The man behind OF Hubble’s “Pillars” p. 26 SPECIAL 2 5COLLECTOR’STH ANNIVERSARY EDITION APRIL 2015 HUBBLEThe world’s best-selling astronomy magazine SPACE TELESCOPE • Top science discoveries p. 28 • Space missions To celebrate 25 years of discovery, the Hubble that saved the Space Telescope used its latest camera to telescope p. 44 capture this image of the Eagle , the subject of a famous 1995 photo dubbed the • How Hubble “Pillars of Creation.” changed the world p. 50

BEST www.Astronomy.com BONUS 43 Vol. ONLINE • IMAGES 4 Issue 28 CONTENT FROM HUBBLE p. 56 CODE p. 4 WorldMags.net

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M57Pelican Nebula M51The Moon NGC 6946

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some pictures say a thousand words. others say more. WE SALUTE THE HUBBLE SPACE TELESCOPE ON ITS 25TH ANNIVERSARY.

April 24 marks 25 years since the Hubble was launched into orbit and forever changed what we know about the universe. Celebrate the milestone at Kennedy Space Center Visitor Complex, where you can view a full-sized Hubble replica, watch Hubble 3D on IMAX® and experience awe-inspiring Hubble images. It’s a fitting always exploring tribute to the first of NASA’s great observatories. TourKSC.com WorldMags.net Online Content Code: ASY1504 Enter this code at: www.astronomy.com/code APRIL 2015 to gain access to web-exclusiveWorldMags.net content VOL. 43, NO. 4 I/AURA C NASA/ESA/THE HUBBLE HERITAGE TEAM STS TEAM HERITAGE HUBBLE NASA/ESA/THE ON THE COVER The Hubble Space Telescope recently revisited the Eagle Nebula’s famous “Pillars of Creation,” capturing the iconic -forming region with its CONTENTS 56 newest camera. FEATURES COLUMNS 11 26 36 50 Strange Universe BOB BERMAN The man behind the The Sky this Month How Hubble changed Pillars A brief glimpse of totality. the world Secret Sky 16 STEPHEN JAMES O’MEARA What has JEFF HESTER’s iconic MARTIN RATCLIFFE AND Think today’s society would be Hubble Space Telescope image of ALISTER LING the same without the big eye in Observing Basics 20 the Eagle Nebula meant to him the sky? Think again. LIZ KRUESI GLENN CHAPLE personally? 38 Cosmic Imaging 70 StarDome and 56 ADAM BLOCK 28 Path of the Planets 25 years of dazzling Hubble’s top seven RICHARD TALCOTT; images science discoveries ILLUSTRATIONS BY ROEN KELLY The space telescope’s extraor- QUANTUM GRAVITY From the incandescent brilliance dinary vision has revealed star Snapshot 9 of the first stars and galaxies to clusters, nebulae, and galaxies in 44 Breakthrough 10 the overwhelming power of dark Saving Hubble detail no one could have imag- matter and energy, the space ined. RICHARD TALCOTT How astronauts continually Astro News 12 telescope has illuminated many reinvented the most important cosmic mysteries. MARIO LIVIO telescope ever. BEN EVANS 68 Ask Astro IN EVERY ISSUE From the Editor 6 BONUS ONLINE FEATURE! Letters 11, 20, 70 How the Hubble Space Telescope Web Talk 24 changed the cosmos New Products 71 Exclusive interviews, interactive graphics, and much more! Advertiser Index 72 28 www.Astronomy.com/Hubble25 Final Frontier 74

Visit Astronomy.com/toc for bonus material — it’s ONLINE exclusive to Astronomy FAVORITES magazine subscribers. Astronomy (ISSN 0091-6358, USPS 531-350) is pub- Go to www.Astronomy.com Superstars of Trips & Tours Tour the Equipment lished monthly by Kalmbach Publishing Co., 21027 Crossroads Circle, P. O. Box 1612, Waukesha, WI for info on the biggest news and Astronomy Travel the Solar System Review 53187–1612. Periodicals postage paid at Waukesha, observing events, stunning photos, Interviews world with the Videos about Archive WI, and additional offices. POSTMASTER: Send with top staff of our planetary What to know address changes to Astronomy, 21027 Crossroads informative videos, and more. Circle, P. O. Box 1612, Waukesha, WI 53187–1612. scientists Astronomy neighborhood before you buy Canada Publication Mail Agreement #40010760. WorldMags.net 4 ASTRONOMY • APRIL 2015 WorldMags.net

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® Tele Vue 32 Elkay Dr., Chester, New York 10918 (845) 469-4551. televue.com Visionary WorldMags.net FROM THE EDITOR BY DAVID J. EICHERWorldMags.net Editor David J. Eicher Art Director LuAnn Williams Belter EDITORIAL STAFF Senior Editors Michael E. Bakich, Richard Talcott Production Editor Karri Ferron Associate Editors Eric Betz, Korey Haynes Editorial Associate Valerie Penton ART STAFF

Hubble’s NASA Senior Graphic Designer Chuck Braasch Illustrator Roen Kelly Production Coordinator Jodi Jeranek CONTRIBUTING EDITORS deep legacy Bob Berman, Adam Block, Glenn F. Chaple, Jr., Martin George, Tony Hallas, Phil Harrington, Liz Kruesi, Ray Jayawardhana, Alister Ling, Steve Nadis, Stephen James O’Meara, Tom Polakis, Martin Ratcliffe, Mike D. Reynolds, Sheldon Reynolds, Erika Rix, wenty-five years ago, a Hubble story I wrote, Haynes. She comes to John Shibley, Raymond Shubinski NASA launched what “How the Hubble Space Astronomy magazine fresh EDITORIAL ADVISORY BOARD Buzz Aldrin, Marcia Bartusiak, Timothy Ferris, Alex Filippenko, promised to be the Telescope changed the cos- from an astronomy Ph.D. Adam Frank, John S. Gallagher lll, Daniel W. E. Green, William K. world’s greatest astro- mos,” with interactive program at George Mason Hartmann, Paul Hodge, Anne L. Kinney, Edward Kolb, Stephen P. Maran, Brian May, S. Alan Stern, James Trefil nomical instrument, graphics, slide shows, videos, University in Virginia. Tthe Hubble Space Telescope. and more, and you can see it Haynes spent most of her Kalmbach Publishing Co. And then, shocked and at www.Astronomy.com/ time in grad school at President Charles R. Croft Vice President, Editorial, Publisher Kevin P. Keefe stunned when they found the Hubble25. NASA’s Goddard Space Senior Vice President, Sales & Marketing Daniel R. Lance optics to be flawed, engineers With the launch of the Flight Center, studying exo- Vice President, Consumer Marketing Nicole McGuire Corporate Art Director Maureen M. Schimmel devised a way to fit Hubble James Webb Space Tele- planet atmospheres and Managing Art Director Michael Soliday with corrective lenses, trans- scope, in some senses a suc- looking for water on alien Production Manager Helene Tsigistras Corporate Advertising Director Ann E. Smith forming it into a machine cessor to Hubble, looming worlds. In addition to Group Circulation Manager Ken Meisinger Single Copy Sales Manager Michael Barbee that has rewritten our under- on the horizon, it’s a fitting research, she was a writer for Marketing Specialist Cathy Muempfer standing of the cosmos. time to look back. Hubble ADVERTISING DEPARTMENT (888) 558-1544 This special issue exam- has at least several years left, Advertising Sales Manager Jamie Rinehart ines the legacy of the instru- but if not captured in orbit Advertising Sales Representative Dina Johnston, [email protected] ment that, in a span of 25 or serviced again, it will Ad Services Representative years, has contributed more reenter the atmosphere, Christa Burbank, [email protected] RETAIL TRADE ORDERS AND INQUIRIES revolutionary observations breaking apart and falling Selling Astronomy magazine or products in your store: than any telescope that pre- back to Earth. Phone (800) 558-1544, Press 3 Outside U.S. and Canada (262) 796-8776, ext. 818 ceded it. It’s fitting that a The astronomer who gave Fax (262) 798-6592 Email [email protected] quarter-century of ground- Hubble its name, Edwin Website www.Retailers.Kalmbach.com breaking science gives way Powell Hubble, was born in CUSTOMER SALES AND SERVICE to an examination of Missouri in 1889. Growing Phone (800) 533-6644; Fax (262) 796-1615 [email protected] Hubble’s triumphs. Our up in Illinois, Hubble Korey Haynes. WILLIAM ZUBACK SPECIAL EMAIL ADDRESSES package delivers some pretty attended the University of Ad Sales [email protected] Ask Astro [email protected] good stuff. Astronomer Chicago before becoming a Astrobites, a blog that posts Books [email protected] Letters [email protected] Mario Livio writes about the Rhodes scholar. The decade daily summaries of astron- Products [email protected] greatest scientific discoveries of the 1920s saw Hubble’s omy journal articles, and she Reader Gallery [email protected] made using Hubble. Science biggest scientific achieve- also enjoyed volunteering at Editorial phone: (262) 796-8776; advertising: (888) 558-1544; customer writer Ben Evans details the ments. Discovering a the Smithsonian’s National service & sales: (800) 533-6644; outside the U.S. and Canada: (262) 796- 8776, ext. 421, Monday through Friday, 8:30 A.M. to 4:30 P.M. CT, Fax: (262) five servicing missions that Cepheid variable star in the Air and Space Museum with 796-1615; Email: [email protected]. Please include your name, mailing address, and telephone number with any correspondence. repaired and then kept Copyright © 2015 Kalmbach Publishing Co., all rights reserved. This publi- “spiral nebula” M31, now their Public Observatory cation may not be reproduced in any form without permission. Printed in the U.S.A. Allow 6 to 8 weeks for new subscriptions and address changes. Hubble going. Contributing known as the Andromeda Program. Subscription rate: single copy: $5.99; U.S.: 1 year (12 issues) $42.95; 2 years (24 issues) $79.95; 3 years (36 issues) $114.95. Canadian: Add $12.00 Editor Liz Kruesi reveals the , Hubble found evi- We’re delighted to have postage per year. Canadian price includes GST, payable in U.S. funds. All other international subscriptions: Add $16.00 postage per year, payable in ways in which the telescope dence that the universe is Haynes join the staff, and U.S. funds, drawn on a U.S. bank. Expedited delivery service surcharges: Domestic first class $30/yr; Canadian air $30/yr; International air $60/yr. changed our culture forever. larger than just the Milky look for her many contribu- BN 12271 3209 RT. Not responsible for unsolicited materials. And Senior Editor Richard Way Galaxy and defined the tions in upcoming issues. Talcott delivers a portfolio of nature of galaxies. Hubble’s greatest images. On a staff note, please Yours truly, We also have a special help me welcome our newest Astronomy online package built around associate editor, Korey Follow

Follow the Dave’s Universe blog: www.Astronomy.com/davesuniverse David J. Eicher www.twitter.com/ www.facebook.com/ plus.google.com/ Follow Dave Eicher on Twitter: @deicherstar AstronomyMag AstronomyMagazine +astronomymagazine Editor WorldMags.net 6 ASTRONOMY • APRIL 2015 WorldMags.net YOU’RE INVITED TO A B33 * Larry Weatherly PICNIC Sales Manager

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MARS BOUND GROUND GAME COSMIC CASH HOT BYTES >> Engineers at Lockheed For the first time, A group of physicists got Martin have started scientists detected a a share of the $3 million TRENDING work on NASA’s next super-Earth passing in Breakthrough Prize in TO THE TOP Mars lander, InSight, front of a Sun-like star Fundamental Physics for which is set to launch using a ground-based their role in finding the in 2016. telescope. accelerating universe.

SNAPSHOT How the Moon formed

Planetary scientists believe CASH COSMIC ST/NASA the Moon resulted from a giant whack Earth experi- enced from a now-gone planetesimal, Theia.

When we walk outside at night and look skyward, it’s usually the Moon, our planet’s natural satellite, that first catches our eye. The fifth-largest moon in the solar system, the Moon is one of the largest in relation to its parent body. Called the Giant Impact Hypothesis, the accepted story of the Moon’s formation suggests that 4.6 billion years ago, two planets floated in the space now occupied by the Earth-Moon system. Proto-Earth had 50 to 90 percent of its current size and mass, and a Mars-sized planet also existed, one that astrono- mers now call Theia (in Greek mythology, mother of the Moon goddess Selene).

Planetary scientists believe TEAM/H SEARCH SUPERNOVA HIGHZ GAME; GROUND AMES/JPLCALTECH NASA BOUND; MARS NASA/JPLCALTECH IRWIN; JIM ASTRONAUT NASA some 4.53 billion years ago, Astronaut Jim Irwin salutes the U.S. flag during the Apollo 15 mission in 1971. Theia struck Earth, creating a short-lived ring of debris that into Earth’s mantle. The evi- contain nearly identical oxygen there. Where did Theia go? accreted into the Moon. The dence for this scenario comes isotopes as those found in Earth You’re standing on it. majority of Theia’s mass accreted from Apollo rock samples, which rocks. But the story doesn’t end — David J. Eicher WorldMags.net WWW.ASTRONOMY.COM 9 BREAK THROUGHWorldMags.net A party of fireflies The southern Carina holds some of the ’s most spec- tacular star clusters. Case in point: NGC 3532, also known as the Firefly Party Cluster and Wishing Well Cluster. Its hottest stars glow with a characteristic blue color, while the cool- er red giants appear bright orange. This 300-million- year-old cluster lies some 1,300 light-years from Earth. Astronomers cap- tured this image through the European Southern Observatory’s 2.2-meter telescope at La Silla in Chile. NGC 3532 is an appropriate subject on the 25th anniversary of the Hubble Space Telescope’s April 1990 deployment because it was the orbit- ing observatory’s first target. ESO/G. BECCARI

WorldMags.net 10 ASTRONOMY • APRIL 2015 STRANGEUNIVERSE FROM OUR INBOX BY BOBWorldMags.net BERMAN Educating our youth While I always enjoy Astronomy magazine, the opening pages of the October issue, in particular, had an exceptionally wel- come effect on me. “Separating fact and fiction” (p. 6) by Editor Dark vs. super David J. Eicher was a genuine piece of visionary thinking! In my view, Eicher nailed a major dilemma of our modern The difference between good culture and the goal toward which we should, and can, aspire. dark and outstanding skies. We do live in a society where “we are immersed in a constant stream of entertainment” and where both the younger and older generations celebrate “the trivial … not caring for the meaning- ecturing takes me to strange one, truth be told. The ful,” as he aptly puts it. But, indeed, we can overcome these ten- star parties around firmament becomes so amaz- dencies by educating our youth to focus their energies on the U.S. It’s fun to see ing — and I’m talking naked- realizing “where we are and why we are here.” what excites backyard eye — that it’s worth time and Eicher strikes a resonating chord by challenging us to call astronomers, and I feel expense to travel to experience forth our human potential and liberate ourselves to contribute to Lhonored to look through home- it. We all know where such con- a “great forward-moving civilization of the future.” These mus- built telescopes. Yet interest- ditions may be found. Southern ings bring to mind a piece of wisdom reaching us from over a ingly, many of these gatherings Arizona’s Organ Pipe Cactus century ago from the Orient, the words of Bahá’u’lláh (1817– are held under skies that are National Monument. The west- 1892): “All men have been created to carry forward an ever- good — but not excellent. ern states far from any town. advancing civilization.” — Partow Izadi, Lapland, Finland This isn’t a criticism. In The White Mountains of New three northeastern states, the Hampshire. Upstate New York’s most rural possible location is Adirondacks. I’d love to hear innumerable faint stars, the sky nature designed. It is far still within 30 miles (50 kilo- about your favorites. Milky Way is the most prominent superior to the view astronauts meters) of a city, producing Outside the U.S., many feature of the heavens, and the get in space. Up there, stars are bright glows in multiple direc- abound. Chile’s northern half. Hercules globular M13 is steady. dim because of the four thick tions. This is a central issue Australia’s Outback. The Sahara. It doesn’t merely come and go. glass layers in space station and battle cry for organizations The Persian desert southeast Now here’s the difference portholes, while spacewalkers like the International Dark-Sky of Isfahan — alas, not a good as we jump up to outstanding must peer through visors of Association, which tirelessly travel idea these days, which is a skies. It’s not subtle. In such polycarbonate plastic. tries to limit waste lighting and shame because the Iranians gen- conditions, are But these premier earthly unshielded yard lights. erally like Americans and love initially confusing because so skies are not truly black. Air Since I also lead annual over- astronomy. Here’s a quick guide many stars pepper the scenery. glow, caused mostly by solar seas trips to perfect sites in des- to what happens. The Milky Way “pops” and ultraviolet, is always present. It erts and such, I’m keenly aware bathes the unpolluted country- of the dark skies issue, to which side with five times more light we can all relate. Strangely OUTSTANDING CONDITIONS PROVIDE than all the stars combined. It enough, in all these years, it’s AN UNUSUAL EXPERIENCE. looks brightest about 10° above never been this column’s main the horizon. Unless you’re topic. But it now comes vividly In poor urban skies, the totally dominates the sky dome. under a canopy of trees (and to mind because of something Little Dipper only has two stars, It casts shadows. It does not have what would be the point of that happened last night. maybe three if you can glimpse rifts or splits. Instead, intricate that?), it lets you always see well It was midnight, and I couldn’t 3rd-magnitude Gamma (γ) inky nebulae become the night’s enough not to stub toes, once sleep, so I walked out to the Ursae Minoris. most prominent feature. Black eyes adapt to the dark. meadow behind my house in a In the near-city suburbs, crablike tentacles of abstract Ah, what wonder! It’s evoca- bathrobe and bare feet. The cold about 130 stars appear across the art — numerous filaments and tive of whatever got us hooked dewy grass was uncomfortable, sky at any given time, but there’s sharp-edged blotches — form on astronomy in the begin- but the moonless sky erased all no sign of the Milky Way. distinct cameos in front of the ning. It still awaits. True, these body-awareness. Normally my In the farther-out suburbs, the brilliant Milky Way. These places are often farther away rural area has good — but not Milky Way appears dimly. The ebony structures, I rediscovered than in the old days. They usu- superb — skies, yet something Little Dipper has five or six stars. last night, are so detailed and ally entail time and expense. odd unfolded last night. Maybe In good rural regions, the 3-D-seeming, they’re the most But not last night, when I got it was the extraordinarily dry Little Dipper displays all seven in-your-face aspect of the night. a gift. And who do I thank? air. In any case, I was given a stars and the Milky Way is clear, If Andromeda is up, the large Insomnia? reminder of the dramatic differ- its rifts showing conspicuously. round Pinwheel Galaxy (M33) It must be insomnia. ence between skies that are good The Andromeda Galaxy (M31) dimly comes and goes in its and those that are outstanding. is obvious. vicinity. Fourteen Pleiads can Contact me about Outstanding conditions pro- In very good rural skies, be counted, though three may my strange universe by visiting http://skymanbob.com. vide an unusual experience. A Orion’s Belt is embedded in blink in and out. This is the BROWSE THE “STRANGE UNIVERSE” ARCHIVE AT WorldMags.netwww.Astronomy.com/Berman. WWW.ASTRONOMY.COM 11 MASSIVE MERGER. Astronomers believe the massive stars in the binary MY are orbiting so close to each ASTRONEWSWorldMags.netother that they will soon merge into one massive sun. The find forwards a theory that the largest stars form this way. TSUNAMI SIGNAL. As of November, BRIEFCASE Voyager 1, illustrated here, is still feeling the TITAN’S DUNES CREEP SLOWLY effects of a large shock In two independent papers published online December wave that it originally 8 in Nature and Nature Geoscience, scientists announced detected last February. that surprising winds sculpt the dunes of Saturn’s moon NASA/JPLCALTECH Titan. Most of Titan’s winds blow from the east, but only the stronger, more intermittent westerly winds can heave the dunes’ massive weight. Scientists found that the dunes morph slowly over timescales of around 3,000 Saturn years (about 88,000 Earth years), meaning the process relates to long-term climate change, far beyond the cycles of tides• or seasons. PLANCK SHEDS LIGHT ON DARK MATTER Scientists have finished analyzing data from the European Space Agency’s Planck satellite, which observed between 2009 and 2013. The team announced December 1 that VOYAGER 1 EXPERIENCES they are now able to rule out an entire class of dark mat- ter candidates. These particular candidates are known for dark matter-antimatter annihilation, which would mani- LONGLASTING SHOCK WAVE fest observable cosmic rays. While other experiments have found cosmic-ray excesses they tentatively attrib- uted to dark matter annihilation, Planck disagrees and hen the Voyager 1 spacecraft huge explosion of plasma from the Sun attributes these to less exotic sources such as pulsars. passed the realm of the planets — runs into the interstellar plasma that • and headed toward interstel- exists between the stars. The first two NASA GETS BUDGET BOOST lar space, scientists couldn’t be tsunami waves Voyager detected lasted Congress raised NASA’s budget 2 percent December 9, to W $18 billion. The science mission directorate in particular sure what to expect. After all, this was a around a month each, but the spacecraft received an almost hundred million dollar increase, with new frontier of space exploration. And was still feeling the effects of one that planetary science getting a big boost. Earth science fund- according to the University of Iowa’s Don began in February 2014 as of November. ing remained flat, while human spaceflight received Gurnett, who presented new Voyager In that time, Voyager traveled 250 million strong support both for private companies like SpaceX and NASA’s own Space Launch System rocket and Orion data December 15 at the American miles (400 million kilometers). crew capsule. Overturning the White House’s suggested Geophysical Union meeting in San “Most people would have thought cancellation, Congress also decided to continue funding Francisco, the the the interstellar medium would have SOFIA, NASA’s infrared telescope that flies in its own modified Boeing 747. — Korey Haynes spacecraft officially entered in 2012 has been smooth and quiet,” Gurnett said in had its surprises. December. “But these shock waves seem Since October 2012, Voyager 1 has to be more common than we thought.” In experienced three “tsunami waves.” Such addition, scientists are still not sure what shock waves occur when a wave of pres- the length of the most recent tsunami sure from a coronal mass ejection — a wave means. — Karri Ferron

