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Astronomy on Tap becomes a hit p. 58 ONLINE • CONTENT 12 Issue Meet the master of stellar vistas p. 52 CODE p. 3 iOptron’s new mount tested p. 62 ˜ÛiÃÌʈ˜ÊޜÕÀÊi˜œÞ“i˜Ì°°°

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Tele Vue APO refractors earn a high yield of happy owners. 35 years of hand-building scopes with care and dedication is why we see comments like: “Thanks to all at Tele Vue for such wonderful products.” The care that goes into building every Tele Vue telescope is evident from the first time you focus an image. What goes unseen are the hours of work that led to that moment. Hand-fitted rack & pinion focusers must withstand 10lb. deflection testing along their travel, yet operate buttery-smooth, without gear lash or image TV-60 shift. Optics are fitted, spaced, and aligned using proprietary techniques to form breathtaking low-power views, spectacular high-power planetary performance, or stunning wide-field images. When you purchase a TV-76 Tele Vue telescope you’re not so much buying a telescope as acquiring a lifetime observing companion. Comments from recent warranty cards

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*"ÊÌ >ÌÊÜ>ÃÊ>vvœÀ`>Li°ÊÊ/ >˜ŽÃÊvœÀÊ “>Žˆ˜}ÊÃÕV Ê>Ê}Ài>ÌÊÃVœ«i°ÊʏœœŽÊvœÀÜ>À`Ê̜ʓ>˜ÞÊÞi>ÀÃʜvÊi˜œÞ“i˜Ì°»p,°°]" NP127is/fli Tele Vue® Visionary /iiÊ6ÕiÊ"«ÌˆVÃ]ʘV°]ÊÎÓÊ Ž>ÞÊ ÀˆÛi]Ê iÃÌiÀ]Ê iÜÊ9œÀŽÊ£ä™£nÊÊn{x°{ș°{xx£ÊÊÜÜÜ°/ii6Õi°Vœ“ Online Content Code: ASY1612 Enter this code at: www.astronomy.com/code DECEMBER 2016 to gain access to web-exclusive content VOL. 44, NO. 12 NASA, ESA, SAO, CXC, JPL-CALTECH, AND STScI JPL-CALTECH, CXC, NASA, ESA, SAO, ON THE COVER The Antennae galaxies in Corvus, NGC 4038 and NGC 4039, provide a spectacular example of a galaxy merger.

COLUMNS 26 Strange Universe 10 CONTENTS BOB BERMAN For Your Consideration 14 FEATURES JEFF HESTER Secret Sky 18 20 COVER STORY 36 52 STEPHEN JAMES O’MEARA When galaxies Sky This Month Meet the master Observing Basics 65 Inner planet convention. MARTIN become cannibals of stellar vistas GLENN CHAPLE Some galaxies harbor a sinister RATCLIFFE AND ALISTER LING How I took the astroimaging secret: They’ve eaten their siblings. road less traveled. TEXT AND Astro Sketching 66 MICHAEL WEST 38 IMAGES BY ROGELIO BERNAL ERIKA RIX StarDome and ANDREO Binocular Universe 68 26 Path of the Planets PHIL HARRINGTON Explore the impact that RICHARD TALCOTT; 58 killed the dinosaurs ILLUSTRATIONS BY ROEN KELLY I’ll have a Cosmo QUANTUM GRAVITY As scientists drill into Mexico’s By combining science with a few Chicxulub crater, they expose 44 stellar brews, Astronomy on Tap Snapshot 7 geologic clues about the massive Ask Astro has become a hit. LIZ KRUESI Astro News 8 impact that transformed Earth. Black and blue Moon. MAX ALEXANDER 62 IN EVERY ISSUE 46 Putting iOptron’s From the Editor 6 32 How moon dust will put new mount to the test How to observe a ring around Mars Easy setup, whisper-quiet Letters 10, 14, 65 colorful open clusters Phobos, a moon of Mars, operation, and superb accuracy New Products 64 You think star clusters are boring? is destined to be shredded, make this mount a winner. Advertiser Index 73 Wait until you see these colorful changing the Red Planet forever. PHIL HARRINGTON gems — they’ll knock your socks JOEL DAVIS Reader Gallery 70 off. PHIL HARRINGTON Breakthrough 74

Astronomy (ISSN 0091-6358, USPS 531-350) is ONLINE published monthly by Kalmbach Publishing Co., 21027 Crossroads Circle, P. O. Box 1612, Waukesha, WI 53187–1612. Periodicals post- FAVORITES age paid at Waukesha, WI, and additional offices. POSTMASTER: Send address changes to Astronomy, P.O. Box 62320, Tampa, Fla. 33662-2320. Go to www.Astronomy.com Sky This My Science News Trips & Tours Canada Publication Mail Agreement #40010760. for info on the biggest news and Week Shop The latest updates Travel the world observing events, stunning photos, We pick out the The perfect gifts from the science with the staff of best targets for for your favorite and hobby. Astronomy. informative videos, and more. the week ahead. science geeks.

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For information on all of our products and services, or to find an authorized Sky-Watcher USA dealer near you, just visit www.skywatcherusa.com. Don’t forget to follow us on Facebook and Twitter for exclusive offers! FROM THE EDITOR BY DAVID J. EICHER Editor David J. Eicher Art Director LuAnn Williams Belter EDITORIAL Managing Editor Kathi Kube Senior Editors Michael E. Bakich, Richard Talcott Associate Editor John Wenz One frame in the Copy Editors Dave Lee, Elisa R. Neckar Editorial Assistant Nicole Kiefert ART Graphic Designer Kelly Katlaps Illustrator Roen Kelly cosmic movie Production Coordinator Jodi Jeranek CONTRIBUTING EDITORS Bob Berman, Adam Block, Glenn F. Chaple, Jr., Martin George, lthough none of us of infant suns, huge globular were small blobs that lack Tony Hallas, Phil Harrington, Korey Haynes, Jeff Hester, Liz Kruesi, Ray Jayawardhana, Alister Ling, Steve Nadis, knew what a galaxy clusters that contain some of the order and size of more Stephen James O’Meara, Tom Polakis, Martin Ratcliffe, Mike D. was until 1923, when the oldest stars known, and recent galaxies in the nearby Reynolds, Sheldon Reynolds, Erika Rix, Raymond Shubinski Edwin Hubble came gas clouds. universe. Clearly galaxies EDITORIAL ADVISORY BOARD Buzz Aldrin, Marcia Bartusiak, Timothy Ferris, Alex Filippenko, along, we now know Galaxies also give us a way have assembled into larger Adam Frank, John S. Gallagher lll, Daniel W. E. Green, William K. Athe universe is filled with to frame cosmological ideas. structures over time, drawn Hartmann, Paul Hodge, Anne L. Kinney, Edward Kolb, Stephen P. Maran, Brian May, S. Alan Stern, James Trefil them. Estimates from the If cosmic inflation is true — together by gravity, and Hubble Space Telescope and the idea that the universe those encounters and merg- Kalmbach Publishing Co. other survey data suggest hyperinflated in the first ers have produced some President Charles R. Croft Vice President, Content Stephen C. George the cosmos contains at least fraction of a second of its spectacular cataclysms. Senior Vice President, Sales & Marketing Daniel R. Lance 100 billion galaxies, each a existence — the prospects get As West writes, within Vice President, Consumer Marketing Nicole McGuire Corporate Art Director Maureen M. Schimmel magnificent system of stars, even stranger. This would the past generation, astrono- Art and Production Manager Michael Soliday Corporate Advertising Director Ann E. Smith gas, and dust. mean the universe we see is mers have come to realize Single Copy Specialist Kim Redmond Some galaxies are large, not the entire universe, and that one of the primary ADVERTISING DEPARTMENT like the mammoth elliptical in fact the universe could be activities of galaxies is eating (888) 558-1544 Advertising Sales Manager Steve Meni systems that lie at the hearts infinite. But for simplicity’s each other. This is especially Advertising Sales Representative Dina Johnston, [email protected] of huge galaxy clusters. sake, let’s say we have a nice, true in dense galaxy clusters, Ad Services Representative Others are moderately sized, round 100 billion galaxies. as with the enormous central Christa Burbank, [email protected] like our own Milky Way, a Those galaxies we do elliptical galaxies that harbor RETAIL TRADE ORDERS AND INQUIRIES Selling Astronomy magazine or products in your store: majestic barred spiral that know about — or, more pre- supermassive black holes Phone (800) 558-1544, Press 3 Outside U.S. and Canada (262) 796-8776, ext. 818 contains on the order of cisely, the ones relatively and have laid their friends to Fax (262) 798-6592 400 billion stars including close to us — give astrono- waste. But it happens univer- Email [email protected] Website www.Retailers.Kalmbach.com our Sun. But numerous gal- mers excellent laboratories sally, too — even with the CUSTOMER SALES AND SERVICE axies are small — dwarfs in which to study how galax- Milky Way. The Sagittarius Phone (800) 533-6644 Customer Service [email protected] that have a fraction of the ies have evolved over time. Dwarf Galaxy, for example, Digital [email protected] Milky Way’s size and are You do this with the Milky is a tiny galaxy on the fringe Back Issues [email protected] always imperiled, dodging Way every time you step out of the Milky Way that is cur- SPECIAL EMAIL ADDRESSES Ad Sales [email protected] the odds of being swallowed under a dark sky and gaze at rently being shredded and Ask Astro [email protected] Books [email protected] by more massive systems its star clouds running eventually will be absorbed Letters [email protected] that lurk nearby. through Cygnus and into our stately barred spiral. Products [email protected] Reader Gallery [email protected] For the past hundred Sagittarius. Astronomers do West’s story reminds us years, galaxies have given it with observatories and by that, as human beings, gaz- Editorial phone: (262) 796-8776; advertising: (888) 558-1544; customer service & sales: (800) 533-6644; outside the U.S. and Canada: astronomers a really exciting using sophisticated data- ing out into the universe, we (813) 910-3616. Copyright © 2016 Kalmbach Publishing Co., all rights reserved. This publication may not be reproduced in any form without test bed in which to under- collection techniques. What see but one still frame at a permission. Printed in the U.S.A. Allow 6 to 8 weeks for new subscriptions and address changes. Subscription rate: single copy: $5.99; U.S.: 1 year stand how the universe they’ve found is tantalizing. time of a giant, enormously (12 issues) $42.95; 2 years (24 issues) $79.95; 3 years (36 issues) $114.95. Canadian: Add $12.00 postage per year. Canadian price includes GST, payable in U.S. funds. All other international subscriptions: Add $16.00 works. They are the basic In his story on page 20, long cosmic movie. And postage per year, payable in U.S. funds, drawn on a U.S. bank. BN 12271 building blocks of the cos- Lowell Observatory astrono- many of the earlier parts of 3209 RT. Not responsible for unsolicited materials. mos, if you will: Relatively mer Michael West describes this great movie were amaz- little matter exists outside the violent histories of many ingly violent, the scars from them, and they contain the galaxies that show evidence which scientists are just now really interesting stuff we of past chaos. Looking far detecting. love to look at. Aside from back in the universe’s his- stars and planets, this tory, as with the Hubble Yours truly, Follow Astronomy includes star clusters repre- Ultra Deep Field, it’s evident senting the hot birthplaces that very young galaxies www.twitter.com/ www.facebook.com/ plus.google.com/ AstronomyMag AstronomyMagazine +astronomymagazine Follow the Dave’s Universe blog: www.Astronomy.com/davesuniverse David J. Eicher Follow Dave Eicher on Twitter: @deicherstar Editor

6 ASTRONOMY • DECEMBER 2016 QUANTUM QG GRAVITY EVERYTHING YOU NEED TO KNOW ABOUT THE UNIVERSE THIS MONTH . . .

SPITZER BEYOND GASSY STARS GROOVY PHOBOS HOT BYTES >> NASA celebrated The ALMA radio obser- Odd grooves on Mars’ the Spitzer Space vatory reveals that some moon Phobos were TRENDING Telescope’s 13th birth- large stars keep large caused by debris knocked TO THE TOP day on August 25, and amounts of carbon loose from impacts that granted it a two-and-a- monoxide gas in their then fell back to the half-year extension. debris disks. moon’s surface.

SNAPSHOT Why do spiral galaxies spiral? Some 30 percent of galaxies in the cosmos are spirals. What makes their beautiful arms go?

Today we’re going to a time and place no one has yet witnessed. Early in the history of the universe, astronomers believe, gravitational instabilities between bright and dark matter formed galaxies. Spiral galaxies were born with a high angular momentum; the material that came together to make them was spinning at high velocities, which initiated the galaxy’s rotation, helping to lead to the winding arms. But that’s only part of the story. Many astronomers talk about two major types of spirals. Grand design spiral galaxies have prominent arms, and so-called flocculent spirals have weakly defined arms. Scientists invoke two major ideas to help explain spiral arms: density wave theory and stochastic star formation. Density wave theory, which explains grand design spirals neatly, suggests the galaxy’s spiral arms lie over dense regions of the disk that move at different speeds than the galaxy’s stars. Stars move in and out of

the arms over time, and the difference in DAN SMITH/ADAM BLOCK/NOAO/AURA/NSF; TOP: NASA/JPL-CALTECH, NRAO/AUI/NSF/D. BERRY/SKYWORKS, ESA/DLR/FU BERLIN (G. NEUKUM) gravitational attraction of stars and gas A face-on spiral galaxy like NGC 3184, which lies 40 million light-years away in Ursa Major, reveals the spiral twists of a clouds sets up a pattern that persists for very galaxy in near-eternal rotation. long periods. Stochastic star formation, which that appears spiral in shape. On top of this, maintaining the spiral pattern. addresses flocculent galaxies, proposes that “stochastic” refers to random star formation Computer modeling suggests these ideas surges of star formation occur in a also occurring, driven by supernovae and are solid, but astronomers have much to do self-propagating way that leads to a pattern furious stellar winds, which leads to yet to confirm them. — David J. Eicher

WWW.ASTRONOMY.COM 7 TEST CASE. A researcher used sound and ultra-cold atoms to create an artificial black hole to confirm Hawking radiation, ASTRONEWS providing a strong argument that Stephen Hawking’s idea of black holes emitting radiation is true. IO’S ATMOSPHERE PERIODICALLY COLLAPSES Jupiter’s moon Io is known for its surface when shaded by Jupiter. volcanoes, but a new discovery When temperatures on the suggests an even more complex moon drop below –235° F dur- world than once known. In ing its “nighttime,” Io’s atmo- research published August 3 in sphere appears to deflate. the Journal of Geophysical These periods occur fairly fre- Research: Planets, a group of sci- quently; two hours of every Io entists discovered that Io has an orbit (once every 1.7 Earth days), atmosphere, but only when it’s in the jovian moon is eclipsed. A NEW EXPANSION. This artist’s conception of Io and Jupiter shows the thin sunlight. During this time, most of the atmosphere of the moon as it hazes above the planet. Once out of sunlight, Using the Gemini North sulfur dioxide gas in the atmo- the atmosphere collapses to the surface. SWRI/ANDREW BLANCHARD Telescope’s Texas Echelon Cross sphere settles to the moon’s sur- Echelle Spectrograph (TEXES), face as frost. Once the moon in and out of Jupiter’s shadow for This breakthrough was pos- a group of scientists at the warms from sunlight, the atmo- about 40 minutes before and sible thanks to the specific capa- Southwest Research Institute sphere redevelops. after each eclipse. bilities of the TEXES instrument, documented unique atmo- The observations were made This is the first time astrono- which measures the heat radia- spheric changes on Io. They over a two-night stretch in mers have been able to directly tion emanating from the atmo- found that Io’s thin atmosphere, November 2013 when Io was observe Io’s atmosphere in sphere, allowing Gemini to pick which is mostly sulfur dioxide more than 420 million miles eclipse, as it is very difficult to up the faint heat signatures gas vented from volcanoes, col- (675 million kilometers) from detect the atmosphere in the of Io’s collapsing atmosphere. lapses and freezes onto the Earth. Io was observed moving darkness of Jupiter’s shadow. — Jordan Rice

SIZING UP THE MOONS OF THE SOLAR SYSTEM BRIEFCASE SIZING UP. Just how big are the moons of our solar Ga nym system? The Moon’s diameter may be 2,159 miles LOOKING LOW FOR ALIENS ed e: 3 (3,475 kilometers), but how does it compare to The Murchison Widefield Array, a new telescope ,27 3 m the rest of the solar system? To give you a in Western Australia, has the first low-frequency i (5 good idea, here are the largest moons of capabilities for the Search for Extraterrestrial ,2 M 6 Intelligence (SETI), searching in the 103 and 133 mega- e 8k each planet, along with an indication rc m u ) of how they compare to Mercury hertz band, which places it from the higher end of ry : and Pluto. Looking up at the FM radio up to aeronautical bands. This range makes it 3, 03 Moon at night, you could get easy to rule out terrestrial interference while providing 2 T m it a sense of what the other opportunities to listen for SETI signals while gathering i a ( n 4 : moons might look like at other astronomical data. ,8 3 M 8 ,2 the same distance. Of oo 0 0 • n k 1 : m course, most of them YOUNG STARS STILL FORM LIKE THE SUN 2 m ,1 ) 5 i would melt if they Even though blue giant stars tend to burn out after only 9 ( 5 m , orbited Earth, but a few hundred million years, they still form much like i 1 Tr (3 5 that’s neither the Sun. In research published August 22 in the P ito , 2 lu 4 k t n: 7 here nor there. Monthly Notices of the Royal Astronomical Society, o: 1 5 m 1 , ASTRONOMY: ROEN KELLY , 6 k ) researchers found a Keplerian disk (hot gases in orbit 4 8 m 75 0 AND JOHN WENZ m m ) around a protostar that helps it accrete) spinning close Tit i i an ( ( to a pair of blue giant stars. By witnessing the object ia 2 2 : , , 98 3 7 around an infant high-mass star, researchers discovered 1 7 0 m 4 0 that, despite their mass differences, large and small k k i m (1 m stars form in similar fashions. , ) 5 ) 7 Even though FAST • 8 k Ganymede and STERILE NEUTRINO SEARCH Phobos m FACT 13.7 mi (22.2km) ) Titan are bigger COMES BACK LIFELESS than Mercury, The IceCube observatory in Antarctica, run by the the latter is more University of Wisconsin–Madison, failed to find any massive than both trace of sterile neutrinos. Neutrinos are small particles moons combined. that interact weakly only with other matter, while ster- ile neutrinos take that one step further: They interact only with gravity itself. At least, they would if they existed. Evidence published August 8 in Physical Review Letters suggests that sterile neutrinos don’t exist at all — at least with 99 percent certainty. Had the sterile neutrino been discovered, it could have hinted at the nature of dark matter. Instead, we’re still stuck with the Standard Model — for now. — John Wenz MARS TOOL. Scientists developed a new, more accurate way to interpret Raman spectroscopy, a way of ASTRONEWS identifying atoms and molecules by their vibrations. The Mars 2020 rover will carry such a spectroscope. Much media ado about a SETI nothing QUICK TAKES MARS STREAKS The merest hint of anything involving Data from Mars Odyssey reveal aliens excites the public imagina- that if water exists at dark tion. So when news hit in August of a features called recurring slope potential alien signal, it hit hard. lineae, there is so little that it is Of course, that could be because akin to Earth’s driest deserts. the story is tantalizing. In 2013, a • strong signal in the 11-gigahertz CHARGED band was detected by the RATAN-600 BLACK HOLES radio telescope in Russia. The signal, New research suggests that if which seemed to come from star electrically charged black holes HD 164595, was at an unusually high merge, they might produce frequency and strength. Researchers signals like mysterious gamma- with the Search for Extraterrestrial ray bursts or fast radio bursts. Intelligence (SETI) flagged it for • follow-up. HUBBLE TWEETS “All we know about the HD 164595 In August, @Hubble_live began signal is the power and fit to the tweeting the space telescope’s beam profile,” Eric Korpela, a SETI@ observations both big and small, Home project scientist, said in an HELLO? ARE YOU THERE? This photo shows the RATAN-600 radio telescope in from taking calibration data to email. “If we only look at those two Karachay-Cherkessia, Russia. SETI researchers using the telescope recently detected showing small maps of its quantities, we have 450,000 events in a promising signal that turned out to be nothing out of the ordinary, but not before the current targets. the last 17 years of similar quality. media had a heyday with it. WIKIMEDIA COMMONS • That’s about 72 per day.” NO LIFE HERE The RATAN-600 astronomers lis- scientific vocabulary is different from “It was reported by the media as ‘a Exoplanet GJ 1132b might have tened for repeating signals, and 38 the public vocabulary. Detection, to baffling alien signal’ even though it oxygen in its atmosphere, but subsequent follow-ups found noth- me, means something was detected. was nothing,” Korpela says, adding that the intense heat it has suffered ing, nor did SETI Institute and To the public, it may translate as, ‘We follow-ups failed to find any signals. over eons close to its star has Breakthrough Listen Initiative follow- found aliens.’ ” If the time comes when there is a heated it to inhospitable levels. ups. “We didn’t find anything,” says But the signal could be just about promising signal, Shostak says the SETI • Seth Shostak, senior astronomer at anything. Both Shostak and Korpela Institute would try everything to rule PLEIADES DANCERS the SETI Institute. “Nor did they.” mention a microlensing event — out other possibilities, including pivot- The Kepler spacecraft turned That leaves a single detection, when a stellar object bends light (and ing the telescope to see if the signal its gaze to the Pleiades star which doesn’t meet the criterion for a hence radio waves) from a more dis- moves along with it (which would sug- cluster to learn why its stars full-on signal. But it seems the excite- tant object and amplifies it — as a gest something either terrestrial or spin at different rates. ment was much higher in the public possibility. It could also be any num- otherwise natural). From there, scien- Astronomers learned that eye rather than the SETI community. ber of astronomical objects. Or just tists might get cautiously excited and massive stars rotate slower How did this get out of hand? something on Earth, as Ars Technica reach out to another observatory. than smaller stars. “The initial reports came from a reported. “You’d get everyone in the world • trusted source, and contained words This is just the latest in a series of to aim their instrument, no matter NARROWER HOLE like detection and signal. That’s bound cautionary tales that stretch through what instrument they have, at the A suggested but unlikely to garner attention,” Korpela says. the entire history of SETI, something direction that the signal’s coming solution for dark matter is “There’s always the problem that Korpela is familiar with. from,” he says. — J. W. many small black holes; a new study further narrows the circumstances under which they could• exist. Titan’s COMET LANDSLIDE The Rosetta spacecraft spied an outburst on Comet 67P grand when water ice transformed into water vapor, kicking up canyons dust along the way. Scientists think a landslide DEEP AND DARK. By bounc- exposed the ice. ing radar signals to the bottom of deep and narrow features • around Vid Flumina, seen here, QUARK MATTER the Cassini spacecraft has Physicists suggest that future delivered evidence that Saturn’s gravitational wave observa- moon Titan sports canyons tions could reveal whether some 1,000 feet (300 meters) neutron stars contain only deep, but less than half a mile neutrons, or densely packed (1 kilometer) wide. Scientists had quarks instead. suspected the canyons existed, • as the branching network visible EARLY WORMS in images resembles Earth’s river Astronomers suggest that gorge systems. But the radar data because small stars live so provided the proof researchers long, life in the universe may needed to understand the depth be 1,000 times more likely in of the features, and to know for the distant future, implying sure that methane rivers run humans arrived early in the

NASA/JPL-CALTECH/ASI through them. — Korey Haynes universal timeline. — K. H.

