncis and contains the yellow, 4.6-magnitude star HD 77912. The inchworm is 46′ long with ten stars down to 10th magnitude. The yellow star resides in the humped-up part of the inchworm’s body, and his glowing eyes are at the northwestern end. Moving 2½° northeast of the Inchworm takes us to the peculiar spiral galaxy NGC 2782. In my 130-mm refractor at 23×, it shows up as a little spot of mist just north of a wide pair of very faint stars. At 102× the galaxy is a 1.6′ × 1.3′ oval tipped a bit east of north, and its large core grows much brighter toward the center. My 10-inch reflector at 192× exposes a stellar nucleus and a detached haze 2′ east-northeast, with a very faint star on its western edge. A diaphanous wisp weds the southern end of this haze to the rest of the galaxy. The extended structure east of NGC 2782 is a tidal tail formed about 200 million years ago when a galaxy much like our own merged with a galaxy one quarter as massive. For a change of pace, let’s visit the globular cluster NGC 2419, which garnishes a 3° arc of orange 5th- and 6thmagnitude stars near the Lynx-Auriga border. Through my 130-mm refractor at 63×, I see it as a softly glowing globe off the end of a curve of three progressively brighter stars, magnitude 9 to 7. The center star holds a faint companion 24″ to its north-northeast. The 4′ cluster grows brighter toward the center and has several faint foreground stars scattered around the edges. The highly elongated galaxy NGC 2424 is visible 36′ northeast. At 102× it appears about 2½′ long, and it’s tipped a bit north of east. Only large-scope users can hope to glimpse NGC 2419’s member stars, because the brightest feebly shine at 17th magnitude. The apparent dimness of the stars is due to the globular’s astonishing distance of 275,000 light-years. Because of its remoteness, NGC 2419 was dubbed the Inter-

IC 2233

4 5 6 7 8 9

8h 30m

LYNX +44o 31

8h 20m

8h 10m

28

8h 00m

7h 50m

galactic Tramp, a nickname that has clung with amazing tenacity despite the fact that we’ve long known this globular is well within the gravitational thrall of our galaxy. Our next stop is the Bear Paw Galaxy, NGC 2537, which sits 3.3° northwest of 31 Lyncis. My 130-mm scope at 102× shows a bright, 50″ core that exhibits odd, largescale patchiness. The halo is just a thin fringe around it. My 14.5-inch reflector at 170× reveals three lumps — the

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March 2010 63

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Deep-Sky Wonders

NGC 2537A

IC 2233

POSS-II / CALTECH / PALOMAR OBSERVATORY

NGC 2537

by Rebecca B. Jones and Richard Maury Emberson. Strangely, the bulletin states: “a faint nebular ring has been detected joining two condensations, NGC 2474, observed by Sir John Herschel, and NGC 2475.” While the article’s image does indeed show the nebula, NGC 2474 and NGC 2475 are a galaxy pair found ½° farther south. This misidentification was reproduced in many later references. As you can see, our secretive Lynx holds many unusual treasures. I hope you’ll find them worth uncovering. ✦ Sue French welcomes your comments at [email protected].

ADAM BLOCK / NOAO / AURA / NSF

southward-pointing “toes” of the paw. The face-on spiral NGC 2537A joins the scene as a ghostly little orb floating 4½′ east of the Bear Paw. IC 2233 is an exceptionally thin, edgeon galaxy 17′ south-southeast of the Bear Paw. In my 130-mm refractor at 164×, it slashes the sky just west of a 10th-magnitude star with a dim companion. This ashen filament spans 1½′, and its northern tip is pinned to the sky with a faint star. The view through my 10-inch reflector doubles the wafer-thin galaxy’s length. The Bear Paw is a compact dwarf galaxy patterned by vast star-forming complexes teeming with bright blue stars. It’s about 26 million light-years away. NGC 2357A is perhaps 20 times more distant. We’ll wind up our tour with the huge planetary nebula Jones-Emberson 1 (PK 164+31.1). Elaine Osborne (Virginia) and Dr. David Toth (Ohio) joined me for views through my 130-mm scope at last year’s Winter Star Party. The nebula is quite elusive at 63×. The brightest patch makes a right isosceles triangle with 11th-magnitude stars west and northeast. A dimmer patch is faintly visible 4′ northwest. The two are tenuously connected by phantom arcs that convert the nebula into a 6′ ring. Using a narrowband nebula filter or a higher magnification betters the view. JnEr 1 was first reported in the Harvard College Observatory Bulletin in 1939

The planetary nebula Jones-Emberson 1 is an elusive target through the eyepiece of a telescope.