THE “NEWSIEST” The Rosetta mission to FAST Comet 67P appeared in 25 FACT ASTRONOMY WORDS news stories, while the Curiosity IN 2014 Mars rover appeared in 16. 25 years ago 10 years ago in Astronomy in Astronomy In the April 1990 issue of In April 2005, Huygens Astronomy, spacecraft had recently touched Galileo had recently blast- down on the surface ed off from Earth and was of Titan. Senior Editor five years away from its Richard Talcott spoke Jupiter rendezvous. Joel with mission scientists Harris spoke with project who shared their excite- scientists about the mis- ment and relief over sion’s potential to revolu- the probe’s successful tionize our understanding landing. Its partner of Jupiter. Worry abound- spacecraft, Cassini, spent ed for all the steps yet to six months orbiting come, but Galileo lived a Saturn before dropping long and scientifically Huygens down to the FREQUENT FINDS. In the January issue, Astronomy counted down the biggest news stories of 2014, but prosperous life around surface of Saturn’s larg- what about the topics that most frequently appeared in the year’s headlines? This diagram shows the 100 Jupiter until 2003, when it est moon, where it dis- most popular words in Astronomy.com news headlines in 2014, with each word’s size proportional to the plunged nobly into the covered methane springs number of times it appeared. ASTRONOMY: CHUCK BRAASCH AND KARRI FERRON atmosphere to its demise. and rivers. — K. H. WorldMags.net 12 ASTRONOMY • APRIL 2015 DUST SURVEY. Astronomers used the twin Keck Telescopes in Hawaii to survey dust around 50 mature Sun-like ASTRONEWSWorldMags.netstar systems for several years as a step toward finding planets that might harbor life. Rosetta refreshes debate on Earth’s water QUICK TAKES AMNESIAC EXPLORER The European Space Agency announced December 10 The travel-weary Mars rover that its Rosetta spacecraft had measured water vapor Opportunity continued to struggle from Comet 67P/Churyumov-Gerasimenko and found through flash memory issues in that it is much heavier — by a factor of three — than December as NASA tried to refor- the water in Earth’s oceans. The “heaviness” of water mat. Exploration continues, but is a measurement of how many of the H’s in H2O have data has to be sent to Earth before a proton and a neutron (deuterium) compared to just the craft is put to sleep at night. a proton (normal hydrogen). Earth’s water has a well- • established deuterium/hydrogen (D/H) ratio. STRANGE SPIRAL Scientists have long suspected that Earth’s water Citizen scientists using Galaxy Zoo might have been delivered from space via asteroids or helped find a bizarre comets, so they study these objects’ water compositions shooting off large jets of sub- to find which populations have D/H ratios that match atomic particles from its core at our planet’s. So far, few comets provide good matches, near light-speed. Theory holds that and Comet 67P just struck out as well. only elliptical galaxies, formed by But maybe we don’t need comets anyway: Here on merging spirals, should have jets. Earth, researchers from Ohio State University reported • December 17 at the American Geophysical Union meet- MIRAGE EARTHS ing in San Francisco that our planet might have made A new study warns of “mirage its own water. Scientists have known for a long time Earths,” which would sit in habit- that Earth’s mantle is a potentially huge reservoir of able orbits close to low-mass stars, water, but the idea that Earth could mine that reservoir WATER STRIKE OUT. Dust and gas can be seen outflowing that computer simulations show through plate tectonics and bring water to the surface in from Comet 67P, but the water vapor Rosetta measured doesn’t can be stripped of the chance to host life by intense heat that wipes any substantial amount is a new idea. — K. H. fit the makeup of Earth’s water. ESA/ROSETTA/NAVCAM, CC BYSA IGO 3.0 away water and atmospheres dur- ing their early formation. CANNIBAL • GALAXY. MISSING ATMOSPHERE NGC 3226 can Europa’s icy plumes were not be seen here seen in data NASA’s Cassini craft with its smaller collected at the jovian moon, mis- companion, sion scientists said in December. NGC 3227. The The team found Europa’s atmo- swirls of gas sphere is 40 times more tenuous and dust than thought and its plasma origi- around them nated from volcanoes on Io. are signs that • NGC 3226 likely EARLY FINDS collided with Not long after arriving at Mars, and consumed NASA’s MAVEN orbiter has found a third galaxy interesting clues to how the planet sometime in loses its atmosphere to space, dis- the recent covering a new population of ions past. NASA/CFHT/ scientists can use to study interac- NRAO/JPLCALTECH/ tions with the solar wind. DUC/CUILLANDRE • SOLAR SMASHING An entire family of Pluto-sized Shutting down star factories objects may have been seen stir- In separate studies published in The Millimeter/submillimeter Array show ring up dust around a young Sun- Astrophysical Journal, astronomers that the roiling gas is too turbulent like star, as the planetesimals cause smaller bodies to collide. The find announced two galaxies that at for . pairs with models that predict gas first glance should be churning out NGC 3226 is the site of a recent is prevalent in the outer reaches of NASA/JPLCALTECH/GSFC new stars but instead are too hot merger, but in this case as well, the young solar systems. to bother. The ideal stellar breed- gas is too hot to permit star forma- ing ground has lots of cool gas that tion. It took the combined work • Deep-space telescope INDIA JOINS TMT quietly collapses into baby suns. So of the European Space Agency’s India is now a full member in the looks closer to home supermassive black holes that blow Herschel Space Observatory and behemoth Thirty Meter Telescope the gas right out of their galaxies are NASA’s Spitzer and Hubble space SIZZLING SUN. NASA’s Nuclear (TMT) on Mauna Kea, joining fel- known quenchers of star formation, telescopes to tell this galaxy’s story. low Asian nations China and Japan, Spectroscopic Telescope Array (NuSTAR), a and galaxy mergers that dump new While galaxy mergers usually incite satellite designed to detect hard X-rays in as well as institutions in the U.S. fuel into old galaxies are known har- star formation, in this case the distant objects, turned its eye toward the and Canada. Work on the massive Sun for the first time, capturing the most bingers of stellar population booms. incoming gas is crashing into and project began in October 2014. sensitive picture of our star in high-energy NGC 1266 has a modest central heating up in the galaxy’s disk, stall- • X-rays. The new image, released December black hole and plenty of gas, but ing stellar baby-making. X-RAY HUNTER 22, shows NuSTAR’s X-ray data overlaid on this gas is so dense that the black In both cases, future star for- The European Space Agency’s pro- a photo taken by NASA’s Solar Dynamics hole is merely stirring it madly. The mation is likely, after NGC 1266’s lific X-ray observatory, XMM- Observatory. In the future, NuSTAR will jets streaming from the black hole central black hole quiets down and Newton, celebrated 15 years in seek out the Sun’s hypothesized nanoflares, aren’t powerful enough to eject NGC 3226’s turbulence calms, allow- space December 10. Its replace- smaller versions of our star’s massive erup- the fuel from the system, but new ing the gas to cool enough to form ment, Athena, won’t be launched tions of charged particles. — K. F. results from the Atacama Large new stars. — K. H. for at least a decade. — Eric Betz WorldMags.net WWW.ASTRONOMY.COM 13 CROSS EXAMINATION. Scientists took a second look at Antarctic meteorite ALH84001, once thought to hold martian fos- ASTRONEWSWorldMags.netsils. They unraveled a 4-billion-year journey: Volcanic birth, floods of carbonate-carrying seas, and finally Earth circa 11,000 B.C. SPACE SCIENCE UPDATE NEW TALES OF A WARMER, WETTER MARS In one of the most tantalizing Mars finds to date, NASA’s Curiosity rover caught methane wafting across the surface of the Red Planet. Then it was gone. And then it returned. The methane came and went three times in Curiosity’s data. NASA Jet Propulsion Laboratory scien- tists announced their discovery at a press conference December 16 in San Francisco LAKE LAYERS. NASA scientists say that cross-bedding in these rocks visited by the Curiosity rover is evidence and received international headlines. that Mars’ Mount Sharp area once held a vast lake. NASA/JPLCALTECH/MSSS Methane does not mean there’s life on Mars, but that is one enticing explanation. possible sources, biological or non-biological, California Institute of Technology in The tenfold spike in methane concentra- such as interaction of water and rock.” Pasadena. “Where there’s now a mountain, tions seen in the atmosphere around the The excitement added to a rash of Red there may have once been a series of lakes.” rover were backed up by organics found in Planet news. At the same time, astronomers And as those lakes came and went, they martian soil powder samples made with announced their find that Mount Sharp — dropped layers of sediments and left behind Curiosity’s rock drill. Curiosity’s stomping grounds — was once a clues about the state of the local martian “This temporary increase in methane massive lake. NASA scientists say the sedi- environment. As Curiosity continues its — sharply up and then back down — tells ments there appear to have been laid down uphill climb from the lowest sedimentary us there must be some relatively localized over the course of tens of millions of years. layers, it will observe how the chemistry source,” says Sushil Atreya of the University “We are making headway in solving the changed over time. The rover will drill of Michigan, Ann Arbor, who works on mystery of Mount Sharp,” says Curiosity often, keeping an eye out for more signs of the Curiosity rover team. “There are many Project Scientist John Grotzinger of the organics. — E. B.

BUT WHERE IS SOLAR ACTIVITY The solar cycle currently FAST HERE? Philae sent averages about 11 years from FACT back this image of STARTS TO WANE peak to peak and has been its current sur- proceeding uninterrupted 200 roundings, dubbed since the early 18th century. “Perihelion Cliff.” The white regions probably represent 150 glare from the lander itself. ESA/ ROSETTA/PHILAE/CIVA

100

CYCLE

Sunspot number 50 22 CYCLE 23 CYCLE 24 Little lander lost 0 Like your mother’s worst nightmare, Philae remains lying in 19851990 1995 2000 2005 2010 2015 Year a ditch somewhere on Comet 67P/Churyumov-Gerasimenko, and scientists are hard at work scanning through three days of DOUBLE MAX. Solar cycle 24 seems to be winding down, having reached a second and photos taken by Philae’s partner spacecraft, Rosetta, looking apparently final peak in November 2013. Scientists at NASA’s Marshall Space Flight Center for their lander. But don’t worry: Philae may reawaken when in Huntsville, Alabama, say the number of sunspots (officially the smoothed International the Sun finds the instrument’s solar panels in early spring. Sunspot Number) then reached 75.4. Cycle 24’s first peak delivered 66.9 sunspots in Feb- Meanwhile, Rosetta delivers science results on the nature of ruary 2012. Although many cycles show a two-humped profile, this is the first where the cometary water (too heavy to be the source of Earth’s oceans) second peak beat the first. Still, this is the weakest sunspot maximum since cycle 14 peaked and returns pictures of “dinosaur egg” structures. These struc- at 64 in February 1906. (The outer red curves show the expected range of the monthly sun- tures may indicate the size of the solar system’s building blocks spot numbers.) ASTRONOMY: RICHARD TALCOTT AND ROEN KELLY, AFTER HATHAWAY/NASA/MSFC from which the planets, comets, and asteroids all came. — K. H. WorldMags.net 14 ASTRONOMY • APRIL 2015 WorldMags.net

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DON’T MISS THE NORTHEAST David Lindemann Gordon Haynes Gary Palmer Jim Roselli and many ASTRO IMAGING CONFERENCE Gaston Baudat Jerry Lodriguss Christopher Go Preston Starr more! APRIL 16-17, 2015 AT NEAF Thierry Legault Pete Kalajian Dan Llewellyn Dr. Matthew J. Penn WorldMags.net WWW.ASTRONOMY.COM 15 SECRETSKY BY STEPHENWorldMags.net JAMES O’MEARA NGC 2404 Into the void Supernova This galaxy really is lost in space. 2004dj

he north celestial arms that flaunt robust star- polar region has a forming regions, each rapidly significant void fair- spawning massive stars that ly close to the North will live fast and die young in Star, Polaris (Alpha remarkable supernova explo- α Spiral galaxy NGC 2403 is the standout object within the constellation Camelopardalis. T[ ] Ursae Minoris). To find it, sions. The striking Hubble This image shows the star-forming region NGC 2404 as well as the galaxy’s most recent look in the space bounded by Space Telescope image on this supernova. DATA: SUBARU TELESCOPE NAOJ/HUBBLE LEGACY ARCHIVE; PROCESSING: ROBERT GENDLER it, Capella (Alpha Aurigae), page shows many of these ion- Mirfak (Alpha Persei), and ized hydrogen regions bursting surviving star that’s akin to the 2403. The regions of ionized Omicron (ο) Ursae Majoris forth like pink cosmic fire- Homunculus Nebula around hydrogen in NGC 2403 are so (the nose of the Great Bear). works. The image also includes Eta Carinae. exceptionally large and lumi- This vast emptiness tallies Supernova 2004dj, which nous that at least six of them only three stars in the 4th- flared to magnitude 12 and In search of a giant rival the most massive ones in magnitude range. Nevertheless, shone as brightly as 200 mil- Although NGC 2403 lies in our Local Group of galaxies it hosts one of the oddest and lion Suns. Camelopardalis, it is within — namely the Tarantula most elusive constellations, In 1954, another fantastic sniffing distance (7.5° north- Nebula (NGC 2070) in the Camelopardalis the Giraffe. outburst occurred in NGC west) of the Great Bear’s nose. Large Magellanic Cloud and Despite the figure’s dim appeal 2403. Although it was classified The galaxy shines at magni- NGC 604 in M33. to the unaided eye, it contains as Supernova 1954J, recent tude 7.3 and from a dark sky The brightest of NGC 2403’s one of the most photogenic research has shown it to be a is visible through 10x50 and star-forming regions is NGC galaxies in the northern sky: “supernova imposter.” The star larger binoculars. 2404. It appears as a tiny dif- NGC 2403, the overlooked did not destroy itself but sur- Through a small telescope at fuse knot at the eastern end of masterpiece of the Arctic void. vived a super-outburst similar moderate magnification, it the northern spiral arm. In images, NGC 2403 is a to the “great eruption” in 1843 appears as an extremely well- Guillaume Bigourdan at the near twin to the Pinwheel of Eta (η) Carinae in our Milky defined elliptical glow punctu- Paris Observatory discovered it Galaxy (M33) in Triangulum, Way. Hubble Space Telescope ated by two 11th-magnitude in 1886 with a 12-inch refrac- but with pumped up visual images have since resolved a stars on either side of its amor- tor. This remarkable extra- appeal. It has two tiers of spiral nebula around this outburst- phous, lens-shaped core. Larger galactic treasure spans 2,000 telescopes may show up to light-years, or nearly 50 times about a dozen stars superim- the width of the Orion Nebula COSMIC WORLD posed on the galaxy. (M42). While many observers The arms break into several today have seen it through A look at the best and the worst that astronomy and distinct petals of light, all of scopes of similar size, I chal- space science have to offer. by Eric Betz Cold as Supernova which display delicate irregu- lenge you to observe it through space hot larities — a combination of as small a telescope as possible. superimposed stars from the As always, let me know what Mars or bust Artistic license Space blanket #CometLanding Milky Way and a plethora of details you see in NGC 2403 at star-forming regions in NGC [email protected].