WWW.ASTRONOMY.COM 9 STRANGEUNIVERSE FROM OUR INBOX BY BOB BERMAN Observing sunspots, now and later I’m a solar observer from the Midwest who recently read with You might see interest Steve O’Meara’s column in the September issue, regarding double in Epsilon naked-eye sunspot observing. It was very well done, like all his Just an Lyrae — if your columns I’ve read! eyes are good Anyway, O’Meara’s piece made me think of the brief section I arcsecond! enough. wrote for my book, Observing the Sun: A Pocket Field Guide (Springer, 2013), about this same topic. I’ve always found it fun to try to sight any large umbra that develop but never thought to find a ow well we see binary’s members are separated minimal size for my eyes. I just appreciate the novelty of catching a is central to our by 3.5', more than triple the glimpse. I reference Dawes’ Limit as a factor in determining sunspot observations. And 20/20 resolution requirement. visibility. In retrospect, that might be in error. The other issues sometimes, normal Yet less than 10 percent of adults mentioned may be of greater importance. (20/20) vision isn’t split it. Indeed, astronomy To answer O’Meara’s question about angular extent, I wish I Hquite enough. If we can read handbooks always say it’s resolv- knew, but the spots always have had to be unusually large for me! the eighth line of the Snellen able “only by keen eyesight.” Not Since you have brought up this question I’ll be certain to note eye chart, the examiner will say normal vision, but keen. dimensions in the future, but as we are slipping into a solar that our eyesight is fine. Why is it so oddly tough? minimum it may be several years before I can start. At 20 feet, each of those little Probably because 20/20 is mea- Thanks for the article. letters appears to be 1/6th the sured in bright light, whereas — Jamey Jenkins, Homer, Illinois width of the Moon. In both observing a 3rd-magnitude star breadth and height, they displace uses our far-inferior scotopic, We welcome your comments at Astronomy Letters, P. O. Box 1612, an angle of 5'. But distinguishing or rod-based, faint-light vision. Waukesha, WI 53187; or email to [email protected]. Please between the letters C, G, and O, Still, I remember observing include your name, city, state, and country. Letters may be edited for or between E and F, demands we Epsilon at age 17 and wonder- space and clarity. resolve gaps and lines within ing why it was called a test. I each letter. This requires that vividly recall that its gap looked our eyes see features just one- so wide, it seemed like you bringing it to the threshold of Uranus is 4", Neptune is 2", and fifth that large, or 1'. Thus, 20/20 could drive a truck through it. resolution. For example, the Pluto is just 0.1". Magnifying vision is defined as having one I was far from exceptional. Cassini Division in Saturn’s Pluto enough to be an arc- arcminute of resolution. Most eye doctors stop testing if brilliant rings will be 0.5" wide minute requires 600x. Because A single arcminute is 1/30th the patient can read the eighth next month. It might seem that such extreme power accentu- the width of the Moon. This Snellen line. The few who con- 120x power must be needed to ates air turbulence, the task is distance is quite tiny, since the tinue find that many young peo- enlarge it to the required 1'. But probably hopeless. Moon is smaller than most of ple easily see the ninth (20/15 in practice, most see that gap You and I are happy with a us visualize. The Moon appears vision) and sometimes even the with much lower power. That’s night where stars are globs a to be half the width of your single arcsecond across, but at pinky finger held at arm’s THE ISSUE: CAN YOU SEE THAT EPSILON professional sites they like 0.5" length. Because it’s 2,160 miles viewing. When we get down to (3,476km) across, our naked- IS NOT ONE, BUT TWO STARS? such minuscule angles, we’re eye resolution is 1/30th of that, considering breathtakingly tiny or 72 miles (116km). That’s the bottommost 11th line, which because an extended line is far things. smallest item you could spot on indicates 20/10 vision. In any easier to discern than a con- No star looks larger than the the Moon. You wouldn’t see a case, those with mere 20/20 usu- fined shape, like a Snellen letter supergiant Betelgeuse. Its lunar city. ally cannot resolve Epsilon. So or a jovian festoon. diameter of 1/20th of an arc- All this carries us to the won- its 3.5' gap might be considered The largest-seeming planet is second lies at the exact limit of derful Epsilon Lyrae, the star the actual limit for resolving Venus. At its closest, it’s essen- the Hubble Space Telescope. closest to Vega. For centuries it’s non-brilliant celestial objects. tially 60" wide, or an arcminute, More normal but much nearer been a sky-lover’s favorite. This An arcminute is further which is right at the 20/20 limit. stars, like Sirius and Alpha month it hovers in the west at divided into 60 arcseconds. An Can we therefore see it as a disk Centauri, appear only one- nightfall, directly above Vega. arcsecond, which we use a lot in and not a dot? Sure enough, tenth as wide as that — 1/200th The issue: Can you see that astronomy, is a truly tiny angle. some observers have reported of an arcsecond. Epsilon is not one, but two stars? It is the apparent size of a dime resolving Venus’ crescent shape These are angles resolvable by For 40 years, I’ve asked that seen from 2½ miles (4km) away. in twilight. That means they’ve no telescope. They lie beyond question under the stars, and I The arcsecond lies deep seen detail smaller than an arc- our observable horizon. noticed a clear pattern. Only a within the telescopic realm. minute, an impressive bit of few in a gathering of 50 say they When we use 60x magnifica- visual acuity. Contact me about my see it as double. With children tion, we boost a bright 1" object Jupiter gets up to 50" wide. strange universe by visiting http://skymanbob.com. and teens, it’s closer to half. The to appear an arcminute wide, Mars will be 24" in 2018.

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10 ASTRONOMY • DECEMBER 2016

ANCIENT OXYGEN. Using the Keck Telescope in Hawaii, astronomers measured how much oxygen existed in a galaxy ASTRONEWS from the universe’s toddler years, some 12 billion years ago. The galaxy has only 20 percent of the Sun’s proportion. No new stellar births in the galaxy’s center While numerous older stars can be found in our galaxy’s center, a new study suggests there’s a wide void of new star formation in one expanse of the Milky Way’s central region. The research was published August 2 in the Monthly Notices of the Royal Astronomical Society. Young, pulsating stars called Cepheid variable stars, or Cepheids, are used by astronomers to measure star populations in the galaxy. They are 10 million to 300 million years old — younger than our Sun’s 4.6 billion years — and their brightness pulsates in a repeating cycle. Because this pulsation time is related to luminosity, astron- omers can use this data to determine the stars’ actual brightness. They then compare the actual brightness with the brightness as seen from Earth, to determine the Cepheid’s distance. Finding these stars at the center of the galaxy is difficult because interstellar dust obscures the light and hides many stars from view. Using near- infrared observations from the South African Large Telescope, the researchers were able to see past the dust. To their surprise, they found hardly any Cepheids around an expanse about 1,000 light- years across, in the core of the galaxy. The results suggest that no significant amount

THE UNIVERSITY OF TOKYO UNIVERSITY THE OF of star formation has occurred in this area for VAST EMPTINESS. This map shows the distribution of Cepheid variable stars (in blue) in the Milky Way hundreds of millions of years. Researchers are still Galaxy. Cepheid variables dim and brighten over time, and because they are young stars, they can be working to understand why this region is so indicative of new star formation, which makes their absence in the core of our galaxy all the more stark. devoid of new star growth. — J. R.

12 ASTRONOMY • DECEMBER 2016 DEAD VOLCANOES. Astronomers determined that Mercury’s ASTRONEWS volcanoes probably shut down 3.5 billion years ago. Not the supernova you’re looking for

In the year A.D. 386, Chinese universe2go.com astronomers saw a new star light up the sky, and recorded its location carefully. In 1994, astronomers identified a super- WHAT IS UNIVERSE2GO? nova remnant — the glowing debris left behind by the stellar Universe2go is a completely new, explosion — called G11.2–0.3 augmented-reality star viewer and smart- in the right spot to be SN 386. phone app, which shows you the starry But now, a team that includes night sky in stunning detail! Place your one of those same astronomers smartphone in the viewer and observe the says the mystery remains. night sky with numerous, additional bits of information as well as sensational close- Infrared observations from UNSEEN BIRTH. X-ray observations of supernova remnant G11.2–0.3 2013 already cast serious confirm it is not the same supernova that exploded and wowed Chinese ups of various celestial bodies. doubt on G11.2–0.3. A team of astronomers in 386. X-RAY: NASA/CXC/NCSU/K. BORKOWSKI ET AL; OPTICAL: DSS researchers studied the dense clouds of material surround- Chinese astronomers, it still has star ignites again and explodes. ing the remnant and realized some claims to fame. The new The X-ray data also give the supernova at its heart data suggest it is one of the astronomers a better idea of would have been far too faint most recent core-collapse how the remnant’s debris cloud to see from Earth, no matter supernovae in the Milky Way, is expanding. While it appears Images of all 88 More than three how bright the explosion. at an age of only 1,400 to 2,400 to be a symmetric shell, constellations of hours of audio Now, new data from the years, exploding from a single detailed observations reveal the heavens explanations Chandra X-ray Observatory massive star collapse rather instead a complex and irregular confirm this finding. than a dense white dwarf steal- shape, helping researchers bet- Close-ups of Enjoyable But while G11.2–0.3 isn’t the ing material from a bigger ter understand the explosion’s planets, galaxies, exploration in quiz supernova recorded by companion until the smaller parent star. — K. H. star clusters and mode nebulae 3 The radial velocity of planet Proxima Centauri b, about THE PRESS SAYS mph the same speed as a human walking down the street. ASTRONOMY NOW: “For those at all levels of AVERAGE NUMBER OF CLEAR DAYS ANNUALLY experience in astronomy, it is definitely the next leap in the evolution of interactive sky map devices.” FAST FACT ORDER NOW Throughout $99 incl. Universe2go app unlock code. the year, Free shipping! on average, Order now with a 5% READER’S REBATE! Arizona is Promo-code: u2goatm16 the clearest (valid until 12/31/2016) state, and Washington is www.universe2go.com the cloudiest. Omegon is one of Europe‘s leading astronomy brands, now available in the US. You will find more information at www.omegon.com.

Less than 59.5 – 75.4 75.5 – 90.4 90.5 – 105.4 105.5 120.5 – 135.4135.5 – 150.4 150.5– 180.4 More than : MICHAEL E. BAKICH AND ROEN KELLY, AFTER NOAA AFTER KELLY, ROEN AND BAKICH E. MICHAEL : 59.5 180.4 – 120.4 ASTRONOMY

WWW.ASTRONOMY.COM 13 FORYOURCONSIDERATION BY JEFF HESTER In a shark’s eye Science and the experience of wonder.

een from above, the ocean trench where waves and Bahama Banks are a currents keep nutrient-rich spectacular sight. As I waters agitated, providing food write this, I’m looking for corals. out the window of an Even after three decades as an Sairplane and taking it in. Ripples avid diver, I still find it eerie to of color paint the ocean for miles be at the edge of the reef when on end. Bands of light green the flat bottom abruptly gives and blue give way to deeper way, becoming a vertical wall, turquoise. Beneath crystal clear covered in life. I can follow that Bahamian shark fest. From left: Jeff Hester’s son-in-law Casey, daughter Patricia, Jeff, water, undersea sand dunes wall down for about 100 feet and Jeff’s wife, Vicki (with shark and shark wrangler at top). JEFF HESTER formed by ocean currents stretch before I have to stop. My dive across vast expanses of flat- computer reminds me that I features pictures of celebrities countless billions of creatures bottomed shallows. The Bahama can’t stay here long. If I do, the who have come to watch divers lived or died over the millions Banks are the submerged top pressurized nitrogen in the air hand-feed sharks. We did a cou- of years that it took to evolve of the Bahama Archipelago, that I am breathing will turn my ple of those dives, and they are reactions so attuned to this limestone grown by corals mil- blood into deadly bubbles when spectacular to see, but they are environment? limeters at a time over the past I return to the surface. But the controlled. There is something Evolution offers me no such 100 million years or so. wall itself continues to plummet, compelling about having a shark advantages here. My survival But suddenly, the pastels give vanishing into the depths. This check me out, just the two of us depends on training and the way to sharp-edged, soul-swal- is the abyss. in open water, passing by closely technology that I carry on my lowing blue as dark as any the If the dive computer’s warn- enough to overfill the field of back. So why am I so at peace? seas have to offer. This is the ing is not enough of a reminder view of a wide-angle lens. What I feel here calls to Tongue of the Ocean, a trench that I am an interloper here, a We both know which of us is mind the first time that I that drops as much as 14,000 feet large dark shadow materializing at home, and who has the upper looked at the rings of Saturn to the ocean floor. out of the gloom adds empha- hand. I am aware of the sleek through a 3-inch refractor, or The boundary of the Tongue sis. It is far from the first time form, hard muscles and keen saw protozoans in a drop of of the Ocean is every bit as that I’ve encountered a shark eyes taking me in. I am also pond water under a micro- abrupt up close as it appears to under water. This is a aware of the teeth. I have never scope. It is what I felt as a kid be from 30,000 feet. I spent the Caribbean reef shark, an oppor- really felt in danger around working on a wheat farm when past week with family scuba tunistic feeder with a preference sharks, but let’s face it: There is at the end of the day I would diving on the living reefs that for an easily scavenged meal a reason the divers who feed shut down the tractor, lie down built these islands. Some of the over the need to hunt. them wear chainmail! on the ground, and look at the most spectacular of those reefs Sharks here are accustomed Sharks patrolling a reef usu- spectacularly dark skies of live right along the edge of the to divers. A local dive shop ally have a slow, relaxed motion. northwestern Oklahoma. Work at it and you can swim What I feel hanging there alongside for a time. But don’t with a shark in that column of FROM OUR INBOX imagine that means anything. saltwater is a sense of wonder. As this shark swims past, some- It is a sense of awe. It is a deli- Spreading the word thing catches its attention. With cious blend of pure aesthetic My other passion besides astronomy is cruising the waters and no warning it flicks its tail, and experience heightened by intel- islands of British Columbia and Washington state in our boat. before I fully register the change lectual understanding of the Most marinas up here have some kind of place to swap books in behavior, the shark is easily patterns and processes that and magazines as boaters tend to be readers of anything they 30 feet away and moving fast. shape the world. can get their hands on. I think to myself about the And I remember why I am a I always bring my Astronomy magazines with me on cruises evolutionary arms race that scientist. and drop them off going to any of the marina offices when we gifted the ancient and efficient dock. Like clockwork, by the time I come back in 15 minutes shark with such bursts of speed, Jeff Hester is a keynote speaker, they are all gone! What better way to celebrate the wonders of while also giving the fish that coach, and astrophysicist. astronomy? — Roland “Captain Triggerfish” Gorgas, Yelm, Washington attracted its attention a fair Follow his thoughts at jeff-hester.com. chance of escape. How many

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14 ASTRONOMY • DECEMBER 2016 NOVA LIVE. Astronomers using the OGLE sky survey saw a white ASTRONEWS dwarf devour matter from another star, brightening into a nova. Dark galaxy is mostly invisible DOKKUM/ROBERTO ABRAHAM/GEMINI OBSERVATORY/SLOAN DIGITAL SKY SURVEY SKY DIGITAL OBSERVATORY/SLOAN ABRAHAM/GEMINI DOKKUM/ROBERTO PIETER VAN HARD TO SEE. Dragonfly 44 is a galaxy with roughly the mass of the Milky Way, yet it has only a smattering of stars. By measuring the speed at which those stars whip around the galaxy’s center, astronomers determined that 99.99 percent of Dragonfly 44’s mass is in hidden dark matter. This is not the first time such dark matter- heavy galaxies have been found, but the others have mostly been dwarf galaxies much smaller in total mass. Dragonfly 44 is some 10,000 times heftier than most of its dark matter-dominated brethren. — K. H. Astrobabble From asterisms to Thorne-Żytkow objects, we turn gibberish into English.

AEGIS Chthonian planet >> Short for Autonomous This hypothetical type of Exploration for terrestrial planet began life Gathering Increased as a gas giant before stellar Science, it’s the new wind or other forces stripped artificial intelligence off its layers of hydrogen and system aboard the Mars helium. It could be identifi- Curiosity rover that able by having extreme mass enables the craft to target compared with its radius. interesting rocks without A few candidates do exist. input from NASA. Radio-quiet quasar Gravitational vortex A young galaxy that, while The spinning motion as a bright and visible to tele- material flows down scopes, doesn’t emit radio through an aperture, signals or have a large jet of much like a draining tub. material streaming out of its Some black holes may central supermassive black create these gravitational hole. A recent microlensing vortex swirls as materials event led to the discovery of are drawn in. mini-jets from radio-quiet quasars.

— John Wenz, [email protected] NASA AND FRANCE) CNRS, PARIS, DE D’ASTROPHYSIQUE (INSTITUT VIDAL-MADJAR ALFRED AGENCY, SPACE EUROPEAN

WWW.ASTRONOMY.COM 15 SPITZER GOES “BEYOND.” The Spitzer Space Telescope, ASTRONEWS an infrared observatory, may hunt exoplanets in its new mission. NASA/JPL-CALTECH/UNIVERSITY OF ARIZONA OF NASA/JPL-CALTECH/UNIVERSITY Red Planet’s reversed riverbeds UPSIDE DOWN. Scientists using the Mars Reconnaissance Orbiter identified signs of ancient rivers on Mars’ Arabia Terra. While fossilized rivers exist in many areas on Mars, they had not been seen in great numbers on Arabia Terra. Models suggested the area should have received heavy rainfall in Mars’ younger days. The rivers there, similar to those seen on other parts of the Red Planet, are not canyons but instead are ridges where dry riverbeds resisted erosion as the ground around them wore away. — K. H. The weirdest star in the galaxy keeps getting weirder Everyone’s favorite mysterious star, KIC 8462852, otherwise known as Tabby’s Star, has seen a lot of press in the past year, thanks to a strange and as-yet-unexplained dim- ming trend that has led to wild speculation of everything from comet swarms to black holes to alien megastructures. But now, the read- ings have gotten even stranger. Two researchers — Ben Montet from California Institute of Technology and Joshua NOT ALIENS. PROBABLY. This image shows Simon from the Carnegie Institution — found KIC 8462852, aka Tabby’s Star. Long-term dimming evidence that not only did the star’s light dip — combined with periodic dimming of more than up to 20 percent in some kind of transit event, 20 percent of the star’s light — has left astronomers but the total stellar flux also decreased contin- scratching their heads. DIGITAL SKY SURVEY/NASA/STScI uously over all four years that the Kepler spacecraft studied it. researchers, claims the star may have dimmed The team completed a new photometric by 19 percent over a century of observations. analysis of Tabby’s Star by closely examining Tabetha Boyajian, for whom Tabby’s Star is all of the full-frame images taken during named, used a Kickstarter campaign to secure Kepler’s mission. In the first 1,000 days, the observing time with the Las Cumbres Observa- star’s luminosity decreased about 0.34 per- tory Global Telescope Network for a full year. cent per year. In the following 200 days, the This should help determine why the star keeps flux dropped 2 percent, then leveled off. dimming — and what is causing those enor- Throughout the four years of Kepler’s mission, mous dips in light reported by Kepler. Though Tabby’s Star faded approximately 3 percent. if the past is any indication, it may lead to more Another report, disputed by some questions than it answers. — J. R.

16 ASTRONOMY • DECEMBER 2016 LATE STARTS. Hubble imaged two dwarf galaxies amid a flurry of star formation after entering a crowded ASTRONEWS region of space. Previously, the two galaxies spent billions of years in the empty Local Void. LAYING DOWN THE LAW Newly discovered solar system 100 Pluto object unveils new mystery Neptune Uranus Plenty of weird objects reside Saturn in our solar system, but the 10 newly discovered trans- Jupiter Neptunian object (TNO) Niku

Ceres (2011 KT19 ) might be one of the weirdest. 1 Mars Earth It’s not the composition of : RICHARD TALCOTT AND ROEN KELLY ROEN AND TALCOTT RICHARD : Semimajor axis (AU) Venus Niku that makes it strange. It Mercury seems to be a chunk of ice about 124 miles (200 kilome- ASTRONOMY 1 10 100 1,000 ters) in diameter, placing it at Period (years) the lower threshold of objects that might be considered KEPLER RULES. In 1619, German astronomer Johannes dwarf planets. There are Kepler discovered his third law: The square of a planet’s plenty of objects its size and orbital period (P) is proportional to the cube of its aver- composition in the Kuiper age distance from the Sun, or semimajor axis (a). Measure Belt and beyond. the period in years and the semi- Niku’s weirdness stems major axis in astronomical units FAST Kepler’s from its position far above FAR OUT, MAN. This illustration depicts a common distant (AU; one AU is the average Earth- the ecliptic, the sort of FACT third law works Sun distance), and the relation solar system object. Newly discovered trans-Neptunian object Niku “plane” of the solar system on for all groups becomes P2=a3. This plot depicts orbits in a retrograde orbit 110 degrees above the ecliptic. No one of orbiting the eight major planets and the which the planets lie, with is sure yet what pulled it to that orbit. ASA, ESA, AND G. BACON (STScI) objects, two brightest dwarf planets. Earth at the 0 degree point including Isaac Newton later found that an on the ecliptic. Niku is 110 itself very apparent. Instead, dwarf planets, like Sedna. The moons and object’s mass relative to the Sun degrees above it in a retro- Niku, detected by the answer may require finding exoplanet plays a small role, which is why grade orbit. Pan-STARRS 1 survey, is an more objects just like it — if systems. bulky Jupiter falls almost imper- Whatever pulled Niku into oddity, not part of the “Planet there’s an easy-to-find answer ceptibly above the line. its present orbit isn’t making Nine” series of elongated at all. — J. W.

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WWW.ASTRONOMY.COM 17 SECRETSKY BY STEPHEN JAMES O’MEARA Seven dwarfs of winter It’s worth seeking these objects in the snow-white Milky Way.