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Ken Hewitt-White Going Deep

A Pride of Galaxies Take the road less traveled to the NGC 3158 group. Poor Leo Minor. Although it’s high overhead on March evenings, the Lesser Lion is easy to miss sandwiched between its two impressive neighbors: Leo to the south and Ursa Major to the north. Seventeenth-century astronomer Johannes Hevelius created Leo Minor from 18 faint stars overlooked in a celestial no man’s land between the Lion and the Great Bear. Despite its small size (64th in area among the 88 constellations), Leo Minor features several interesting galaxy fields. My favorite is the NGC 3158 group in the northern part of the constellation. The target area, 3½° northwest of 4.2-magnitude Beta (β) Leonis Minoris, contains the bright namesake galaxy, seven dim NGC galaxies, and a few very faint PGC galaxies, within a circle of sky ¼° in diameter. A lowpower eyepiece will corral this field of fuzzies between an east-west pair of 9th- and 10th-magnitude stars ½° apart, as shown on the chart at right. A line connecting these two stars grazes NGC 3158, so let’s begin our exploration there. Unless otherwise noted, the following observations were made with my 17.5-inch f/4.5 reflector at 285×. With a magnitude of 11.9 and dimensions of 2.0′ × 1.8′, NGC 3158 is easily the group’s most prominent member. This E3 elliptical galaxy exhibits a well-defined core embedded in a slightly oval halo. Four tiny companions hover nearby. To the southwest of NGC 3158 are PGC 2135625 and 2135428. The latter is

the brighter of the two and is not hard to locate 30″ north of a 14th-magnitude star. East-southeast of NGC 3158 are PGC 29842 (the best of the four companions) and PGC 29849, which lies 1′ southwest of another 14th-magnitude star. George Kepple records all these in his fine sketch of the NGC 3158 group in the Night Sky Observer’s Guide (vol. 2, page 252). The night I inspected this region I detected just the two brightest attendants, even with a friend’s 20inch f/4, but the sky transparency wasn’t perfect. Nudging my scope nearly 5′ north of NGC 3158 centers two galaxies 4′ apart, aligned east-west. The more photogenic specimen is 14.1-magnitude NGC 3160, an edge-on spiral (the only one in the group) conveniently located

10h 30m

10h 20m

10h 10m

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URSA MAJOR

+42° 3184

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+40°

NGC 3158 is located 3½° northwest of Beta Leonis Minoris. Oddly, this inconspicuous constellation has no Alpha star. Its brightest star, east-southeast of Beta, is 46 Leonis Minoris. 32 3158

CANES VENATICI

+38°

B

URSA MAJOR

LEO MINOR

Star magnitudes

LYNX

+36° 29 LEO MINOR

66 March 2010 sky & telescope worldmags

26

21

4 5 6 7 8 9 10

worldmags

3152

3160

3158 PGC 2135625 PGC 29849 PGC 29842 PGC 2135428

3161 PGC 29818 3163

3159

3150

3151

5´ SLOAN DIGITAL SKY SURVEY

between an 11.4-magnitude star to the north-northeast and a 12.9-magnitude star to the south-southwest. The galaxy measures 1.3′ × 0.3′, but its strongly elongated form was barely apparent to my eye — again, probably because conditions weren’t ideal. Nevertheless, I consider it an easier target than its neighbor, 14.2-magnitude NGC 3152. This 0.8′ × 0.7′ galaxy appeared diff use and round. If we return to NGC 3158, then scan 7′ south-southeast, we encounter another east-west row of galaxies. They are NGC 3163, 3161 and 3159. All three are of comparable shape (roughly spherical), size (approximately 1′), and brightness (magnitude 13.3 to 13.6). The middle galaxy, NGC 3161, is the least prominent, while the eastern one, NGC 3163, is the brightest. The two flankers exhibit compact cores. Immediately northwest of NGC 3159, my averted vision picked up 15.0-magnitude PGC 29818. To the west of NGC 3159 is a solitary 12.4-magnitude star, and a bit west of that are two more sub-arcminutewide smudges, slightly more than 2′ apart, aligned northsouth. The better of the two is 13.8-magnitude NGC 3151, which, though very small, is brighter in the middle than

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Redshift measurements indicate that the NGC 3158 group is 300 million light-years from Earth. That means that NGC 3158 is close in inherent brightness to Messier 87, the giant elliptical galaxy at the heart of the Virgo Cluster.

at the edges. By contrast, 14.6-magnitude NGC 3150 is pale and wispy, with no central brightening. Altogether, this ragged subgroup of five NGC galaxies spans just 8′ of sky. After observing all of these in my 17.5-inch telescope, I detected the eight principal members of the NGC 3158 group in another friend’s 12.5-inch Dobsonian working at 227×. Needless to say, only the anchor object was easy, but the other pale blobs materialized after several minutes of patient staring. The telescope’s owner was suitably impressed. This collection of galaxies in Leo Minor isn’t quite the “cat’s meow,” but it’s a worthy treasure for midsize and larger scopes. Check it out the next clear, moonless evening. ✦ Ken Hewitt-White hunts galaxies from dark sites in western Canada. Sk yandTelescope.com