FROM OUR INBOX NASA tests the Dr. Black Holes Eager attendees ESA lands on Orion spacecraft, himself, Kip line up at a Texas Comet 67P and Excellent issue calling it the next Thorne, publishes quilting show for draws more ador- I just got into the December Astronomy magazine and found it step to Mars. Now findings from his a glimpse of ing fans with little they just need a work with artists astronaut and Philae than Kim to be one of the best of many of the ones I have read over the lander, habitat, on the movie first-ever space Kardashian’s years. Thank you for the sound articles based on astrophysics propulsion, water Interstellar. Sadly, quilter, Karen simultaneous such as the “Five stars that could go bang,” “How Gaia will map extractors, radia- his paper on Nyberg, and her #BreakTheInternet a billion stars,” and others. Even my old favorite Bob Berman tion shields, and bookshelf beings sewn stars. High derrière photo. hundreds of bil- is held up in marks for float- Faith in humanity had a timely article (his humor lives on). Great job and solid lions in cash. review. ing with scissors. restored. good work! — Edmund Anderson, Cary, North Carolina NASA/JPL/CORNELL MARS OR BUST; ESO/M. KORNMESSER ARTISTIC LICENSE; #COMETLANDING MEDIALAB NASA ESA/ATG BLANKET; SPACE BROWSE THE “SECRET SKY” ARCHIVE AT www.Astronomy.com/OMeara.WorldMags.net 16 ASTRONOMY • APRIL 2015 WorldMags.net$7.995M

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WorldMags.net WWW.ASTRONOMY.COM 17 MOVIN’ RIGHT ALONG. The most prolific planet finder to date, NASA’s Kepler spacecraft, proved it’s still got what it ASTRONEWSWorldMags.nettakes in December, discovering a new world after the space agency gave the hobbled telescope a second chance. Van Allen Belts still hold surprises

Outer belt 12,000–25,000 miles GPS satellites 12,500 miles

Geosynchronous orbit NASA’s Solar Dynamics MISSION COMPLETE. During its last months Inner belt Observatory before running out of propellant, the Venus Express 1,000–8,000 miles 22,000 miles spacecraft dove deeper into our sister planet’s atmo- Low Earth orbit sphere, as illustrated here. ESA/C. CARREAU International Space Station 230 miles Van Allen Probe-A Venus Express

Van Allen Probe-B runs out of fuel After eight years orbiting our sister world, pro- viding extensive data on its atmosphere and BELT BARRIER. A newly discovered barrier in the Van Allen Belts protects Earth from “killer electrons.” NASA allowing scientists to make conclusions on the properties of its surface, the European Space Our planet’s magnetic field holds a toroidal “Somewhat like the shields created by Agency’s (ESA) Venus Express probe exhausted band of radiation in a belt around Earth. These force fields on Star Trek that were used to the last of its propellant, and the mission Van Allen Belts protect us from solar eruptions, repel alien weapons, we are seeing an invis- officially ended December 17. Mission leaders growing and shrinking as they’re excited. ible shield blocking these electrons. It’s an initially lost contact with the satellite November The find is known as the first great discovery extremely puzzling phenomenon.” 28, but they were able to re-establish limited of the space age. And despite Americans get- The main belts start at an altitude around telemetry information that ultimately led them ting to space second, the discovery was ours. 600 miles (1,000 kilometers) above Earth and to conclude that Venus Express used up the last But even after nearly 60 years, the belts still can stretch to some 25,000 miles (40,000km). bit of its propellant and was losing altitude. hold new surprises. On November 27, astrono- The particles come from the solar wind and Mission scientists knew they were nearing mers announced in the journal Nature they cosmic rays. This newly discovered barrier sits the end in 2014, so they decided to “go out had found an impenetrable barrier within at some 7,200 miles (11,600km). with a bang” by having Venus Express perform the belts that prevents the most energetic And this isn’t the first time the belts have a complicated aerobraking campaign that particles — so called “killer electrons” that can offered up surprises. In 2012, NASA launched brought the spacecraft as close as 80–84 miles threaten astronauts and spacecraft — from the two identical Van Allen Probe spacecraft (130–135 kilometers) above the planet’s surface reaching Earth. to confirm what scientists thought they knew. from mid-June to mid-July before returning to “It’s almost like these electrons are run- At first, Baker says he figured the instruments an altitude of 285 miles (460km). As the orbiter ning into a glass wall in space,” says Daniel were faulty because the data seemed so naturally would lose altitude over time and Baker of the University of Colorado, Boulder, improbable. But NASA’s probes had turned required routine thruster burns to return it who did his doctorate with the belts’ discov- up a new radiation belt. “The textbooks higher above Venus, mission scientists decided erer, James Van Allen, and was lead author on always said two belts, and here we had three to raise the spacecraft again in late November the study. belts,” Baker says. — E. B. in order to possibly prolong the mission. But as Venus Express has no fuel gauge, they did not know such maneuvers would exhaust what little fuel was left. “While we are sad that this mission is ended, AVERAGE NUMBER OF CLEAR DAYS IN APRIL we are nevertheless happy to reflect on the great success of Venus Express as part of ESA’s planetary science program and are confident that its data will remain [an] important legacy FAST for quite some time to come,” says Martin FACT Kessler, head of ESA Science Operations. “The mission has continued for much longer than its planned lifetime, and it will now soon go out in April’s sky a blaze of glory.” — K. F. features two of the finest deep-sky objects: Omega Centauri (NGC 5139) and 2 million mph the Whirlpool Galaxy (M51). (3.2 million km/h) The speed of cold gas being ejected : MICHAEL E. BAKICH AND ROEN KELLY, AFTER NOAA AFTER KELLY, ROEN AND BAKICH E. MICHAEL : from the compact galaxy SDSS J0905+57 Less than 3.5 – 6.4 6.5 – 9.4 9.5 – 11.4 11.5 – 13.4 13.5 – 15.4 15.5 – 17.4 17.5 – 20.4 3.5 ASTRONOMY as star formation shuts down. WorldMags.net 18 ASTRONOMY • APRIL 2015 COMING IN OUR Telescopes.net NEXT ISSUEWorldMags.netCome visit our new booth at NEAF OFFICINA STELLARE ORION Lunt Engineering 100mm Binoculars •

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Astronomy has always been Rainy-day Web an interest of mine, but lately it has taken center stage as my passion. I found this article particularly interesting because it Astronomy.com offers spoke to me about the barriers that many women have to over- lots to explore on April’s come to really be taken seriously in the field of science. I feel surfing cloudy nights. these barriers, and the article reassured me that I am not alone. — Noelle Moser, Maryville, Tennessee pril showers bring be able to enjoy when (fingers May flowers. They crossed!) skies clear. also bring frustra- No matter what our level accessories like eyepieces, finder video series of particular inter- tion to observers of expertise, we need to pay scopes, or filters? “Equipment est are “Observing Basics” (not kept indoors by attention to the techniques that Use” has the inside scoop. my column — that comes later) AApril’s ever-present cloudy make us successful backyard Some Web content is avail- and “Seasonal Observing.” The nights. Outer space may be out astronomers. To that end, the able only to registered users of former is a collection of Bakich of reach, but cyberspace isn’t. “Observing” section serves up Astronomy.com. Don’t worry; video clips that help you get the If inclement weather has you an assortment of how-to articles registration is free — even to most from your equipment. The and your telescope grounded, and videos. The subsection those who aren’t Astronomy latter includes a video of easy-to- Astronomy.com will keep you “Get to Know the Night Sky” subscribers. You can sign up at find targets in the current sea- cosmically connected. There’s a includes articles on “The starry www.Astronomy.com/register. son’s sky, which is available to lot to explore, so let’s get to our sky” (a seasonal primer on star Among the benefits to registered users, as well as other computers, log on, and see what and constellation identifica- being a registered user is access videos available exclusively to we can find. We’ll begin with tion), “How to use a star chart” to Senior Editor Michael E. subscribers of Astronomy maga- sections accessible to anyone, (a guide to using the StarDome Bakich’s “Observing Podcasts,” zine (as are all Astronomy.com regardless of subscription status. map in the center of each issue weekly spotlights on currently items accompanied by an “A+” A good place to start is “The of Astronomy), “Choose a star visible deep-sky destinations. symbol) that feature seasonal Sky this Week,” a day-by-day atlas that’s right for you,” and Last month, I stressed the lists of deep-sky objects. account of celestial happenings articles dedicated to urban sky- importance of having a pre- I’ve been writing the spanning the current 10-day gazing. The “Observe the Solar pared list of sky objects prior “Observing Basics” column for period. It’s one of a dozen System” and “Tour the Deep to observing. A rainy evening over a dozen years. If you’re an topic selections found in the Sky” subsections combine basic gives us time to assemble lists Astronomy subscriber, you can “Observing” drop-down menu facts about the solar system for future clear nights, and access an archive of these arti- at Astronomy.com. “The Sky bodies with pointers on how to “Observing Podcasts” is our cles at www.Astronomy.com/ this Week” might find us gaz- observe them. go-to place to get started. We Chaple. I can’t say I’ve covered ing wistfully at a description of A key “Observing” subsection can work on the objects featured every astronomy-related topic what’s currently going on above is “Equipment Use” — a must- in this week’s edition or scroll (it’s a big universe!), but you’ll the clouds, but do we really visit destination for anyone down to April podcasts of previ- find pieces devoted both to want to know that we’re missing seeking information on astro- ous years to add even more. backyard astronomy techniques a major meteor shower or rare nomical equipment. Looking There’s much more to and easy-to-observe sky objects. planetary alignment? Better to for guidance on purchasing that Astronomy.com’s “Observing” There’s so much to see on think positive and look ahead first telescope or binoculars? section, but we’ll move on to Astronomy.com that we may to upcoming sky events we’ll It’s here. Want to know about the “Videos” section next. Two wish for the April rains to con- tinue for the next few evenings so we can further explore its offerings. OK, that’s a stretch, but at least it gives us the option of pursuing our hobby on cloudy nights. So disparage not the rains of April, my friend! They bring not only May flowers, but also the chance to enhance our backyard astronomy experience. Questions, comments, or sug- gestions? Email me at gchaple@ hotmail.com. Next month: We track down the “runaway star.” Clear skies! BROWSE THE “OBSERVING BASICS” ARCHIVE AT www.Astronomy.com/Chaple.WorldMags.net 20 ASTRONOMY • APRIL 2015 NEAFWorldMags.netCelebrating 24 Years April 18-19, 2015 www.rocklandastronomy.com/neaf.html Northeast Astronomy Forum America’s Premier Astronomy Expo

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In a Milky Way , about half FAST ASTROASTRONEWSCONFIDENTIAL BY KARRI FERRON of the stars contain 50–100 times more WorldMags.netnitrogen than the other cluster members. FACT WHAT ARE WE LEARNING Søren Larsen ABOUT GLOBULAR CLUSTER FORMATION? Assistant professor at Radboud University in The Milky Way is home to about 150 globular picture, present-day globular Nijmegen, The Netherlands clusters, of which the brightest are spectacular clusters are the remnants of sights when viewed through an amateur tele- systems that initially may scope. Yet it remains a mystery how exactly have been at least 10 times larger! these massive swarms of stars formed. In par- If this is true, then the lost stars should ticular, their chemical composition is a puzzle: now be “free-floating” among the field stars In about half of the stars in a typical globular in their parent galaxies. However, our recent cluster, the “light elements” (up to aluminum) observations of globular clusters in the Fornax are found in relative amounts that are only Dwarf Galaxy have challenged this picture. seen in these stellar conglomerations. We found that the four most metal-poor The explanation favored by some is that clusters together account for about a quarter globular clusters consist of an original “pris- of all the metal-poor stars in that galaxy. tine” population of stars formed by normal Furthermore, our new observations with the processes and a polluted population formed Hubble Space Telescope show that the Fornax out of enriched ejecta produced by the original clusters display the same chemical abundance stars. The main problem with this idea, how- anomalies as globular clusters in the Milky ever, is that the amount of polluted ejecta that Way, so the same formation scenario should the original stars could produce only would apply to them. But it seems that these clusters be a few percent of the total mass — in stark could not have lost the required large fraction contrast to the observed 1:1 ratio. To balance of their initial stars — there are simply not the budget, a large fraction of the original stars enough metal-poor stars in the Fornax Dwarf!

must have been lost from the cluster. In this So we need to go back to the drawing board. 2 NETHERLANDS FORNAX THE UNIVERSITY, RADBOUD LARSEN NASA/ESA/S. PORTRAIT; LARSEN SØREN COURTESY

INSIDE EINSTEIN. Princeton University Press has made tens of thousands of original Albert Einstein documents avail- ASTRONEWS able online free for the first time via The Digital Einstein Papers, enabling open access for all to the mind of a genius. Dawn approaches Ceres for asteroid encounter NASA’s Dawn spacecraft will reach the asteroid belt’s largest object, Ceres, this spring, heralding in new knowledge of the SPACE ATTACK. Scientists think that Earth’s early atmosphere was stripped Texas-sized space rock that under bombardment from an onslaught of small asteroids. NASA astronomers once called a planet. Ceres remains the largest unexplored body Asteroids stripped Earth’s atmosphere between Earth and Pluto. Early in its history, Earth was impacts can be much more effi- Dawn launched in 2007 bombarded by a cosmic blitz- cient in the damage they cause. and visited asteroid Vesta krieg of space rocks that likely And exactly such a period of for just over a year starting

stripped the fledgling world bombardment is thought to NASA/JPLCALTECH/UCLA/MPS/DLR/IDA in 2011. Astronomers had of its atmosphere, according have happened around the DAWN APPROACHES. The Dawn spacecraft cap- some ideas about that to a paper published in the time the Moon formed, which tured this better-than-Hubble shot of the dwarf planet dwarf planet from study- journal Icarus in February. was still early in Earth’s history. Ceres on approach in January. By March, the craft will ing meteorites thought to A team of researchers mod- The astronomers think their start orbiting the asteroid belt’s largest object. have originated at Vesta. eled what would happen if tens find could help explain geo- But that’s not the case of thousands of small asteroids chemical evidence that indi- for Ceres, which will be studied for the first time. Dawn is also just beginning smashed Earth and found that cates Earth has lost its entire to see the asteroid with any clarity. The navigation images NASA captured all the little impacts add up to a atmosphere at least twice in with the craft’s camera in January are the first with better detail than the major loss. the long period since it first Hubble Space Telescope. So scientists don’t even know what the world looks Whereas it would take a formed some 4 billion years like. One strange feature has piqued curiosity — a large white spot (upper left collision with a near-Earth-sized ago. Their find also could be of image), which was also seen in Hubble photos. body to strip our planet of its important in explaining the “All we can predict with confidence is that we will be surprised,” says the atmosphere, the scientists atmospheres of the other rocky Dawn mission’s principal investigator, Christopher Russell of the University of show that each of the small planets, Venus and Mars. — E. B. California, Los Angeles. — E. B. WorldMags.net 22 ASTRONOMY • APRIL 2015 WorldMags.net

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Superstars of OBSERVING TOOLS Astronomy Equipment Review Archive Astronomy.com/equipment is the place to get reviews on the latest Exclusive interviews with observing equipment — from binoculars and telescopes to filters, eye- world-renowned scientists pieces, cameras, and mounts. The archive’s search engine allows you to filter equipment by category, manufacturer, or keyword. Plus, Astronomy.com lets Ever wonder what’s happening behind the scenes you comment on these articles, so after you make a purchase, leave your at various astronomical institutions? Wish you could thoughts about your new piece of equipment to benefit others. hear more than just the occasional sound bite from the people making the biggest discoveries in science today? It’s time to tune in to Superstars COMMUNITY of Astronomy, our new series of in-depth audio podcast interviews. With the generous support of Celestron and Editor David J. Eicher serving as your Reader Photo Gallery host, the monthly installments feature hourlong interviews with some of Browse thousands of beautiful astroimages like the world’s foremost astronomers, astrophysicists, planetary scientists, and this one of the Pleiades Cluster (M45) by Craig cosmologists as they take listeners into the worlds of their research in a and Tammy Temple. Submit your own images new and unique way. at www.Astronomy.com/readergallery. By listening to Superstars of Astronomy, you’ll examine the latest research on galaxies, go behind the scenes at the Starmus Festival, preview Events NASA’s Pluto encounter, explore how life will end on Earth, learn about Find star parties or lectures in your area or post an invite to your astron- Mars’ past and future, understand the Milky Way’s eventual collision with omy club event at www.Astronomy.com/events. It’s a great way to intro- the Andromeda Galaxy, and much more. Guests already scheduled include duce people to the hobby or get to know others who share your passion Jeff Hester, Garik Israelian, Alan Stern, Debra Fischer, Bruce Balick, Avi Loeb, about the night sky. Seth Shostak, Martin Rees, and many oth- ers. Start listening to these extensive inter- FOLLOW www.twitter.com/ www.facebook.com/ plus.google.com/ views with the world’s top scientists today ASTRONOMY AstronomyMag AstronomyMagazine +astronomymagazine at www.Astronomy.com/superstars.

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ASH-DOME is recognized internationally by major astronomical groups, amateurs, universities, colleges secondary & primary schools for their performance durability and dependability. Manual or electrically operated units in sizes from 8 to 30 feet in diameter; sensibly priced. Brochures and specifications available. WorldMags.net 24 ASTRONOMY • APRIL 2015 Experiencing Hubble: WorldMags.netUnderstanding the Greatest Images of the Universe TIME ED O Taught by Professor David M. Meyer T FF I E NORTHWESTERN UNIVERSITY IM R L 70% LECTURE TITLES 1. The Rationale for a Space Telescope off 2. Comet Shoemaker-Levy 9 and Jupiter O 2 R IL D R 3. The Sagittarius Star Cloud ER BY AP 4. The Star Factory inside the Eagle Nebula 5. The Cat’s Eye Nebula—A Stellar Demise 6. The Crab Nebula—A Supernova’s Aftermath 7. The Sombrero Galaxy—An Island Universe 8. Hubble’s View of Galaxies Near and Far 9. The Antennae Galaxies— A Cosmic Collision 10. Abell 2218—A Massive Gravitational Lens 11. The Hubble Ultra Deep Field 12. Hubble’s Legacy and Beyond

Experience the Wonders Experiencing Hubble: Understanding the Greatest Images of the Universe of the Hubble Telescope Course no. 1884 | 12 lectures (30 minutes/lecture) For more than 20 years, the Hubble Space Telescope has been amassing discoveries that rival those of history’s greatest scientists and explorers, SAVE $160 making it the most important—and most productive—scientific instrument ever built. Experiencing Hubble: Understanding the Greatest Images of the DVD $199.95 NOW $39.95 Universe is an unforgettable visual feast of carefully chosen images taken +$5 Shipping, Processing, and Lifetime Satisfaction Guarantee Priority Code: 112446 by this fascinating telescope. Noted astronomer and award-winning Professor David M. Meyer’s 12 spectacularly illustrated lectures take you on a dazzling voyage of discovery that will delight your eyes, feed your For 25 years, The Great Courses has brought the imagination, and unlock new secrets of the cosmos. world’s foremost educators to millions who want to go deeper into the subjects that matter most. No Off er expires 04/02/15 exams. No homework. Just a world of knowledge available anytime, anywhere. Download or stream THEGREATCOURSES.COM/7ASTR to your laptop or PC, or use our free mobile apps for iPad, iPhone, or Android. Over 500 courses 1-800-832-2412 WorldMags.netavailable at www.TheGreatCourses.com. WorldMags.net

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The Eagle Nebula’s “Pillars of Creation” were captured April 1, Pillars 1995, with the Hubble Space Telescope’s Wide- Field and Planetary Camera 2. Jeff Hester and What has Jeff Hester’s iconic Hubble Space Telescope Paul Scowen assigned different colors to emis- image of the Eagle Nebula meant to him personally? sion from different atoms in the false-color image: red shows sulfur, green hydrogen, and blue oxy- ot everyone winds up For as long as there have been gen. NASA/ESA/STSCI/J. HESTER AND P. seeing their work on a humans, we have looked at the SCOWEN ARIZONA STATE UNIVERSITY U.S. postage stamp or in night sky in awe and wondered NTime’s collection of the about our connection with the 100 most influential pho- heavens. Now for the first time tographs in history. It’s cool to see the in history, we can tell that story, “Pillars of Creation” on the big screen beginning with the Big Bang and in a sci-fi blockbuster or hanging on ending with us sitting here talking the window of Sheldon and Leonard’s about it. Knowledge of our place in apartment on The Big Bang Theory. It’s the universe is no longer a matter fun to hear the phone ring and have of speculation or mythology. It is a friend say, “Hey, I just saw you on hard science. For many, the Pillars TV again!” It’s been quite a ride, made of Creation became the recognized especially rewarding because I was face of that human triumph. part of the team that built Hubble’s I have spent countless hours Wide-Field and Planetary Camera 2. discussing the image not only with The Eagle Nebula image symbol- fellow scientists, but also with art- ized an end to what had been a ists, musicians, writers, and in fact very difficult period for NASA. That people from all backgrounds. They is what it was designed to do. The would speak of beauty and passion press conference was scheduled and inspiration. The more I listened, to coincide with a feature article in the more familiar their reactions Time heralding Hubble’s phoenix-like sounded to my own. We were all rise from early disaster. How better expressing our experience of the to illustrate that story than with a human drive to find patterns and stunning image unlike anything the meaning in the midst of the com- public had ever seen? But no one plexity of the world. imagined a reaction that would turn Astronomy asked me, “What has the image into a cultural icon. the image meant to you personally?” There is no doubt that it reshaped Jeff Hester is a professor emeritus of my career as a scientist. But more Arizona State University. These days, he is than that, it changed not only the working as a professional coach and speak- way I think about science and art, er, sharing his experiences and perspectives but also my understanding of what WorldMags.netwith individuals and organizations. it is to be human. WWW.ASTRONOMY.COM 27 WorldMags.net