’ve always liked the new complex as NGC 1333. Push year’s sky. In the theme of Atik out of the field of view the season, it’s filled with for the best results. Or, see if one surprise after another. you can duplicate the result As sunset transitions to of Jack Kramer of the Lake Idarkness, you’ll find several County Astronomical Society dwarf nebulae and clusters in in Illinois. He saw the nebula IC 348 glows blue because it scatters nearby starlight and reflects it in our direction. a pair of constellations riding using only a 2" UltraBlock fil- The bright star in the field is magnitude 3.8 Atik (Omicron [ο] Persei). DON GOLDMAN high. These little gems visually ter held up to his eye! Although span less than 10' in angular the cluster contains more than object may spark some warm NGC 1624 extent, but most observ- 300 stars, a small telescope will memories. The Northern Trifid For those of you who like the ers can view them through show only a couple embedded is a 6'-wide combination emis- Cocoon Nebula (IC 5146) in a 4-inch telescope. A few of in the nebula. sion and reflection nebula Cygnus, you’ll note that my them demand a dark site, and about 8° east-northeast of Zeta next object is a bit reminiscent for some a nebula filter is a NGC 1857 (ζ) Persei. The nebula’s trifold of it. This tiny (3'-wide) open requirement. The ones I’ve The first open cluster I chose appearance is due to large cluster surrounded by a dim chosen populate the bound- glows at 7th magnitude and streamers of obscuring dust. nebula lies 4½° east-northeast ary region between Auriga lies 20,000 light-years distant. You’ll need magnifications of 4th-magnitude Mu (μ) Persei. and Perseus, which now reigns Look about 45' south-southeast of 60x or more — and lots of Through most amateur scopes, supreme around 9 p.m. local of magnitude 4.7 Lambda (λ) patience — to see any traces of it consists of a tight triangle of time. I’ll start with the most Aurigae. At low power through these features. Most obvious roughly 12th-magnitude stars conspicuous ones and then lead a 4-inch scope, the 10'-wide is NGC 1579’s round comet- embedded in an almost ficti- you to fainter quarry. cluster appears as a faint fog of like core, followed by a broad tious breath of nebulosity. light around a magnitude 7.5 southern spray of fainter light. NGC 1333 star. At 60x or greater, about NGC 2126 You’ll find this bright (6th- two dozen faint stars form an My final choice this month is magnitude) but tiny (3'-wide) irregular skirt of dim light a 10th-magnitude open clus- reflection nebula about 3¼° extending to the southwest. ter that small-telescope users west-southwest of magnitude might find difficult to see 3.8 Atik (Omicron [ο] Persei). NGC 1931 well. It lies in remote northern Start with low power, and look My fourth pick is a combina- Auriga about halfway between for a magnitude 10.5 star sur- tion object I’ve always liked. Menkalinan (Beta [β]) and rounded by a halo of light. This roughly 5'-wide nebula Xi (ξ) Aurigae. Fortunately a Higher magnifications reveal a and cluster floats about 50' 6th-magnitude star sits atop it, faint curved tail of nebulosity east-southeast of magnitude 5.1 making it easy to locate. Use connecting to a magnitude 12 Phi (ϕ) Aurigae. The roughly low power and averted vision, star to the southwest. If you 10th-magnitude glow is highly and imagine the cluster as an spot it, do you, like me, think condensed, but it takes mag- ill-defined fog of faint light the nebula resembles a comma? nification well. The cluster’s around the bright star. brightest members form a tight If you observe a feature in IC 348 triad at its core; a few fainter one of these objects that makes Next up is this 7th-magnitude jewels join them at high power. an impression on you, or if you star-forming complex that lies have a suggestion for an eighth immediately south-southeast Amateur astronomers often call “dwarf,” I’d love to hear about NGC 1579 NGC 1579 the Northern Trifid because of Atik. The 8'-wide nebula lies If, like me, you’re a fan of the of its resemblance to the Trifid Nebula it. Send your thoughts to in the same molecular cloud summer Milky Way, our next (M20) in Sagittarius. R. JAY GABANY [email protected].

BROWSE THE “SECRET SKY” ARCHIVE AT www.Astronomy.com/OMeara.

18 ASTRONOMY • DECEMBER 2016 SEE THE UNIVERSE LIVE AND IN COLOUR WITH MALLINCAM SKYRAIDER DS2.3PLUS The SkyRaider DS2.3PLUS video/imager/autoguider is the newest The DS2.3PLUS utilizes a 2.38 effective megapixel, ceramic CMOS in the SkyRaider family of astronomical video/imaging cameras. sensor. The sensor measures 13.4mm diagonally. The camera It includes the very latest Sony EXmor CMOS sensor to deliver delivers high-resolution images using all telescope types, and an the increased sensitivity needed for astronomical observation and optional focal reducer further increases the field of view needed imaging. The new SkyRaider DS2.3PLUS is ready for the most for those spectacular large astronomical objects. The EXview demanding applications in video/imaging astronomy, excelling at HAD is borrowed from Sony’s CCD sensor line, called EXmor. live observing of both deep-sky and solar system objects. The The CMOS sensor has significantly improved sensitivity and has MallinCam SkyRaider DS2.3PLUS is the most versatile video/ square 5.86 μm unit pixels with a high signal-to-noise ratio. The imaging camera ever created for computer use. Astronomical ceramic CMOS sensor used in the SkyRaider DS2.3PLUS is the objects can be observed live while images are captured or video very latest technology and the latest in high-tech sensors, with is being recorded. CCD-like performance. Using USB 3 technology, the MallinCam SkyRaider DS2.3PLUS delivers near instantaneous download speeds to the computer, perfect for displaying live images, capturing long and short exposures or recording video files. A fan-assisted passive cooling system ensures sensor temperature stability and super-low noise ratio. By utilizing the MALLINCAM SKY Software application’s Dark Field Correction feature, an internal Peltier cooler (TEC) is not needed. This results in the use of only a single cable from the camera to the computer’s USB 3 port. The Dark Field Correction feature removes all hot pixels, warm pixels and amp glow and keeps dark current noise low on the fly, making this premier astronomy camera the ideal choice in the field or in an observa- tory. The Dark Field Correction technology has been implemented by MallinCam for all its SkyRaider Series of cameras, elimi- nating the need for a Peltier cooler. Additionally, the new Live Stacking feature allows star registration to take place and further increases the signal-to-noise ratio, making it possible to keep exposures super-short and usable with an Alt-Az mounted motorized telescope, with excellent results in live mode or full imaging mode. If you are looking for the ultimate latest technol- ogy in an electronic assisted astronomy (EAA) camera system, large 13.4mm (diagonal) sensor, sealed optical multi-coated window, T mount and C mount included, look no further. The professional- grade MallinCam SkyRaider DS2.3PLUS camera delivers results that no other camera on the market can match in its price range. And it’s a MallinCam—a leader in live video Introducing the most versatile astronomy and imaging technology. video/imaging camera ever (U.S. FUNDS) created for computer use. $899.99 MallinCam.com SEE THE UNIVERSE LIVE AND IN COLOUR Available in the U.S.: Jack’s Astro Accessories, Louisiana. http://mallincamUSA.com 56-5450 Canotek Rd. For a list of Canadian dealers, contact us directly at [email protected] Ottawa, Ontario, Canada K1J 9G4 613-749-7592 CSI: Galaxies

When galaxies

Some galaxies harbor a sinister secret: They’ve eaten their siblings. by Michael West early a century after Edwin Hubble estab- lished the nature of galaxies as distant “island universes,” our understanding of their birth and evolution remains incomplete. While much current astro- nomical research focuses on galaxy forma- tion, a growing body of evidence suggests that galaxy destruction is also common. Countless galaxies have met their demise over the 13.8 billion-year history of the cosmos. The carnage is everywhere. Eat and be eaten! Galaxies are a gregarious bunch — where there’s one, there are usually others. This makes isolated giant galaxies like NGC become 1132 and ESO 306–017 cosmic oddities. Even more strangely, these hermits reside in vast seas of dark matter and hot gas that normally would be home to tens or hun- dreds of other galaxies. NGC 1132 and ESO 306–017 have a sinister secret: They’re cannibals. Evidence suggests that these behemoths grew to their bloated sizes by devouring their neighbors in a galactic feeding frenzy that would make Hannibal Lecter proud. And they’re not the only ones. Telescopes capture images of large galaxies devouring smaller ones in brazen acts of cosmic cannibalism, a single moment of a billion-year struggle frozen in time. Other galaxies are ripped apart by violent gusts of gravity from passing neighbors, scattering luminous shards along their path like a jet fighter breaking up in flight. The universe is littered with disembodied streams of stars, gas, and dust — the ghostly remains of once normal galaxies. Galaxy clusters, the urban centers of the cosmos, are especially dangerous places. Here, hundreds of galaxies are crammed into a region roughly spanning the dis- tance between the Milky Way and

Gravity shepherds galaxies together to form systems ranging from small groups to immense cosmic cities with thousands of members, like the Fornax galaxy cluster. But monsters lurk among them: cannibal galaxies. ESO/JOSÉ FRANCISCO (JOSEFRANCISCO.ORG)

WWW.ASTRONOMY.COM 21 Andromeda galaxies. Trapped galaxies. Tiny “ultracompact have now spotted hundreds of The local bully in such close confines, they dwarfs,” an intriguing class of ultracompact dwarfs, most in Astronomers began to suspect turn on each other. And as a galaxies discovered less than the nearby Fornax, Virgo, and that our own galaxy might be cannibal moves up through the two decades ago, appear to Coma galaxy clusters. a cannibal back in 1978 when weight classes, its increased have been slowly flayed by The surviving nuclei of Leonard Searle and Robert gravity makes grabbing new repeated encounters with larger some stripped galaxies might Zinn noticed that globular clus- victims easier. Survival of the brutes until all that remains are even masquerade as globular ters in the Milky Way’s outer biggest is the rule. their exposed innards — a clusters. Some researchers have regions have a surprisingly It’s a harsh reality for small compact nucleus. Astronomers speculated that several of the wide range of ages. This could Milky Way’s largest globular be explained, they reasoned, clusters, such as 47 Tucanae if our galaxy had snacked on and Omega Centauri, were smaller companions, inherit- once small galaxies. ing their globular clusters in G1, the brightest globular the process. The evidence was, cluster in the Andromeda admittedly, circumstantial. Galaxy — and indeed the entire Then, in 1994, Rodrigo Local Group — has a number Ibata, Mike Irwin, and Gerry of puzzling features that set it Gilmore found the smoking apart from other globulars. gun, proof of the Milky Way’s These include an unusually cannibalistic ways. Hidden elongated shape and the pres- against the dense backdrop of ence of multiple generations of stars toward the Milky Way’s stars within it. (Most globular center was the battered body of clusters are composed of mem- a small galaxy. The Sagittarius bers with uniform ages.) Dwarf, as the trio of astrono- There’s even evidence that G1 mers named it, is a barely dis- might harbor a black hole with cernible pile of stars slowly a mass equal to 20,000 Suns, relinquishing its four remain- something not seen in normal ing globular clusters to the globular clusters. Milky Way like lunch money to a schoolyard bully. Some evi- dence suggests that the Sagittarius Dwarf may have Clockwise from top left: Isolated giant galaxies like NGC 1132 are survived several trips around believed to be cannibals that the Milky Way, allowing our have devoured their neighbors. galaxy to savor its snack over Most of the smaller galaxies seen hundreds of millions of years. in this image are foreground or background objects not associated There’s now overwhelming with NGC 1132. NASA/ESA/THE HUBBLE evidence that our galaxy is a HERITAGE (STScI/AURA)-ESA/HUBBLE COLLABORATION serial cannibal. Astronomers The Hubble Space Telescope have discovered more than a captured this image of cosmic dozen long streams of stars in cannibal ESO 306–17, a gargantuan the Milky Way, vestiges of past galaxy about 500 million light- victims that it pulled apart like years away. NASA/ESA/THE HUBBLE HERITAGE (STScI/AURA)-ESA/HUBBLE COLLABORATION taffy before devouring. Researchers have dubbed NGC 5907 is an edge-on spiral galaxy one particular patch of sky surrounded by a ghostly stream of stars, the vestiges of a smaller (observed as part of the Sloan neighbor that it slowly devoured, Digital Sky Survey) the “Field leaving behind a trail of debris. of Streams” because it has sev- R. JAY GABANY/COSMOTOGRAPHY.COM eral crisscrossing ribbons of Caught in the act! Lurking in the stars, including one or more heart of the galaxy cluster Abell 3827 that snake back to the is one of the most massive galaxies in the local universe, a behemoth that Sagittarius Dwarf. Others, like could swallow dozens of galaxies the the appropriately named size of the Milky Way. The partially Orphan Stream, have no digested remains of several recently known ancestor galaxy. cannibalized galaxies are still visible in its center. R. CARRASCO ET AL./GEMINI The Pan-Andromeda OBSERVATORY/AURA Archaeological Survey, an

22 ASTRONOMY • DECEMBER 2016 NGC 660 bears the scars of a violent encounter that probably occurred about a billion years ago. The ring of gas, stars, and dust that encircles NGC 660 may be the twisted remains of a smaller galaxy that strayed too close. GEMINI OBSERVATORY/AURA

One way or another, cannibal galaxies usually give themselves away. international effort by research- ers to map the Andromeda Galaxy using the Canada- A FORENSIC TOOLKIT France-Hawaii Telescope on Edmond Locard, the father of modern forensics, tumultuous past. Careful analysis Mauna Kea, has found similar said, “Every contact leaves a trace.” Like forensic sci- can even provide insights into the stellar streams there. entists investigating a crime, astronomers search for number, types, and sizes of can- Which object will be the clues to reconstruct the histories of cannibal galax- nibalized victims. ies and their victims. As with any detective work, dif- Many other tools also can be Milky Way’s next victim? It’s ferent tools provide different information. used to dissect galaxies. hard to say — our galaxy Globular clusters are superb tracers of galaxy his- Spectroscopy provides informa- doesn’t appear to be a picky tories. Most galaxies are surrounded by tens, hun- tion on their internal motions, in eater. The Canis Major dwarf dreds, or even thousands of globular clusters that some cases revealing groups of galaxy, whose very existence is swarm around them like bees around a hive. These stars moving opposite to the rest. controversial because of its low massive, compact stellar systems — which have up These are most likely fragments of cannibalized gal- density of stars, is the nearest to a million stars packed into a region not much axies that haven’t yet been fully digested. In the larger than the distance from the Sun to its nearest Milky Way and other nearby galaxies, it’s also possi- potential target and may already neighbor, Alpha Centauri — are held together so ble to measure the chemical compositions of indi- be feeling the Milky Way’s grav- tightly by gravity that they’re almost indestructible. vidual stars and map them on the sky, which allows itational fury. It would add an Many survive the demise of their parent galaxies, the partial remains of defunct galaxies to be identi- estimated 1 billion new stars to providing a rich source of forensic material that’s as fied by their distinctive elemental abundances. Also, our home galaxy. valuable to astronomers as blood spatters, bodily numerical simulations of galaxy interactions serve Beyond that, dozens of small fluids, fingerprints, and DNA samples are to police as virtual telescopes that allow astronomers to peer galaxies surround the Milky investigators. into the past and future, guiding interpretation of Astronomers have studied globular cluster popu- observations. Way, and new ones are still lations in more than 400 galaxies to date, many of “Crime is terribly revealing,” wrote Agatha being discovered, such as the them with the Hubble Space Telescope’s exquisite Christie. “Try and vary your methods as you will, Crater 2 dwarf galaxy found vision. These observations reveal that most large your tastes, your habits, your attitude of mind, and earlier this year. The Large and galaxies possess two or more subpopulations of your soul is revealed by your actions.” One way or Small Magellanic Clouds, the globular clusters with distinct orbits, chemical com- another, cannibal galaxies usually give themselves Milky Way’s two largest positions, and spatial distributions — evidence of a away. — M. W. remaining companions, also

WWW.ASTRONOMY.COM 23 In about 4 billion years, residents of the Milky Way will have a stunning view of the approaching Andromeda Galaxy as it looms ever larger in the night sky before eventually merging with the Milky Way. NASA/ESA/Z. LEVAY AND R. VAN DER MAREL (STScI)/A. MELLINGER

Despite their voracious appetites, cannibals are messy eaters. Not all of the could end up as meals someday, almost 10 times faster than the think the cannibalism will end patches” of material in the and features like the ribbon of speed of New Horizons, the there. With dozens of other space between galaxies. He gas called the Magellanic fastest spacecraft launch to small galaxies in the Local realized that this diffuse glow Stream connecting the two date. A few billion years from Group, there’s plenty for was the collective light of clouds might be evidence of our now, our descendants — who- Milkomeda to munch on in innumerable stars that are not galaxy starting to nibble. But ever or whatever they may be the future. gravitationally bound to any recent evidence suggests the — will have a spectacular view In 2000, Swinburne galaxy but move freely between clouds are moving fast enough as Andromeda looms ever University astronomer Duncan them. Zwicky suggested that to escape the Milky Way’s grav- larger in the night sky before Forbes and colleagues won- rogue stars like this might be itational clutches — for now. engulfing the Milky Way. dered what complete cannibal- the most abundant luminous Outweighed two to one, the ism of the Local Group might objects in the universe. Cosmic karma Milky Way doesn’t stand much look like. Using computers, But where did these interga- Gravity, like death, is a great of a chance. After a flurry of they digitally assembled a lactic vagabonds come from? equalizer. The Milky Way, hav- encounters that will batter and Frankensteinian mix of all While it’s possible that some ing victimized countless galax- bruise both of them, the two known Local Group galaxies. might have been born outside ies over its lifetime, is destined galaxies will slowly come The final result — the last gal- of galaxies, most probably to become prey itself in 4 bil- together like tired boxers in a axy standing — turns out to be weren’t. Despite their voracious lion or 5 billion years. clinch until eventually indistinguishable from large appetites, cannibals are messy The Andromeda Galaxy, the Andromeda absorbs the Milky elliptical galaxies found eaters. Not all of the material largest member of our Local Way. From this chaos, a new, throughout the universe, a torn from victims is consumed. Group of galaxies, is heading larger galaxy will emerge that placid collection of stars and Some escapes into empty space our way. Although currently has already been nicknamed star clusters with few obvious where it accumulates over time separated by 2.5 million light- Milkomeda. The Sun, with its signs of past trauma. Forbes into a sea of orphaned stars and years, the Milky Way and planets in tow, will be one of and his colleagues christened it star clusters. Andromeda are hurtling more than a trillion stars that “the elliptical galaxy formerly Astronomers have already toward each other at 250,000 call this new galaxy home. known as the Local Group.” found thousands of free-roam- mph (112,000 meters/second), But there’s no reason to ing globular clusters in the Messy eaters nearby Virgo, Fornax, and Michael West is deputy director for science at Lowell Observatory in In 1951, pioneering Swiss Coma galaxy clusters, though Flagstaff, Arizona. His most recent book is A Sky Wonderful with Stars: 50 astronomer Fritz Zwicky none yet in the Local Group. Years of Modern Astronomy on Maunakea (University of Hawaii Press, 2015). noticed “large luminous But recently, Yale University

24 ASTRONOMY • DECEMBER 2016 CRIMES AGAINST GALAXIES Galaxies can suffer a variety of fates, some more macabre than oth- ers. Here are a few of the colorful terms that astronomers use to describe them:

CANNIBALISM The act of one galaxy devouring another.

HARASSMENT Coined by astronomer Ben Moore and colleagues in 1996, this term refers to frequent high-speed gravitational encounters that occur between galaxies in dense environments, such as galaxy clusters. These encounters are especially harmful to small galaxies and can even destroy them over time.

SHOCK A sudden compression of stars or gas, the cosmic equiva- lent of a gasp. Shocks can trigger the birth of new stars or cause old star clusters to break apart.

STRANGULATION When a galaxy’s gas supply is cut off, curtail- ing the birth of new stars. (Cold gas is the fuel of star formation.) Galaxies can die by slow strangulation in some environments.

STRIPPING The escape of stars from one galaxy caused by the gravitational pull of others. It also can refer to the removal of gas from galaxies when they plow through the hot plasma that perme- ates space in galaxy clusters.

THRESHING Similar to stripping, this is a more gradual removal of stars through repeated interactions that leave a galaxy’s inner- most regions intact. material torn from victims is consumed. VIOLENT RELAXATION Rapid fluctuations in a galaxy’s gravita- tional field during its birth or cannibalization cause stars to lose astronomers Graziella Di Tullio “The universe is made of memory of — and stray from — their original orbits, creating a sort of dynamical amnesia. — M. W. Zinn and Robert Zinn identi- stories, not of atoms,” wrote fied a dozen possible intergalac- poet Muriel Rukeyser. Every tic globular clusters in the Local galaxy has its own unique Group after they sifted through story, with harrowing tales of 183,791 candidates from the cannibalism, either happening Sloan Digital Sky Survey, like to them or that they created, miners prospecting for gold. woven throughout. Telling Further investigation will deter- those stories is the goal of mine whether these objects are astronomers — the forensic bona fide intergalactic globular scientists of the cosmos. clusters or faint faraway galax- ies that have been misidentified. Counterclockwise from top: The Long live the Milky Way might someday make a meal of the Large Magellanic Cloud, cannibal! seen here as a whitish smudge of Gravity’s relentless pull means light above the Atacama Large that cannibalism will continue Millimeter/submillimeter Array for billions of years to come. (ALMA) in Chile. ESO/C. MALIN It’s a future of fewer but big- The author observed giant elliptical ger galaxies. Eventually the galaxy 2MASX J01202313–0004443 carnage must end, however, as in the constellation Cetus with Lowell Observatory’s 4.3-meter the supply of available victims Discovery Channel Telescope. What dwindles. One hundred billion secrets of a violent past lie hidden years from now, long after the within it? MICHAEL J. WEST Sun has expired, a fully gorged 47 Tucanae is one of the largest Milkomeda will settle into globular clusters in the Milky Way. quiet old age as an elliptical Or is it? Some evidence suggests galaxy, the last survivor of the that 47 Tucanae might be all that remains of what was once a dwarf free-for-all that was once called galaxy. NASA/ESA/HUBBLE HERITAGE TEAM (STScI/ the Local Group. AURA)-ESA/HUBBLE COLLABORATION

WWW.ASTRONOMY.COM 25 Blast from the past EXPLEXPLOREORE THE IMPAIMPACTCT that killed the dinosaurs

As scientists drill into Mexico’s Chicxulub crater, they expose geologic clues about the massive impact that transformed Earth. words and location photos by Max Alexander

26 ASTRONOMY • DECEMBER 2016 ixty-six million years ago, a My journey to the Chicxulub city-sized asteroid collided with impact site begins on the long road from Cancún to Earth just off the coast of what Mérida. The highway cuts is now Mexico. The 6-mile- across the northern part wide (10 kilometers) space rock of the Yucatán Peninsula, crashed down near the town of where it crosses the buried outer rim of the crater. SChicxulub, some 180 miles (290km) west of Cancún. Tourists now enjoy the sunshine and warm waters here, but 66 million years ago, it was dinosaurs that claimed their place in the Sun. I am here on behalf of the Asteroid Day/ B612 Foundation to visit an offshore drill- ing platform where scientists are taking core samples to study both the geology and the The big dig biology of this catastrophic event. The sub- merged impact crater spans about 110 miles The enormous asteroid whose impact killed off much of Earth’s (180km). It’s less than the distance I travel life, including the dinosaurs, from Cancún to Chicxulub (pronounced struck just off the coast of Atlantic Mexico’s Yucatán Peninsula near CHICK-soo-loob) when I arrive on May 5, Ocean the town of Chicxulub Puerto. but the journey helps me grasp the enor- Gulf of Mexico

mous scale of the crater. It also hits me that M E the bottom of the crater is 12 miles (20km) X IC beneath me while the crater’s rim lies some O 2,000 feet (600 meters) below the surface — covered up by nature over tens of mil- lions of years. Caribbean The following day, armed with my Sea cameras, a GoPro for video, my shot list, and a sense of adventure, I head down to Chicxulub Puerto — ground zero for the Pacific Gulf of Mexico Ocean asteroid impact. Over time, geologic forces have thrust the Yucatán Peninsula upward to its current position. However, this is the spot where the asteroid struck, gouging out Outer rim a giant chasm in our planet and quickly Drilling 0 50 miles changing the direction of Earth’s history. site Peak ring 0 100 km I’m up before dawn to catch the early morning light. This so-called magic hour, Chicxulub which occurs around sunrise and sunset, Puerto offers a sumptuous period of lighting for Cancún taking pictures. If seen from space, this Mérida time would effectively coincide with Earth’s terminator, the transition from night to day (or day to night). The initial twilight gives Chichén Itzá way to what photographers call “bounce light” — sunlight bouncing off the atmo- sphere just before our star rises. It’s a beau- tiful soft light, still directional with some YUCATÁN PENINSULA degree of light and shade. It also possesses

warm colors, often magenta, depending on Campeche : ROEN KELLY how much dust hangs in the atmosphere. ASTRONOMY (Left) Scientists drill into the peak ring of the Chicxulub crater from this platform about 18 miles

(30 kilometers) off the Yucatán coast. AND NASA/JPL

WWW.ASTRONOMY.COM 27 This thick layer of rock in the Great Museum of the Maya World in Mérida is rich in iridium — an element rare on Earth but relatively abundant in asteroids. It is the smoking gun for the impact British astronaut Tim Peake photographed the Yucatán Peninsula and the surrounding Gulf of Mexico, that wiped out the dinosaurs and a majority of centered roughly on the Chicxulub impact site, from the International Space Station. ESA/NASA our planet’s other life 66 million years ago.