March 2010 67

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Gary Seronik Telescope Workshop

Pushing Glass in Delaware Telescope makers meet for the 10th Mid-Atlantic Mirror Making Seminar. Books and the internet

DON SURLES

are great sources of information for anyone wanting to learn how to make a telescope mirror today. Nevertheless, even the best of these resources can’t approach the depth and understanding that comes from person-to-person instruction. All over the world, numerous mirror-making events, both formal and informal, take place regularly. Vermont’s Springfield Telescope Makers — hosts of the annual Stellafane convention — maintain an excellent list of these events on their website: http://stellafane.org/tm/mc/other.html. One highly successful annual gathering has been quietly chugging along in Delaware since 2001. Hosted by the Delmarva Stargazers, the Mid-Atlantic Mirror Making Seminar is a glass-pusher’s boot camp. For three days, participants live, breathe, eat, and sleep the ins and outs of mirror making at the suitably rustic Mallard Lodge, located on the Delaware River near the town of Smyrna, about 50 miles southwest of Philadelphia. The event’s leading light is Don Surles, who was bitten by the mirror-making bug 20 years ago. “At the Stella Della Star Party, I was viewing Mars at opposition with my storebought telescope,” he recalls. “I was pretty pleased with the

68 worldmags

Wes James readies his 6-inch mirror for polishing during the 2009 workshop at Mallard Lodge in Delaware.

March 2010 sky & telescope

views — that is, until I looked through a nearby homemade 6-inch reflector. The very next day I purchased an 8-inch mirror kit from the swap table and resolved to learn the fine art and science of mirror making.” After working on a succession of mirrors ranging in size from 4¼ to 24 inches, Don’s enthusiasm for the craft moved him to approach his local club about putting together an event like those in other parts of the country. “The Delmarva Stargazers have always been a very active organization; so, when I asked if they’d consider sponsoring a mirror-making weekend, they didn’t say no. Within a couple of weeks we had laid plans for the first MidAtlantic Mirror Making Seminar.” The emphasis at Mallard Lodge is on ensuring that by the end of the event all participants leave with a working mirror. As Don reports, “Last year everyone completed their mirror — we even finished early. I have to confess that the superb quality of some mirrors crafted during the event make me envious!” The 2010 seminar is scheduled for March 12th through 14th. This year participants will be assisted by the experienced hands of Steve Swayze, David Groski, and Bill Hanagan, as well as members of the local club. You can turn up and get working on glass that has been pre-ordered for you, or you can bring along your own materials and tap into the expertise of the seminar’s leaders. While the focus is on mirror making, camaraderie and friendship are happy byproducts of the Mallard Lodge experience. As 2009 attendee George Moore notes, “Although I was pleased to complete my 8-inch f/10 mirror, the event was so much more. We lucked into some pretty decent skies that weekend and got to view through several of the club’s homemade scopes. Conversations of projects past, present, and proposed carried on into the wee hours. Hearty food and good company — a truly great weekend.” To join Don and his cohorts at this year’s event, email him at [email protected], or visit the club’s website (www.delmarvastargazers.org) for more information. ✦ Contributing editor Gary Seronik observes his Canadian night sky with home-built telescopes near Victoria, British Columbia. He can be contacted through his website, www. garyseronik.com.

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March 2010 69

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Astro Q&A

The editors of Sky & Telescope answer your astronomy questions.

Near the Pointer stars of the Big Dipper (the two bright stars on the right here) are many faint targets plotted on Sky Atlas 2000.0 — including the elongated galaxy M108 and the Owl Nebula, both in the large ring. A century-old trick is to make wire rings to slide around your map showing the size of your finderscope’s field of view (typically about 5°) and your telescope’s widest view (typically about 1°). This greatly helps you match star patterns on the map to those you see. With the aid of these little patterns, you can put your finder’s crosshairs on exactly the right point.

Finding Things with a Telescope I’ve learned the constellations and can find the general location of deep-sky objects in them. But when I look there with a telescope, I can’t identify any objects. How do I narrow in so I can locate an object and know it? — Dave Boettcher, North Fork, California Welcome to the crucial first hurdle for every new telescope user. Once you know your way around some naked-eye constellations, you need a good, detailed star atlas showing fainter stars, to 7th or 8th magnitude, at larger scale. And you need to learn how to use these maps with your telescope’s finderscope. The standards are Sky Atlas 2000.0, which plots stars to as faint as magnitude 8.5, and the Pocket Sky 70 March 2010 sky & telescope worldmags