’ Top seven science

WorldMags.net a l o ri h

WorldMags.netGalaxies like the beautiful Whirlpool (M51) played a key role in many of Hubble’s great- est discoveries. Such island universes are held together by dark matter, harbor supermas- sive black holes at their cen- ters, help define the Hubble constant, and fly away from one another at increasing rates thanks to dark energy. NASA/ESA/S. BECKWITH STSCI/THE HUBBLE HERITAGE TEAM STSCI/AURA

From the incandescent brilliance of the first stars and galaxies to the overwhelming power of dark matter and energy, the space telescope has illuminated many cosmic mysteries. by Mario Livio I WorldMags.net WWW.ASTRONOMY.COM 29 Space shuttle astronauts saw the Hubble Space Telescope for the last time in 2009 when they bid WorldMags.netit farewell following the last ser- vicing mission. NASA; BACKGROUND IMAGE OF NGC 265: NASA/ESA

ew scientific experiments have enjoyed 25 years of relentless pro- ductivity and a continuous stream of discoveries. Yet this is only one of the Hubble Space Telescope’s remarkable achievements. Not only have Hubble obser- vations transformed our ideas about almost Dark energy every topic in astronomy and astrophysics, but The gravitational attraction the drama associated with space shuttle astronauts servicing the of all the matter in the uni- Fobservatory and the impact the telescope has had on the public’s verse should cause cosmic appreciation of science also have made Hubble unique in the expansion to slow down. history of science. But in 1998, two groups Hubble’s scientific successes are so numerous that it is not easy of astronomers discovered to select its greatest hits. Consequently, the list on the following the exact opposite: The rate pages represents my own personal biases as to what the telescope’s of universal expansion is most important contributions have been. Supernova 1994D (lower left) in galaxy accelerating. The research- I also should emphasize that it is rare in astronomy to be able NGC 4526 helped astronomers pin down ers based their discovery to attribute a discovery to one particular observation or a specific the universe’s accelerating expansion, on observations of stellar which is powered by a repulsive force observatory. More often, progress in understanding phenomena explosions known as type exerted by dark energy. NASA/ESA/THE HUBBLE results from a series of observations at different wavelengths by KEY PROJECT TEAM/THE HIGHZ SUPERNOVA SEARCH TEAM Ia supernovae, which occur a variety of telescopes over a long period of time. I do not claim, when white dwarf stars grow therefore, that Hubble acted alone in making these seven discover- to their limiting mass of ies. Instead, I chose findings in which space telescope observations about 1.4 solar masses. Only Hubble could view the most distant played a crucial role. of these explosions and thus confirm the acceleration. In selecting Hubble’s most important breakthroughs, I was All current studies indicate that a still-mysterious form of guided by two principles: Either the discovery had to contribute energy, dubbed dark energy, propels this speed-up. Although sci- significantly to our understanding of the universe as a whole, or entists do not yet understand the precise nature of dark energy, it had to represent a major step in the quest to determine whether they have deduced some of its properties. These efforts suggest extraterrestrial life exists. The second point arguably ranks as one that it is the energy associated with empty space, or what scientists of the most intriguing pursuits in science today. call the physical vacuum. That the vacuum contains energy is not surprising in itself. Mario Livio is a senior astrophysicist at the Space Telescope Science Quantum mechanics — the physics that describes the universe Institute in Baltimore, which conducts the scientific program of Hubble. His at the smallest scales — predicts that the physical vacuum is far most recent book is Brilliant Blunders (Simon and Schuster,WorldMags.net 2013). from empty. Instead, it teems with virtual pairs of particles and 30 ASTRONOMY • APRIL 2015 WorldMags.net I/AURA/R. GENDLER FOR THE HUBBLE HERITAGE TEAM C NASA/ESA/THE TEAM STS HUBBLE HERITAGE Water megamasers — amplified microwave emissions from water molecules — orbiting the central supermassive black hole in spiral galaxy M106 pinned down this object’s distance. Hubble’s calibration of Cepheid variable stars in the galaxy played a crucial role in determining the Hubble constant. antiparticles that appear and disappear within tiny fractions of a And each side in the argument insisted that their data supported second. The problem has been that every theoretical attempt to an improbable error of only about 10 percent. calculate what the energy density of the vacuum should be has One of Hubble’s “key projects” was to resolve this conundrum. missed the target by several orders of magnitude. Using the space telescope’s superb optical resolution, the key project Given the quickening expansion, what will the fate of our uni- team examined a number of distance indicators, including Cepheid verse look like in the distant future? If dark energy does represent variable stars, the Tully-Fisher relation that links a spiral galaxy’s the energy of empty space, which has a constant rotation rate to its intrinsic luminosity, and type density, then the expansion will continue to accel- Ia supernovae. By 2001, the team refined the erate. About a trillion years from now, astrono- Few scientific Hubble constant’s value to 72 km/s/Mpc with mers living in the merged product of the Milky a precision of about 10 percent. Way and the Andromeda Galaxy — the two are experiments have A combination of this new value with the expected to collide about 4 billion years from now enjoyed 25 years discovery of cosmic acceleration and a new (another Hubble result, by the way) — will not be assessment of the ages of globular star clusters able to see any other galaxy. The universe then will of relentless resolved yet another mystery — the universe is be well on its way toward a cold death. indeed older than its oldest known stars. For productivity and cosmologists who believed in a Hubble constant The Hubble constant a continuous of 100 km/s/Mpc, a simple calculation shows and the universe’s age that the universe would be only about 10 billion Ever since the 1920s and the seminal works of stream of years old, yet the ancient stars in globular clus- astronomers Vesto Slipher, Georges Lemaître, and ters appeared to be at least 12 billion years old. Edwin Hubble, scientists have known that the uni- discoveries. According to the most recent determination of verse is expanding. The so-called Hubble constant cosmological parameters by the European Space is a measure of the current expansion rate, and its value is inverse- Agency’s Planck satellite, the universe is 13.8 billion years old with ly proportional to the age of the universe. Until the space tele- an uncertainty of just 40 million years. scope’s launch, published values of the Hubble constant differed But scientists have not rested on their laurels. Thanks largely to by as much as a factor of two. One large group of astronomers further Hubble observations, in the past decade astronomers have claimed a value around 50 kilometers per second per megaparsec, made impressive progress in measuring the Hubble constant more while the other main faction declared a rate near 100WorldMags.net km/s/Mpc. precisely. By cross-calibrating several distance indicators — such WWW.ASTRONOMY.COM 31 Each deep field exposed thousands of WorldMags.netgalaxies in an area of sky you would see looking through a drinking straw.

cosmos appears to be homogenous and isotropic — the same at every location and in every direction — these findings imply that the observable universe holds a few hundred billion galaxies. The deep observations have provided astronomers with a treasure-trove of data about galaxy evolution. One key result has been learning the cosmic star-formation rate — how fast the uni- verse as a whole creates new stars as a function of distance, or cos- mic time. (See “How fast do stars form?” below.) Knowing how quickly stellar mass builds up in galaxies provides fundamental constraints on models of how galaxies form and evolve. Black holes at the centers of galaxies Even before Hubble opened its eyes to the universe, observations indicated that at least some galaxies harbor supermassive black holes in their cores. And theoretical models of active galaxies and of — extraordinarily energetic point-like objects in the distant universe — suggested that matter accreting onto such black holes from their surroundings powered their emissions. Hubble observations turned these hints and tentative ideas into certainty. The Hubble Deep Field South seen here is one of a series of observations astronomers made with Hubble that helped establish the cosmic star- The space telescope has shown that essentially every galaxy formation rate. R. WILLIAMS STSCI/THE HDFS TEAM/NASA/ESA that has a bulge of stars at its center hosts a supermassive black hole. These black holes range in mass from perhaps as low as a few tens of thousands of times the Sun’s mass in dwarf galaxies as Cepheid variables, type Ia supernovae, and the amplified micro- to a few billion solar masses in massive galaxies. Hubble also has wave emissions from water molecules (so-called megamasers) in directly imaged the host galaxies of a few quasars, demonstrating orbit around the supermassive black hole at the center of galaxy unambiguously that the engines driving these objects reside at M106 — they reduced the uncertainty in the Hubble constant’s the centers of galaxies. value to about 5 percent by 2009 and to 3 percent by 2011. Most significantly, however, Hubble observations revealed a Currently, researchers are using new scanning techniques with fairly tight correlation between the relative speeds of the stars in Hubble’s Wide Field Camera 3 to get even more precise distances the galaxy’s central bulge (what astronomers call the velocity dis- to Cepheids in the Milky Way at distances of about 3,000 to 10,000 persion) and the mass of the black hole. The velocity dispersion, light-years. These promise to shrink the Hubble constant’s uncer- in turn, depends on the mass of the bulge. tainty to just 2 percent. And the European Space Agency’s ongoing Gaia mission should make robust progress by extending accurate Cepheid observations out to 33,000 light-years. How fast do stars form? Refining the Hubble constant in the relatively nearby universe to a precision of 1 percent may help resolve the latest apparent Best fit Ultraviolet tension between different measurements. The so-called local 0.1 ) Ultraviolet + infrared 3 value currently stands at about 73 km/s/Mpc, while that inferred Hydrogen-alpha from Planck observations of the distant universe holds at about Infrared/far-infrared 68 km/s/Mpc. The discrepancy may reflect only higher systematic 1.4 gigahertz errors than anyone suspects, but if it turns out to be real, it hints at some potentially new physics.

The cosmic star-formation rate (Solar masses/year/Mpc

Cosmic star-formation rate rate star-formation Cosmic 0.01 Some of Hubble’s most dramatic observations have been long- exposure photographs of what, at first blush anyway, appeared to be rather bland areas. Starting with the original Hubble Deep Field — an observation made of a tiny region in the constellation Ursa 02468 Major over 10 days in December 1995 — the space telescope has (z) carried out several deep observations of small patches of sky. The cosmic star-formation rate peaked at a redshift of around 2 These programs have revealed just how small our physical exis- (which corresponds to a look-back time of 10 billion years). Today’s universe produces only 0.01 solar mass of stars per year in a typical tence is in the grand cosmic scheme. cubic megaparsec (Mpc), which is approximately 35 million cubic Each deep field exposed thousands of galaxies in an area of sky light-years. ASTRONOMY: ROEN KELLY, AFTER P. S. BEHROOZI, R. H. WECHSLER, AND C. CONROY APJ, 770, 57 you would see looking through a drinking straw. GivenWorldMags.net that the 32 ASTRONOMY • APRIL 2015 WorldMags.net GARY BOWER AND RICHARD GREEN NOAO/THE STIS INSTRUMENT DEFINITION TEAM/NASA A spectrum of the central regions of M84, a giant in the Virgo Cluster, shows a sharp shift in the velocity of gas clouds from high- A jet of high-speed particles shoots from the center of an accretion disk that speed approach (blue) to rapid recession (red), indicating the presence of surrounds the black hole at the center of the galaxy M87. The black hole tips a supermassive black hole at the center. the scales at about 3.5 billion solar masses. NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA

This relation has important implications for galaxy evolution. It demonstrates that a galaxy and its central black hole do not evolve independently. Rather, the masses of the stellar bulge and the black hole grow in tandem. The picture that emerges suggests that as long as gas flows into a galaxy’s center and the black hole accretes some of this material, the bulge continues to form new stars. Once radiation from the central engine and kinetic energy from supernova explosions blow the gas out, the growths of both the black hole and the bulge terminate. Dark matter As its name implies, dark matter neither emits nor absorbs elec- tromagnetic radiation. Astronomers can infer its presence only through its gravitational effects. On the scale of a single galaxy, stars and gas clouds move too quickly for the pull of visible matter alone to hold them in bound orbits. The same is true for galaxies moving within galaxy clusters, which would disperse quickly Hubble observations of the Bullet Cluster show its distribution of dark mat- without the dark matter glue. Dark matter constitutes about 85 ter (inferred from gravitational lensing) in blue; Chandra X-ray data (in red) reveals the site of ordinary hot gas. XRAY: NASA/CXC/M. MARKEVITCH, ET AL.; OPTICAL: NASA/STSCI; percent of the universe’s mass and provides the scaffolding on MAGELLAN/U. ARIZONA/D. CLOWE, ET AL.; LENSING MAP: NASA/STSCI; ESO WFI; MAGELLAN/U. ARIZONA/D. CLOWE, ET AL. which nature erects its visible large-scale structure. Hubble scientists used the phenomenon of gravitational lensing, in which the gravity of dark matter surrounding a distorts the Cosmologists long suspected light from more distant objects, to create that dark matter creates a uni- versal weblike structure that acts the largest three-dimensional map of as scaffolding for normal matter. dark matter’s distribution. In addition, In 2007, researchers combined studies by Hubble of specific galaxy Hubble observations with those clusters, such as Abell 1689, have helped from large ground-based instru- ments to come up with this first researchers create detailed dark-matter large-scale 3-D map of dark maps for these objects. These maps have matter. NASA/ESA/R. MASSEY CALTECH helped constrain models for how galaxy clusters grow. WorldMags.net WWW.ASTRONOMY.COM 33 WorldMags.net

The Hubble eXtreme Deep Field (XDF) shows galaxies out to the most distant reaches of the cosmos, close to the time when the first stars were starting to reionize the universe. NASA/ESA/G. ILLINGWORTH, D. MAGEE, AND P. OESCH UNIVERSITY OF CALIFORNIA, SANTA CRUZ/R. BOUWENS LEIDEN UNIVERSITY/THE HUDF09 TEAM

Perhaps most importantly, Hubble observations in combination This phase transition marks not only the birth of the cosmic with those of the Chandra X-ray Observatory and ground-based microwave background but also the beginning of the so-called telescopes have shown a clear separation between the dark matter Dark Ages, the period when no sources of light such as stars or and the hot ordinary gas present in colliding galaxy clusters. galaxies yet existed. When the universe reached an age of about Astronomers were not surprised to see such a division. After 100 to 200 million years, it started forming stars. Astronomers all, the ordinary gas in the two clusters collides and forms shock think that these earliest stars produced ultraviolet radiation that, waves while the dark matter passes through without any electro- perhaps with the help of X-rays emitted by X-ray binary systems, magnetic interaction. reionized the cosmos. By the time the universe was about a billion Hubble now has observed this phenomenon in the Bullet years old, this reionization was complete. Cluster (1E 0657–56), Pandora’s Cluster (Abell 2744), and MACS One of the key questions in modern cosmology asks what the J0025.4–1222. Scientists consider it to be the best evidence yet for main energy sources responsible for reionization were. By reaching the weakly interacting nature of dark matter. back to times when the universe was about 500 million years old, the various Hubble deep fields have explored the galaxy popula- Reionization in the early universe tion well into the reionization era. A few minutes after the Big Bang, the universe was filled with a Aided by some reasonable assumptions about the fraction of hot plasma composed mainly of protons and free electrons. As photons capable of ionizing hydrogen atoms that escaped from the cosmos expanded and cooled, it reached a point some 380,000 these young galaxies and the clumpiness of the intergalactic years later at which it went through a phase transition — protons medium at these early times, these studies show that if star- and electrons combined to form neutral hydrogen atoms. With the forming galaxies fully reionized the universe, the population electrons trapped inside atoms, the universe became transparent of these objects must extend to luminosities fainter than Hubble to light. In the 13.8 billion years since, the expanding cosmos has can reach. This is an interesting constraint because the upcoming shifted this radiation to much longer wavelengths in the micro- James Webb Space Telescope (JWST) will be able to explore such wave part of the electromagnetic spectrum. WorldMags.netfaint objects — if they indeed exist. 34 ASTRONOMY • APRIL 2015 The atmospheric structure WorldMags.netof HD 209458b Hydrogen envelope of escaping atmosphere (10,000–15,000 K) Carbon and oxygen detected

The Sun (to scale) HD 209458b Transition zone (5,500 K)

Middle atmosphere Sodium detected

Lower atmosphere (1,200 K) Possible clouds

Jupiter (to scale)

Hubble observations allowed astronomers to deduce the atmospheric This artist’s illustration shows the atmosphere of the planet HD 209458b, structure of HD 209458b, which features a lower and middle a “hot Jupiter” in a 3.5-day orbit around a star with about 15 percent more atmosphere surrounded by an extended hydrogen envelope that bleeds mass than the Sun, as it evaporates under the intense radiation. ESA/ALFRED into space. ASTRONOMY: ROEN KELLY, AFTER NASA/ESA/A. FEILD STSCI VIDALMADJAR INSTITUT D’ASTROPHYSIQUE DE PARIS, CNRS, FRANCE/NASA