In exactly the opposite direction to the sources of water as well as sacred places Sun, I can see Earth’s shadow as a dark that served as gateways to the afterlife. PROTECT OUR PLANET blue band, drained of most of its color, On day two of the shoot, I visit the right down to the horizon. This shadow Chicxulub Crater Museum at the Yucatán ON ASTEROID DAY descends quickly, in concert with the rising Science and Technology Park. This is Asteroid Day is an annual global event that Sun. Above that appears the rosy-pink where some of the best samples from the brings together people from around the color of the Belt of Venus and, higher drilling will return after scientists have world to educate them and raise awareness still, a transition back to blue again. It’s analyzed them in Bremen, Germany. I then about the threat of asteroids — both to magic indeed! photograph iridium rock samples at the Earth and to life on our planet. It also I have to work quickly as the lighting Great Museum of the Maya World in actively supports ways to protect Earth from this threat through its partnership changes, and I shoot both toward the light Mérida. Researchers find this layer of irid- with various international space agencies and then in the other direction, using the ium, laid down 66 million years ago at the and prestigious institutions. rising Sun’s warm and still-soft light before boundary between the Cretaceous and Asteroid Day (asteroidday.org) is held it hardens. Meanwhile, I’m looking for help Paleogene periods, around the world. It is on June 30, the anniversary of the 1908 from Lady Luck — maybe pelicans dive- the smoking gun for the global events that Tunguska event in which an asteroid bombing for fish (birds evolved from dino- included the annihilation of 75 percent of exploded in the atmosphere and flattened saurs, right?), a passing boat, or some living species, providing an opportunity 800 square miles (2,000 square kilometers) of Siberian forest. This is the largest impact drama in the sky. for humans to one day evolve. in recorded history. The following day brings exciting news. Astronomy magazine is a major partner Scouting the crater British astronaut Tim Peake tweeted a pho- of Asteroid Day, with Editor David J. Eicher Back at the hotel, I meet up with my guide tograph he took of the Yucatán Peninsula serving as its editor-in-chief. I’m proud to be for the day. By lunchtime, we’ve made the from the International Space Station (ISS). Asteroid Day’s photographer-in-residence drive through remote villages to a cenote This image required a lot of planning and have been involved with this move- ment since its inception. — M. A. — a sinkhole that forms as groundwater because the ISS had to be in a favorable dissolves the surface limestone and causes orbit when he had some free time. Peake a collapse. Nearly 1,000 of these holes form scored a bull’s-eye, with the impact site training by email while he was on the ISS. an arc at a radius of about 55 miles (90km) lying smack in the middle of the photo. I suggested that he photograph impact cra- from ground zero, tracing out the south- I had asked Peake to take the photo- ters, and I provided him with a list of pos- ern boundary of the crater’s outer rim. To graph to coincide with the scientific expedi- sible targets that included Chicxulub. the ancient Maya, cenotes were valuable tion drilling into the impact crater, and also to help raise awareness for Asteroid Day Drilling for geologic gold Photographer Max Alexander specializes in (see “Protect our planet on Asteroid Day,” at On my final day, May 11, I join a mixture science communication, which has included two right). As part of my work for the UK Space of media, scientists, and returning drillers exhibitions at the Royal Albert Hall in London. Agency, I photographed Peake’s astronaut on a one-hour journey by supply boat to the He has a lifelong interest in astronomy and training in Germany and Russia. I also gave drilling platform. Expectations are running travels the world for his photographic projects. him some general on-orbit photography high, and many of us are no doubt thinking

28 ASTRONOMY • DECEMBER 2016 Snorkelers enjoy the deep-blue waters of the Yaluts’il Cenote, a sinkhole. Nearly 1,000 similar sinkholes trace the Chicxulub crater’s outer rim.

A pelican dives toward the sea off the coast of Chicxulub Puerto, the town closest to where a large asteroid smashed into Earth 66 million years ago.

A boatman plies the waters near Chicxulub Puerto. The asteroid that killed The shoreline of Chicxulub Puerto would have been within the blast zone of the dinosaurs and some 75 percent of all species crashed not far offshore. the impact that formed the crater named after the town.

WWW.ASTRONOMY.COM 29 Researchers used this massive drill (left) to dig deep into the peak ring of the Chicxulub crater. A drill operator (above) makes sure all systems are go for the next stage of drilling. The European Consortium for Ocean Research Drilling runs this operation.

drilled to a depth of 2,710 feet (825m), with a goal to get to 4,920 feet (1,500m) by early June — the cutoff date due to the start of hurricane season. (They ultimately would reach about 4,265 feet [1,300m].) The peak ring starts at about 2,130 feet (650m), so they already are drilling into this buried treasure. We only have about three hours on about the asteroid that crashed here so long tweeted his photograph of the drilling area board, and there’s a lot to see and photo- ago, convulsing the planet and causing from space. They are now on the lookout graph. Crew members bring three cores tsunamis, earthquakes, volcanic eruptions, for the ISS passing over at night. wrapped in thick protective plastic out and, most significantly for the larger world, The drilling, run by the European from the refrigeration unit for me to pho- an ash cloud that covered the planet for Consortium for Ocean Research Drilling tograph. Each one comes from a different many years and blocked out the Sun. as part of the International Ocean depth and has distinctive properties: sedi- The platform slowly appears on the Gulf Discovery Program, targets the crater’s mentary rock, impact melt (the crystallized of Mexico horizon. It is actually a boat, the peak ring — the structure created when the remnants of the rock that melted from the L/B Myrtle, raised about 115 feet (35m) impact’s heat liquefied the granite bedrock, heat of the asteroid impact), and a hybrid above the ocean floor by three pylons, each which rebounded to form a circular ridge. of impact melt and the pre-existing granite with a large pad that sits on the seafloor. It extends about 25 miles (40km) from bedrock known as breccia. The two lead We are loaded four at a time into what is ground zero. Planetary scientists see simi- scientists, Sean Gulick from the University called a Billy Pugh basket, with only two lar peak rings in large craters on the Moon, of Texas at Austin and Joanna Morgan vertical ropes keeping us from a plunge Mercury, and Mars. from Imperial College London, discuss the into the sea below, and hoisted aboard by Scientists chose this section of the samples while I take photos. a crane. There’s a real buzz on board, and impact feature partly because it lies at a The scientists are extremely excited about the crew is delighted that astronaut Peake depth that’s fairly easy to reach. They have their bounty. Morgan tells me that she can’t

30 ASTRONOMY • DECEMBER 2016 (Top) A crew member holds a diamond-tipped drill bit used to penetrate Earth’s crust and retrieve core samples from the peak ring of the Chicxulub crater.

(Above) Researchers used these drill bits to probe the parts of Earth’s crust modified by the giant Chicxulub impact. Core samples lie next to the bits. sleep for thinking about the science models that will come out of what they are seeing. Their discoveries are sure to rewrite part of Earth’s history, unlocking secrets about both the geology and how life re-established itself — and underpinning the serious dam- age asteroids can do to our planet. I then shoot some of the onboard labs, samples, diamond-tipped drills, and the drilling operation itself. Finally, I take some portraits of the scientists before they have to rush off for a live radio show. It’s all over very quickly. Almost before I have a (Top) Lead scientists Joanna Morgan (left) and chance to fully appreciate my visit, I’m back Sean Gulick inspect some core samples recently in the basket and positioned so I can get a brought up from the seafloor. high shot overlooking the drilling area as we are hoisted back onto the supply boat. (Above) Researchers analyze a core sample in the ship’s petrophysics laboratory. These initial Astronomy and dinosaurs — you really studies measure the core’s density, resistivity, can’t go wrong when you combine those and other properties. two things! The trip has been a blast — (Left) A scientist working in one of the labs on thankfully more muted than the one the drilling platform uses a microscope to study 66 million years ago — and certainly one a piece of shocked quartz formed as a result of I will long remember. the massive Chicxulub impact.

WWW.ASTRONOMY.COM 31 DEEP-SKY OBSERVING

How to

You think star clusters are boring? Wait until you see these colorful gems — they’ll knock your socks off. by Phil Harrington

Visible to the naked eye, the Pleiades star cluster (M45) stands out as a dipper-shaped grouping of brilliant blue- white suns. WARREN A. KELLER he universe is full of wonderful, telescope. Records show that Hipparchus colorful vistas. One glance at some was first to record its existence as far back of the glorious color photographs as the second century b.c. Further proof of found throughout this magazine the cluster’s pre-telescopic prominence is certainly makes that clear. evident by the pair’s alter egos of h and Chi But when we look toward the (χ) Persei, assigned by early celestial car- heavens through our telescopes, tographers and originally intended to many people come away disap- denote bright stars. pointed to find that those colors Both clusters are primarily composed of are not as brilliant as they had hoped. Sadly, hot type A and type B supergiant, superlu- the fault is not with the stars, but with our minous suns. Some 200 stars call NGC 869 eyes. It turns out that under dim lighting, home, while NGC 884 is made up of about the human eye is nearly colorblind. 150 stars. Several red supergiants are vis- Yet not all color remains hidden from ible in NGC 884, but they are con- our view. Scattered throughout the sky are spicuously absent in NGC 869.

many vibrant open star clusters that shine The Pleiades. Is with a luster that can only be appreciated there any star clus- Forming the center of the con- by the eye of an observer peering carefully ter more spectacular stellation Taurus, through a telescope. There, strewn across a through binoculars the Hyades star velvety-black backdrop, is a king’s ransom than the Pleiades cluster is one of the closest to in stellar diamonds, rubies, and sapphires (M45)? If so, I don’t our solar system, shining with sparkling, iridescent hues of know of it. One look and in this image blue, red, yellow, and orange. at the Pleiades it hosts a tiny Before we begin our survey, here’s a through 7x or 10x greenish comet, Kushida. CHRIS SCHUR quick trick of the trade. When you look for binoculars and colors in stars, it helps to defocus the view you’ll feel like ever so slightly. By racking your scope’s eye- you’ve broken into the vault of that great piece outside of focus (move it toward your jewelry store in the sky! There before our eye) just a bit, you’ll actually enhance color eyes glow a dozen or more stellar blue sap- saturation. How far out of focus do you phires. Speckles of diamond dust, the clus- need to move the ter’s fainter stars, surround them. NGC 2244 is a eyepiece? It depends The Hyades. Even though it is not an colorful star largely on your eyes. actual member of the cluster, the brilliant cluster that is But give it a try; you orange star Aldebaran [Alpha (α) Tauri] condensing out of the surrounding may be surprised at adds dramatic color to the V-shaped Rosette Nebula, the improvement. Hyades. At 151 light-years away, the visible as a Now on with our Hyades is one of the closest open star clus- reddish wreath survey. ters to our solar system, with more than of nebulosity in the constellation NGC 869 and 130 of its stars brighter than magnitude 9. Monoceros. NGC 884. Except for Aldebaran is even closer, only about RICHARD MCCOY the Pleiades, no 60 light-years away. Together, they create other autumn cluster a beautiful scene through 7x to 10x binocu- compares to either NGC 869 or NGC 884, lars, ranking as one of the northern winter and when you add both together, the view literally overflows with splendor. Although Phil Harrington is a longtime contributing Charles Messier apparently never saw the editor of Astronomy. He is the author of our Double Cluster in Perseus, its discovery monthly column on observing with binoculars, dates to long before the invention of the and has written many astronomy books.

WWW.ASTRONOMY.COM 33 Bright Scorpius star cluster M6 is often called the Butterfly Cluster because of its graceful, of the “clusterites” shine with the charac- winglike shape. teristic blue-white hue of young stars, BERNHARD HUBL although a lone, ruddy beacon punctuates its center. binoculars M67 in Cancer is a crowded horde can pick up of some 500 stars that shine at 10th about two dozen magnitude and below. This great of the cluster’s population creates an impressive stars, while tele- sight in all instruments, but scopes cause the cluster especially through 4-inch and to burst with splendor. larger scopes. With low power, When first encountering many small- to medium-size M41, most observers immedi- telescopes display what appears ately notice how some of the brighter to be nebulosity engulfing the members create a central “keystone” figure cluster. This is only an illusion strongly reminiscent of the central part in because when you increase the the constellation Hercules. Many shine aperture and magnification, the with hints of yellow, orange, and blue- “clouds” blow away. In their place white. Most of the suns are crammed are myriad stars, many glowing with within 30', though some stragglers may be traces of yellow, orange, traced out to 45'. and red. These colors The Double Collinder 135 is a large, scattered open point to the fact that Cluster in Perseus, consisting of cluster in Puppis, south of Canis Major. M67 is largely made up NGC 869 and The brightest star in the cluster, magni- of mature stars, making NGC 884, forms tude 2.7 Pi (π) Puppis, is classified as an it is one of the oldest an incredibly orange supergiant and stands out nicely open clusters known. rich area of stars. THOMAS V. DAVIS among the other blue-white cluster stars. M6, north of the tail sky’s best binocular Collinder 135 includes the double star of Scorpius, has been The rarely clusters. Upsilon1 (υ1) and Upsilon2 (υ2) Puppis, just nicknamed the Butterfly Cluster for its observed cluster NGC 2244. Set north of Pi, and a solitary 5th-magnitude remarkable resemblance to one of those NGC 7209 in Lacerta appears in Monoceros about star to the west that collectively gives the graceful insects in flight. Most observers scattered 10° east-southeast of cluster a distinctive arrowhead shape. If can immediately spot two “wings” of stars throughout a Orion’s Betelgeuse, you have a good view to the south, as they spread out from the group’s more rich star field. ANTHONY AYIOMAMITIS open cluster Collinder 135 will quickly become one of densely packed “body.” While many tele- NGC 2244 is best your wintertime favorites, a hidden secret scopes have too restrictive a field of view to known to deep-sky for binocular observers that is missed by take in its full glory, binoculars and rich- observers as the power source behind the those viewing through telescopes alone. field instruments display a wondrous sight. famous Rosette Nebula (NGC 2237–9). Although the clouds of the Rosette are dif- ficult to glimpse visually, the cluster is bright enough to be seen through finder scopes and even with the naked eye on exceptional nights. M50, the only Messier object in Of the 80 stars that make up the celestial Binoculars immediately reveal the Monoceros, is a magnificent open cluster butterfly, more than a third are bright group’s half-dozen brightest stars held in a that sadly seems to be ignored by many enough to be seen through 10x binoculars. distinctive rectangular pattern. Brightest amateur astronomers. To locate this lovely Observers viewing through big binoculars of all is 6th-magnitude 12 Monocerotis, a flock, draw an imaginary line between can count almost 50 suns, while 6- to yellowish sun, followed close behind by a Sirius [Alpha Canis Majoris] and Theta (θ) 8-inch rich-field telescopes reveal just nearby blue-white star. Scattered within Canis Majoris, a 3rd-magnitude star about about all of the cluster members. The and surrounding the stellar rectangle lie 5° to the northeast. Using your finder, brightest star within M6 is a blazing orange more than 90 fainter stars. Together, they extend this line 5° northeast. There, lighthouse known as BM Scorpii, which is create a magnitude 4.8 splash across nearly within a triangle of faint stars, you should an irregular variable. Across an average a quarter-degree of sky. spot the 6th-magnitude glow of M50. period of 850 days, this star fluctuates M41 in Canis Major is one of the most M50 covers 16' and is made up of 80 between magnitudes 7 and 9. dazzling open clusters in the sky, regard- stars. About two dozen of these are visible M7, just southeast of M6, was first less of the instrument used to view it. through small telescopes, while an 8-inch recorded in the second century a.d., when Even through suburban skies, low-power scope easily quadruples that count. Most Claudius Ptolemy identified it as a

34 ASTRONOMY • DECEMBER 2016 Open star cluster M41 in the con- yellow 6th-magni- stellation Canis tude star lying close Major provides a dazzling array to the group’s center. of stellar gems Another yellowish south of the star is near its north- sky’s brightest NGC 7209. Few amateurs are familiar western border. star, Sirius. with this glittering treasure chest of stellar ANTHONY AYIOMAMITIS nebulous patch in his monumental work, NGC 6940 is a jewels because of its remote location in the Almagest. Sixteen centuries later, Messier striking open cluster obscure constellation Lacerta the Lizard. It included it in his now-famous catalog of lying just inside the northern border of lies 16° east of Deneb [Alpha Cygni] in deep-sky objects, where it remains as his Vulpecula. Astronomy columnist Stephen neighboring Cygnus, about a degree north list’s southernmost entry. James O’Meara, noting that this cluster of a tight isosceles triangle of 5th- and 6th- Messier’s description of M7 reads, in looks like a moth, called it “Mothra.” magnitude stars. part, “a cluster considerably larger than the All of the five dozen stars that make up Nearly all apertures show NGC 7209 preceding (M6).” To me, this seems a bit this rich collection shine like ice-blue sap- well. Through a 6-inch scope, the cluster sterile for such a magnificent cluster of phires against an inky-black backdrop, appears as a warm glow peppered with stars. My 7x50 binoculars give the illusion save for one renegade. That maverick also many stars 10th magnitude and fainter. of a three-dimensional effect, with many happens to be the group’s brightest star, Larger instruments increase the count to of the brighter stars almost floating in FG Vulpeculae, a ruby-red semi-regular almost 100 suns scattered loosely across a front of a field strewn with fainter points variable star. FG ranges in brightness from field 20' wide. of light. Colors abound in the stars of M7, magnitude 9.0 to 9.5 over about 80 days The colorful clusters mentioned here with several displaying soft hues of yellow and offers a striking color contrast with its provide just a sampling of what awaits and blue. The brightest star in M7 is a blue-white brethren. deep-sky observers in search of buried treasure hidden in the firmament.