Atlas, which goes to magnitude 7.6. The bigger your finderscope the better. To match what you see in it to a map, you need to know two things: how large its field of view appears on the map, and which way in the view is north (so you can turn the map around to match the orientation). To find north, just nudge the telescope a bit in the direction toward Polaris; new sky will enter the view from its north edge, wherever that is. You also need to be looking at a “correct” view, which matches the map, not a mirror-image view. This way you can carefully “star-hop” from a known naked-eye starting point, working your way step by step along faint star patterns — little triangles and quadri-

laterals — to your target’s precise spot. Can you skip all of this with a computer-pointed scope? In theory, yes. In practice, a decade of experience has shown that beginners tend to find self-pointing scopes no easier than learning to locate things for themselves. For a complete, hand-holding guide, see our online article “Using a Map at the Telescope” (SkyandTelescope.com/ MapTelescope). For other useful tips, also check out “The Art of Using a Telescope” (SkyandTelescope.com/ArtTelescope). — Alan MacRobert

The Right Tool for the Job I’m starting to do astrophotography with a DSLR camera. How do you subtract a dark frame in Photoshop? Dozens of articles and books explain how and why to make a dark frame, but not how to subtract it from your images to improve them. — Ernest Molenaar, The Hague, Netherlands Photoshop isn’t the best tool for this; using it to subtract the dark frame would be possible but complex. Instead, use an astrophotography software package. In any of these programs, subtracting the dark frame involves about two clicks in the image calibration routine. I’d recommend DeepSkyStacker (http://deepskystacker. free.fr/english/index.html) as the cheapest to start with. Photoshop is good for bringing out information in astro-images after they’ve been calibrated. — Sean Walker

Send questions to [email protected] for consideration. Due to the volume of mail, not all questions can receive personal replies.

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Since

1975

Colors vs. Redshifts

I recently acquired an image erector for my small refractor. With the erector, I can’t bring my eyepiece far enough in to come to focus. I must be missing something. — Tom Johnson, New York, New York

I know the apparent color of a star is how we tell its temperature, but how is the color affected if its light is redshifted or blueshifted by the star’s motion? — Tim Brewster, Acheson, Alberta, Canada

This is common. On many telescopes, the focuser has too small a range of travel to accommodate some accessories. Most eyepieces are made so that the telescope’s focal plane needs to fall at or near the eyepiece’s “shoulder,” where the shiny barrel meets the larger top. Most telescopes are built to do this first and foremost. Your image erector adds too much space between the scope and the eyepiece. Return it or sell it, unless you can rebuild the body of the scope. Cameras are a common problem in this regard. The telescope’s focal plane needs to fall on the sensor in the camera’s back, meaning most of the camera body has to be in front of the focal plane. Newtonian reflectors are especially prone to problems with this, because (for good reason) they should keep the focal plane close to the secondary mirror. Compound telescopes, on the other hand, tend to have lots of available back focus. Bottom line: Don’t buy an accessory without checking that it will reach focus on your system. Ask the maker, and be sure you can return it if necessary. — Alan MacRobert

For a star? Not at all. Stars typically have radial velocities (speeds toward or away from us) of a few dozen kilometers per second, roughly a ten-thousandth the speed of light. That’s much too slight to shift the star’s overall color. Redshift does, however, change the color of extremely distant objects receding at a fair fraction of lightspeed. A galaxy with a look-back distance of 7.7 billion light-years (far beyond the reach of nearly all amateur scopes) has a redshift of 1, meaning each wavelength is doubled. If the galaxy’s peak emission is blue in its own “rest frame,” this peak will be shifted all the way to the red as seen by us. Below is part of a new infrared Hubble ultra-deep field, released in December, that records a few galaxies at redshift 8. Their wavelengths are stretched by a factor of 9. That brings even ultraviolet light way into the infrared — giving such galaxies a vivid red look in this rendition (in which infrared light at 1.05 microns shown as blue, 1.25 microns as green, and 1.6 microns as red). — Alan MacRobert

NASA / ESA / G. ILLINGWORTH / R. BOUWENS / HUDF09 TEAM

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Hubble’s newly installed Wide Field Camera 3 took a 4-day infrared exposure, the Hubble Ultra-Deep Field 09, from which this piece is cropped. The very reddest objects are at redshift 8.

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In the fall of 2006 we completed the installation of the 40.375 foot Observa-DOME at Magdalena Ridge Observatory which will house a 2.4 Meter Telescope.

2010 Skygazer’s Almanacs (. !

Magdalena Ridge Observatory Socorro, NM www.mro.nmt.edu

Now Available for Sky Gazing




ALL STARS POINT TO . . .

worldmags

Seeing Double

DOUBLE STARS in

u n o r d a

a nd

LEO

The Lion is a treasure house of bright, rewarding visual binaries.

richard jaworski

I love to observe double stars. I have a demanding job as a pathologist, and it’s a joy to step out into my suburban garden of an evening, relax, and track down these beautiful objects with my trusty 6-inch (150-cm) f/8 Dobsonian reflector. For the very difficult pairs, I travel to nearby Crago Observatory (www.asnsw.com) to use its 16-inch f/7 motor-driven Dobsonian. In this article we will explore double stars in and around Leo, which is high in the evening sky from Febru12h 00m