The atmospheres of oxygen, and water vapor in this planet’s atmosphere. Hubble also Since 1991, a series of observations made from the ground and by found water vapor in the atmosphere of HD 189733b. the Kepler spacecraft has revealed nearly 2,000 planets orbiting Spitzer researchers have detected water vapor in planetary stars other than the Sun. Although some astronomers continue to atmospheres during secondary eclipses, when the planet hides hunt for new exoplanets, others have started to focus on exploring behind the star. In this technique, scientists subtract the light of the the atmospheric compositions of known exoworlds. Ultimately, star alone (when the planet is behind it) from the combined light of researchers hope these investigations will lead to star and planet (when the planet is in view) to see the detection of significant biosignatures — signs emission from the orbiting world’s atmosphere. of life produced by plants, photosynthetic bacte- Observations of Both Hubble and Spitzer have discovered ria, or other biological processes. Biosignatures clouds in the atmospheres of several exoplanets, include molecules such as oxygen, ozone, and transiting planets including Kepler-7b, GJ 436b, and GJ 1214b. chlorophyll, as well as atmospheric conditions on … have detected Astronomers expect to be able to characterize the Earth-like exoworlds that are not in equilibrium. atmospheres of even smaller exoplanets with the Observations of transiting planets — those several atoms upcoming JWST, scheduled for launch in 2018. whose orbital planes lie edge-on to our line of sight — made with Hubble and the infrared- and molecules Twenty-five wonderful years sensitive Spitzer Space Telescope already have Through these discoveries and more, Hubble has detected several atoms and molecules in the atmo- in … a few “hot informed or altogether changed our views on the spheres of a few “hot Jupiters” and “hot Neptunes.” Jupiters” and universe and on the potential existence of life These giant planets orbit close to their host stars within it. On one hand, Hubble has shown us how and, as a result, have toasty extended atmospheres. “hot Neptunes.” small we are compared to the vastness of the cos- During a so-called primary eclipse, when a mos and how brief our lives are compared to cos- transiting planet slides in front of its star, a small fraction of the mic time. On the other hand, the space telescope has proved that we star’s light must pass through the planet’s atmosphere. Analyzing actually can attempt to understand all the phenomena we observe the stellar spectrum can reveal the presence of certain elements in out to the universe’s most distant corners. As Albert Einstein once that gaseous envelope. This is how Hubble discovered sodium in said: “The eternal mystery of the world is its comprehensibility … the atmosphere of a world cataloged as HD 209458b. In another the fact that it’s comprehensible is a miracle.” There is no doubt that set of observations, the space telescope detected hydrogen, carbon, the Hubble Space Telescope has helped to make it comprehensible. DISCOVER MORE ON WHAT SCIENTISTS HAVE LEARNEDWorldMags.net FROM THE HUBBLE DEEP FIELDS AT www.Astronomy.com/toc. 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. MONTHWorldMags.net Visible with a telescope April 2015: A brief glimpse of totality

eclipse’s initial partial phases observers. It will reach its during morning twilight. peak separation from the Sun Everyone else will see totality, in early May, but appears but the Moon will appear brighter in late April. much higher and in a dark You can look for Mercury sky from the West Coast. The beginning April 19. Use bin- eclipse’s partial phases begin oculars to search for the mag- at 6:16 a.m. EDT (3:16 a.m. nitude –1.4 planet 7° to the PDT), and totality starts at lower right of a barely day-old 4:58 a.m. PDT. Moon. Three days later, on Let’s begin our tour of the 22nd, Mercury stands 1.3° April planets in the western north of Mars. The inner sky during evening twilight. world should be easy to spot Mars sets about 90 minutes at magnitude –1.1, but the after the Sun on the 1st and Red Planet is 10 times fainter stands 5° above the horizon and will be a challenge even a half-hour later. It shines with binoculars. rather dimly at magnitude 1.4 Mercury’s motion against and should show up to naked the background stars contin- eyes, though binoculars cer- ues through month’s end, and tainly will help the cause. The by the 30th, it reaches a point Red Planet becomes increas- 1.7° south of the Pleiades star ingly hard to see as the month cluster (M45). The magnitude Viewers in western North America can expect a bright total lunar eclipse April 4 because the Full Moon will be traveling through the northern edge progresses and it dips lower –0.4 planet then lies 7° high of Earth’s umbral shadow. This image captures the nearly reversed lighting in twilight. in the west-northwest an hour seen during totality April 15, 2014. JOEL TONYAN Although Mercury passes after sunset. behind the Sun on April 9, it As Mercury swings toward pril showers may bring occurring on specific dates. reappears in the evening sky Earth in late April, a telescope May flowers, but this But you can spy the best of within 10 days. This starts the shows its increasing size and month’s finest shower April’s planets on any clear innermost planet’s best eve- dwindling phase. On the could deliver a tem- night. Venus and Jupiter dom- ning appearance of the year 19th, the planet appears 6" pest of meteors. inate the evening scene, while for Northern Hemisphere across and about 90 percent ALyrid meteors will rain down Saturn appears at its best in the night of April 22/23, pro- the early morning hours. The totally eclipsed Moon viding viewers with their first When it comes to record- Moon-free major shower of setting events, the April 4 2015. The Moon will be in total lunar eclipse certainly plain sight for the month’s top ranks high. The Full Moon celestial event, however, when passes through Earth’s dark VIRGO Denebola our fully lit satellite passes umbral shadow for 4 minutes through Earth’s shadow for a and 43 seconds, which makes Spica LEO spectacular total eclipse in the this the 21st century’s briefest Eclipsed Moon wee hours of April 4. view of totality. In fact, you These short-lived events need to go back to October 17, depend on nice weather 1529, to find a shorter total CORVUS lunar eclipse (only 1 minute 5° Martin Ratcliffe provides plane- and 41 seconds long). tarium development for Sky-Skan, From North America, bet- Inc., from his home in Wichita, ter views of the eclipse come April 4, 5:00 A.M. PDT Looking west-southwest Kansas. Meteorologist Alister the farther west you live. works for Environment Ling From east of the Mississippi The eclipsed Moon of April 4 stands among the background stars of Virgo, just Canada in Edmonton, Alberta. River, people willWorldMags.net see only the 10° from 1st-magnitude Spica. ALL ILLUSTRATIONS: ASTRONOMY: ROEN KELLY 36 ASTRONOMY • APRIL 2015 WorldMags.net RISINGMOON

A marvelous night for a Moon dance Byrgius and Byrgius A

The endearing couple of Terra does. The youngster Byrgius A and Luna glides quietly across boasts a bright ray system that the solar system’s dance floor appears quite prominent even every month. From our earthly through binoculars. Each night perspective, the Moon appears after the April 4 Full Moon, this to circle us, at times leading and dazzling dimple rotates into then following, but it actually better view because the Moon N

never moves backward relative is moving more slowly than nor- NASA/GSFC/ASU INSET: /UA/LPL; to the audience of stars. What it mal, letting us peek a bit past its E does do is change speeds as its normal southwestern limb. distance from Earth changes, ini- We swap places during the Byrgius A tiating a dance astronomers call passage through New Moon and “libration.” If you concentrate on arrive at First Quarter on April 25 CONSOLIDATED LUNAR ATLAS our neighbor’s face during April, getting great views of the oppo- Inconspicuous when the Sun lies low in the lunar sky, as seen here, you can see this libration as the site limb. Using binoculars on Byrgius A displays bright rays near Full Moon. phases wax and wane. the 25th or 26th, look for a trio Start with the crater Byrgius, of dark spots on the northeast- trio rotates away from us. Mare Although we’ve come back which resides in the Moon’s ern limb: Lacus Spei, Endymion, Humboldtianum will disappear to the same spot relative to the southwestern corner. Although and Mare Humboldtianum. May 1, while the other two reach Sun’s spotlight, Luna’s more this 54-mile-wide impact fea- With each step toward the the limb at Full Moon on May 3. involved dance does not repeat ture doesn’t stand out, a much next Full phase, Luna moves But by that time, Byrgius A has exactly. That grander cycle takes smaller crater on its eastern rim more slowly than usual and the spun back into view. some 18 years to complete.

lit. By the 30th, its disk spans 7" but sunlight illuminates METEORWATCH Lyrid meteors less than 60 percent of it. You won’t have any prob- Active Dates: April 16–25 Peak: lem finding Venus even dur- No Moon means good news for the Lyrids April 22/23 Moon at peak: Waxing crescent ing bright twilight. The planet Maximum rate at peak: shines at magnitude –4.1 for We’re already four months into the Lyrid meteor shower 18 meteors/hour most of April, a dazzling dia- new year, and the skies still haven’t mond hanging in the western delivered a good meteor show. sky for three hours after sun- A Full Moon blasted January’s set. Venus begins the month Quadrantids, and we’ve had only Radiant Vega in the constellation Aries but minor showers since. But that changes the night of April 22/23 LYRA soon crosses into Taurus, when the annual Lyrid meteor where it remains the rest of shower reaches its peak. The wax- the month. It passes 3° south ing crescent Moon sets around of the Pleiades on April 10 midnight local daylight time, Deneb CYGNUS and 7° north of 1st-magnitude which leaves the prime viewing AQUILA Aldebaran, Taurus’ brightest hours before dawn Moon-free. star, on the 20th. The Bull’s Although the Lyrids typically Altair luminary appears to be the deliver between 15 and 20 meteors brightest member of the per hour at their peak for observers 10° V-shaped Hyades , at excellent sites, this year could be though the star actually lies better. Some meteor scientists pre- April 23, 1 A.M. Looking east only half as far away. dict enhanced rates in 2015, so it You’ll want to be sure to could pay dividends to be watch- The April 23 morning sky features many shooting stars as the best catch the whole vista on the ing before dawn April 23. meteor shower of 2015’s first half reaches its peak. evening of the 20th. Not only is Venus 7° north of Aldebaran, but the waxing OBSERVING On April 4, viewers from central North America westward to HIGHLIGHT Australia and eastern Asia will see a 5-minute total lunar eclipse. — Continued on page 42 WorldMags.net WWW.ASTRONOMY.COM 37

STAR N

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orient it so one of the labels matches NE

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c b STAR c ` MAGNITUDES VIRGO a _ ` Sirius Saturn a 0.0 SEXTANS 3.0 _ 1.0 ` Spica 4.0 M104 _ 2.0 5.0 CRATER b b b i LIBRA a

STAR COLORS ¡ m ` A star’s color depends / a CORVUS_ on its surface temperature.

• The hottest stars shine blue SE M83 _ LI Slightly cooler stars appear white • j ANT • Intermediate stars (like the Sun) glow yellow e • Lower-temperature stars appear orange f • The coolest stars glow red i 5128 Fainter stars can’t excite our eyes’ color • + receptors, so they appear white unless you V E CENTAURUS use optical aid to gather more light a b WorldMags.net 38 ASTRONOMY • APRIL 2015 S Note: Moon phases in the calendar vary in size due to the distance from Earth

and are shown at 0h Universal Time.

869 869 APRIL 2015

C WorldMags.net NG SUN. MON. TUES. WED. THURS. FRI. SAT.

MAP SYMBOLS 884 884 a

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6 Uranus is in conjunction with opposition, 6 A.M. EDT b g the Sun, 10 A.M. EDT

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h W 8 The Moon passes 2° north of Aldebaran, midnight EDT

M44 A.M. Betelgeuse Betelgeuse Saturn, 9 EDT 21 The Moon passes 0.9° north of CANCER ` Jupiter is stationary, 4 P.M. EDT Aldebaran, 1 P.M. EDT

` 9 Mercury is in superior The Moon passes 7° south of

_ CANIS Jupiter Procyon conjunction, midnight EDT Venus, 2 P.M. EDT ¡ MINOR c SPECIAL OBSERVING DATE 22 Lyrid meteor shower peaks 10 Venus passes 3° south of 25 First Quarter Moon the Pleiades star cluster occurs at 7:55 P.M. EDT in the evening sky.

MONOCEROS _ 26 The Moon passes 0.1° south of asteroid Juno, 3 A.M. EDT _ 11 Last Quarter Moon M47 P.M. occurs at 11:44 EDT The Moon passes 5° south of P.M. 15 The Moon passes 4° north of Jupiter, 2 EDT A.M. Neptune, 9 EDT 28 The Moon is at apogee (251,707 miles from Earth), 11:55 P.M. EDT j 16 The Moon is at perigee (224,329 PUPPIS l miles from Earth), 11:48 P.M. EDT

17 Pluto is stationary, 3 A.M. EDT

A SW LI _ PYXIS

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BEGINNERS: WATCH A VIDEO ABOUTWorldMags.net HOW TO READ A STAR CHART AT www.Astronomy.com/starchart. WWW.ASTRONOMY.COM 39 PATH OF THE PLANETSWorldMags.netThe planets in April 2015

CAS DRA Objects visible before dawn UMa

AND LAC CVN CYG HER

TRI LYR BOÖ

VUL CrB COM ARI PEG SGE Pallas Sun SER PSC A total lunar eclipse Nysa occurs April 4 AQL SER Herculina Uranus Celestial equator AQR SCT VIR OPH LIB P ath of t CET he S Path o Saturn un (e f the Moon CRT Neptune cliptic ) CRV CAP Pluto PsA Ceres FOR SGR Asteroid Massalia reaches SCL opposition April 20 GRU MIC CrA SCO LUP CEN Moon phases Dawn Midnight

19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 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. 30

The planets These illustrations show the size, phase, and orientation of each planet and the two brightest dwarf planets 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 Saturn N Ceres Neptune Pluto Venus 10" Jupiter

Planets MERCURY VENUS MARS CERES JUPITER SATURN URANUS NEPTUNE PLUTO Date April 30 April 15 April 1 April 15 April 15 April 15 April 15 April 15 April 15 Magnitude –0.5 –4.1 1.4 9.0 –2.2 0.2 5.9 7.9 14.2 Angular size 6.7" 15.0" 4.0" 0.5" 39.8" 18.1" 3.4" 2.2" 0.1" Illumination 59% 73% 99% 97% 99% 100% 100% 100% 100% Distance (AU) from Earth 1.011 1.114 2.362 2.860 4.958 9.177 20.991 30.657 32.678 Distance (AU) from Sun 0.337 0.718 1.457 2.893 5.352 9.972 19.998 29.966 32.853 Right ascension (2000.0) 3h41.6m 4h05.4m 1h51.9m 20h24.0m 9h00.7m 16h09.4m 1h02.6m 22h42.5m 19h05.5m Declination (2000.0) 22°02' 22°31' 11°22' –23°33' 17°59' –18°48' 6°00' –9°00' –20°30'

WorldMags.net 40 ASTRONOMY • APRIL 2015 This map unfolds the entire night sky from sunset (at right) until sunrise (at left). Arrows and colored dots show motionsWorldMags.net and locations of solar system objects during the month.

CAS Objects visible in the evening Jupiter’s moons AND Dots display positions LYN Io PER of Galilean satellites at 11 P.M. EDT on the date Europa LMi AUR shown. South is at the GEM top to match TRI S Venus the view CNC ARI WE Ganymede Mercury through a Jupiter telescope. N Callisto LEO Mars Sun Juno TAU CMi 1 Iris PSC 2 SEX ORI MON 3 Jupiter

CET 4 HYA CMA 5 LEP SCL PYX FOR 6 Ganymede ANT PUP ERI 7 COL CAE 8 Early evening 9

1 10

11 29 28 27 26 25 24 23 22 21 20 19 18 12 Europa

13

14

15 Jupiter 16

Venus 17 Mars 18

Mercury 19 Earth Superior conjunction is April 9/10 20

21 Callisto

22 Ceres 23 Io

24

25

Jupiter Uranus 26 The planets Solar conjunction in their orbits is April 6 27 28 KELLY ROEN : Arrows show the inner planets’ Neptune monthly motions and dots depict Saturn 29 the outer planets’ positions at mid- ASTRONOMY month from high above their orbits. 30 Pluto ILLUSTRATIONS BY BY ILLUSTRATIONS WorldMags.net WWW.ASTRONOMY.COM 41 — Continued from page 37 Mutual admiration society

WHEN TO VIEW THE PLANETS S WorldMags.net Jupiter EVENING SKY MIDNIGHT MORNING SKY Mercury (west) Jupiter (west) Saturn (southwest) Venus (west) Saturn (southeast) Uranus (east) Mars (west) Neptune (east) W Jupiter (south) crescent Moon stands 7° west falls short only of Venus. The of the Hyades’ center. The giant world remains visible Europa 30" arrangement of the Moon, well into the morning hours, Io April 8, 11:50 P.M. EDT Venus, Hyades, and Pleiades setting around 4:30 a.m. local creates a beautiful scene as the daylight time April 1 and two Europa occults Io the evening of April 8 starting just a minute after the sky darkens. The next evening hours earlier by month’s end. scene shown here. Less than two hours later, Europa eclipses Io. isn’t too shabby either, with a Jupiter resides among the noticeably fatter Moon stand- background stars of Cancer, turbulent atmosphere. The bright dots beside the planet ing 7° to the planet’s left. some 5° east-southeast of the first things you’ll see are two and lined up with the jovian Like Mercury, Venus’ tele- Beehive star cluster (M44). parallel dark belts that strad- equator. Occasionally, how- scopic appearance changes Typical 7x50 binoculars will dle a brighter zone tracing the ever, one or more hide behind during April. The apparent show them both in the same planet’s 40"-diameter equator. Jupiter or transit directly in diameter of its disk grows field of view. A whole series of light zones front of the planet. In the lat- from 14" to 17" while the Swing a telescope toward and darker belts appears on ter case, the moon also drops phase shrinks from 78 percent Jupiter, and you’ll be quickly nights with steady seeing. its shadow onto the planet’s to 68 percent lit. impressed with the rich detail Once you’ve studied cloud tops. Jupiter already appears visible in its cloud tops. The Jupiter’s atmosphere for a The four moons appear high in the south as twilight best views come in the early while, turn your attention to in order of increasing dis- drops its dark blanket over evening when the planet lies the planet’s family of moons. tance (Io through Callisto) to Earth. Shining at magnitude highest and its light passes Typically Io, Europa, Gany- Jupiter’s west after midnight –2.2, it beats every star and through less of Earth’s mede, and Callisto show up as April 2/3. This alignment COMETSEARCH Catch Lovejoy before it’s gone Comet Lovejoy (C/2014 Q2) N The inner solar system hosts a the ghostly puffball. Target the 21 never-ending parade of periodic time around midmonth when 26 comets. The star of these local the Moon interferes least. On 23 objects is the infrequent visitor the plus side, Lovejoy remains 23 1P/Halley, but few others give visible all night as it drifts in Path of rise to much interest. Luckily, the front of Cassiopeia’s stars. 40 20 Comet once-only renegades from the The comet’s dust output Lovejoy 50 distant Oort Cloud can prove likely is shutting down as the E CASSIOPEIA quite entertaining. That’s what dirty snowball heads away from 17 happened early this year with the Sun, so Lovejoy should Comet Lovejoy (C/2014 Q2). This appear small and round. Bump 48 14 fresh comet brightened unex- the magnification up to 150x or 42 pectedly to 4th magnitude in more to see detail. Can you spy April 11 January and put on a nice show the false nucleus — a dot of for anyone who braved the cold. bright light at the comet’s cen- 31 1° If the more optimistic pre- ter — through the thinning dictions hold, Comet Lovejoy layers of gas and dust? This Oort Cloud visitor continues its northward trek through Cassiopeia still might be an 8th-magnitude Let Comet 88P/Howell serve in April. The best views come in the Moon’s absence around midmonth. object in April, but don’t be sur- as a backup plan. This periodic prised if it’s a couple of magni- visitor comes closest to the Sun Aquarius this month, which the challenge right away: tudes fainter. If it is on the in early April and could grow means it’s best placed for more Howell lies near M30, typically fainter side, you’ll need a 6-inch brighter than 10th magnitude. southerly observers. Messier the toughest object at the end scope under a dark sky to detect Howell moves slowly through marathoners will understand of a long night’s observing. WorldMags.net 42 ASTRONOMY • APRIL 2015 The Moon and Venus join twoWorldMags.net Taurus clusters LOCATINGASTEROIDS Betelgeuse Nysa plays nice in Virgo the Maiden TAURUS Main-belt asteroid 44 Nysa to locate 10th-magnitude Nysa. Venus PERSEUS shows up well through a 3-inch On the evenings of April 23–27, Aldebaran telescope from the country or a distinctive trapezoid of stars ORION a 6-inch scope from the sub- makes a perfect background for Pleiades urbs in April. The 44-mile-wide seeing the solar system object’s Hyades space rock lies about halfway night-to-night movement. The Moon up in the southeastern sky asteroid lies out in the open the during evening hours. You can rest of the month, so it should find the right area easily. Start be easy pickings except when with the bright tail star of Leo, the Moon is nearby through 5° magnitude 2.1 Denebola, and April 4 and after the 27th. April 20, 9 P.M. then drop 8° due south to 4th- German-French astronomer Looking west magnitude Nu (ν) Virginis. Nysa Hermann Goldschmidt discov- lies within 5° of Nu all month. ered Nysa in May 1857. By the A brilliant planet, several bright stars, and two pretty clusters form a scin- It won’t be hard to track time he was done four years tillating backdrop for the crescent Moon during evening twilight April 20. the asteroid, but it will require later, Goldschmidt had 14 aster- attention to detail. Western oids to his credit, the record at follows an earlier transit of Later that night, Europa’s Virgo has a sprinkling of stars that time. In Greek mythology, Io and its shadow across the shadow washes over Io for with a nice range of magni- Nysa was the homeland of the planet’s face. The transit four minutes beginning at tudes, a real help when trying Hyades nymphs. begins at 12:04 a.m. EDT 1:38 a.m. EDT. followed about an hour later The last bright planet rises A trek through the Maiden’s head by the shadow. around 11:30 p.m. local day- After Io and its shadow light time in early April and j N 4 leave Jupiter’s disk (at 2:21 a.m. two hours sooner by month’s and 3:26 a.m. EDT, respec- end. Saturn lies low in the tively), you may notice another southeast by midnight and alignment in the works. Io appears about a third of the passes just 1.4" south of way from the southern hori- / Europa at 4:32 a.m. EDT. And zon to the zenith shortly May 1 E 21 26 i 16 about 90 minutes later, Io before morning twilight Path of Nysa eclipses Europa. Observers in begins. The planet shines at 11 western North America can magnitude 0.2, significantly 6 see Europa dim for six min- brighter than any star in its April 1 VIRGO utes starting at 3:06 a.m. PDT. host constellation, Scorpius. This eclipse is part of a Only 1st-magnitude Antares, rare series of mutual events located 9° southeast of Saturn, among the four Galilean sat- comes close. 7 0.5° ellites. They occur when the Saturn moves slowly west- orbits of the moons turn ward relative to the starry Main-belt asteroid Nysa glows at 10th magnitude in April as it rides high edge-on to the Sun and Earth, background this month as it in the southeast evening sky among the background stars of Virgo. which happens twice during approaches opposition and Jupiter’s 12-year circuit of the peak visibility in late May. Sun. One moon may pass in It stands 0.5° north of 4th- eyes off the stunning rings, and show up through 4-inch front of another (an occulta- magnitude Nu (ν) Scorpii on which span 41" and tilt 25° to and larger instruments. All tion), or one may cast its April 1. By the 30th, it has slid our line of sight. orbit inside Titan and thus shadow on another (an to a position 1.2° north of You’ll also see Saturn’s change positions from night eclipse). The current series 2nd-magnitude Beta (β) Sco. biggest and brightest moon, to night. will run through August. Any telescope will deliver 8th-magnitude Titan, through Although Uranus and A particularly nice pair spectacular views of Saturn any scope. You can find it due Neptune are both morning of mutual events occurs the and its rings. The planet’s north of the planet April 2 objects, neither climbs high night of April 8/9. Europa disk measures 18" across at and 18 and due south April 10 enough before dawn to merit partially occults Io for five midmonth and likely will and 26. Three other moons a look. You’re better off wait- minutes starting at 11:51 p.m. appear bland. But few observ- — Tethys, Dione, and Rhea ing a couple of months for EDT. Through a telescope, you ers will be able to take their — glow at 10th magnitude better views. will see the two moons merge and then slowly separate. GET DAILY UPDATESWorldMags.net ON YOUR NIGHT SKY AT www.Astronomy.com/skythisweek. WWW.ASTRONOMY.COM 43 Celestial mechanics Astronauts Steven Smith and John Grunsfeld repair Hubble in December 1999, squeezing in WorldMags.netthree spacewalks and spending Christmas in orbit before a dash home ahead of the much-feared SAVING Y2K computer problems. NASA/MSFC