Another notable open cluster in Monoceros, M50, rarely gets observed — and deserves Lying near M6, more attention. Ptolemy’s Cluster BERNHARD HUBL (M7) is bigger, brighter, and one of the most dazzling in the summer sky. THOMAS V. DAVIS

WWW.ASTRONOMY.COM 35 SKYTHIS Visible to the naked eye MARTIN RATCLIFFE and ALISTER LING describe the Visible with binoculars solar system’s changing landscape as it appears in Earth’s sky. MONTH Visible with a telescope December 2016: Inner planet convention

Venus’ right on the 2nd and a similar distance above the planet the following night. By December 4, the Moon moves to a point 6° to Mars’ right. Truth be told, however, you won’t need the Moon’s help to find Venus. The planet shines brilliantly at magnitude –4.2 in early December and brightens to magnitude –4.4 by month’s close. No other object comes close except when the Moon shares the sky. Venus also gains consider- able altitude during Decem- ber. The planet appears some 15° high in the southwest an hour after sunset early in the month. By New Year’s Eve, it Brilliant Venus pointed the way to Mercury (below) in this desert scene from January 4, 2015. The two planets will stands 25° high and sets light up evening twilight again this month. ALAN DYER nearly four hours after the Sun. The greater altitude hree bright planets should see Mercury. The disk that measures 8.0" across means that a telescope will adorn December’s innermost planet shines at and is just one-third lit. deliver sharper views. On the evening sky. Mercury, magnitude –0.5, bright The Moon pointed the way 31st, Venus shows a disk 22" Venus, and Mars line up enough to see against the to Mercury on December 1, across and 57 percent lit. above the southwestern twilight with the naked eye, and it performs a similar ser- The inner planet calls Thorizon, changing positions though you may need binocu- vice for the other evening three different constellations relative to one another night lars to locate it initially. Point planets in the days after. The home this month. It spends by night. As a bonus, the Red a telescope at Mercury and waxing crescent lies 8° to December’s first week in Planet passes breathtakingly you’ll see a 5.6"-diameter disk close to Neptune on New that is 82 percent lit. An inner planet’s star turn Year’s Eve. The morning sky With each passing day, the appears more subdued, with inner world becomes a bit Venus brilliant Jupiter the lone planet easier to see as it climbs into visible in a dark sky. a darker sky. At greatest elon- The action gets underway gation on December 10, early on the evening of Decem- Mercury lies 21° east of the ber 1. Thirty minutes after sun- Sun and appears 7° high a set, a two-day-old Moon stands half-hour after sunset. A tele- 15° high in the southwest. If scope reveals a disk that spans you drop two-thirds of the way 6.6" with sunlight illuminat- Mercury to the horizon from there, you ing 63 percent of it. SAGITTARIUS Although the planet starts 5° Martin Ratcliffe provides plane- to dim after greatest elonga- tarium development for Sky-Skan, tion, it maintains its altitude Inc., from his home in Wichita, for another week. The view December 10, 30 minutes after sunset Looking southwest Kansas. Meteorologist Alister through a telescope also Ling works for Environment improves. On the 17th, mag- Mercury lies low in evening twilight during December’s first half. Use Venus Canada in Edmonton, Alberta. nitude 0.0 Mercury shows a as a guide to find the innermost planet. ALL ILLUSTRATIONS: ASTRONOMY: ROEN KELLY

36 ASTRONOMY • DECEMBER 2016 RISINGMOON At the edge of a tranquil sea Julius Caesar and Rima Ariadaeus

The gorgeous crescent Moons nature create this weird land- Julius Caesar that adorn early December’s eve- scape? Scientists have pieced ning sky show an abundance of together the likely story. First, features through any telescope. an asteroid slammed into the Mare Tranquillitatis The most striking details appear young Moon, carving out the Arago along the terminator, the line huge Mare Tranquillitatis basin. that divides day from night, Next, a smaller impactor when the low Sun casts long scooped out the 55-mile-wide N Rima Ariadaeus shadows that exaggerate the crater Julius Caesar. The crater Ariadaeus apparent height of features. formed on a slope, which left its E Under a higher Sun, the topogra- eastern rim lower. Later still, lava phy seems to vanish. The north- welled up through cracks in the The crater named for Julius Caesar formed on a slope, and lava flows south ridges crossing the plains large basin next door. The rising later breached its eastern side. CONSOLIDATED LUNAR ATLAS/UA/LPL; INSET: NASA/GSFC/ASU of Mare Tranquillitatis stand out lava breached Julius Caesar’s on December 4, when sunlight eastern wall and swallowed the created when two zones pulled eastern end. By the next eve- first touches the ramparts of the central peak, too, but could not apart. The low Sun highlights ning (the 6th), the Sun reveals sharply defined crater Arago. reach the higher western wall. the roughness of the terrain the equally impressive Rima By the 5th, the illumination The long line south of Julius here. Ariadaeus Crater is the Hyginus to the west, though nearly matches that in the image Caesar is Rima Ariadaeus, a col- larger of the two overlapping Rima Ariadaeus has started at right. How did the forces of lapsed valley a half-mile deep craters just south of the valley’s to disappear.

eastern Sagittarius, passing 0.8° south of 9th-magnitude METEORWATCH Ursid meteors globular star cluster M75 on Active dates: December 17–26 the 6th. It crosses into Capri- Ursid meteor shower Peak: December 22 Will the Bear Moon at peak: cornus the following day and Waning crescent Maximum rate at peak: then makes a beeline through best the Twins? 10 meteors/hour the heart of the Sea Goat. The planet slides 1° north of this December typically features two CASSIOPEIA URSA constellation’s brightest star, fine annual meteor showers: the Polaris MAJOR magnitude 2.8 Delta (δ) prolific Geminids and the minor Radiant Ursids. Unfortunately, a bright Kochab Capricorni, on the 28th. The CEPHEUS Moon interferes with the Geminids URSA final day of 2016 sees Venus MINOR slip across the next constella- this year. The shower peaks on the tion boundary into Aquarius. night of December 13/14, the same night as this month’s Full Moon. The planet’s rapid motion DRACO Scattered moonlight will drown makes it appear as if it is chas- out all but the brightest meteors. ing Mars. The two planets The “shooting stars” appear to radi- stand 23° apart on the 1st; the ate from Gemini the Twins, while 10° gap shrinks to 12° by the 31st. the Full Moon lies one constella- At magnitude 0.8 in mid- tion to the west, in Orion. Although December 22, 1 A.M. December, Mars glows 100 rates can reach 120 meteors per Looking north times more dimly than Venus. hour in good years, the Moon likely Expect to see up to 10 meteors per hour coming from Ursa Minor on the Still, the Red Planet appears will reduce this by 90 percent. night of December 21/22, at least before the Moon rises around 1 A.M. conspicuous because of its You’ll probably have more suc- greater altitude and distinc- cess viewing the Ursids. This after 1 A.M. local time. The best Little Dipper’s bowl, in the con- tive color. shower peaks on the night of views should come within an stellation Ursa Minor the Little Mars begins the month in December 21/22 under a waning hour of midnight. The shower’s Bear. Expect to see 10 meteors central Capricornus. Its east- crescent Moon, which rises just radiant lies near Kochab in the per hour under a dark sky. ward journey carries it 1.5° north of Delta Cap on Decem- OBSERVING Mercury shines brightly in evening twilight around the time ber 11, and it crosses into HIGHLIGHT — Continued on page 42 of its December 10 greatest elongation.

WWW.ASTRONOMY.COM 37

STAR N

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DOME MAJOR URSA _ _

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sky as seen near 35° north latitude. Located O

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the direction you’re facing. The NE

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P.M. ` Castor 9 December 1 Pollux

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7 P.M. December 31 _ +

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` a o ¡ ` STAR COLORS A star’s color depends NGC 253 on its surface temperature. FORNAX SGP The hottest stars shine blue _ • SE _ Slightly cooler stars appear white T • SCULP • Intermediate stars (like the Sun) glow yellow • Lower-temperature stars appear orange • The coolest stars glow red e _ • Fainter stars can’t excite our eyes’ color a receptors, so they appear white unless you PHOENIX use optical aid to gather more light `

38 ASTRONOMY • DECEMBER 2016 S Note: Moon phases in the calendar vary in size due to the distance from Earth DECEMBER 2016 and are shown at 0h Universal Time. SUN. MON. TUES. WED. THURS. FRI. SAT. MAP SYMBOLS

Open cluster ` 123

O Globular cluster i DRAC

Diffuse nebula a 45678910

NW Planetary nebula

` Galaxy

Vega 11 12 13 14 15 16 17 _

: ROEN KELLY ROEN :

¡ LYRA

18 19 20 21 22 23 24 ASTRONOMY

M57 a

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25 26 27 28 29 30 31

ILLUSTRATIONS BY BY ILLUSTRATIONS

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VULPECULA Calendar of events A

2 Asteroid Vesta is stationary, 18 The Moon passes 1.0° south of

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3 The Moon passes 6° north of 19 Mercury is stationary, 2 A.M. EST c

a Venus, 8 A.M. EST

SAGITTA 20 Last Quarter Moon _

_ 5 The Moon passes 3° north of occurs at 8:56 P.M. EST

Altair d

` Mars, 6 A.M. EST AQUILA ` 21 Winter solstice occurs at

` W 6 The Moon passes 0.7° north of 5:44 A.M. EST +

DELPHINUS Neptune, 5 P.M. EST M15 22 Ursid meteor shower peaks 7 First Quarter Moon occurs at 4:03 A.M. EST The Moon passes 2° north of Enif

PEGASUS _ Jupiter, noon EST _ 9 The Moon passes 3° south of c EQUULEUS P.M. 25 The Moon is at apogee (252,196 e Uranus, 3 EST miles from Earth), 12:55 A.M. EST _ 10 Saturn is in conjunction with

` a the Sun, 7 A.M. EST 27 The Moon passes 4° north of Saturn, 4 P.M. EST Mercury is at greatest eastern 28 Mercury is in inferior CAPRICORNUS elongation (21°), midnight EST Pa c onjunction, 2 P.M. EST th of the Sun (ecliptic) 12 The Moon is at perigee UARIUS Q a (222,737 miles from Earth), 29 New Moon occurs at b P.M. 1:53 A.M. EST b Mars 6:29 EST The Moon passes 0.5° north of Uranus is stationary, 11 A.M. EST Aldebaran, midnight EST SPECIAL OBSERVING DATE PISCIS 13 Full Moon occurs at AUSTRINUS 31 Mars appears within 0.1° .M. 7:06 P EST of Neptune during the evening hours. Fomalhaut Geminid meteor shower peaks _ SW TOR 15 Dwarf planet Ceres is stationary, 2 A.M. EST

BEGINNERS: WATCH A VIDEO ABOUT HOW TO READ A STAR CHART AT www.Astronomy.com/starchart.

WWW.ASTRONOMY.COM 39 PATH OF THE PLANETS The planets in December 2016

DRA Objects visible before dawn UMa LYN

HER CVn LMi PER LYR BOÖ GEM AUR

CrB COM Path of the Sun (eclip LEO Vesta tic)

SER CNC TAU OPH SER CMi Eunomia Celestial equator ORI VIR SEX LIB MON SCT oon Jupiter ERI of the M CRT Path HYA CRV Sun Saturn CMa LEP

PYX ANT COL LUP SCO PUP CAE CEN TEL VEL

Moon phases Dawn Midnight To locate the Moon in the sky, draw a line from the phase shown for the day straight up to the curved blue line. Note: Moons vary in size due to the distance from Earth and are shown at 0h Universal Time. 12

29 28 27 26 25 222324 21 20 19 18 17 16 15 14 13 12

The planets These illustrations show the size, phase, and orientation of each planet and the two brightest dwarf planets at 0h UT in the sky for the dates in the data table at bottom. South is at the top to match the view through a telescope.

Mercury Uranus Mars

S

WE Pluto N Saturn Venus Ceres Neptune Jupiter 10"

Planets MERCURY VENUS MARS CERES JUPITER SATURN URANUS NEPTUNE PLUTO Date Dec. 15 Dec. 15 Dec. 15 Dec. 15 Dec. 15 Dec. 31 Dec. 15 Dec. 15 Dec. 15 Magnitude –0.4 –4.3 0.8 8.3 –1.8 0.5 5.8 7.9 14.3 Angular size 7.3" 18.7" 6.1" 0.6" 33.9" 15.1" 3.6" 2.3" 0.1" Illumination 49% 64% 89% 98% 99% 100% 100% 100% 100% Distance (AU) from Earth 0.916 0.893 1.528 2.251 5.808 10.976 19.473 30.175 34.136 Distance (AU) from Sun 0.339 0.725 1.396 2.842 5.456 10.048 19.942 29.952 33.232 Right ascension (2000.0) 18h58.4m 20h45.3m 21h56.4m 1h30.8m 13h11.2m 17h21.3m 1h16.3m 22h44.4m 19h09.5m Declination (2000.0) –24°12'–20°21'–13°48'–0°05'–6°13'–21°51'7°24'–8°55'–21°25'

40 ASTRONOMY • DECEMBER 2016 This map unfolds the entire night sky from sunset (at right) until sunrise (at left). Arrows and colored dots show motions and locations of solar system objects during the month.

CAS DRA Objects visible in the evening Jupiter’s moons Dots display positions AND LAC Io CYG HER of Galilean satellites at 5 A.M. EST on the date Europa TRI LYR shown. South is at the top to match S ARI VUL the view PEG Ganymede through a WE SGE telescope. N Callisto Mars and Neptune approach Uranus PSC within 0.1° of each other OPH on December 31 AQL SER 1

2 Ceres AQR Melpomene 3 SCT CET Neptune Mars Pluto 4 Venus Sun 5 Jupiter SCL PsA CAP FOR SGR 6 CrA Mercury appears bright MIC in the evening sky during 7 PHE SCO GRU the first half of December 8 Early evening 9

10 31 30 29 28 27 11

12 11 10 9 8 1234567 13 Io

14

15 Earth Winter solstice is 16 Europa December 21 17 Ceres Venus Mercury 18 Callisto Ganymede Mars Greatest eastern elongation 19 is December 10 Jupiter 20

21

22

23

24

25

The planets 26 in their orbits Uranus 27 Jupiter

Arrows show the inner 28 KELLY ROEN : planets’ monthly motions Neptune Saturn 29 and dots depict the outer Solar conjunction planets’ positions at is December 10 30 midmonth from high above their orbits. Pluto 31 ILLUSTRATIONS BY ASTRONOMY BY ILLUSTRATIONS

WWW.ASTRONOMY.COM 41 — Continued from page 37

Mars visits Neptune WHEN TO VIEW THE PLANETS N EVENING SKY MIDNIGHT MORNING SKY Mercury (southwest) Uranus (west) Jupiter (southeast) Venus (southwest) Saturn (southeast) h Mars (south) Uranus (southeast) Neptune (south) E Neptune Mars

Aquarius on the 15th. The world providing a striking AQUARIUS planet reaches the middle of contrast to the warm, ruddy this constellation by New glow of Earth’s neighbor. Year’s Eve, when it has a Mars spans 5.7" on the 31st, spectacular reunion with 70 some 2½ times bigger than 0.5° Neptune. It’s the closest con- Neptune’s 2.2"-diameter disk. junction between these two One constellation east of The Red Planet skims within 0.1° of distant Neptune on New Year’s Eve, planets in more than 700 years. Aquarius lies Pisces the Fish, their closest approach since March 22, 1305. For observers in North the home of Uranus. The America, the two planets stand region stands high in the Piscium. This nice double star magnitude 6.0 star 88 Pis- 9.8' apart from the East Coast southeast after nightfall and lies 17° east-southeast of mag- cium, which lies 38' south- and just 4.4' apart from the climbs nearly two-thirds of the nitude 2.8 Algenib (Gamma [γ] southeast of Zeta. A telescope West Coast an hour before way to the zenith in the south- Pegasi), the star at the south- can confirm a planet sighting they set. Those in Hawaii see ern sky an hour or two later. eastern corner of the Great by revealing its 3.6"-diameter, closest approach, when Mars Although the planet shines at Square of Pegasus. Uranus blue-green disk. skims 1.3' north of Neptune. magnitude 5.8, bright enough lies less than 1° east of Zeta At about the time that The view through a telescope to see with the naked eye from throughout December. The Uranus dips below the west- will be spectacular. Neptune a dark-sky site, binoculars gap between the two closes ern horizon, Jupiter rises in looks like an 8th-magnitude make it much easier to spot. from 52' on the 1st to 35' dur- the east. There’s no mistaking satellite of Mars, with the icy To track it down, first ing the month’s final days. the giant planet — at magni- blue-gray hue of the distant locate 5th-magnitude Zeta (ζ) Don’t confuse Uranus with the tude –1.8, it is the brightest COMETSEARCH The start of good comet viewing Comet 45P/Honda-Mrkos-Pajdusakova N The next eight months promise 1.5° to the west-northwest. You’ll ` to be a comet-chaser’s paradise. actually see the globular first Astronomers predict that as because it shines about a mag- many as five comets could shine nitude brighter than 45P. But the e l at 10th magnitude or brighter, dirty snowball brightens at a p and three of them should come wonderful rate and should crack / k m within binocular range. The peak 8th magnitude by month’s end. E 31 Path of Comet 45P SAGITTARIUS should come in February and The best aspect of viewing d 27 March, but the exhibition begins this comet will be its razor-sharp 23 in the second half of December. tail. On December 21, comet M75 19 Comet 45P/Honda-Mrkos- watchers get an edge-on view CAPRICORNUS Pajdusakova arrives first. The of its fan-shaped dust outflow. Dec 15 Moon moves out of the evening Based on previous visits of this sky on December 15, opening a periodic comet, astronomers dark-sky window for the rest of expect it to show a round, blue- s 1° the month. You’ll need an open green head at the front of a This comet should brighten from 10th to 8th magnitude in the second view to the southwest and have gray-white spike. Imagers likely half of December as it glides eastward through the stars of Capricornus. eye to eyepiece an hour after will capture the faint blue emis- sunset. The comet lies about 15° sions from the tail’s ionized gas. Japanese astronomer Minoru after. The comet returns to the above the horizon on the 15th. Ten days later, on New Year’s Honda spotted the comet on inner solar system every 5.25 A bonus that evening is the Eve, astroimagers can catch a December 3, 1948, and Antonin years, but we don’t always get a presence of the 9th-magnitude pretty crescent Moon posing Mrkos and Ludmila Pajdusakova good view. Fortunately, this is globular star cluster M75 just just 3° from 45P. independently found it soon one of its best appearances.

42 ASTRONOMY • DECEMBER 2016 Ganymede plays hide-and-seek S LOCATINGASTEROIDS Callisto

Io A whale of a good show The largest object in the aster- magnitude 3.6 Theta (θ) Ceti, Jupiter oid belt by far is the dwarf located on the Whale’s back. planet Ceres, which spans an Then head 8° north to the W Ganymede impressive 600 miles and holds magnitude 5.6 star 42 Ceti, approximately one-third of the the brightest star on the chart asteroid belt’s entire mass. Two below. Ceres lies about 3° east years ago, astronomers knew of this star during the first half precious little about this giant of December before it starts 30" ball of rock and ice. But that moving northward at a signifi- Europa December 3, 4:30 A.M. PST changed dramatically starting cantly faster pace. in April 2015, when NASA’s The dwarf planet shines On December 3, people in western North America can see this jovian moon emerge from the planet’s shadow and then disappear behind its limb. Dawn spacecraft went into about as brightly as any of the orbit. Each month brings new background stars in its immedi- point of light anywhere in the behind the planet (an occulta- discoveries as planetary scien- ate vicinity. The map shows tists analyze the latest observa- stars down to magnitude 9.5, morning sky. tion). Only outermost Callisto tions. What better time could so you should be able to tell Jupiter moves slowly against avoids Jupiter entirely; you there be to track down this cap- which object is out of place the backdrop of central Virgo can find it due north of the tivating world through binocu- simply by comparing your eye- this month. On December 1, planet’s disk around 3 a.m. lars or a telescope? piece view with the chart. If you it stands 8° northwest of that EST on the 11th, for example. Fortunately, Ceres now can’t tell which of the myriad constellation’s luminary, 1st- A trio of satellite events climbs more than halfway to points of light is Ceres, make a magnitude Spica. The planet’s occurs on December 14. the zenith in the southern sky sketch of the area showing the eastward journey carries it to Ganymede, the solar system’s in early evening. Although it relative positions of five or six a point 4° north-northwest of largest moon, begins to transit dims from magnitude 8.1 to 8.6 stars. Return to the same field the star by the 31st. Jupiter’s north polar region at during December, it lies in a a couple of nights later to con- For the best views of Jupiter 2:40 a.m. EST. Although only fairly sparse region of Cetus the firm which object moved — through a telescope, wait until observers in eastern North Whale. To find it, first locate that one is Ceres. it climbs some 30° above the America can witness the tran- southeastern horizon an hour sit’s start, nearly everyone can Ceres loops through Cetus or so before twilight begins. see the conclusion at 5:08 a.m. The giant planet offers a disk Io’s shadow begins a transit N large enough (34" across at just seven minutes later, at 31 midmonth) to deliver exquisite 5:15 a.m., followed by Io itself detail through even the small- at 6:21 a.m. 26 est telescopes. Two broad, December 17 finds Europa CETUS dark, atmospheric belts — one beginning to transit Jupiter at Path of Ceres 21 on either side of a brighter 3:56 a.m. EST, just 17 minutes E zone that coincides with the before the same moon’s 16 equator — show up easily. shadow leaves the planet’s Under excellent observing con- disk on the opposite limb. 11 42 ditions, a series of alternating A nice set of events involv- 43 belts and zones pops into view. ing Ganymede takes place 6 But not all of the action from western North America Dec 1 resides in Jupiter’s atmosphere. on December 3. Because Earth 0.5° The planet boasts four large currently lies west of a line The asteroid belt’s only dwarf planet shines at 8th magnitude against moons that change positions joining the Sun and Jupiter, the faint background stars of northern Cetus the Whale. from night to night and some- we see the giant planet’s times within an hour or two. shadow extending to the west. Each of the three inner moons Ganymede orbits far enough the 3rd and remains in bright 90 minutes before the Sun and typically appears east or west from its host that it can vanish sunlight until it slips behind climbs 6° above the southeast- of Jupiter, but once each orbit, into Jupiter’s shadow, briefly Jupiter’s disk at 5:24 a.m. ern horizon some 45 minutes it will pass in front of (transit) emerge into sunlight, and then Saturn briefly appears in before sunup. Saturn shines at the giant world. Shortly before disappear behind the planet’s the morning sky at the end of magnitude 0.5, bright enough a transit, the moon’s black disk. The moon comes out of December. On the 31st, the to see against the twilight shadow sweeps across the shadow at 4:02 a.m. PST on ringed world rises nearly through binoculars. jovian cloud tops. Half an orbit later, the moon disappears GET DAILY UPDATES ON YOUR NIGHT SKY AT www.Astronomy.com/skythisweek.