11h 30m

11h 00m 41521

10h 30m

10h 00m

M

3344

E

54 2

D

H

3607 90

M105 M65

X

S

worldmags

83

U

Regulus

R P

C

VIRGO

N

A

M96 M95

J

N

B

H

3489

W P

LEO

Q

Denebola 88 3628 M66

41575

+20°

49 35

SEXTANS

+10° Star magnitudes

B

O

Z

2 3 4 5 6 7

ary through May. Living as I do in Australia, I never fully appreciated Leo’s resemblance to a crouching lion until a visit to Hawaii, where I saw it inverted from my usual Southern Hemisphere view. I hope you like this selection of double and multiple stars; I certainly had fun compiling and observing them. Let’s start with the fine multiple star Alpha (α) Leonis, also known as Regulus. The 1.4-magnitude primary star (the A component) has an 8.2-magnitude secondary (the B component) almost 3′ to its northwest — an easy split in any telescope. To my eye A is white and B is yellowish. But E. J. Hartung describes the companion as orange-red in his book Astronomical Objects for Southern Telescopes. Regulus A and B are both 79 light-years from Earth, give or take a light-year, and they’re moving through space at the same velocity. Barring an amazing coincidence, they must be held together by gravity — but we can’t prove it. To appear so widely separated through a telescope, the stars must be at least ½ light-year apart in space, giving them a likely orbital period of 100,000 to 200,000 years. So the stars haven’t moved perceptibly in their orbits since the prolific double-star observer F. G. W. Struve first measured them accurately in 1832. The fainter star is itself a close double, with the 13.1magnitude component C lying 2.5″ east of B. These stars appear to orbit each other every 1,000 to 2,000 years. In 2008, spectroscopic measurements proved that Regulus A also has a companion that orbits it every 40 days. But this pair is so close that it couldn’t be split by any telescope that we can now imagine. If your sky is dark and moonless, try to spot the dwarf galaxy Leo I 20′ north of Regulus, as shown on page 75. Sk yandTelescope.com

March 2010 73

worldmags

Seeing Double North 0o

East 90o

Primary star

West 270o

Separation Position angle South 180o

Secondary star

49 Leonis

Gamma Leonis

2 Comae Berenices

Left: Double stars are described by their separation and the position angle (PA) of the dimmer star with respect to the primary. Position angle is measured from north around through east — counterclockwise in binoculars and most reflecting telescopes, clockwise in the mirror-reversed view of most telescopes with star diagonals. Center and right: Arizona graphic artist and stargazer Jeremy Perez sketched the double stars in this article as seen through his 6-inch reflector at 240×. Only the very center of the field of view is shown here, greatly magnified. Note how 49 Leonis’s secondary is hiding in the diffraction rings of the bright primary star.

An 8-inch telescope may show this Local Group galaxy as a faint 5′ smudge if Regulus is kept out of the field. Now let’s head southeast to 49 Leonis, a very tight pair of unequally bright stars. The A component is white and B is bluish. I could just split them at 190×. The pair appears to be physically connected, and the primary is an eclipsing variable with a period of 2.4 days. Continuing in the same direction just across Leo’s southern border, 35 Sextantis is a lovely pair of unequally bright yellowish and bluish stars 6.8″ from each other. It also has an 8th-magnitude C component 5.5′ southwest of the brighter stars. Returning to Leo, our next target is a stunning bright pair of gems. Gamma (γ) Leonis, also known as Algieba, is an excellent one to show your friends at 100× or higher.

Both stars are yellow giants, and their separation has been widening ever since this double was first measured (see the box below). Moving to the northeast, we find 54 Leonis near the Leo Minor border. This is a beautiful pair of bright stars 6.6″ from each other. The primary appears white and the companion bluish-white. Continuing in the same direction, Σ1521 is a close, faint, slightly unequal pair with a white primary. Just across Leo’s eastern border, 2 Comae Berenices is a close pair of bright yellowish-white and bluish gems, and a fine sight at high power. By contrast, Σ1575, in northwestern Virgo, is a very wide, nearly equal pair that looks lovely at low magnification. Its A component is yellow, and B appears bluish.