How astronauts continually reinvented the most important telescope ever. by Ben Evans

merican astronaut Jeff Hoffman and his wife, arrays. Each trip transformed Hubble’s capabilities and contrib- Barbara, hosted friends at their home in Houston on uted to its enduring reputation as the most successful telescope New Year’s Eve 1993. Three weeks earlier, Hoffman ever placed into space. had been part of an ambitious space shuttle mission However, Hubble wasn’t always so clearly destined for success. to repair the Hubble Space Telescope. The guests When it rose into orbit a quarter-century ago, the telescope departed by the end of the evening, and Hoffman was alone in boasted five instruments whose imaging range not only encom- his kitchen, clearing away the dishes. Suddenly, the telephone passed the visible region of the electromagnetic spectrum, but also rang. It was one of his astronomer friends. stretched into the ultraviolet and infrared. Hubble had early trou- “Jeff, hi,” came the greeting. “Do you have any champagne left?” bles with jittery solar arrays. Then, in June 1990, the telescope fell “Yeah, I still have a half-bottle in the refrigerator. Why?” foul to a much-publicized spherical aberration, triggered by a “Well, crack it open because we’ve just gotten the first pictures design flaw in its primary mirror that left it unable to focus. NASA back from Hubble. It works!” was soon the target of late-night talk show hosts and public scorn. Each time the space shuttle left Hubble, a new observatory The blurring was worst for the crucial Wide-Field and Planetary and a new chapter of discovery was born. From its launch in Camera (WFPC) and Faint Object Camera. Both instruments suf- April 1990 to the departure of its final human visitors in May fered in clarity and their ability to acquire detailed images. 2009, Hubble was reinvented on five occasions. These missions The space agency’s investigation pinned blame on an instru- brought new and improved instruments, better computers, a new ment called a reflective null corrector, used by manufacturer mechanical heart, hardier gyroscopes, and enhanced solar Perkin-Elmer to aid the accuracy of Hubble’s mirror. A lens in the device was incorrectly positioned and guided the polisher to shape a perfectly smooth mirror, but with the wrong curvature. The improper grind specification polished the glass too flat by a mere 1⁄50 the width of a human hair. It meant that incoming light rays from distant sources couldn’t focus at the same point. A fix would be essential to restore Hubble to its pre-launch bill- ing as the most important advancement in astronomy since the time of Galileo. The spacecraft’s primary mirror could not be changed, so an instrument had to be designed that would let astronauts give Hubble “glasses” while orbiting some 350 miles (560 kilometers) above Earth. The Corrective Optics Space Telescope Axial Replacement (COSTAR) would see 10 small mirrors — each no larger than a coin — placed into the telescope’s focal path to cor- rect the effect, restore the potential of the instruments, and bring their performance close to original specifications. In the decades Kathy Thornton replaces Hubble’s solar panel array on STS-61, the first of that followed, each new instrument used corrective optics built five shuttle missions to service the space telescope. NASA WorldMags.netinto its design. 44 ASTRONOMY • APRIL 2015 WorldMags.net

WorldMags.net Astronaut Jeff Hoffman holds Hubble’s Wide-Field WorldMags.netand Planetary Camera during the space tele- scope’s first servicing mis- sion in 1993. NASA

These before-and-after images of spiral galaxy M100 show the extent of Hubble’s pre-servicing blur and exactly how well the fix worked. NASA

The astronauts completed both tasks, though not entirely smoothly. The Sun had warped the gyro compartment doors, and they stubbornly refused to close, threatening Hubble’s ability to stay at the proper temperature. Musgrave struggled for some time to close the doors and even tried to push them shut with his hel- meted head at one point before the astronauts eventually brought them together. The old solar arrays posed their own issues. One folded up perfectly, but a bent strut prevented the other from doing the same, forcing the crew to dump it overboard. Next came the installation of WFPC2, which slid perfectly into place and passed an “aliveness” test with flying colors. This cleared the way for the smooth installation of COSTAR, which would bump out an existing instrument, the High Speed Photometer. The first servicing mission pushed the shuttle’s capabilities to its limits. The astronauts faced an unprecedented task, with integrated spacewalking and robotics over five days. The crew brought more than 200 tools into space, from power ratchets to portable work lamps. All told, their spacewalks exceeded 35 hours, and one of them established itself as the second longest in history at that time. One of those spacewalks also gave Hoffman the fright of his life when he removed Thornton’s gloves and noticed her fingers were bright red. His fear that it was blood was quickly calmed by the realization that a chunk of Thornton’s red-colored food bar had floated away from her mouth and somehow made its way through her suit, down one of the arms and into the glove. “Not nearly as serious as it looked,” Hoffman said in a NASA oral history inter- view, “but I got quite a shock when I pulled her glove off.” The successful repairs came as a relief for Musgrave, who had Hubble’s big fix been intimately involved in the minute-by-minute planning of the This wasn’t just a repair trip. NASA also made improvements. spacewalks for two years. He once joked that his only peace and So when Hubble’s first servicing mission eventually launched in quiet away from the mission came while sitting in the dentist’s chair. December 1993, the astronauts were tasked with installing the Hubble underwent rigorous testing in the following weeks. NASA upgraded WFPC2 — originally designed as a spare. Before launch, configured COSTAR, optically aligned and focused WFPC2, and the crew was told that if they installed either COSTAR or WFPC2, made test observations. Then, in January 1994, the first stunning astronomers would be “deliriously happy,” but with congressional images from the rejuvenated telescope were revealed to the world. funding for NASA hanging on a knife-edge, this wasn’t enough. The But this was just a taste of what would come. Almost two years mission had to be a full success. NASA Administrator Dan Goldin later, WFPC2 supported 10 days of “deep field” observations, identi- told the crew that the space agency’s future lay in their hands. fying galaxies that dated to within a billion years of the Big Bang. Working in two teams, Hoffman and fellow astronauts Story The image was instantly iconic. NASA followed their triumph with Musgrave, Kathy Thornton, and Tom Akers labored to service Deep Field South in 1998 and then Ultra Deep Field in 2003–2004, Hubble on five spacewalks. The first two excursions replaced a which surveyed celestial sources more than 13 billion years old. pair of rate-sensing units — whose internal gyroscopes controlled the telescope’s orientation — and the two solar arrays. New millennium telescope Even as NASA basked in this success, it launched a second servic- Ben Evans is a British spaceflight writer and author of the multi-volume ing mission in February 1997. The 10-day, five-spacewalk extrava- History of Human Space Exploration, published by Springer-Praxis.WorldMags.netganza by Mark Lee, Steven Smith, Greg Harbaugh, and Joe Tanner 46 ASTRONOMY • APRIL 2015 first removed two instruments to replace them with new ones: the Space Telescope Imaging Spectrograph (STIS) and the Near Failure to focus Infrared Camera and Multi-ObjectWorldMags.net Spectrometer (NICMOS). These new arrivals promised to revolutionize Hubble. STIS 40 millimeter breaks light up into its component colors, which allows astronomers error in focus to study an object’s chemical composition, motion, temperature, B and density on a level drastically higher than previously possible. A In time, STIS would reveal fine details of star birth, help identify Optical axis supermassive black holes, and investigate the distribution of matter throughout the universe. Meanwhile, NICMOS was designed to shed new light on infrared-light emitters like brown dwarfs. The first spacewalk of the second servicing mission started later View from B telescope than planned after one of Hubble’s solar arrays inadvertently “wind- A milled,” spinning as oxygen escaped from the shuttle’s new air lock. Rays from mirror rim “We coincidentally were trained to recognize an uncommanded Rays from mirror center slew of the solar arrays,” astronaut Steven Hawley, whose job was Smallest Image with to operate the robotic arm from inside the shuttle, later explained blur circle sharp core

in an oral history interview. But he and Tanner exchanged nervous No sharp image can form when a mirror suffers from spherical aber- : ROEN KELLY glances when they spotted the rapid motion. Both men knew the ration. Rays entering across the mirror can’t focus together.

arrays were not supposed to spin so quickly, and with all cameras ASTRONOMY focused on the air lock and not Hubble, mission control was unaware of the full extent of the problem. time by Chief Hubble Scientist Ed Weiler as “the Super Bowl” of Hawley was convinced that if the event had been captured on spacewalking because it placed the telescope “into a position of television, the spacewalk would have been scrubbed and the entire having world-class scientific capability well into the 21st century.” mission thrown into jeopardy. Fortunately, that was not the case, The astronauts, however, identified several cracks, a pit-like and Lee and Smith swiftly set to work fitting the new instruments. crater, and evidence of age-related wear on Hubble’s thermal The team also added technology to enhance Hubble’s pointing insulation. NASA had an extensive overhaul planned for the even- ability and improve data storage. Their work was lauded at the tual third mission, but the space agency considered it prudent

Antennae

Inside the Reaction wheels Science computer Hubble Space Telescope Solar arrays Fine guidance sensors

Space Telescope Imaging Spectrograph Astronaut handrails

Aperture door

Advanced Camera for Surveys

Insulation Star trackers Primary Nickel-hydrogen batteries mirror Wide Field Camera 3

NASA/GEORGE LADAS, BASE24.COM HUBBLE; NASA EARTH NASA HUBBLE; NASA/GEORGE BASE24.COM LADAS, WorldMags.net back on the ground before the dawn of the new millennium. To achieve this, mission managers shaved two days and one space- WorldMags.netwalk from the flight. For only the third time in history, American astronauts spent Christmas in space, a fact that Scott Kelly had taken time to discuss with his 5-year-old daughter. “I told her that we were going to point the telescope at the North Pole and get a picture of Santa,” Kelly said from orbit, according to news reports at the time. “She was all excited and really didn’t mind too much her dad being away for Christmas.” Nevertheless, the SM-3A astronauts completed a major over- haul in three spectacular spacewalks, each of which exceeded eight hours in length. “Eight hours was a long time,” astronaut John Grunsfeld told a NASA interviewer. “I felt comfortable with that. … But I would say at the end, we were getting pretty darn tired.” The remaining tasks took place on SM-3B, which flew in March 2002. Astronauts removed the last of Hubble’s original instruments to make room for the Advanced Camera for Surveys (ACS). The instrument would cover twice as much sky with double the clarity and four times the speed of WFPC2. ACS, with its built-in corona- graph to block out light from stars, would allow astronomers to see their surrounding environments and permit observations of extremely dim exoplanets. Astronauts also hooked up a new exper- imental cryocooler for NICMOS on the final spacewalk. After three years out of action, the infrared camera was back in service. Astronaut Drew Feustel practices working on an underwater mock-up of Their success was fortuitous, and Grunsfeld, also a professional the Advanced Camera for Surveys in Houston. After its installation in 2002, astronomer, joked that failure would have meant he could never the instrument became Hubble’s workhorse. NASA show his face at American Astronomical Society (AAS) meetings. The Hubble huggers to immediately attempt a repair. So mission control added a last- NASA Administrator Sean O’Keefe canceled a long-planned fifth minute fifth spacewalk to the second mission. The astronauts had servicing mission to Hubble in January 2004 following the space to use spare pieces of insulation, high-temperature tape, parachute shuttle Columbia disaster, which claimed the lives of seven astro- cord, and alligator clips. nauts. Grunsfeld, then serving as NASA’s chief scientist, took it as Returning safely to Earth, the crew had completed a mission a hammer-blow. He considered quitting the space agency. that enhanced Hubble far more than the first servicing mission “As a certified ‘Hubble hugger,’ that hit me like a two-by-four in that overshadowed it. It was profoundly satisfying for the seven the head,” he recalled. “I just couldn’t believe that we would pre- astronauts. After two years of training and a flawless execution, maturely make that decision.” Lee declared that he was ready to buy his crew mates a drink. “Up The cancellation was also met with criticism from the public and here,” he said from orbit, “we’ve got some orange mango drink and politicians, most notably Senator Barbara Mikulski of Maryland, some lemonade, but that’s about as stiff as it gets. So I’m ready for whose home state plays host to the Space Telescope Science Insti- a margarita!” tute, which operates Hubble. Several months later, in June 2004, “Hubble 2” was Weiler’s description of the telescope when the O’Keefe explained his decision before an AAS meeting in Denver. second servicing mission crew departed. Their work had trans- formed Hubble from a 1970s spacecraft with 1980s optics into an observatory fit for the new millennium and laden with modern instrumentation. A wider view However, in March 1997, NICMOS, Hubble’s infrared camera, suffered an electrical short that caused it to lose all of its nitrogen coolant by January 1999, and it was shut down. This proved bit- terly disappointing, as the instrument had already shed new light on the changing atmospheres of both Uranus and Neptune. An instrument repair was planned for the third servicing mis- sion, which NASA broke into two phases. The first, SM-3A, was delayed until December 1999, and by the time the crew reached Hubble, the telescope had lost its fourth of six gyroscopes and been forced to suspend its observations. Hopes to make four spacewalks on SM-3A came to naught as the mission slipped Joe Tanner poses for a picture by fellow astronaut Greg Harbaugh in 1997 dur- toward the end of 1999 and NASA — worried about the implica- ing Hubble’s second servicing mission. The trip revolutionized Hubble with tions of the much-hyped Y2K computer bug — wantedWorldMags.net the shuttle instruments fit for the new millennium. NASA 48 ASTRONOMY • APRIL 2015 WorldMags.net

Mike Massimino, who flew to Hubble twice, smiles for the camera outside a space shuttle window dur- ing Hubble’s (seen in the background) final servic- ing mission in 2009. NASA

“The easy route would have been for us to keep plugging along The final servicing mission took place in May 2009 and and hope for the best,” he said. “But hope is not a management involved five spacewalks intended to carry Hubble through at method we should rely on to keep Hubble operating.” least 2014. Spacewalkers Grunsfeld and Drew Feustel replaced In O’Keefe’s mind, he was faced with two undesirable options: WFPC2 with Wide Field Camera 3 (WFC3). Despite some dif- fly a shuttle mission without fully complying with the recommen- ficulty removing the old camera’s bolts — which required more dations of the Columbia Accident Investigation Board, or allow torque than expected after 16 years in space — they succeeded in Hubble to die prematurely. pulling it out and installing the telescope’s most technologically His solution was for NASA to explore a robotic mission to advanced visible-light instrument. Hubble before the end of 2007. Grunsfeld participated extensively They also installed the Cosmic Origins Spectrograph, allowing in the early planning phase, but ultimately such a mission was Hubble to perform far- and near-ultraviolet spectroscopy of faint too complex. point sources — white dwarfs, cataclysmic variables, and binary O’Keefe’s resignation from NASA in December 2004 kindled a stars — and study the origins of large-scale structures in the uni- spark of hope that his successor might approve another shuttle verse, including the formation of galaxies and the birth of stellar mission, and when Michael Griffin became the new NASA admin- and planetary systems. istrator in April 2005, he was far warmer to the idea. As with his two previous visits to Hubble, Grunsfeld took a poignant moment to pat the telescope goodbye, knowing that he In need of TLC would never see it again. But when the shuttle departed, Hubble However, Hubble had other difficulties. STIS, whose impressive was left in its best-ever condition, with present estimates suggesting accolades would eventually include the first spectrum of an exo- that it may remain functional until 2020. planet’s atmosphere, had suffered an electronics failure in August The work performed by the five shuttle crews between 1993 2004 and was shut down. In addition, Hubble’s main camera, and 2009 transformed Hubble from a white elephant into a white ACS, malfunctioned in June 2006 and was later hit by a short cir- knight of astronomy. Twenty-eight astronauts supported 23 space- cuit in its backup power supply, which put it out of action. This walks, totaling 166 hours. And of the 10 longest spacewalks ever left the aging WFPC2 as the primary visible-light camera. undertaken, four of them were done while working on Hubble. More trouble was afoot. With the fifth servicing mission finally “Three hundred years from now,” said Hubble’s senior project planned for October 2008, Hubble endured a failure of its Science scientist, David Leckrone, “none of us in all likelihood will be Instrument Command and Data-Handling Unit in late September. remembered as individuals, but certainly the Hubble Space Tele- This forced NASA to postpone the astronauts’ trip to train the scope will be remembered as a high point in human civilization. crew on another repair task. Meanwhile, a software upload caused That’s an awe-inspiring thought and something that motivates us NICMOS’ cooling system to operate sporadically. to do our very best for Hubble and for science.” FIND IN-DEPTH COVERAGE OF EACH HUBBLE SERVICINGWorldMags.net MISSION AT www.Astronomy.com/toc. WWW.ASTRONOMY.COM 49 POP CULTUREWorldMags.net TELESCOPE How Hubble

Think today’s society would be the same without the big eye in the sky? Think again. by Liz Kruesi