WWW.ASTRONOMY.COM 43 ASKASTR0 Astronomy’s experts from around the globe answer your cosmic questions. BLACK AND BLUE MOON Q: IF TWO FULL MOONS IN ONE CALENDAR MONTH ARE CALLED A BLUE MOON, THEN WHAT, IF ANYTHING, ARE TWO NEW MOONS CALLED, AS OCCURRED IN SEPTEMBER? Ronald R. Greene, Kingman, Arizona

A: The length of time between which lunar apparition should any two occurrences of the be the “blue” one is sometimes Moon’s phase is always 29.5 up for debate. One can imagine days, but thanks to the varying a scenario in which two Full length of calendar months, this Moons rise in June, but the means we can occasionally get third Full Moon of summer two Full Moons in one month doesn’t appear until July. No matter how many Full Moons appear in any given timespan, its color (except for February); this is Which one should count as the will not actually change to blue. JOHN CHUMACK indeed called a blue Moon. A blue Moon? blue Moon can also (and more Astronomically speaking, it nomenclature, one occurred on A: Many astronomers (me traditionally) refer to the third doesn’t matter in the slightest, October 30, following a New included) are somewhat puz- of four Full Moons in one sea- but it makes for some delightful Moon on October 1 (both with zled as to why massive stars son. In fact, the former — and barroom trivia, and exemplifies regard to Universal Time), just only rarely exhibit strong mag- much more well known — how language evolves with use. in time for an extra-spooky netic fields at their surfaces. usage arose from confusion The New Moon equivalent is Halloween. Part of the reason certainly over applying the seasonal rule. usually referred to as a black Alternatively, a black Moon arises from the fact that mas- This means that exactly Moon, and, depending on your can also refer to a month with sive stars do not contain con- no Full Moon at all. A simple vective zones in their outer comparison of the length of the layers, unlike lower-mass stars lunar period and the length of such as the Sun. Consequently, calendar months reveals that massive stars do not support a February is the only month magnetic dynamo near the that can host such darkness. surface that converts convec- This phenomenon next occurs tive and rotational energy into in February 2018. magnetic energy. Any magnetic Korey Haynes field at the surface would have Associate Editor to be a remnant of a past phase of magnetic activity, or would have to emerge from deep Q: WHY ARE MAGNETIC down in the star. Long-lived FIELDS RARE IN MASSIVE magnetic fields generated by STARS AND IN CLOSE PAIRS? such mechanisms appear to be AS FAR AS I KNOW, ALL rare, although the reasons are STARS HAVE ROTATING not well understood. PLASMA INTERIORS, SO However, many massive THEY SHOULD ALL HAVE stars may contain strong mag- MAGNETIC FIELDS. WOULD netic fields buried within their THE LACK OF A MAGNETIC cores. Unlike their surfaces, FIELD MEAN THAT THE STAR the cores of massive stars are DOES NOT HAVE SOLAR convective due to vigorous Our Sun’s activity is difficult to understand, even with close-up views. FLARES? nuclear fusion near their cen- Astrophysicists are still struggling to match theory to observation Suzanne Farkas ters. The combination of rota- for stars both more massive and smaller than our home star. NASA/SDO Amherst, Ohio tion and convection likely

44 ASTRONOMY • DECEMBER 2016 generates a magnetic dynamo in the core, although we can’t easily detect these magnetic fields at the surface. Still, there is new evidence from astroseis- mology that these magnetic fields exist, because they can be detected through their effect on stellar pulsations later in a star’s life, when it evolves into a red giant. Basically, magnetic fields inhibit the pulsations due to the strong magnetic tension force associated with bending magnetic field lines. This line of research is preliminary, but it may provide an exciting new way to probe magnetic fields deep inside of stars. Jim Fuller California Institute of Technology

Q: WHY DOES A GRAVITA- The “Cosmic Horseshoe” is the result of a luminous red galaxy gravitationally lensing a background blue galaxy TIONAL LENS SOMETIMES that is almost — but not quite — perfectly aligned to make a ring. HUBBLE/NASA/ESA CREATE AN EINSTEIN CROSS WITH FOUR IMAGES AND the special case when the back- of the overall system. Once we parachute system without some SOMETIMES A CIRCLE? ground source is point-like determine a shape, we use what degradation, so we build sev- Javier Soto (usually a quasar — but in the we know about the planet’s eral parachutes and mortars at Avila, Spain fascinating case of the lensed atmospheric profile (altitude the same time with the same SN Refsdal, it was a super- vs. air density) and standard materials. From that group, or A: Actually, there are many nova), we see four star-like aerodynamic equations to cal- lot as we call it, we select our possible configurations besides appearances of the source, and culate the size the chute needs test units and reserve a flight an Einstein Cross and a circle the image would be what we to be to achieve the desired unit. We perform a final series (also known as an Einstein call an Einstein Cross. drag profile, force, and time on of tests on the lot to qualify ring). The exact configuration Keren Sharon chute, and get the payload and accept the design as flight- formed by gravitational lensing Assistant professor safely to ground. We also have worthy. At that point, the para- depends on a few things: the University of Michigan to consider parachute materials chute system is ready to be gravitational lens, the back- and refine the design based on packed into the spacecraft and ground source, and the align- the type and weight of the load do its job. ment between them. Q: HOW ARE PARACHUTES and the specific environment Dave Buecher An Einstein ring can form if DEVELOPED AND TESTED of the planet or moon. Parallel Mechanical engineer a background galaxy is posi- FOR LANDINGS ON THE to the parachute design, we Lockheed Martin tioned exactly behind the cen- PLANETS BEYOND EARTH? also design and test the mortar ter of a gravitational lens. Robert Smith — the device that deploys the When the two are perfectly Orlando, Florida parachute. Send us your aligned, there is circular sym- After the initial design is questions metry; having no preferred A: Parachute design, develop- completed, we start testing, Send your astronomy angle, the image of the back- ment, and testing for planets and update the design based on questions via email to ground galaxy will form at all beyond Earth is very similar to results. Once the flight design [email protected], the angles, and a circle will those designed for Earth. First, is completed, we manufacture or write to Ask Astro, appear around the gravita- we pick a parachute type or multiple parachutes and mor- P. O. Box 1612, Waukesha, tional lens. shape based on the expected tars for both the final testing as WI 53187. Be sure to tell us We see four bright images speed of the probe when the well as the specific “flight” unit your full name and where (instead of a ring) if the back- parachute needs to deploy, and that will actually operate on you live. Unfortunately, we ground galaxy is not exactly the craft’s stability require- Venus or Mars — or wherever cannot answer all questions behind the center of the lens, ments. The parachute shape our spacecraft takes it. We submitted. but slightly off to one side. In dictates the drag and stability can’t deployment test our flight

WWW.ASTRONOMY.COM 45 Red Planet mayhem

Someday, Mars’ moon Phobos will slip past a certain point in its degrading orbit and get ripped apart by tidal forces, form- ing a ring. This illustration depicts Phobos midway through that process, overlooking the Red Planet. RON MILLER FOR ASTRONOMY

46 ASTRONOMY • DECEMBER 2016

Phobos, a moon of Mars, is destined to be shredded, changing the Red Planet forever. by Joel Davis

WWW.ASTRONOMY.COM 47 Lord of the rings While we know of thousands of exoplanets, only one exoring system has been found. J1407b is a massive planet with rings so large they block out their parent star’s light. It has a total of 30 systems in its rings, and the system has a diameter of 74 million miles (119 million kilometers). To put that in perspective, if the ring system were around our Sun, it would stretch all the way past Venus and fall a bit short of Earth’s orbit. J1407b is massive enough that it may not technically qualify as a planet, and may instead be a brown dwarf, a class of objects encompassing “failed stars.” The object is estimated to be 20 times more massive than Jupiter. RON MILLER

It appears the process of coming apart at the seams has Phobos, it seems, is not long already begun. Images of Phobos taken by the Viking orbiters and other spacecraft show a network of grooves in the tiny for this universe — at least moon’s surface. At first they appeared to radiate from near Stickney Crater, and geologists assumed that the grooves were on the large cosmic timescale. cracks caused by the ancient impact. Some certainly are just that, Astronomers have long known that Phobos, the larger and but not all. In 2015, Terry Hurford of NASA’s Goddard Space nearer of the two martian moons, is slowly spiraling inward to Flight Center and his colleagues reported a new analysis of the eventual destruction. The end result won’t be pretty: Phobos will grooves. Most of them actually radiate from the side of Phobos slip closer and closer toward Mars, then strike a gravitational line that constantly faces Mars; tidal forces caused by Mars’ gravita- where the planet’s tidal forces will be strong enough to tional pull are deforming Phobos. Hurford believes the rip it apart. The rubble pile-like moon will break grooves are stretch marks, a visible sign of the inexo- into smaller boulders, rocks, and dust, and rable grip of tidal forces on the moon. will spread out in orbit around Mars. The future martian ring will not be the only one Mars will join the gas giants in having a in the solar system, of course. Nor will it be the spectacular feature: a ring system. only ring whose existence depends on a moon. It could be 25 million years from now. There are rings across the giant planets: the four It could be up to 75 million years. Recent dusty rings of Jupiter; Uranus’ 13 dark, thin rings; discoveries about the little moon’s composi- and Neptune’s five faint rings and four enigmatic tion and density, however, make it far more ring arcs are — like the future ring around Mars likely that its death dive will happen sooner. — all intimately linked to moons and moonlets. The pieces that don’t form a ring will fall to the And of course, the most familiar ringed planet is surface, smashing with enough force to pockmark Saturn, whose icy surrounding matter can be seen Mars with new craters. even through a small telescope. “A lot of planetary science focuses on what happened in the past and what’s happening now,” says planetary scientist Saturn’s magnificent rings Benjamin A. Black. “It’s not often that we look at the future, at Galileo Galilei saw what turned out to be Saturn’s spectacular ring what will happen.” Black, a City University of New York professor, system in 1610. (He said the features looked like ears or handles.) and graduate student Tushar Mittal from the University of But it wasn’t until 1655 that Christiaan Huygens identified them California, Berkeley, have carried out a detailed examination of as an entire system of icy rings. In 1856, famed physicist James

the eventual fate of Phobos. Clerk Maxwell showed that the rings must be composed of a huge (PHOBOS)NASA

48 ASTRONOMY • DECEMBER 2016

RINGS OF THE GIANT PLANETS Jupiter’s four faint and dusty rings proba- impacts. What’s more, the current rate of JUPITER bly formed by a different mechanism than meteoroid impacts among moons and Saturn’s — and more recently — but its other icy bodies at Uranus’ distance is moons still play a vital role. Amalthea and enough to create all the observed rings Main Thebe Thebe Thebe are the likely sources of the material and dust bands circling that planet. Halo gossamer extension in Jupiter’s outer two “gossamer” rings. Because the rings appear to be young, Thebe orbits within the outer gossamer probably not more than 600 million years ring, while Amalthea lies near the outer old, the material in the rings must be con- Amalthea 50,000 km gossamer edge of the inner gossamer ring. Metis and tinually renewed. Particles blasted off the Adrastea, two other small moons, orbit tiny moons and still-unseen moonlets by 30,000 miles near the outer edge of Jupiter’s main ring, collisions and meteoroid strikes continually and are the sources of the dust grains mak- add material to the rings, while the dust SATURN ing up the main and innermost halo rings. continues to dissipate. Janus/Epimetheus D B Some forces work against the rings, Neptune’s five rings and various dust A keeping them relatively thin. bands are probably even younger than Electromagnetic forces, a phenomenon those of Uranus, and the same processes G Pallene E called plasma drag, and even pressure are likely responsible for them and the F from sunlight (called the Poynting- moons that orbit in or near them. Naiad 50,000 km Robertson effect) continually remove the and Thalassa orbit in the gap between the micron-sized particles from the rings. But innermost Galle and Le Verrier rings, and C Cassini Division 30,000 miles particles sputtered off the moons by Despina orbits just inside the Le Verrier meteoroid impacts create dust and con- ring. Galatea lies slightly inside the outer- URANUS 645 αεβ η γ δ λ tinually replenish the rings. most Adams ring. These tiny moons are The 13 known rings of Uranus are likely rubble-pile objects, agglomerations unlike those of Jupiter or Saturn. All but of fragments from earlier neptunian the innermost and two outermost of the moons, weakly held together by gravity. ν μ rings are quite narrow, ranging from just The ring particles are material continually 0.6 to 59.6 miles (1 to 96 kilometers) wide. blasted off the moons by meteoroid Their particles are larger than those in impacts. Unlike the uranian rings, the rings ζ Jupiter’s rings, but there’s little dust. of Neptune are quite dusty, thanks to the 1986U2R/ 50,000 km Instead, they’re largely made up of ice destruction of a satellite; at least 20 per- 30,000 miles with organic chemicals mixed in to give cent of the material is the size of smoke the dark appearances, unique among the particles, and in some of the rings, that NEPTUNE outer solar system rings. rises to 70 percent. Le Verrier But there are similarities: Like Jupiter’s The Adams ring also has five distinct Galle Arago and Saturn’s rings, Uranus’ rings are inti- clumps or arcs of dust spanning about 40° Adams mately associated with moons and moon- in longitude. How they can exist for any lets. Primordial moons the size of Puck, 100 length of time is a mystery, as these tenu- miles (162km) in diameter, or larger would ous rings should have faded away. One Arcs Lassell 50,000 km have had a good chance of surviving for explanation, by planetary ring expert 30,000 miles several billion years. But not all would Carolyn Porco, leader of the Cassini orbit- escape a devastating fate. Computer simu- er’s imaging team, is that a resonance lations show that the 11 inner moons of effect caused by Galatea’s eccentric orbit All four giant planets — gas giants Jupiter and Saturn, Uranus are likely the remains of original may act to keep the particles in the arcs and ice giants Uranus and Neptune — have ring systems. larger moons broken up by cometary from spreading out and dissipating. — J. D. But each one is very different. ASTRONOMY: ROEN KELLY number of tiny particles (he called them “brick-bats”), each inde- formed the planet’s main rings. This, she says, explains why the pendently orbiting Saturn. particles making up the rings are 99.9 percent pure water ice. It Since then, debate has raged over the origin, age, and composi- also explains the striking difference between Jupiter’s and Saturn’s tion of Saturn’s rings. Are they leftovers from the formation of rings and satellites. Saturn, or the remains of a shattered moon? As old as Saturn itself, “The existence of Saturn’s much more massive ring system is or a relatively new addition? And why so much ice? Planetary sci- linked to Saturn having lost its large primordial inner moons,” entist Robin M. Canup of the Southwest Research Institute in Canup explains. “Jupiter retained its large inner moons, [while] its Boulder, Colorado, recently published a proposal that answers dusty ring system is vastly less massive than the ring system at these questions. Canup suggests that Saturn’s rings are the very Saturn.” ancient remains of a Titan-sized moon. “Saturn originally had multiple massive moons like Jupiter,” Creating a martian ring says Canup. These moons were large enough for their interiors to Phobos isn’t nearly the size of a planet, but many of the same differentiate into layers of ices and a rocky core — less like a large mechanisms will drive its destruction. Its companion moon comet and more like the four larger moons of Jupiter. When the Deimos is about 7.8 miles (12.6 kilometers) in diameter and orbits large moons spiraled inward as Saturn finished its accretion, Mars at an average distance of 14,580 miles (23,460km), far enough Canup says, the outer icy layers of at least one were stripped away. away to avoid Phobos’ fate. Phobos is 13.8 miles (22.2km) in The core plunged into Saturn, and the icy remains eventually diameter. It circles the planet at an average distance of 5,827 miles

WWW.ASTRONOMY.COM 49 The lines cutting across Phobos are caused by tidal stresses from the gravity of Mars slowly ripping its largest moon apart. NASA

The white object in the center of Saturn’s diffuse E ring is Enceladus, a tiny moon with a liquid ocean. Geysers at the moon’s south pole eject water into space, forming the ring. NASA/ESA

(9,377km). With an orbital period of just 7 hours, 39.2 minutes, Then there’s Stickney Crater, the giant impact basin on Phobos is one of only 18 of the 181 known moons in the solar sys- Phobos. Sometime in its past, Phobos was hit by an object that tem whose orbital period is less than its planet’s rotation period. left a crater 5.6 miles (9km) wide — nearly half the moon’s diam- That’s one of a few reasons why Phobos is doomed. “There are eter. The impact surely fractured much of Phobos’ interior, leav- four factors in action,” explains Mittal. “The tidal force of Mars; ing it even weaker. From there, billions of years of meteoroid the centrifugal forces on Phobos, which is rotating; the gravity of impacts have churned the surface of Phobos into a layer of fine Phobos; and the strength of Phobos. There’s a balance among dust about a hundred meters deep. Given the extremely weak sur- these. Tidal and rotational stresses act to pull Phobos apart; self- face gravity (escape velocity for Phobos is a mere 4.56 feet per gravity and [tensile] strength act to hold Phobos together.” second), the rock making up the rubble pile just barely stays put. Just as our own Moon’s gravity raises tides in both Earth’s Black and Mittal used a numerical geotechnical model oceans and landmasses, Phobos creates a tiny tidal bulge in Mars. designed for large underground construction projects to estimate The bulge moves as the moon circles Mars, just as the Moon- what they call the moon’s “rock mass strength.” The results place caused tidal bulge moves around Earth. Because Phobos has an the finale for Phobos between 20 million and 40 million years orbital period faster than the martian day, the tidal bulge lags from now, and give more details on its violent end. behind Phobos and acts to gradually slow it in its orbit, sending As Phobos reaches its Roche limit, about 3,400 miles Phobos slowly spiraling in toward the martian surface. The rate is (5,470km) from the martian surface, tidal forces will start pulling about 0.79 inch (2 centimeters) per year. It’s not much, but there is Phobos apart. Just as Saturn’s tidal forces may have peeled away nothing to stop it. the icy mantle of a Titan-sized moon billions of years ago, the “As Phobos gets closer to Mars,” says Mittal, “the tidal stresses hundred meters or so of regolith will be stripped off Phobos. It increase.” The moon’s self-gravity and tensile strength oppose the will happen quickly: In as little as a week, the dust will spread tidal forces, but eventually Phobos will drop to a distance — into a ring circling Mars, the moon no more. called the Roche limit — where the martian gravity will win the Depending on how much material is stripped off Phobos, the tug-of-war. Several studies confirm that Phobos’ inward spiral ring could initially have a mass density similar to that of today’s will lead to its destruction in 25 million to 75 million years. rings of Saturn. The martian ring will be very dark, unlike Phobos could stave off obliteration if it were a dense body, more Saturn’s bright icy rings, more like the dusty rings of Jupiter that able to resist the pull of gravity past the Roche limit. Unfortunately, are darker, thinner, and more diffuse. It will practically hug Mars, data from the European Space Agency’s Mars Express orbiter show closer in relative terms to the planet than the other planetary rings that the moon has a density of just 1.9 grams per cubic centimeter. in the solar system. And the ring, say Black and Mittal, will not By comparison, our Moon has a density of 3.3g per cubic centime- last long; they estimate its lifetime at between 1 million and 100 ter. Even tiny Themisto, Jupiter’s smallest regular moon at just 4.9 million years. miles (8km) in diameter, has an estimated density of about 2.6g per cubic centimeter. Mars Express also revealed that Phobos is Roche limit porous, likely containing large voids, so it is probably a rubble pile, Phobos oche limit like many of Uranus’ and Neptune’s tiny moons. R As Phobos spirals inward, it will In addition, Phobos’ makeup is similar to carbonaceous chon- reach a distance, drite meteorites like the ones that fell on Canada’s Tagish Lake in Mars called the Roche 2000. These primitive meteorites are made of a bevy of loose, eas- limit, where the moon will be ily broken materials, including magnetite, olivine crystals, phyl- pulled apart losilicates, and complex organic molecules such as amino acids, by Mars’ gravity. and are about 10 percent water, formed in oxygen-rich regions of The end result will the early solar system. Phobos is not only a rubble pile with a weak be a temporary ring around Mars. gravitational field, but the rubble itself is somewhat frangible. ASTRONOMY: ROEN KELLY

50 ASTRONOMY • DECEMBER 2016 Small system You don’t have to be a planet to have a ring. An object known as Chariklo (classified as a centaur, or outer solar system minor planet) has a thin ring system around it. Chariklo’s diameter of 144 miles (232 kilometers) puts it at the lower limits of the size of dwarf planets. The formation mechanism of the rings, and indeed much information beyond their existence, is not yet known. Chariklo was the first minor planet or asteroid to have a known ring system. Another centaur, Chiron, may have one as well. The rings were discovered in 2014. Chariklo orbits in a highly inclined orbit between Saturn and Uranus. ESO/L. CALÇADA/NICK RISINGER

Eventually, the rocky rubble left behind will meet a quicker but Curiously, our Moon also could end as it began, according to equally dramatic end. It will plummet down along slanting paths astronomer Lee Anne Willson, university professor emerita at to impact the surface of Mars and leave a string of elongated cra- Iowa State University. As part of her research on the fate of Earth ters along the planet’s equator. as the Sun expands into a red giant, she found that the Moon stood a chance of becoming a ring around Earth. Other once and future rings The Moon is receding from Earth at a rate of about 1.6 inches Is it possible that Mars possessed a ring system in its distant past? (4cm) per year. Left unchecked, the Moon will eventually migrate “We’re not certain,” says Black, “but it would be worth investigat- out to a distance where it will take 47 days to orbit Earth. By then, ing whether past inwardly migrating moons may have existed. Earth’s rotation also will have slowed to 47 days. The two will Some fraction of moons might be expected to have an orbital con- then keep the same face to each other, as Pluto and its moon figuration similar to that of Phobos and Mars.” Charon do today. Some planetary scientists think Mars Before this happens, though, some 5 bil- once did have more than two moons. Several studies confirm lion years from now, the Sun will enter its Researchers have identified 258 elliptical red giant phase. It will start expanding in craters on Mars formed by objects hitting that Phobos’ inward spiral size, and swallow up Mercury and Venus. the surface at grazing angles. At least some will lead to its destruction As the Earth-Moon system orbits through of them could well have been made by the Sun’s expanded outer atmosphere, drag oblique impacts of ancient martian moons. in 25 to 75 million years. forces will cause the Moon’s orbit to begin If so, others may have broken up before hit- decaying. The Sun probably will continue ting the atmosphere, leaving short-lived rings of rocks and dust to expand, and destroy both Earth and the Moon. On the other around Mars. hand, if the Sun should blow off about 20 percent of its mass first, There’s no evidence that Mercury or Venus ever possessed ring the Moon will continue to spiral down to its Roche limit. Tidal systems. Earth did, though, for an extremely brief period during forces will tear it apart, just as they will destroy Phobos. the formation of the Moon 4.5 billion years ago when our planet And then, 9 billion years after the Moon’s birth from a ring of was struck by a Mars-sized body dubbed Theia. Much of Theia molten impact ejecta, and nearly 5 billion years after the birth and merged with Earth, but the “Big Splash” would have blown the death of the ring around Mars, Earth will once again have a ring. remaining material into space. Computer simulations indicate about 20 percent of Theia’s mass would have gone into orbit Joel Davis is a freelance science writer and editor living in Bellevue, around Earth as a ring. About 10 percent of the ring’s material Washington. In addition to Astronomy, his articles have appeared then quickly coalesced into the Moon, with the rest eventually in Analog, Final Frontier, New Scientist, and Science Digest. His books falling back to Earth. The ring would not have lasted long, perhaps include Flyby: The Interplanetary Odyssey of Voyager 2 and Journey as little as a month but probably no more than 100 years. to the Center of Our Galaxy.

WWW.ASTRONOMY.COM 51 IMAGING PROFILE

StellarMEET THE MASTER Vistas OF

How I took the astroimaging road less traveled. text and images by Rogelio Bernal Andreo

often say that life is what happens faint photons from faraway objects into between the decisions we all have to gorgeous photographs. I had no clue that, make. It took a single event in my life years later, some of my work would actually to turn me from a complete astropho- become a reference for many other imagers. tography outsider into someone who At the time, nearly every astrophotogra- Iembraces it fully. pher was using Photoshop to process images, I was driving with my family down the but I thought a new software program called California Pacific Highway just south of Big PixInsight was more suitable for me. Not Sur one warm September evening in 2007. having tutorials, workshops, references, or An unexpected stop allowed us to witness a documentation about PixInsight led me to gorgeous Milky Way for the first time in our create my own techniques, and so image lives. My first thought as I came back to processing became a field in which I would reality was whether I could capture that in a continuously try new things — something photograph. The rest is history. that is still true today. On image processing On curiosity, composition, I produced my first deep-sky images in 2008 and mosaics with a cheap rig, and they did not impress Once the technical aspects of this discipline Rogelio Bernal Andreo is one of the world’s top me. I soon found out that such images had were no longer a limitation, my own curios- astroimagers and a highly requested speaker to be processed, so I started learning about ity took over. Rather than looking at and on the subject of image processing. image processing — the skill of transforming following what other people were doing, I

52 ASTRONOMY • DECEMBER 2016 1 1. If you think Hawaiian beaches seem idyllic during the day or at sunset, you should try visiting one at night. This image shows magical Punalu’u Beach on the Big Island. (20-pane mosaic, Canon 5D Mark II DSLR, 20mm lens at f/2.5, ISO 2000, 30-second exposures)

2. As the author put it, “Nothing in the con- stellation Orion disappoints, so capturing the entire area shouldn’t either, right?” He created this 56-pane mosaic by accumulat- ing some 242 hours of exposure time. (Dual 4-inch Takahashi FSQ-106EDX refractor with focal length reducers to yield f/3.6, dual SBIG STL-11000 CCD camera, LRGB image with an astounding 220 hours of exposures) decided to explore the celestial canvas for interesting views. It took a single image I produced back in 2009 that included Orion’s Belt and the Orion Nebula (M42) to make me realize that I wasn’t interested in creating a collec- tion of objects — as nearly everyone else was doing — with each target perfectly centered. I wanted to create stellar land- scapes: gorgeous deep-sky panoramas, entire constellations like Orion and Leo, the region of sky showing the entire

Rogelio Bernal Andreo is a longtime image contributor to Astronomy. He images mostly from remote areas in California. 2

WWW.ASTRONOMY.COM 53 Stellar Vistas

Big Dipper, large vistas with objects not usually seen in the same image, and more. I pursued celestial landscapes because I wanted to see them. Sometimes that meant having to build a 50-panel mosaic. Other times it involved framing a view in a way that would give people a different perspec- tive on the object. On nightscapes On December 30, 2011, my father, a lifelong traveler, left us unexpectedly. One way I coped with his departure — without real- izing it at the time — was to spend many hours driving, traveling to some of the most beautiful places in the Northwest and capturing them at night. I nearly stopped deep-sky imaging. My new goal was to shoot nightscapes — that is, photography featuring landscapes under the night sky. I immediately fell in love with night- scapes and quickly became prolific at cap- turing them. This passion related to deep-sky imaging not only took me to places like Yosemite, Big Sur, and Death Valley countless times, but it developed into my first book, Hawai’i Nights, a pho- tographic documentary of the night sky in all the Hawaiian Islands. On outings and life I am not against robotic astrophotography (capturing images at a distant observa- tory located under a clear sky). In fact, I may embrace it someday. For me, however, imaging always has been an experience directly linked to having to “go out.” 3 After beginning my nightscape photog- raphy, I quickly discovered that those and deep-sky outings are very different beasts. its own, and my anecdotes are plenty, from A deep-sky outing anchors you to the same dealing with wildlife, to getting flat tires spot for the entire session, usually near driving off-road, to falling into a creek at your car. When you’re done, you pack and 2 a.m. during freezing temperatures, to go home. Other than that, you’re not going finding myself alone at night in places anywhere during the night. whose beauty is beyond words. With nightscape outings, however, For me, deep-sky and nightscape astro- mobility is everything and vantage points photography are not just about producing matter. A lot. It’s not rare to hike for a few images. This pursuit gives me unique per- hours at night to reach the right location. sonal experiences. More importantly, it Also, a typical nightscape panorama rarely helps me pause everything else. takes longer than five minutes to acquire, It allows me to create, to dream, and to so you can visit several locations in a single have countless exceptional moments that I night. Going alone as a nightscape photog- would have never had otherwise. It makes rapher can be more daring than doing me feel alive, positive, and happy, and deep-sky photography, and while I try to because of that, I choose to do more of it avoid it, when I go to shoot nightscapes I — lots of it! If there is anything in your life am alone more often than not. that can do this for you, then you should Either way, every trip is an adventure on do more of that, too.