You Can’t Hurry Love — or Double Stars

74 March 2010 sky & telescope worldmags

Gamma Leonis Orbits

Secondary

abe in

tar s

2000 2100 2100

og tal Ca h t Six

2200

O of

ted b

o its rb

i fV

pu

1900

yW .R

ry S

na

2000

su al

Bi

1900

2200

1958

Primary

1800

1800

Co m

measurements aren’t accurate enough to predict reliably what will happen in the next century or two. The diagram at right shows two possible orbits, one computed in 1958, and one from the recent Sixth Catalog of Orbits of Visual Binary Stars. Both orbits are essentially identical throughout the 19th and 20th centuries, so historical evidence can’t tell us which is closer to reality. But their predictions diverge wildly after the year 2100. To compute a really accurate orbit, you need to observe the stars near periastron, when they’re closest, and most strongly affected by each other’s gravity. — Tony Flanders

S&T: CSAEY REED

Stars appear close to each other in the sky far more often than can be explained by chance alone. So a large fraction of the 100,000 systems in the Washington Double Star Catalog must be binary stars, whose components are bound together by gravity. But many binaries take thousands or even millions of years to orbit each other, and we haven’t been observing them long enough to calculate their trajectories. The components of Gamma Leonis have been moving farther apart ever since their separation was first measured, but the rate of increase has slowed dramatically — an effect that can only be due to gravity. Unfortunately, our

2300

1˝

worldmags

1900 1875

1925

Secondary

Iota Leonis Orbit

1850 2025

Primary

Name (Con.)

Mag.

Sep.

PA

Spect.

RA

Dec.

α Leo AB BC

1.4, 8.2 8.2, 13.1

176″ 2.5″

308° 86°

B7 V K2 V

10h 08.4m

+11° 58′

49 Leo

5.8, 7.9

2.2″

154°

A2 V

10 h 35.0m

+8° 39′

35 Sex AB AC

6.2, 7.1 6.2, 8.1

6.8″ 334″

239° 210°

K3 III

10 h 43.3m

+4° 45′

γ Leo

2.4, 3.6

4.6″

126°

K0 III

10 h 20.0m

+19° 50′

54 Leo

4.5, 6.3

6.6″

112°

A1 V

10h 55.6m

+24° 45′

Σ1521 (Leo)

7.7, 8.1

3.7″

97°

A5

11h 15.4m

+27° 34′

2 Com

6.2, 7.5

3.7″

235°

F0 IV-V

12h 04.3m

+21° 28′

1950

2000 1˝ 1975 S&T: CSAEY REED

Double Stars in and around Leo

Iota Leonis reached periastron in 1948. Its separation is currently increasing ¼″ every decade.

Returning to the tail of Leo, 90 Leonis is a lovely triple. The A and B stars form a close pair and are yellowish and bluish. Their separation appears to have widened since 1782, and the pair is probably gravitationally bound. The 9.8-magnitude C component appears as a faint speck of light about 1′ from the AB pair. About 2½° to this triple’s south-southwest lies 88 Leonis, a lovely, wide, easy, and very unequally bright pair of stars with a yellowish-white primary.

Σ1575 (Vir)

7.4, 7.9

30.6″

210°

K0

11 52.0

90 Leo AB AC

6.3, 7.3 6.3, 9.8

3.5″ 63.2″

208° 235°

B4 V

11h 34.7m

+16° 48′

88 Leo

6.3, 9.1

15.3″

331°

G0 IV

11h 31.7m

+14° 22′

ι Leo

4.1, 6.7

1.9″

105°

F4 IV

11h 23.9m

+10° 32′

h

h

m

+8° 50′

m

+3° 01′ +2° 51′

83 Leo

6.6, 7.5

28.2″

150°

G7 V

11 26.8

τ Leo

5.1, 7.5

88.9″

181°

G8 II-III

11h 27.9m

All data are from the Washington Double Star Catalog. Right ascension (RA) and declination (Dec.) are equinox 2000.0.

RUSSELL CROMAN

Another 4¼° to the south-southwest we come to Iota (ι) Leonis, our most challenging double for the night. I could not split this pair with my 6-inch telescope, so I used the 16-inch reflector at Crago Observatory. At 450× I was treated to an exquisite pair. The bright primary appeared creamy white while the very close companion was yellow. This pair has completed almost a full orbit since it was first measured in 1828. Our final targets are 83 Leonis and Tau (τ) Leonis. These stars are only 20′ apart and form an attractive, easy “double double” in a low-power field. Tau is a 5.1-magnitude, deep yellow primary with a yellow-white, 7.5-magnitude companion widely spaced to its south. In contrast, 83 Leonis is a somewhat close pair with a yellowish 6.6-magnitude primary and a pale orange, 7.5-magnitude secondary to its south-southeast. Through a finderscope or binoculars, Tau and 83 form an evenly spaced, shallow arc with 6.7-magnitude 82 Leonis. I hope this article inspires you to go out and do some double-star observing. You’ll be surprised how enjoyable and addictive it can be. ✦ The faint Leo Dwarf Galaxy lies 20′ due north of Regulus. Regulus B is the bright, slightly orange star upper right of Regulus A, right next to the diffraction spike.

worldmags

Richard Jaworski is the double-star section leader for the Astronomical Society of New South Wales and can be contacted at [email protected]. Sk yandTelescope.com

March 2010 75

Sean Walker Gallery

▶ PACMAN IN CASSIOPEIA Larry Van Vleet The nebulous star-forming region NGC 281 contains several back-lit dark clumps of gas and dust known as Bok Globules. Details: Takahashi BRC 250 astrograph with FLI ProLine PL16803 CCD camera. Total exposure time was 22 hours through Astrodon narrowband filters.