WorldMags.net For the observatory’s 20th anniversary, Hubble took this image of the Carina he Hubble Space Telescope — Nebula (NGC 3372). arguably one of the greatest tech- WorldMags.netnological achievements ever — T was in trouble. Astronauts were to conduct a fifth and final ser- vicing mission of the observatory in 2004, but in January of that year NASA canceled the mission, citing safety concerns. The public, however, wanted to save the great scope. They wrote to astronomers, the space agency, members of Congress, and the media to reinstate the mission. And it worked. In 2006, NASA announced that it The “Pillars of Creation,” a star-forming region in the Eagle Nebula (M16), is probably the Hubble would send astronauts to service Hubble Space Telescope’s most iconic image. NASA/ESA/STSCI/ one last time. JEFF HESTER AND PAUL SCOWEN ARIZONA STATE UNIVERSITY The telescope clearly has had a pro- found impact during its quarter-century of observations — on science and exploration, just three years. In December 1993, astro- of course, but also on a much wider audi- nauts aboard the space shuttle Endeavour ence. Other scientific facilities have tried to installed two instruments on the telescope: emulate Hubble’s formula, but none has a new camera and the Corrective Optics come close to the impact this telescope has Space Telescope Axial Replacement had. A combination of attributes makes (COSTAR) that acted like eyeglasses. Hubble an immensely influential project. The new lenses worked. Hubble could Its incredible views of the cosmos, which resolve details never before imaged, like the are both gorgeous and real, bring the wisps of gas around baby stars and suns in excitement of discovery to households distant galaxies. across the globe. Its images have inspired Since the repairs, the telescope has con- artists in many mediums to produce musi- tributed to countless scientific discoveries cal compositions, paintings, and choreog- and even a Nobel Prize in physics (see raphy. But another aspect — the direct “Hubble’s top seven science discoveries” on human interaction and involvement in the p. 28). On a more public level, teachers post mission — helps hold Hubble’s science in Hubble’s spectacular images in classrooms, the public mind. and outreach materials from the project are part of education curricula throughout the The early years United States, explains STScI’s Kenneth It was a different story in 1990. When Sembach, who began working with the scientists saw Hubble’s first images in May telescope when it launched. of that year, they were disappointed and frustrated. Technicians had ground and A familiar tone polished the telescope’s 2.4-meter mirror Hubble’s pictures strike a chord with peo- to the wrong shape, so it couldn’t focus the ple. Of course, they are gorgeous, which is light it collected into crisp points; Hubble no mistake. When the telescope images a had fuzzy vision. Politicians ridiculed the celestial object, it does so through filters, project, comedians made it the brunt of each of which allows specific wavelengths jokes, and the U.S. public thought of it as a to pass through. But Hubble collects more costly mistake. People were angry — after than visible light. Its detectors also can all, it was a primarily federally funded record ultraviolet and infrared radiation. mission, so taxpayers had footed much of For those images, scientists assign the col- I C the bill, some $2.5 billion at that point. ors red, green, or blue to each filter. The But scientists and engineers had devel- end product is a false-color rendition of oped Hubble to be serviced. And that the target, but one that effectively conveys aspect of the mission is what saved it. its essence while retaining the valuable NASA and the Space Telescope Science scientific data. Institute (STScI), which operates Hubble, Many of the images look like works of faced the problem and found a solution in art, but what’s important, says STScI’s Mario Livio, “is that as beautiful as these Hubble images collected in the mid-1990s inspired things are, they actually exist somewhere Astronomy Contributing Editor Liz Kruesi to in our universe.” The laws of physics and study physics to understand the science respon- chemistry have created these incredible sible for the structures in those gorgeous shots. NASA/ESA/M. LIVIO/THE HUBBLE20TH ANNIVERSARY TEAM STS WorldMags.net structures, and Hubble has revealed them. WWW.ASTRONOMY.COM 51 WorldMags.net

On December 18, 2012, scientists at the Space Telescope Science Institute, realizing that the public loves Hubble’s images, released this one they called “A Cosmic Holiday Ornament.” The image shows planetary nebula NGC 5189. NASA/ESA/ THE HUBBLE HERITAGE TEAM STSCI/AURA

This image, dubbed the Hubble Deep Field, captured the imagination of scientists and the public when the space agency released it in early 1996. R. WILLIAMS STSCI/THE HUBBLE DEEP FIELD TEAM/NASA

Art historians also have extended the comparison. Elizabeth Kessler of Stanford University, for example, has studied many Hubble images and written a book about the artistic choices that researchers have used in the photographs. She looked at how scientists frame objects and what colors they assign to different filters. While astronomers designate specific “colors to communicate physical attributes of the nebulae or galaxies, different temperatures, Hubble took this image of star-forming region NGC 3324 to celebrate its 10th anniversary in space. or the locations of different kinds of gases, NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA/N. SMITH UNIV. OF CALIFORNIA, BERKELEY those same colors often also suggest a kind of earthly landscape,” says Kessler. Hubble images are ethereal and eerie Probably the most iconic image from But that image struck a chord with peo- but at the same time familiar. “I think the Hubble is its portrait of the “Pillars of ple for another reason, too. The colors sci- images themselves walk this really careful Creation” in the Eagle Nebula (M16), entists chose for the composition are line between looking very alien and strange which astronomers released in November familiar. The pillars resemble structures on and exciting,” Kessler says, “and yet they 1995 (see p. 26). Those three columns of Earth, which makes this image relatable. also remind us of places that have been gas and dust, shaped by the radiation and When STScI released the image, the explored and understood here on Earth.” particle winds of newborn stars, fill the accompanying text drew the following For researchers, Hubble satisfies a desire field of view. “That image, the way it was comparison: “The pillars are in some ways to explore, whether by imaging a nearby framed was brilliant,” says Sembach. “It fit akin to buttes in the desert, where basalt world or investigating galaxies billions of within that chevron shape of the camera and other dense rock have protected a light-years away. The telescope has imaged that was on board at the time so beauti- region from erosion, while the surrounding dust storms on Mars, discovered disks of fully, and it was orientated in a way that landscape has been worn away over millen- material around young stars, and seen qua- you get the full pillar effect.” nia.” And although the scales of these sars across the universe. And through all The image shows depth that many pho- objects are vastly different — earthly rock the research, Hubble has brought the public tographs of celestial objects can’t capture formations can extend from a few to hun- along for the ride. “It has taken the excite- and gives the pillars three-dimensionality. dreds of feet, while the cosmic pillars are a ment that the scientists usually feel with They look like something you could touch, few light-years, or trillions of miles, long new discoveries and brought it to homes of and that quality helps draw the public in. — theWorldMags.net public embraced the connection. nonscientists,” says Livio. 52 ASTRONOMY • APRIL 2015 2015 NOVEMBER 15, 2012 Key (and not so key) Hubble has A Hubble image of the Hourglass Nebula appears on a poster in Raj observed Koothrappali’s office in The Big Bang Theory. WorldMags.net40,000 objects Hubble moments and produced 1 million 2011 1946 images. Hubble makes its millionth science observation, and the 10,000th sci- American physicist Lyman Spitzer ence paper based on its observations is published. proposes a space telescope.

MAY 15, 2009 The film Angels & Demons shows a large poster of the Hourglass Nebula in a character’s office at the Large Hadron Collider.

AUGUST 11, 2008 DECEMBER 24, 2002 Hubble flies its Hubble has traveled 2 billion miles since astro- 100,000th orbit. nauts placed it in orbit.

MAY 16, 2000 Pearl Jam releases Binaural, an album whose cover sports a Hubble image of the Hourglass Nebula.

NOVEMBER 7, 1999 In the 12th episode of the television series Futurama, the characters destroy the Hubble Space Telescope by mistake.

JULY 13, 1999 After 9 years and 80 days, Hubble flies its 50,000th orbit.

FEBRUARY 11, 1997 The launch of STS-82, space shuttle Discovery, marks the second servicing mission.

AUGUST 23, 1996 1969 Hubble has traveled 1 billion miles The National since astronauts placed it in orbit. Academy of Sciences gives its approval for the Large Space Telescope project. APRIL 24, 1990 JUNE 28, 1991 DECEMBER 2, 1993 : ROEN: KELLY STAR FIELD; ESA/HUBBLE M. KORNMESSER HUBBLE 1977 The space shuttle In the movie The The launch of STS-61, The U.S. Congress 1981 Discovery (STS-31) Naked Gun 2½: The space shuttle Endeavour, approves funding The Space launches, carrying ASTRONOMY Smell of Fear, film- marks the first servicing for a space tele- Telescope Science the Hubble Space makers place a pic- mission. Shuttle astro- scope. In 1983, Institute begins Telescope and ture of Hubble in the nauts install COSTAR. NASA names it in operations in deploying it into Blue Moon Cafe on a honor of Edwin Baltimore. orbit the next day. wall displaying fail- : CHUCK BRAASCH; Hubble. ures; it appears between the Titanic and the Hindenburg. ASTRONOMY

The intersection with art created a contemporary dance titled The Natural History in New York City and at While scientifically important, Hubble’s Matter of Origins, in which the first half of the Maryland Science Center in Baltimore images are works of art and have appeared the piece focused on the physics of the uni- in 2010; his Heaven’s Carousel showed at in exhibits in places like the Walters Art verse. Lerman used images from Hubble, Accademia dei Lincei in Rome in 2014. Museum in Baltimore and the Istituto data from particle accelerators, and scien- Composer Paola Prestini recently Veneto di Scienze, Lettere ed Arti in the tific equations throughout. worked with Livio on a contemporary clas- Palazzo Loredan in Venice, Italy. Even German artist Tim Otto Roth created sical multimedia composition that mixes artists of different mediums have drawn two pieces incorporating light and sound an orchestral arrangement, vocalists, spo- inspiration from the telescope. that he based on Hubble’s investigation of ken word, and film — all to connect Choreographer Liz Lerman, once the the universe. His From the Distant Past (see human life to the lives of stars. (The col- recipient of a MacArthur “genius grant,” p. 55)WorldMags.net showed at the American Museum of laboration also includes a librettist, Royce WWW.ASTRONOMY.COM 53 Vavrek, and filmmaker Carmen Kordas.) The Hubble Cantata “fuses the story of the WorldMags.netstruggle associated with human life with the continuous cosmic battle that stars have to conduct against the universal force of gravity,” says Prestini. To commemorate Hubble’s “The structure of the work includes 100,000th orbit, astrono- mers released this image of movements and songs by the soloist, with a nebula near star cluster interjecting interludes that include the NGC 2074. NASA/ESA/M. LIVIO STSCI choir and an electronic tapestry made of [Livio’s] voice, imagined space sounds, plus the improvising of a very special violin soloist,” she adds. “The Hubble images appear during the interludes and take on a life of their own: They contort, grow, and fuse with physical life — reminding us of where life originated and where we might be all headed.” The Hubble Cantata debuted July 2013 and was performed again in November of that year. The collaboration is expanding the cantata, says Prestini, and the full- length version should be complete for the telescope’s 25th anniversary. While these examples incorporate the beauty of Hubble photographs, artistic messages, and science, the telescope’s cos- mic imagery also has been used in more commercial instances, like album covers, stamps, and clothing — because, heck, why FROM THE CLASSROOM TO POP CULTURE not wear a dress, swimsuit, or tie adorned Editor’s note: The Hubble Space Telescope has with Hubble images? catapulted few people into pop culture as fast Hanny van Arkel as Hanny van Arkel. So, invited was a Dutch Astronomy schoolteacher Hubble house calls the Dutch schoolteacher to tell her story here. prior to discov- But it’s not just about the images. Another ering her voor- major reason the telescope has had such Back in 2007, I signed up for the online citi- werp (Dutch for an impact is the “human involvement in zen science project Galaxy Zoo. Chris “object”). The Lintott had invited the public to help him media frenzy car- the servicing of Hubble over the years,” classify galaxies acquired with the Sloan ried her into the says Sembach. “It’s like sending a doc- Digital Sky Survey using a home computer heart of pop cul- tor on a house call. The telescope is sick; ture. HANNY VAN ARKEL interface. I had heard about this through somebody goes up to fix it.” Queen guitarist and astrophysicist Brian This month, Hubble turns 25, and luck May, who mentioned it on his website. isn’t what got the telescope to this point. That my passion for music would one day lead me to become a somewhat well- Scientists and engineers planned the mis- known amateur astronomer was some- sion well: place the telescope into near- thing I never could have guessed. Earth orbit, at a distance where the space In one of the pictures, I spotted a shuttle can reach it, and then have astro- remarkable looking blotch. I sent Lintott an nauts service it. During the five servicing email to ask what it was. Lintott then missions, astronauts have upgraded the invited me on the team to investigate electronics, replaced the telescope’s gyro- using follow-up images taken with Hubble. I certainly learned a lot — not only about scopes (which are crucial for pointing the the object, but about the process, too. observatory at celestial targets), and Meanwhile, the press got interested and I installed new scientific instruments. became a spokesperson, giving lectures Humans have essentially created a new across the world. observatory during each servicing mission, There’s also a comic out about my story, says Sembach. And that, he adds, “really and Lintott and May mention Hanny’s In 2007, van Arkel discovered this strange helps to keep it at the cutting edge of what Voorwerp (Hanny’s object) in their latest object (now classified as a ionization book. I am grateful for these experiences, echo) near the spiral galaxy IC 2497. Since scientists are working on. It helps it to then, astronomers have discovered 19 similar and I feel fortunate to be able to tell the actually push that edge.” objects. NASA/ESA/W. KEEL UNIVERSITY OF ALABAMA/THE GALAXY world that it is a lot of fun to be an amateur ZOO TEAM It also helps that humans — including astronomer. — Hanny van Arkel WorldMags.net the public — got involved to fight a vocal 54 ASTRONOMY • APRIL 2015 public battle to convince NASA to send up the final servicing mission. (For more on this, see “Saving Hubble” WorldMags.neton p. 44.) The astronomical culture In addition to Hubble’s tremendous impact on the public’s interest in science, the project has helped drive research and collaboration in the professional astron- omy community. Just a quick look at sta- tistics compiled by the American Institute of Physics shows a drastic increase in the number of students studying astronomy over the past three decades. WWW.IMACHINATION.NET/ PROJECTS IMACHINATION ROTH, OTTO TIM DISTANTPAST Artist Tim Otto Roth’s From the Distant Past translates spectra of distant objects that Hubble captured In the mid-1980s, there were some 700 into green animated laser projections on prominent facades in public spaces, as for instance at the students enrolled in U.S. graduate astron- Maryland Science Center in Baltimore in autumn 2011. omy programs; by 2012, the number was up to roughly 1,100. Three decades ago, universities awarded between 70 and 80 back its incredible images and contributing undergoing the peer review process to doctorates per year; in 2012, the number to major discoveries are now early-career obtain telescope time, “the panelists who had doubled to about 150. professors or postdoctoral researchers. review especially larger proposals tend to On average, some 40 doctoral research “Astronomy departments have grown, favor groups who propose and promise that projects each year are based on Hubble and, equally important, physics depart- they will make the data available immedi- data, says Sembach. “The pool of postdoc- ments have been adding astronomers to ately,” he adds. Future projects, like the toral fellows in astronomy is now two or their faculty,” Urry says. The statistics are Large Synoptic Survey Telescope, set to three times bigger than it was just 20 years even more telling when looking at under- come online within a decade, will follow ago,” says Meg Urry, the current president graduate degrees: In the mid-1980s, this trend and make all data available of the American Astronomical Society. The about 140 students earned a immediately. students who were in their formative edu- bachelor’s degree in cational years — elementary, middle, and astronomy, but in A long life high school — when Hubble began sending 2012, two and a half While other space times as many observatories have graduates earned contributed to an astronomy major astro- bachelor’s. nomical dis- Hubble also coveries, none has influenced has remained how and when operational astronomy proj- for as long ects release their as Hubble. In data. When that time, it has For Hubble’s 20th anniversary, the Robert Williams, European Space Agency conducted a clearly ingrained then director of Hubble Pop Culture Contest. ESA itself in the minds STScI, and his team of the public, popular collected the individual culture, and the media. frames for the Hubble Deep Williams credits many of Field (HDF) composite in 1995, they pro- Hubble’s later years to the public who cessed and released the data in two weeks. fought alongside astronomers to save it a Scientists who use federally funded astro- decade ago. “The telescope has been work- nomical instruments have one year to keep ing perfectly since,” he says. Scientists the data to themselves for analysis. But the expect to operate Hubble until at least HDF scientists “thought for a facility like 2020, but “you never know how long it will Hubble, which was very expensive and paid last,” says Williams. “Space is a hostile for by the public, that we owed it to the environment.” community, both the professional and the Whenever that fateful day arrives, says public, to make the important HDF data Sembach, “A lot of us are going to feel like A Hubble image of the Hourglass Nebula appears available immediately,” says Williams. we’ve lost a family member.” It’s likely sci- on the cover of the 2000 CD Binaural by the rock band Pearl Jam. California Guitar Trio’s 2010 CD, They helped change the culture of entists involved in the mission won’t be the Andromeda, uses a Hubble image on its cover. astronomical observing. And now, when only ones to feel the loss. LEARN HOW SCIENTISTS PRODUCE HUBBLE’S ICONICWorldMags.net IMAGERY AT www.Astronomy.com/toc. WWW.ASTRONOMY.COM 55 WorldMags.net

WorldMags.net WorldMags.netUNLOCKING THE HUBBLE VAULT 25 YEARS of dazzling images The space telescope’s extraordinary vision has revealed star clusters, nebulae, and galaxies in detail no one could have imagined. by Richard Talcott

he calendar says a quarter-century has passed since the space shuttle Discovery lifted its cargo of dreams into low Earth orbit. Elevated above the distorting effects of our planet’s turbulent atmosphere, the school-bus- sized Hubble Space Telescope promised clearer views of the night sky than humans had ever witnessed. Sure there were glitches, most notably a primary mirror ground to the wrong shape and equipment that inevitably wore down under the harsh conditions of space, but NASA anticipated problems. A series of five servicing Tmissions not only restored Hubble to its original specifications but also rebuilt the observatory into a 21st-century science machine. With new cameras and spectrographs operating nearly 24/7, much of what Hubble does today could hardly be dreamed of in 1990. Just how much has Hubble accomplished during its 3-billion- mile (5 billion kilometers) journey around Earth? Scientists have published more than 12,000 papers in peer-reviewed journals using Hubble data. And not all of that science has come from new observations — researchers routinely plumb the Hubble archives, which currently hold more than 100 terabytes of data. But to most of us, Hubble’s greatest contribution has been its The Eagle Nebula. Scientists recently tar- images, which span the cosmos from next door (the Moon) to the geted one of Hubble’s universe’s earliest galaxies. In its 25 years, Hubble has snapped iconic subjects — the more than 1 million images of nearly 40,000 objects. The 28 we Eagle Nebula’s (M16) show here are the cream of the crop, though, truth be told, it would “Pillars of Creation” — with the space tele- be easy to pick an entirely different set and say the same thing. scope’s Wide Field Camera 3 (WFC3). Senior Editor Richard Talcott has covered Hubble’s trials and triumphs Inset: In the near- throughout the observatory’s 25 years in space. infrared, WFC3 shows the pillars silhouetted against background stars. NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA WorldMags.net WWW.ASTRONOMY.COM 57 WorldMags.net

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1. Abell 1689. Scientists estimate that Abell 1689 contains thousands of galaxies and holds up to 500 trillion times the Sun’s mass. All that matter warps surrounding space, distorting and magnifying light 3 from more distant galaxies. NASA/ESA/N. BENITEZ AND H. FORD JHU/T. BROADHURST THE HEBREW UNIVERSITY/M. CLAMPIN AND G. HARTIG STSCI/G. ILLINGWORTH UCSC/LO/THE ACS SCIENCE TEAM 3. The Cone Nebula. Massive stars off the top of this image emit ultraviolet radiation that erodes the 2. NGC 1300. Like the Milky Way, NGC 1300 is a edges of the Cone Nebula (NGC 2264). This process barred spiral galaxy that spans a bit more than liberates gas, and the ultraviolet light then excites 100,000 light-years. In such galaxies, spiral arms this hydrogen-rich material, causing it to glow with a wind out from the ends of a star-filled bar. NASA/ESA/ characteristic red color. NASA/ESA/H. FORD JHU/G. ILLINGWORTH THE HUBBLE HERITAGE TEAM STSWorldMags.netCI/AURA UCSC/LO/M. CLAMPIN AND G. HARTIG STSCI/THE ACS SCIENCE TEAM 58 ASTRONOMY • APRIL 2015 WorldMags.net

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4. The Horsehead Nebula. In visible light, this cloud of cold gas and dust appears dark against bright emission. But at the near-infrared wavelengths captured here, the nebula glows as its gas reradiates energy it absorbs from embedded young stars. ALL IMAGES THIS PAGE: NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA

5. V838 Monocerotis. In January 2002, the star seen at center flared to become one of our galaxy’s most luminous. This view from two years later cap- tures surrounding dust shells lit up by the eruption.