54 ASTRONOMY • DECEMBER 2016 3. Kilauea on the Big Island of Hawaii is an active volcano that often puts on quite a show. The Pleiades (M45, upper center in glow) and Orion (upper left) watch from above. (Six-pane mosaic, Canon 5D Mark II DSLR, 50mm lens at f/2.8, ISO 2500, 20-second exposures except an 8-second exposure for the lower center pane)

4. The Angel Nebula lies in Ursa Major. The author’s image is one of the most detailed ever of this extremely faint high-latitude interstellar dust that soars some 300 light-years above our galaxy’s plane. (4-inch Takahashi FSQ-106EDX refractor with focal length reducer, SBIG STL-11000 CCD camera, LRGB image with expo- sures of 300, 75, 75, and 75 minutes, respectively)

5. The author calls this image “Downtown Auriga.” It shows the Flaming Star Nebula (IC 405) and Simeis 147 forming a gorgeous couple. Few imagers, however, have shown them together. (Dual 4-inch Takahashi FSQ-106EDX refractor with focal length reducers to yield f/3.6, dual SBIG STL-11000 CCD camera, LRGB image)

6. The telescopes atop Mauna Kea in Hawaii — one of the best sites for astronomy — appear as true vigilantes of the sky. (14-pane mosaic, Canon 5D Mark II DSLR, 20mm lens at f/2.5, 4 ISO 2000, 30-second exposures)

5 6 Stellar Vistas

7 8 9

7. The Blue Horsehead (IC 4592) is a reflec- tion nebula in Scorpius. Its illumination comes from ultraviolet light emitted by the bright star Nu (ν) Scorpii, which marks the horse’s eye. (4-inch Takahashi FSQ-106EDX refractor with focal length reducer, SBIG STL-11000 CCD camera, LRGB image with exposures of 200, 40, 40, and 40 minutes, respectively)

8. This image of the Rho Ophiuchi region, the Blue Horsehead, and emission nebula Sharpless 2–1 is a perfect example of a cos- mic vista where not two, but three objects compete for our attention while maintain- ing a solid composition.

9. Lenticular clouds hover above Yosemite National Park with Half Dome dominating the scene, all crowned by our Milky Way. (10-pane mosaic, Canon 5D Mark II DSLR, 20mm lens at f/2.5, ISO 4000, 13-second exposures)

10. You don’t need to travel to Hawaii for dazzling night seascapes. McWay Falls in Big Sur, California, is a small cove that beats the fictional paradises we often see in the movies. (Two-part composite before and after moonset, Canon 5D Mark II DSLR, 20mm lens at f/2.8, ISO 6400, 29-second exposures) 10

WWW.ASTRONOMY.COM 57 BLUE MOON By combining science with a few stellar brews, Astronomy on Tap has become a hit.

by Liz Kruesi

ore than 250 people funnel into the It also motivates people to learn more about the North Door bar on the East Side of Science, Technology, Engineering, and Medicine Austin, find a place to sit or stand, and (STEM) fields, Schwamb says. look toward the stage. A projector “Astronomy is the gateway drug,” says beams trivia questions about astron- Schwamb. “It’s the thing that gets people into omy onto a nearby wall, and astron- STEM.” Since the first few events only four years omers give away NASA stickers ago, Astronomy on Tap has sprouted in 19 other and Eagle Nebula posters at a locations, and it continues to grow. table. As University of Texas at Austin astronomers Rachael Branding a trend Livermore and Jeff Silverman In early 2012, Schwamb organized two walk across the stage, the Astronomy Uncorked events at a wine bar in New crowd starts to hush. Haven, Connecticut, while she was a postdoc at “Welcome to Astronomy on Yale University. A few months later, she sat down Tap, Austin, Texas,” with Emily Rice, then a postdoc at the American Livermore says into the microphone. Museum of Natural History in New York City, This monthly public event is a hit, and it’s and told her about those outreach events and how not the only one. In cities around the globe, she wanted to bring her brainchild to New York. hundreds of fans gather in bars, taverns, or pubs Rice, now an assistant professor at the College on weekday evenings to hear about a potpourri of Staten Island, loved the idea of reaching the of the current hottest topics in astronomy. non-academic community and opening up astron- Themes range from how astronomy is portrayed omy to those who don’t think of themselves as in the movies to why Pluto isn’t a planet to what armchair astronomers or hobbyists. First, though, the heck dark matter is. The talks are brief, fun, she thought it needed a new, more-inclusive name: and accessible — plus, there’s beer. Astronomy on Tap. They planned the first When Meg Schwamb, now a postdoctoral Astronomy on Tap event for April 2013. When fellow at the Institute of Astronomy and Schwamb moved to Taiwan later that summer, Rice Astrophysics at Academia Sinica in Taipei, took over the New York City events. Taiwan, planted the Astronomy on Tap seed and The program continues to grow, in part, Rice organized the first event, the idea was just to says, because “it unites the stereotypical scientist have fun communicating astronomy and create an environment where people can enjoy them- Contributing Editor Liz Kruesi writes about our incredible selves while also learning about the science. universe from Austin, Texas.

WWW.ASTRONOMY.COM 59 persona with the very human, very social, very that the organizers are only around for a few years, creative persona.” and so the Astronomy on Tap programs are in Often, scientists hold public lectures that dive flux. The good is that they often bring the program deep into one topic. But those events can feel with them to their next homes. stuffy, academic, and, frankly, less inviting for For example, both Livermore and Silverman are most people. Instead, Schwamb and Rice wanted to moving on from organizing the Austin program. create an environment that encourages humor and Silverman’s postdoc position at the University of a conversational tone, to make the topics more Texas at Austin ended in August 2016, and he accessible, and to do this at a place where people plans to start an Astronomy on Tap program wher- already hang out. “I think in my mind, it was like ever he goes next. Livermore will remain in Texas bringing astronomy to the people rather than hav- for another year, but she decided to pass the baton ing the people come to us,” Schwamb adds. to a group of excited organizers: 10 postdocs and Whereas most public outreach in the field is graduate students. geared toward kids — how you, yes you, can be an astronomer and study the universe — Astronomy A successful combination on Tap takes a different approach. It’s aimed exclu- Astronomy on Tap seems to grow by diffusion. At sively toward adults. the American Astronomical Society meeting in Each event has several 10- to 15-minute talks January 2014, Rice presented a poster about the giving the audience snippets of the best parts of New York City Astronomy on Tap events. That was astronomy. That timespan is long enough to over- Silverman’s introduction to the program. He view new and interesting science yet short enough bounced the idea around with University of Texas to keep the audience’s attention. After each presen- at Austin faculty and postdocs, but it didn’t go tation, people are encouraged to ask those ques- anywhere until Livermore joined the department tions they wouldn’t feel comfortable voicing in a that August. The two began building up the Austin lecture hall. (How does terraforming work? What satellite of Astronomy on Tap and hosted their first does dark energy mean for the universe’s future?) event in November 2014. There’s been one every Each Astronomy on Tap event also usually has a month since. pub game — like trivia questions with answers The program has grown organically due to embedded in the talks, with prizes like a enthusiastic organizers, the so-called “Host Stars” McDonald Observatory apron (for the Austin of each satellite location. At no location is that event), astronomy-themed stickers, and even Neil more apparent than Austin, which consistently deGrasse Tyson’s trash. Yes, literally, trash that he has more than 200 people in the audience, mak- picked up and threw in his trash can, says ing it the best-attended recurring Astronomy on Schwamb. (The Astronomy on Tap organizers then Tap. It’s a testament to the work and dedication bring said trash can to the bar and people can dig Silverman and Livermore have put into the pro- through — if they so choose.) And, of course, gram, Schwamb says. “It’s amazing to see what there’s beer. they’ve built.” One look around a room at an Astronomy on Rice told Livermore and Silverman to expect 50 Tap event shows that the plan she and Rice came to 60 people at the initial Austin event, but instead up with is working. 140 showed up. (Some of the credit for this impres- sive turnout goes to Nerd Nite, a more general A different spin cool-talks-at-a-bar event, which already had a So far, there are 20 Astronomy on Tap programs: strong fan base in Austin. Plus, this Texas city has Ann Arbor, Michigan; Austin, Texas; Baltimore; a booming technology industry.) Bay Area, California; Champaign-Urbana, Illinois; The Austin Astronomy on Tap logged 402 at its Chicago; Columbus, Ohio; Denver/Boulder; January 19, 2016, event. That’s not quite the most- Lansing, Michigan; Los Angeles; New Haven, attended Astronomy on Tap event, however. That Connecticut; New York City; Rochester, New York; prize goes to a New York City event held at the Santa Barbara, California; Santiago, Chile; Seattle; Intrepid Sea, Air & Space Museum to celebrate the Taipei, Taiwan; Toronto; Tucson, Arizona; and Hubble Space Telescope’s 25th anniversary, which Washington, D.C. 430 people attended. The combination of beer and Part of the beauty of this program is that while astronomy seems to make a winning recipe, no there are many similarities — short, fun talks matter the city. about astronomy held at a bar — event organizers That enthusiastic turnout makes the many put their own local spin on it. “I think it’s great for hours of organization and planning worth it, say everyone to adapt it to their community, to their the astronomers I spoke with. Organizers are audience,” says Rice. responsible for finding presenters who can share While not by design, Astronomy on Tap is astronomy in a fun way, scouting and renting a most-often organized by postdoctoral fellows, and space at a bar, organizing games or trivia, procur- such positions are usually two or three years long. ing prizes, and advertising the event. “But the huge That has both bad and good aspects. The bad is crowds we get at each event and the enthusiasm

60 ASTRONOMY • DECEMBER 2016 The audience gathers at a January 2016 Astronomy on Tap event in Austin, Texas. Since its inception in 2012, the event has driven in thousands with the promise of science and beer. LIZ KRUESI

and excitement of our audience — dare I say, fans And at the American Astronomical Society — both at the events and on social media between meeting this past January, Astronomy on Tap events is super rewarding,” says Silverman. His organizers presented another poster about the favorite part? “When a speaker mentions one of program, and it immediately inspired several their most interesting astronomical observations other groups. They had interest from people in (like the most distant galaxy or the smallest planet Boston; San Diego; Florida; Edinburgh, Scotland; around another star) and the crowd cheers wildly London; and Leiden, Netherlands — although as if a rock star was strumming the opening chords none of those locations has yet hosted an to their hit single!” Astronomy on Tap event. Also at that January meeting, Schwamb, Rice, Continually growing Silverman, Livermore, and Brian Levine (of the The success of the satellite program — events like American Museum of Natural History) drafted a those in Austin — also help launch new ones. At master document, which they call the Launch the August 2015 International Astronomical Union Manifesto — “because we love space puns,” says meeting, Silverman and Livermore presented about Rice — that they can send to those interested in the Austin Astronomy on Tap program. Since then starting a program in their city. The document Ann Arbor, Michigan, and Tucson, Arizona, have isn’t publicly available, “but we share it with vetted

: KELLY KATLAPS joined the Astronomy on Tap “constellation,” as organizers after they reach out to us,” she adds. the Host Stars call it. (Tucson already had a pro- Astronomy on Tap has filled a niche in science gram called Space Drafts, but they reworked it outreach, and contains the right mix of ingredi- slightly to join with the global phenomenon.) “We ents to grow. Rice sees no sign of its stopping. also had interest from people in Los Angeles and “Astronomy is very international, and so it’s really San Francisco,” Livermore adds, and those loca- only a matter of time I think before we take over

ALL ILLUSTRATIONS ASTRONOMY ILLUSTRATIONS ALL tions are now up and running. the world.”

WWW.ASTRONOMY.COM 61 EQUIPMENT REVIEW Putting

to the test Easy setup, whisper-quiet operation, and superb accuracy make this mount a winner. by Phil Harrington

ne of the current evolutions and-go” technology and revolutions going on for simplified setup. in equipment for amateur All this and more is astronomers is the reinven- contained in a mount The new tion of the portable tele- that weighs just AZ Mount Pro Oscope mount. Thanks to the miniaturiza- 13 pounds (5.9kg). from iOptron is based on tion of advanced electronics and computer The mount also the company’s control, telescope mounts have shrunk in comes with a cabled tried and true size and weight, but have grown by leaps Go2Nova 8407 hand cube design. and bounds with regard to features. controller. In addition, The dovetail base at upper One of the leading manufacturers of full ASCOM (short for right accepts sophisticated portable mounts is iOptron. AStronomy Common Losmandy or One of the first to enter this burgeoning Object Model) using Vixen types. ALL PHOTOS: ASTRONOMY: field with its Cube mount, the company iOptron Commander lets WILLIAM ZUBACK continues to innovate with the recent you control the mount using introduction of the AZ Mount Pro. planetarium software such as Cartes du Ciel. The AZ Mount Pro also It’s here! Control and features features built-in Wi-Fi, letting you control I recently had a chance to put an AZ Designed for telescopes weighing up to the mount using the popular Sky Safari Mount Pro and matching tripod to the 33 pounds (15 kilograms), the AZ Mount app from your smartphone or tablet. test using my 6-inch (15cm) catadioptric Pro is a compact all-in- A dedicated AC charger, cables, a telescope. The results were impressive. one mount that features 6-inch (15-centimeter) dual dovetail base The mount and tripod arrived well full computer con- that accepts both Losmandy- and Vixen- packed in separate boxes. The mount came trol, a rechargeable style mounting plates, and a 10-pound in a custom-fit aluminum carrying case for lithium-ion battery, (4.5kg) counterweight are also included. secure storage and transport. While I and something the Instructions are not; however, you can would not trust checking it as baggage on a company terms “level- view and download both a quick-start flight, it’s certainly small enough to come guide and full instructions from iOptron’s aboard as carry-on luggage. The mount’s hand website as PDF files. The matching tripod Assembly out of the box proved to be controller accesses a database with more features 2-inch (5cm) stainless steel legs easy. The mount attaches to the tripod than 212,000 celestial that you can adjust from 33 inches (84cm) with a central bolt. Three equidistant ball- objects. to 55 inches (140cm) in length. tipped bolts protrude from the top of the

62 tripod and line up with matching holes on 32-channel GPS, it calculates its pre- the underside of the mount’s base. Use cise location along with the date, them to level the mount before use. time, and heading, spinning slowly and silently until the The real world scope aims at the zenith, the In the field, I discovered that setup is a mount’s “zero position.” simple, four-step process. Then the mount moves to a Step 1: Level the mount on the tripod bright sky object of its own selec- by adjusting the three bolts until the bubble tion. The hand controller’s dim red level built into the base reads level, and readout then asked me to confirm Cords for the then tighten the central bolt. that the bright object matches the hand controller, Step 2: Attach the telescope and coun- name on the LCD screen and that it is mount power, and computer interface terweight. Before attaching the scope, slide centered in the field of view. The entire are included. out the stainless steel counterweight shaft, process took less than three minutes. which remains neatly hidden inside the For my initial test run, the mount chose mount when not in use. If the scope weighs the Moon, which was a thin crescent hang- more than 12 pounds (5.4kg), using the ing low in the western sky at the time. PRODUCT INFORMATION supplied 10-pound counterweight is rec- While the aim wasn’t perfect, the Moon ommended. Add a second (sold separately) was well within the field of view. To iOptron AZ Mount Pro if it exceeds 24 pounds (11kg). My scope improve precision, a user can select “Sync Type: Alt-azimuth mount weighs less than 12 pounds, but I followed to Target” on the menu and then press the Primary payload: 33 pounds (15kg) iOptron’s advice to use the single counter- directional arrows on the hand controller Secondary payload: 10 pounds (4.5kg) weight to improve go-to accuracy. to center the object. Resolution: 0.1" The telescope sidesaddle dovetail plate is Several other initialization options are Slew speeds: 1x to 2,400x dual purpose, accepting both industry- provided as well for syncing the mount’s Weight: 13 pounds standard Losmandy- and Vixen-style go-to brain to the sky, including “One Price: $999 mounting bars. It’s important to attach the Star,” “Two Star,” “Three Star,” and “Solar Contact: iOptron telescope so that the front aims in the System.” In all cases, leveling the mount is 6F Gill Street direction of the small arrow on the dovetail critical for ensuring go-to and tracking Woburn, MA 01801 plate. The instructions mention it, but you accuracy. [t] 866.399.4587 could miss the arrow setting up in the dark. [w] www.ioptron.com Then, slide the telescope fore and aft until it Performance balances, and finger-tighten both dovetail Now I was ready to take it for a spin. I saddle locking screws to hold it securely. purposely tried to confuse it by select- Incidentally, using a low-power eyepiece The counterweight shaft also can hold a ing widely separated targets. I couldn’t. for initial aiming and finding is a good rule second scope by using the optional second- Toggling through the library of objects, of thumb with just about any computerized ary saddle (iOptron part number 8953). no matter which I chose, if it was up in system. For my tests, I used a 32mm Plössl The secondary saddle accepts Vixen dove- the sky, the mount steered my telescope its eyepiece for a 1° true field of view. It tail plates only. After attaching the tele- way and placed it in the field of view of my worked like a charm. scope, you can align it with the primary low-power eyepiece. If I chose an object The AZ Mount Pro’s tracking precision scope by loosening two setscrews and that was below the horizon, the mount was just as impressive as its aiming accu- rotating the secondary saddle’s base. would not budge. I would have preferred it racy. Objects stayed in view for as long as I Step 3: Plug the hand if the menu said “Below wanted to view them. In fact, one night I controller into the mount Horizon” or some such left it aimed at the Ring Nebula (M57) and and turn on the power. note, but at least it didn’t went inside. When I went back out several The battery should last up give me false hope. hours later, there was M57 — still in view. to 10 hours on a single I also want to give The stepper motors had tracked the sky charge, iOptron says. For kudos to iOptron for how with enviable precision. me, one charge tracked quiet the mount is. While The mount and tripod are extremely the sky for just under some go-to mounts pierce stable. Doing the “tap test” with the heel of nine hours. That’s much the night, the AZ Mount my hand, I found any reverberations were better than older mounts Pro’s stepper motors barely minor and settled out quickly. that used sets of alkaline purr above a whisper as I came away impressed with iOptron’s batteries. If the battery the mount moves AZ Mount Pro. While it is not suitable for becomes depleted, the from object to long-exposure imaging because of field mount can run off the object. rotation, it is an outstanding choice for included AC adapter. visual observers looking for a travel-ready, Step 4: Once level and A foam-lined alumi- state-of-the-art way to view the universe. num case protects powered on, the mount the mount and its will take it from there. accessories during Phil Harrington has been a contributing editor Using an integrated shipping or travel. of Astronomy for many years.