FIFTH-DAY CRESCENT Necati Demiral The waxing crescent Moon presents a smorgasbord of detail that is visible with many instruments. Sunrise on the craters Hercules and Atlas draws our attention to the top right in this image, while daylight strikes the western wall of Mare Nectaris near the South. Details: Tele Vue-102iis refractor with Canon EOS 250D DSLR camera. Exposure time was 1/50 second at ISO 100.

76 worldmags

March 2010 sky & telescope

worldmags

worldmags

worldmags

Gallery showcases the finest astronomical images submitted to us by our readers. Send your very best shots to gallery@SkyandTelescope. com. We pay $50 for each published photo.

See SkyandTelescope.com/ aboutsky/guidelines.

WASTING AWAY Ivan Eder The 2nd-magnitutde variable star Navi (γ Cassiopeiae) slowly evaporates the nebulosity IC 63 (at left) and IC 59 (top right). Navi is an eruptive variable that spins so fast it bulges at its equator and sheds mass. The expelled material orbits the star in a disk that blocks light from the star at irregular intervals. Details: 12-inch Newtonian refl ector with a Canon 350D DSLR camera. Total exposure was almost 4 hours.

◀

Sk yandTelescope.com

March 2010 77

worldmags

Gallery

▶ M42 AND BEYOND Frank S. Barnes, III Although the Orion Nebula easily captivates many observers’ attention, it’s only a small portion of a massive complex of gas and dust that permeates the entire constellation. Details: Takahashi FSQ-106N astrograph with an SBIG STL-11000M CCD camera. Total exposure was 18½ hours through color and Hα filters recorded over the course of several nights.

▾ CREPUSCULAR SUNSET Stefano De Rosa While vacationing on the Tuscan island of Elba, Stefano De Rosa captured this stunning display of crepuscular rays. Details: Canon EOS 1000D DSLR with 21-mm lens at f/3.5. ✦

▴ GALLERY.TITLE Gallery.byline Text1 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx. Details (Gallery.details lede in): Gallery.details xxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxx Gallery.details.roman xxxxxxx xxxxxxxxxxxxxxxxxxxxx. ▶ NGC 2403 Keller Plesko After a long stretch of solar inactivity, sunspot complex NOAA 10960 treated observers to a marvelous display last May. Details: Takahashi FS-102 refractor, Coronado SolarMax 90 hydrogen-alpha filter, and Lumenera Infinity 2-1M CCD webcam. ✦

78 worldmags

March 2010 sky & telescope

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March 2010 sky & telescope

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Product Locator

Inside This Issue BINOCULARS Celestron (Pages 25, 69, 88) Celestron.com 310-328-9560 Meade (Pages 7, 53) Meade.com 800-919-4047 | 949-451-1450 Orion (Pages 13, 71) OrionTelescopes.com 800-447-1001 | 831-763-7000

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Index to Advertisers Adorama . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Meade Instruments Corp. . . . . . . . . . . . .7, 53

Ash Manufacturing Co., Inc. . . . . . . . . . . . . 47

New Mexico Southern Skies. . . . . . . . . .62, 63

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

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

Astrobooks. . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Observa-Dome Laboratories . . . . . . . . . . . . 72

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

Oceanside Photo & Telescope . . . . . . . . . . . 69

Astronomical Tours. . . . . . . . . . . . . . . . . . . . 50

Officina Stellare s.r.l. . . . . . . . . . . . . . . . . . . . 72

Astronomics . . . . . . . . . . . . . . . . . . . . . . . . . 60

Orion Telescopes & Binoculars . . . . . . .13, 71

Astronomy Technologies . . . . . . . . . . . . . . . 56 Atik Cameras . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Bob’s Knobs . . . . . . . . . . . . . . . . . . . . . . . . . 80 Celestron . . . . . . . . . . . . . . . . . . . . . .25, 69, 88 CNC Parts Supply, Inc. . . . . . . . . . . . . . . . . . 80 Cyanogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

IN THE NEXT ISSUE

Peterson Engineering Corp. . . . . . . . . . . . . . 81

Cosmic Blowtorches

PlaneWave Instruments . . . . . . . . . . . . . . . . 83

Quantum Scientific Imaging, Inc. . . . . . . . . 64

Scientists struggle to understand how various stars and black holes can shoot out enormous jets traveling at near-light speed.

Santa Barbara Instrument Group . . . . . . . . . 3

Is the Solar System Stable?

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For centuries, astronomers have tried to calculate whether planetary orbits will remain steady as clockwork.