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64 ASTRONOMY • DECEMBER 2016 OBSERVINGBASICS BY GLENN CHAPLE Circlet Double your observing fun STF 21 Compile your own list for double-star viewing. The double star Struve 21 (STF 21) lies in Pisces, some 10° east of that constellation’s Circlet asterism. BILL AND SALLY FLETCHER

ast month, I spotlight- I scrolled down the WDS and declination of +2°21', Struve 21 shine with an off-yellow hue, ed entries 11 through stopped at any entry identified lies in southern Pisces near its but at 10th magnitude, the 20 in the Struve cata- with “STF” (the WDS code for border with Cetus. color may not be obvious. For log of double stars. It a Struve double). I then high- The next two figures, 1902 that reason, we’ll omit the was a follow-up to an lighted and copied the row and and 2010, give the years of the spectral class. LOctober 2014 article in which I pasted it into a Word document. first and most recent acceptable After some tweaking and wrote about Wilhelm Struve, To pave the way to creating measures of Struve 21, and are rearranging of the remaining the catalog of double stars he your own 21–30 list (or the rest followed by a number (19) that data, we get (drum roll): compiled in the 1820s, and the of the Struve catalog if you have indicates the number of mea- STF 21 0h17.4m +02°21' first 10 Struve pairs. His catalog lots of time), let’s analyze the surements made during that 10.31+10.6 7.7" 52° remains a favorite of double- complete entry for Struve 21 as period. We’ll keep them for Now we can scroll on to STF star observers because many of it appears in the WDS: now. The meat-and-potatoes 22 and repeat the process. its pairs can be viewed through 00174+0221STF 21 1902 2010 data begin with 51 and 52, Struve’s 3,100-plus pairs common backyard telescopes 19 51 52 7.6 7.7 10.31 10.6 G0 which refer to the position angle aren’t the only game in town. (I’ve split one-third of them +013+050 +014+049 +01 34 of Struve 21 in 1902 and 2010, The WDS includes data for with a 3-inch f/10 reflector). NV 001721.25+022050.6 respectively. The 7.6 and 7.7 are more than 100,000 double, Will an article on Struve 21 OK, that’s a lot of numbers. the separations (in arcseconds) triple, and multiple stars from through 30 be a future offering? But we can eliminate the final in those years. dozens of catalogs. I like to I’m afraid not — there are more two rows, which include infor- Comparing the earliest with scroll through the entries look- than 3,100 Struve doubles, and mation on proper motion, the the most recent measurements ing for new doubles to observe. it would take me 25 years to Durchmusterung (DM) number tells us that the component stars You can try it yourself. To tar- cover them all! Instead, I — don’t worry, we won’t need it are relatively fixed. It’s been six get pairs appropriate for your encourage you to put together — notes, and a precise position. years since the latest measure, scope, key in on the magni- your own list of Struve double The remaining (top two) rows but with this double’s slow tudes of the component stars, stars using the Washington begin with the right ascension motion, we can expect STF 21 to their separations, and finally Double Star Catalog (WDS), and declination (in epoch 2000.0 appear about the same tonight the declination. Observers at which is accessible online at coordinates), then the catalog as it did then. The numbers mid-northern latitudes, like ad.usno.navy.mil/wds. To get identification STF 21. At a right 1902, 2010, 19, 51, and 7.6 are me, will want to bypass any- data on the first 20 Struve pairs, ascension of 0h17.4m and a now extraneous, so we’ll remove thing below –40°. Doubles here them, leaving us with just the will either be obscured by most recently measured posi- atmospheric turbulence or lie FROM OUR INBOX tion angle and separation. below the southern horizon. The magnitudes of the com- Let me conclude with a word Close encounters? Not likely . . . ponent stars, which are 10.31 for to all you double-star fanatics In September’s issue of Astronomy magazine, I found the article the primary star and 10.6 for the who are concerned that I’m by Jeff Hester “Where are they?” thought provoking. secondary, complete our run of cutting loose the remainder of I totally agree that barring some poorly understood funda- pertinent data. As Struve dou- the Struve catalog. I’m not com- mental law of physics, it is unlikely that Earth has ever been or bles go, this one is relatively pletely abandoning double stars ever will be visited by extraterrestrial aliens. The stars are too far faint. For a satisfactory view, I’d — no way! Their sheer numbers apart and travel is too costly for such a long and dangerous jour- use a scope with at least a 5-inch and unique beauty can’t be ney, and we are not that interesting to encourage such a venture. aperture and a magnifying ignored. As I always say, Evidence is growing that given the right materials and condi- power no less than 150x. “Double stars are twice the fun!” tions, life may be ubiquitous throughout the universe. I anticipate A final (and optional) piece Questions, comments, or that evidence for life, either dead or alive, will soon be discovered of information is the spectral suggestions? Email me at on Mars or elsewhere, proving that life is not limited to planet class — typically given for just [email protected]. Next Earth. — Richard Smith, Garden Valley, ID the primary star. A spectral month: Start the year with 10 class of G0 means it should cosmic picks. Clear skies!

BROWSE THE “OBSERVING BASICS” ARCHIVE AT www.Astronomy.com/Chaple.

WWW.ASTRONOMY.COM 65 ASTROSKETCHING BY ERIKA RIX Astronomy Tools Actions Set

Scanning a sketch and then Astronomy Tools Actions Set, able to spot them within the inverting it to a positive format and after you follow the down- same field of view 2° can lead to unexpected results load instructions, you can south-southwest of when it comes to stellar mag- access it through the “Actions” magnitude 2.7 nitudes. During the scanning panel under the “Windows” Ruchbah (Delta [δ] process, the faintest stars may tab within Photoshop. To pur- Cassiopeiae). become bloated and overly chase a copy ($21.95), visit The larger bright, while those that should ProDigital Software at www. of the two, appear glowing with zeal prodigitalsoftware.com. Click NGC 457, has diminish to look flat and dull. “Products,” and scroll down to a prominent Thankfully, there’s an easy fix Astronomy Tools. shape that that requires only a few steps I’ve found three of the sparks the imag- in Adobe Photoshop to set action sets in this software to ination. A variety things right. be particularly handy for star of names have Astrophotographer Noel fields. I’ll explain using been coined for it Carboni created software that sketches of the Owl Cluster based on the form it has 34 Photoshop functions, (NGC 457) and NGC 436, a most resembles to an each with predefined steps pair of open clusters in observer. Some call it the E.T. fashioned to save time and Cassiopeia. The clusters are Cluster, the Airplane Cluster, or The author used a 16-inch f/4.5 reflector make processing an image — only 0.7° apart, so if you use the Kachina Doll. To me, it’s the on a non-tracking Dobsonian mount or a sketch — a breeze. It’s the low magnification, you’ll be Owl Cluster because — as to create this sketch of the Owl Cluster Astronomy Editor David J. (NGC 457) and the other sketch of Eicher noted in 1977 — it bears NGC 436. For this drawing, she used a zoom eyepiece set at 24mm (yielding an uncanny resemblance to a 76x). Can you visualize the owl swoop- bird with striking eyes (the 5th ing downward? ALL SKETCHES BY ERIKA RIX and 7th magnitude components of multiple star system Phi [ϕ] adjust their luminosity without Cassiopeia), outstretched wings, affecting the others. and an elongated concentration NGC 436 may not be as con- of stars that forms its body. spicuous as its neighbor, but it The Owl Cluster glows softly does have a fairly rich concen- at magnitude 6.4 and tration of stars that spans 5' stretches 13' in diameter. and shines at magnitude 8.8. A After inverting the chain of three equally spaced scanned version of my stars (of magnitudes 9 through sketch in Photoshop, the 11) runs 4' east to west along next step was to reduce the southern portion of the the bloated appearance of cluster. A curved strand of the stars so that the small- fainter stars forms the shape of est would appear faintest. a backward bass clef through- Scrolling through the set of out its middle. available Astronomy Tools When I inverted my sketch actions, I selected “Make Stars of NGC 436, the darkened Smaller,” and then clicked the background of the star field “Play” icon. To create a sepa- became excessively grainy. rate layer for the changes, sim- Running the “Space Noise ply choose the “. . . As Layer Reduction” action set allowed On Top” action, and press me to soften the harsh back- “Play” again. ground, which produced a For this sketch of open cluster NGC 436, the author changed the setting of her zoom I ran the “Select Brighter more natural-looking result. eyepiece to 8mm (229x). For both sketches, she used white printer paper with a black Stars” action set next. This Questions or comments? felt-tipped pen for the brightest stars, a #2 pencil for medium-magnitude stars, and a 0.5mm mechanical pencil for the faintest stars. Both sketches have north up and highlighted only the largest Contact me at erikarix1@ west to the right. stars, which allowed me to gmail.com.

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WWW.ASTRONOMY.COM 67 BINOCULARUNIVERSE BY PHIL HARRINGTON Going deep for Andromeda How many times has someone seeing tonight left M31. And yet, asked you, “What’s the farthest there it is, weakened by the trip thing you can see with your to appear as a small, fuzzy patch eyes?” Me? I’ve long lost track. just off Nu (ν) Andromedae. But my stock answer is always Isn’t it amazing that we can see The Andromeda Galaxy appears like an oval smudge in binoculars, and it is even visible the same, the Andromeda it with just our eyes? to the naked eye as the most distant object most people can see. DEAN SALMAN Galaxy (M31). Unless you are The Andromeda Galaxy is under very dark, very trans- also well known as M31, the While you are gazing at M31, But they are slowly getting parent skies, Andromeda is 31st entry in French astronomer keep an eye out for its two brighter. So are M31, M32, and it, at 2.5 million light-years Charles Messier’s catalog. neighbors, M32 and NGC 205. NGC 205. Slowly — very slowly! away. That’s an incredible Messier bumped into it for the M32, the smaller and brighter That’s because they are all distance when you stop and first time on August 3, 1764. of the pair, looks like a small headed our way. In fact, M31 think about it. The light we see Historical records, however, smudge due south of M31’s core. and our Milky Way are on a tonight, traveling at more than show that Persian astronomers NGC 205 is larger, but also collision course. Studies show 186,000 miles every second, observed it as far back as fainter. Spotting it can be very that gravity is pulling them took 2.5 million years to reach a.d. 905. challenging. First, brace your toward each other at a rate of your eyes. Good binoculars expand the binoculars against something to about 75 miles (120 kilometers) What was going on here on faint blur of M31 into a dis- steady the view, then look for its per second. At that speed, it’s Earth when that light left the tinctly football-shaped disk dim glow northwest of M31’s going to take about 4 billion Andromeda Galaxy? Well, for measuring a full 5°. That’s as core. It’s about twice as far away years for the two to collide and one, we weren’t. Humans — wide as 10 Full Moons stacked as M32 is to the core’s south. merge. Some call the end result that is, Homo sapiens — weren’t end to end, and probably about M32 and NGC 205 are great Milkomeda. While it is unlikely even around. No, 2.5 million the same width as your binocu- examples of dwarf elliptical gal- that the Sun will collide with years ago, our evolutionary lar’s field of view. axies, the most common type of another star, things here will be ancestors known as Homo At first glance, you may only galaxy in the universe. M32 getting dicey for other reasons. habilis made their first appear- see the galaxy’s bright, central appears almost perfectly round In 4 billion years, the Sun will ance. And they had a tough core. But with patient observa- and is referred to as an E2 ellip- be running out of fusible hydro- time of it back then, too. That tion and using averted vision, tical. NGC 205 is an E6 ellipti- gen in its core. So, while was also the beginning of the the full extent of the spiral arm cal galaxy for its more oblate Milkomeda is just evolving into Pleistocene epoch, which saw disk will become more appar- profile. M32 and NGC 205 are existence, the Sun will be start- repeated global glaciations. ent. Giant binoculars even add the two brightest of as many as ing its slow departure. Just as Ice ages and an Earth popu- subtle texture and irregularities 10 companion galaxies associ- our distant ancestor Homo habi- lated by half-human, half-ape to the disk, as well as a hint of ated with M31. The others are lis lived in interesting times, so creatures — that was the state of the galaxy’s two dark dust lanes too small and faint to be visible will our far future generations affairs when the light we are bisecting lengthwise. through most binoculars. — though life on Earth may last only a billion years, until the water is gone due to the Sun’s increasing radiation. Back to today. We all have favorite binocular objects. I’d enjoy hearing about yours, and possibly feature them in future columns. Contact me through my web site, philharrington.net. Until next month, remember that two eyes are better than one.

Phil Harrington is a longtime

ANTHONY AYIOMAMITIS ANTHONY observer and contributing Satellite galaxy M32 stays close to the side of the Andromeda The faint, elliptical galaxy NGC 205 orbits Andromeda slightly editor of Astronomy. Galaxy and is visible in hefty binoculars. ADAM BLOCK/NOAO/AURA/NSF farther afield than M32 and is also visible in good binoculars.

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P24640 trademark of Microsoft Corporation in the United States and other countries. READER GALLERY

1

1. MOONSTRUCK On July 19, 2016, the Full Moon rose over the dome of the famous 100-inch Hooker Telescope atop Mount Wilson, California. The 100-inch dome stands at right, and to the left is the dome of one of the six telescopes that together form the CHARA interferometer. • John Fisanotti

2. NOT TIGHTLY WOUND Palomar 8 is a globular cluster about 42,000 light-years away in the constellation Sagittarius. It carries a classification of X (out of XII), meaning that it has a loose concentration of stars. • Dan Crowson

2

70 ASTRONOMY • DECEMBER 2016 3. STELLAR SPECTACLE The Large Magellanic Cloud is one of two large irregular satellite galaxies of the Milky Way. It lies 163,000 light- years away and appears to straddle the border between the constellations Dorado and Mensa. • Carlos Eduardo Fairbairn

4. WORLD VIEW The photographer compiled this high-resolution map of the entire face of Jupiter from images he acquired during the first half of June 2016. The Great Red Spot lies just below center. • Damian Peach

5. LIKE NEPTUNE 3 Abell 39 is a striking planetary nebula with a deep-blue hue. It lies in the constellation Hercules about 6,800 light-years away. Although spherical, it has numerous brightness variations across its face. • Adam Block/Mount Lemmon SkyCenter/University of Arizona

6. THE CORSAGE GALAXY IC 5332 is a face-on spiral galaxy in the constellation Sculptor. It lies 1.6° north of magnitude 4.4 Beta Sculptoris. It glows at magnitude 10.7 and lies some 27 million light-years away. • Warren Keller/Steve Mazlin/Steve Menaker

7. DARK SURROUNDINGS This region in the far-southern constellation Chamaeleon contains 4 vast amounts of dust. The bright star to the upper right of center is magnitude 4.2 Beta (β) Chamaeleontis. Just below it lies irregular galaxy IC 3104. • Gerald Rhemann

5

Send your images to: Astronomy Reader Gallery, P. O. Box 1612, Waukesha, WI 53187. Please include the date and location of the image and complete photo data: telescope, camera, filters, and exposures. Submit images by email 6 7 to [email protected].

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WWW.ASTRONOMY.COM 73 BREAK THROUGH Orion with a twist Few stellar nurseries rival the beauty of the Orion Nebula (M42). Thanks to its vast size (some 25 light- years across) and proxim- ity (only about 1,350 light- years away), this glowing gas cloud looks stunning through any telescope. Yet visible light tells only part of the nebula’s story. In this infrared image, taken with the HAWK-I instrument on the Very Large Telescope in Chile, astronomers found about 10 times more brown dwarfs and free-floating planets than they had pre- viously seen. Researchers were able to capture these low-mass objects because the infrared radiation they emit can escape from deep within the nebula. ESO/H. DRASS ET AL.

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Adorama – 800.223.2500 – www.adorama.com High Point Scientifi c – 800.266.9590 – www.highpointscientifi c.com Astronomics – 800.422.7876 – www.astronomics.com OPT Telescopes – 800.483.6287 – www.opttelescopes.com B&H Photo – 800.947.9970 – www.bhphotovideo.com Optics Planet – 800.504.5897 – www.opticsplanet.com Focus Camera – 800.221.0828 – www.focuscamera.com Woodland Hills – 888.427.8766 – www.telescopes.net SOUTHERN MARTIN GEORGE describes the solar system’s changing landscape SKY as it appears in Earth’s southern sky. February 2017: Venus dazzles at dusk

As darkness falls on February 1, before Jupiter rises in the east our line of sight, making deli- Magellanic Cloud (LMC) in a lovely crescent Moon stands later in the evening. The giant cate structures within them this month’s early evening sky. above Venus and Mars in the planet appears 4° north (lower relatively easy to see. The brightest of the Milky western sky. Although the left) of 1st-magnitude Spica, the You can track down Way’s satellite galaxies, the Moon departs the scene in a luminary of the constellation Mercury in morning twilight LMC lies high in the south few days, the bright planets Virgo, and barely budges rela- during February’s first half. soon after darkness falls. remain an attractive couple tive to this background all The innermost planet shines at This month marks 30 years throughout the month. month. At magnitude –2.2, magnitude –0.2, bright enough since Supernova 1987A blazed Brilliant Venus dominates Jupiter shines far brighter than to see with the naked eye forth in the LMC. This explod- the view. It becomes easy to see its companion. though easier to spot through ing star reached 3rd magnitude, just 20 minutes after sunset. Jupiter is a wonderful sight binoculars against the twilight. which made it an easy naked- And if the inner planet looks through any telescope. Its disk On the 1st, it appears about eye object for those in the more dazzling than usual, it’s spans 41" at midmonth and 10° high in the east-southeast Southern Hemisphere. Naked- not your imagination. It shines should show impressive detail 45 minutes before sunrise. A eye supernovae are rare events at magnitude –4.8 this month, on nights with steady seeing. telescope shows a fat gibbous — only six others occurred dur- brighter than at any other time The best views come once disk measuring 6" across. ing the second millennium, and during this evening apparition. Jupiter climbs higher after mid- Observers in Africa and none has appeared since 1987. Venus reached greatest elon- night. Look for two dark cloud South America can witness a Although the LMC super- gation from the Sun in January belts that straddle a brighter rare lunar eclipse on the night nova has long since faded from and is now drawing closer to zone coinciding with the plan- of February 10/11, when the view through amateur tele- our star as it approaches infe- et’s equator. A small instru- Moon tracks completely inside scopes, astronomers continue to rior conjunction in late March. ment also reveals the world’s Earth’s light penumbral track its evolution with large This makes February the per- four bright moons. shadow but never touches the instruments on Earth and in fect time to observe the planet’s You’ll have to wait until the dark umbra. (Some calculations space. Not long after the explo- changing appearance through a small hours of the morning to show 1 percent of our satellite sion, scientists using the Hubble telescope. On the 1st, Venus see Saturn. Watch the eastern remains in full sunlight, but Space Telescope detected a ring shows a disk that is 31" in sky for the distinctive shape of why quibble?) Only 3 percent of gas surrounding the blast diameter and 40 percent lit. By Scorpius the Scorpion; about an of all lunar eclipses fall in this site. The progenitor star had the 28th, the planet has swollen hour after it clears the horizon, category. The eclipse begins at ejected this material thousands to 46" across but the Sun illu- the ringed planet rises. Saturn 22h32m UT on February 10 of years earlier, and it lay in the minates only 18 percent of its glows at magnitude 0.5 and and ends at 2h56m UT on the path of the supernova’s expand- Earth-facing hemisphere. easily outshines the back- 11th, reaching a maximum at ing shock wave. When the Mars lies to Venus’ upper ground stars near the border 0h44m UT. shock collided with the material right all month. The gap between Ophiuchus and Sagit- On August 26, people along in the early 2000s, it lit up some between the two worlds grows tarius. (The planet crosses from a narrow path crossing south- 30 dense clumps in a spectacu- from 5° on February 1 to 12° on the former constellation into ern South America, the Atlantic lar display witnessed by Hubble. the 28th. Even though the Red the latter during February’s Ocean, and Africa will experi- Although you can’t see Planet glows six magnitudes final week.) ence an annular solar eclipse. 1987A any longer, I strongly fainter than its neighbor, it is Saturn ascends quickly and You must use a safe solar filter recommend scanning the LMC still easy to spot, and easy to appears more than one-third of to see the Sun reduced to a through binoculars while it identify thanks to its distinctive the way to the zenith by the glowing ring of fire. Just north remains high in the evening color. Unfortunately, Mars time twilight begins. The high of Coyhaique, Chile, annularity sky. The galaxy’s showpiece offers little to telescope owners. altitude then should afford begins at 13h36m UT and lasts object is the wondrous The planet’s disk measures just steady views of the magnificent 1 minute and 5 seconds. Tarantula Nebula (NGC 2070), 5" across and shows no detail. world through any telescope. a massive star-forming region Once Mars dips below the Even the smallest scope reveals The starry sky near the location of 1987A. It western horizon, you’ll have the planet’s 16"-diameter disk If you observe from a reason- ranks as the largest emission some time to explore the won- wrapped by a ring system that ably dark site, you should see nebula known in the entire ders of the summer Milky Way spans 36". The rings tilt 27° to the milky glow of the Large Local Group of galaxies. STAR S

DOME AUSTRALE

THE ALL-SKY MAP TRIANGULUM SHOWS HOW THE CIRCINUS

SKY LOOKS AT:

P.M. α

10 February 1 GRUS

9 P.M. February 15 TUCANA

OCTANS

8 P.M. February 28 APUS

AURUS

NT

β Planets are shown 104 NGC

at midmonth MUSCA

SCP

NGC 4755 NGC

SMC PHOENIX

α

β HYDRUS CHAMAELEON

γ

Achernar δ

MENSA CRUX

CARINA

α

HOROLOGIUM NGC 3372 NGC RETICULUM

NGC 2070 NGC

LMC

SCULPTOR

NGC 253 NGC

VOLANS

DORADO

SGP

PICTOR

NGC 2561 NGC

β

FORNAX

α

VELA

Canopus

γ

COLUMBA

CAELUM

CETUS

ζ

ANTLIA

PUPPIS PYXIS

ERIDANUS

LEPUS ε

W 2477 NGC

M41 PISCES Mira β CANIS MAJOR Uranus ο M47 Rigel Sirius α α α β Alphard M42 MONOCEROS

α

Pa th of th e S α un Procyon (e α cl Betelgeuse β ipt ic) ORION TAURUS CANIS MINOR

` α ARIES γ Aldebaran α ζ M44 M1 CANCER Pleiades M35 GEMINI β β Pollux α MAGNITUDES M36 M37 Algol Castor β Sirius Open cluster PERSEUS M38 0.0 Globular cluster AURIGA LYNX 1.0 Diffuse nebula 2.0 α β 3.0 Planetary nebula Capella 4.0 5.0 Galaxy

N HOW TO USE THIS MAP: This map portrays the sky as seen near 30° south latitude. FEBRUARY 2017 Located inside the border are the four directions: north, south, east, and west. To find stars, hold the map Calendar of events overhead and orient it so a

1 The Moon passes 2° south of 18 Asteroid Irene is at opposition,

NT direction label matches the CE direction you’re facing. Mars, 1h UT 19h UT The stars above the map’s horizon now 2 The Moon passes 3° south of Last Quarter Moon occurs at match what’s Uranus, 8h UT 19h33m UT

NGC 5139 NGC in the sky.

3 The Moon passes 1.0° north of The Moon is at apogee NGC 5128 NGC dwarf planet Ceres, 2h UT (404,376 kilometers from Earth), 21h14m UT 4 First Quarter Moon occurs at 4h19m UT 20 Asteroid Eunomia is at opposition, 11h UT 5 The Moon passes 0.2° north of Aldebaran, 22h UT The Moon passes 4° north of Saturn, 23h UT 6 The Moon is at perigee (368,816 kilometers from Earth), 22 Asteroid Metis is at opposition,

14h02m UT 2h UT CORVUS Jupiter is stationary, 19h UT 23 Jupiter passes 4° north of Spica,

16h UT M104 11 Full Moon occurs at 0h33m UT; penumbral lunar eclipse 26 New Moon occurs at 14h58m UT; annular solar eclipse The Moon passes 0.8° south of

Regulus, 14h UT 27 Mars passes 0.6° north of Uranus, HYDRA CRATER 8h UT E 15 The Moon passes 3° north of Jupiter, 15h UT 28 The Moon passes 10° south of Venus, 20h UT 17 Venus is at greatest brilliancy (magnitude –4.8), 7h UT

SEXTANS Jupiter is at aphelion (816.3 million kilometers from the Sun), 7h UT

M65 Regulus M66

α

γ

LEO STAR COLORS: Stars’ true colors depend on surface temperature. Hot stars glow blue; slight- ly cooler ones, white; LEO MINOR intermediate stars (like the Sun), yellow; followed by orange and, ultimately, red. Fainter stars can’t excite our eyes’ color receptors, and so appear white without optical aid.

Illustrations by Astronomy: Roen Kelly

BEGINNERS: WATCH A VIDEO ABOUT HOW TO READ A STAR CHART AT www.Astronomy.com/starchart. SHOP NOW FOR SCIENCE & ASTRONOMY PRODUCTS

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