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Glatter Instruments . . . . . . . . . . . . . . . . . . . 81 Goto USA, Inc. . . . . . . . . . . . . . . . . . . . . . . . . 5 Half Hitch Telescope. . . . . . . . . . . . . . . . . . . 82 Hands On Optics . . . . . . . . . . . . . . . . . . . . . 82 High Point Scientific . . . . . . . . . . . . . . . . . . . 69

Star GPS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Starlight Xpress, Ltd.. . . . . . . . . . . . . . . . . . . 10

Technical Innovations . . . . . . . . . . . . . . .72, 80

Modern technology is changing the way space artists create their work.

Tele Vue Optics, Inc. . . . . . . . . . . . . . . . . . . . . 2

Observe Active Galaxies

The Imaging Source . . . . . . . . . . . . . . . . . . . 52

Hotech Corp. . . . . . . . . . . . . . . . . . . . . . . . . . 80

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

Hutech Corporation . . . . . . . . . . . . . . . . . . . 82

The Teaching Company . . . . . . . . . . . . . . . . 35

InSight Cruises . . . . . . . . . . . . . . . . . . . . . . . 54

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

iOptron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

University Optics, Inc. . . . . . . . . . . . . . . . . . 80

Kendrick Astro Instruments . . . . . . . . . . . . . 81

Van Slyke Instruments . . . . . . . . . . . . . . . . . 57

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

Willmann-Bell, Inc. . . . . . . . . . . . . . . . . .81, 82

Knightware. . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Woodland Hills Telescopes . . . . . . . . . . . . . 47

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The New Space Art

Stellarvue . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

BOTTOM: MICHAEL C. TURNER; TOP: NASA / HUBBLE HERITAGE TEAM / STSCI / AURA

Foster Systems, LLC . . . . . . . . . . . . . . . . . . . 80

Your observing guide to blazars, an energetic class of active galaxies.

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On newsstands March 2nd! Sk yandTelescope.com

March 2010 85

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Focal Point

Jacob Haqq-Misra & Seth D. Baum

Where Have All the Aliens Gone? The problem of sustainability may explain the absence of extraterrestrials. planets, each of which expands to another 10 new planets, will quickly colonize the entire galaxy. This premise is based on observations of the human population, such as our growth from about 1 million

DAN PAGE

For ages, humanit y has looked to the skies and pondered whether intelligent life ever developed elsewhere. In 1950 physicist Enrico Fermi made a back-of-theenvelope calculation to estimate the time required for a technological civilization to spread throughout our galaxy. Fermi realized that a civilization expanding exponentially at even 1% of light speed could colonize the entire galaxy in just 10 million years. Following his reasoning, we now know that the Milky Way Galaxy is approximately 10 billion years old, whereas life on Earth arose around 4 billion years ago. Plenty of time has elapsed for intelligent life to develop elsewhere. So if any technological extraterrestrial society exists, then they should have visited us by now. Known today as the Fermi paradox, this apparent contradiction between observations and expectations raises the question: Where are they? Many explanations have been proposed to account for the conspicuous absence of extraterrestrials. Perhaps life as found on Earth may be a cosmic anomaly that only arises once or twice in an entire galaxy. A more cynical perspective maintains that civilizations inevitably destroy themselves, facing nuclear winter rather than interstellar domination. Then again, members of an extraterrestrial galactic club could already be observing us, following a Prime Directive to remain hidden until they deem us worthy of contact. We revisited Fermi’s original assumption that civilizations spread exponentially throughout the galaxy. For example, a civilization that deploys colonists to 10 86 worldmags

March 2010 sky & telescope

to nearly 7 billion people over the last 10,000 years. But we are now learning that, despite the seeming vastness of Earth’s resources, this rapid expansion frequently proves unsustainable because it consumes resources faster than they are replenished. If growth outstrips resources, human

civilization may collapse. This could also explain the absence of extraterrestrials: despite the seeming vastness of the galaxy, perhaps exponential expansion is also unsustainable on a galactic scale. If this Sustainability Solution explains the paradox, then rapidly expanding civilizations face severe issues upon complete colonization of the galaxy. With no new available resources and no room left to grow, unsustainably growing galactic civilizations may inevitably collapse. Because this process occurs over millions of years — compared to the multi-billion-year history of the Milky Way — if any extraterrestrial civilization successfully expanded through the galaxy, we would not have seen any signs of them. Their rise and fall would have been too quick for us to notice. We may be able to detect the aftermath of their expansion and collapse, but such “civilization graveyards” would escape our notice much more easily than the civilizations themselves. The galaxy may be fi lled with sustainably living extraterrestrials that grow within the carrying capacity of their environment, expanding too slowly to have yet reached Earth. But if unsustainable rapid growth led to the demise of past galactic civilizations, then perhaps the challenge rests with human civilization to become responsible consumers and ensure our own long-term survival. ✦ Jacob Haqq-Misra is a Ph.D. candidate in meteorology and astrobiology at Penn State University. Seth Baum is a Ph.D. candidate in geography at Penn State University.

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