6. Omega Centauri. The Milky Way’s largest glob- ular star cluster, Omega Centauri (NGC 5139), holds 10 million stars in a sphere some 150 light-years across.

7. Supernova remnant N49. Hubble lets astrono- mers probe objects in nearby galaxies with a clarity previously impossible. Case in point: these splintered remains of a massive star that exploded 160,000 7 light-years from Earth in the Large Magellanic Cloud.WorldMags.net WWW.ASTRONOMY.COM 59 WorldMags.net

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1. The Carina Nebula. One of the Milky Way’s pre- mier star factories is the Carina Nebula (NGC 3372), which came to life about 3 million years ago when stars first ignited in a cloud of molecular hydrogen. Ultraviolet radiation and stellar winds from these stars carved out an expanding bubble of hot gas. Now, as this gas plows into surrounding walls of cold hydrogen, it is triggering a second wave of star birth. NASA/ESA/N. SMITH UCB/THE HUBBLE HERITAGE TEAM STSCI/AURA

2. The Cigar Galaxy. Fiery plumes of glowing hydrogen erupt from the central regions of this star- burst galaxy, also known as M82. Colliding gas clouds there give birth to stars, many of which reside in giant clusters, at a rate 10 times higher than in the entire Milky Way. NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA

2 WorldMags.net 60 ASTRONOMY • APRIL 2015 3. Arp 273. When spiral galaxies interact, tidal forc- WorldMags.netes warp their normal stately shapes. In this pair, the spiral arms of the top galaxy have been stretched and distorted. The bright blue star clusters at top reflect a firestorm of star formation initiated by the encounter. NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA

4. Saturn. Although Hubble spends most of its time viewing distant stars, nebulae, and galaxies, it devotes quality time to the solar system. Saturn’s cloud tops and rings are a frequent target. During its 25 years in space, Hubble has tracked the planet through 85 per- cent of its orbit. NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA

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1. The Helix Nebula. The intricate shapes of planetary nebulae, like the Helix Nebula (NGC 7293) and the others on this spread, make them among Hubble’s most dramatic subjects. These objects are the death throes of Sun-like stars, which puff off their outer layers — often several times — when they exhaust their nuclear fuel. NASA/NOAO/ESA/THE HUBBLE HELIX NEBULA TEAM/M. MEIXNER STSCI/T. A. RECTOR NRAO 2 3 2. The Spirograph Nebula. The progenitor star of the Spirograph Nebula (IC 418) cast off its outer lay- ers multiple times, filling the planetary’s interior with lots of gas. A white dwarf stands out at the heart of the nebula; such stars energize the nebula’s gas and cause it to glow. NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA

3. The . Astronomers nicknamed this planetary the Eskimo Nebula (NGC 2392) because it looks like a human face surrounded by a parka hood through earthbound telescopes. Hubble resolves the parka’s “fur” into myriad streamers of gas that resem- ble giant comets pointing toward the nebula’s center. NASA/A. FRUCHTER AND THE ERO TEAM STSCI

4. The Retina Nebula. An irregular web of dark dust lanes crisscrosses the central regions of the Retina Nebula (IC 4406). Each of the lanes is roughly twice the size of Pluto’s orbit around the Sun. This image has been color-coded so hydrogen appears green, oxygen blue, and nitrogen red. NASA/ESA/THE 4 5 HUBBLE HERITAGE TEAM STSCI/AURA

5. The Red Rectangle. This object hasn’t quite reached the planetary nebula stage. Although the dying star at center has ejected much of its outer atmosphere, it has not yet evolved into a white dwarf. Cool dust, which forms the unique features that look like the rungs on a ladder, reflects starlight. NASA/ESA/ H. VAN WINCKEL CATHOLIC UNIVERSITY OF LEUVEN/M. COHEN UCB

6. The Blinking Planetary. Through amateur telescopes, the Blinking Planetary’s (NGC 6826) cen- tral white dwarf is so bright that it overwhelms the nebula when viewed directly; the nebula “blinks on” when looking to the side. Hubble shows both clearly, along with two red patches near the nebula’s edge. NASA/ESA/B. BALICK AND J. ALEXANDER U. OF WASHINGTON/A. HAJIAN U.S. NAVAL OBSERVATORY/Y. TERZIAN CORNELL U./M. PERINOTTO U. OF FLORENCE/P. PATRIARCHI ARCETRI OBSERVATORY 67

7. The Cat’s Eye Nebula. Mass loss in aging stars doesn’t always follow one pattern. The Cat’s Eye Nebula (NGC 6543) shows at least 11 concentric shells surrounding its central white dwarf, each one ejected at 1,500-year intervals. But about 1,000 years ago, the process changed and forged the bright irregular shells on the inside. NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA

8. The Ant Nebula. Astronomers aren’t sure what causes the narrow “waist” that lies between the two glowing lobes of the Ant Nebula, so called for its resemblance to the common insect. Some suspect an unseen companion sweeps material out of this region, while others think magnetic fields do the job. NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA 8 WorldMags.net WWW.ASTRONOMY.COM 63 WorldMags.net

1. Star cluster NGC 602. The hot young stars in NGC 602 have carved out a cavity in a surrounding cloud of gas and dust located on the outskirts of the Milky Way’s satellite galaxy, the Small Magellanic Cloud. This image combines Hubble observations (shown as red, green, and blue) with X-ray (purple) and infrared (red) data. NASA/ESA/CXC AND THE U. OF POTSDAM/ 1 JPLCALTECH/STSCI

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2. The Veil Nebula. Some 5,000 to 10,000 years ago, our ancestors likely saw a massive star explode in the constellation Cygnus. The star’s tattered remains now span 3°, or roughly 75 light-years. This close-up Hubble image shows a tiny part of it, barely 1-light-year across, at the Veil Nebula’s northwestern edge. NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA

3. Arp 142. Tidal forces unleashed by the gravity of elliptical galaxy NGC 2937 (bottom) distort the previously normal spiral NGC 2936 just above it. The spiral’s arms and dark dust lanes now splay haphaz- ardly across that galaxy’s disturbed disk, while blue knots trace the sites of ongoing star formation. NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA 3 WorldMags.net 64 ASTRONOMY • APRIL 2015 WorldMags.net

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4. The Sombrero Galaxy. This giant spiral galaxy 5. Sharpless 2-106. This hourglass-shaped stellar 6. The Antennae. Galaxies NGC 4038 and NGC lies about 35 million light-years from Earth on the nursery spans 2 light-years and lies less than 1° from 4039 are merging. This cosmic collision is giving birth edge of the Virgo Cluster of galaxies. The Sombrero the Milky Way’s plane in the constellation Cygnus. The to billions of new stars, most of which belong to (M104) looks like a traditional Mexican hat because young star just below center (where the bluish lobes bright blue star clusters. The large yellowish globes at we view its dusty disk from just 6° north of the gal- come together) sculpts the surrounding nebula’s intri- upper right and lower left are the cores of the original axy’s equator. NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA cate shape. NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA galaxies. NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA

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The Orion Nebula. Hubble gives astronomers ringside seats to watch stars come to life in the Orion Nebula (M42). This dense cloud of gas, dust, and young stars lies just 1,500 light-years from Earth. The hottest, most massive stars already have emerged from their natal cocoons. NASA/ESA/M. ROBBERTO STSCI/ESA/ THE HUBBLE SPACE TELESCOPE ORION TREASURY PROJECT TEAM

TAKE IN-DEPTH TOURS OF SOME OF THESE IMAGESWorldMags.net AT www.Astronomy.com/toc. 66 ASTRONOMY • APRIL 2015 ExclusiveWorldMags.net podcasts from Astronomy magazine Superstars of Featured guests: Astronomy JEFF HESTER From the Big Bang to Big Brains: Life and the Universe Editor David J. Eicher interviews the world’s top scientists! GARIK ISRAELIAN Mixing Science and the Arts at the Starmus Festival Monthly hourlong conversations with the greatest minds in astronomy, covering cosmic beginnings, how life will end on Earth, Mars exploration, the search for extraterrestrial intelligence, and much more! ALAN STERN The Journey to Pluto and Why It’s Still a Planet

LISTEN NOW AT www.Astronomy.com/superstars

ESOL. CALÇADA PLUTO SURFACE; ESO BACKGROUND; ESA/MPS FOR OSIRIS TEAM MARS

Brought to you by WorldMags.net P24994 ASKASTR0WorldMags.netAstronomy’s experts from around the globe answer your cosmic questions. ALIEN AIRWAVES Q: THE SETI INSTITUTE IS AFTER ALIEN SIGNALS. ASSUMING ANOTHER WORLD IS BEAMING A 1-MILLION-WATT RADIO SIGNAL IN OUR DIRECTION, HOW FAR AWAY CAN THAT SOURCE BE BEFORE THE SIGNAL IS LOST IN INTERGALACTIC NOISE? The Chinese spacecraft Chang’e 5-T1 returned this image of Earth and the farside of the Moon as part of an engineering test trip for a future lunar Don Schmidt, Oro Valley, Arizona sample return mission. CHINA NATIONAL SPACE ADMINISTRATION

Space beacon A: Many people assume that Still, even if you had a honking, A: The Moon keeps its familiar radio signals only can travel a million-watt narrowband trans- face pointed toward Earth, but 1920 1920 limited distance before they mitter broadcasting in all direc- there are two stable positions. First commercial radio broadcast are, like the Robinson family, tions and located one-tenth of a It also would be stable if its Gamma Crucis lost in space. They believe light-year away, contemporary farside faced our planet. At the there’s a range beyond which SETI experiments wouldn’t be present time, there are small 1930 transmissions reach an inten- able to find it. And that’s not impacts that must kick the 1933 President Regulus sity lower than background even as far as Alpha Centauri! Moon away from perfect ori- Roosevelt’s first static and therefore become On the other hand, suppose entation. When that happens, “fireside chat” thoroughly undetectable. that megawatt transmitter it oscillates about its stable 1940 It’s not true. Yes, radio sig- were mounted on an antenna orientation in two ways. The nals diminish in intensity with the size of the Arecibo radio Moon can rock back and forth Aldebaran the square of the distance just telescope in Puerto Rico, which in the east-west direction. This 1950 as light does (after all, radio is 1,000 feet (300 meters) in oscillation takes 1,056 days, or 1952 and light are both electromag- diameter. Focused in our direc- 2.9 years. The lunar poles also NBC’s Today Delta Leonis Show premieres netic waves). But nonetheless, if tion, the intensity of the signal can become unstable, causing you have a large enough would be increased by more a 75-year wobble. Earth’s poles 1960 antenna and adequate observ- than 10 million times. It would experience a similar effect Castor ing time, you can tease out a be detectable by our current called Chandler wobble. signal no matter how far the SETI experiments at a range of The Moon also experiences 1969 transmitter. The background nearly 300 light-years. There tidal distortion from Earth’s Apollo 11 Capella lands on 1970 noise simply averages out with are about a million star sys- gravitational pull. the Moon time, while the signal relent- tems closer than that. Giant basin-forming im- Arcturus lessly builds up. Astrophotogra- It comes down to this: SETI pacts could have reoriented 1980 Pollux phers know this well. With a scientists are betting that extra- the Moon early in its lifetime. Cosmos 1980 premieres big enough telescope and a long terrestrials are either focusing a Such large impacts would have enough exposure, they can suc- signal in our direction or wield left the Moon rocking by large Vega Radio and TV waves cessfully image objects at great transmitters far more powerful amounts until the friction 1990 distances. than our own. damped the motion. These The best SETI experiments Seth Shostak basin-forming impacts hap- SETI Institute Altair can detect narrowband radio pened when the Moon was signals — those confined to a Mountain View, California much closer to Earth. 2000 2001 Procyon tiny range of frequencies — at a The most obvious effect of a Terrorists attack -25 World Trade Sirius sensitivity level of 10 watts 180° rotation would be to face Center per square meter with a few Q: WHAT WOULD HAPPEN the brighter farside highlands Proxima Centauri minutes of “exposure time.” IF THE MOON WERE SUD- toward Earth at Full Moon, 2015 That’s 0.1 trillionth of a tril- DENLY TURNED SO ITS FAR- causing it to appear about 30 : ROEN KELLY lionth of a watt falling on each SIDE NOW FACED EARTH? percent brighter. It is unclear Any response we might make to square meter of the antenna, Dave Gottschalk how much this would affect the

alien signals only would accom- ASTRONOMY which is stunningly sensitive. Crystal Lake, Illinois tendency of dogs to howl at the pany the TV, radio, and radar signals that have broadcasted our existence for decades. WorldMags.net WorldMags.net

Moon, etc. Would this have an appreciable effect on Earth’s energy budget? I can’t say pre- cisely, but the Full Moon is about two-millionths as bright as the Sun and is only visible during part of the month, so the effect would certainly be less than one millionth of the Sun’s brightness. The Moon is The Moon owes its black sky to not having an atmosphere that can scatter photons. The sky is so dark that an not, contrary to some reports, astronaut hiding from sunlight in a shadow would be able to see the stars. NASA a significant source of lighting (about one lux, vs. 50 to 500 years, or 300 times shorter — a By that time, the Milky Way is some 100 times thinner lux for indoor lighting), but it’s cosmic blink of an eye. will have ceased star production, than our planet’s, there’s still better than nothing during So, do M dwarfs, as small as and what remains will be a large enough of it to cause the sky to harvest time. one-tenth the mass of the Sun, population of low-mass blue appear a deep grayish blue, and Gregory Neumann last 300 times longer, or 3 tril- stars and a menagerie of fading if martian dust is whipped up Goddard Space Flight Center lion years? In fact, they prob- compact objects: brown dwarfs, by the tenuous surface winds, Greenbelt, Maryland ably live even longer than that. white dwarfs, and neutron stars. the sky turns a salmon pink. Stars like the Sun only fuse the Eventually, even M dwarfs will On the Moon, there is no hydrogen present in their cores run out of hydrogen fuel and atmosphere, so there’s nothing Q: ASTRONOMERS KNOW — about 10 percent of the total become helium white dwarfs, to scatter photons, even from a THE FATE OF SUN-LIKE AND supply — before they evolve slowly cooling with time. The brilliant source like the Sun. In MASSIVE STARS, BUT WHAT into red giant stars. universe will become dark, ex- fact, if you could find a deep ABOUT THE MAJORITY OF M dwarfs, which have dense cept for the rare brilliant super- enough shadow that shields STARS — THE M-CLASS RED interiors, transfer heat from nova driven by a white dwarf- your eyes from direct sunlight DWARFS? WILL THEY ALSO core to surface through con- white dwarf collision. Low-mass as well as light reflected off the BECOME GIANTS OR JUST vection, the same process that M dwarfs are likely to be the last surrounding terrain, you’d be FLICKER OUT? causes a boiling pot of water to representatives of the universe’s able to see the stars! Mike Hardin roil. The mixing motion of current stellarifous era. There’s another factor that San Antonio convection allows nearly all of Adam Burgasser plays into images taken by the the hydrogen in an M dwarf to University of California, San Diego Apollo astronauts from the A: The lifetime of a star is the make it through the core and Moon’s surface, and that is the period during which it stably fuse into helium, effectively limited dynamic range of the fuses hydrogen in its core and doubling its lifetime. Accord- Q: HOW IS IT THAT IN SPACE, film used to record their sur- aligns with the main sequence ing to the calculations, the DESPITE THE SUN'S PRES- face activities. The sunlight is on color-magnitude diagrams. smallest-mass star, about 8 ENCE, THE SURROUNDINGS so overwhelmingly bright that, The length of this period percent the mass of the Sun, LOOK BLACK? APOLLO PHO- in order to record highlights, depends on a star’s hydrogen could last over 10 trillion TOS SHOW A BLACK SKY, the shadows and sky had to be supply and the rate at which years, or 1,000 times longer EVEN WITH STRONG SUN- heavily underexposed. hydrogen is turned into helium than the current age of the LIGHT ON THE SURFACE. Geoff Chester via fusion. universe. Percival Hanley U.S. Naval Observatory Like gas-guzzling SUVs, Even when they deplete Basseterre, St. Kitts, West Indies Washington, D.C. more massive stars may con- their hydrogen, most M dwarfs tain more hydrogen fuel, but still won’t become red giants; A: The answer to this ques- they use it up much faster instead, they’ll evolve into tion can be summed up in two Send us your because they are more lumi- blue dwarfs. All fusing stars words: no atmosphere. questions nous (a star’s luminosity is become more luminous over Planetary atmospheres cause Send your astronomy equal to the rate of fusion time as the depletion of hydro- bright light to scatter. Atoms, questions via email to energy production). gen speeds up their nuclear molecules, and dust interact [email protected], As a result, the lifetimes reactions. A star adjusts to with photons, causing them to or write to Ask Astro, of more massive stars are this increased power output by diffuse through increasingly P. O. Box 1612, Waukesha, shorter. While astronomers either boosting its surface area dense layers as they near a WI 53187. Be sure to tell us expect our Sun to have a full (becoming a giant) or getting body’s surface. On Earth, our your full name and where hydrogen-fusing lifespan of hotter (turning blue). M dwarfs atmosphere preferentially scat- you live. Unfortunately, we about 10 billion years, a star take the latter route, or rather ters blue light, so the daytime cannot answer all questions 10 times as massive as the Sun they will — several trillion sky appears blue. And although submitted. lasts only about 30 million years from now. Mars has an atmosphere that WorldMags.net WWW.ASTRONOMY.COM 69 COSMICIMAGING FROM OUR INBOX BY ADAMWorldMags.net BLOCK Corrections On p. 55 of the September issue, the upper-right photo was cap- tioned as Ireland. It was, instead, London. — Astronomy Editors When rejection On p. 16 of the December issue, under “Cosmic World,” Brandon Smith was listed as a congressman from Kentucky. He is actually a Kentucky state senator. — Astronomy Editors is good, part 1 We welcome your comments at Letters, P. O. Box 1612, Astronomy Waukesha, WI 53187; or email to [email protected]. Please The genesis for this column Observatory as part of an include your name, city, state, and country. Letters may be edited for comes from my experience observing program I developed space and clarity. with image processing. When that ran from 1996 to 2005, I I began digital photography in spent countless hours manually the early 1990s, most amateurs removing these “vermin” from counts (brightness units), then at each pixel for a strange plan- would take pictures totaling a pictures while guests often fell in the first exposure I might etary nebula called WeBo 1. few minutes of exposure and asleep behind me. After all, measure 943 counts, and in the Closer inspection shows some add them together. These gray- guests expected to go home next exposure it may be 1,078 bright blips in the single expo- scale images far exceeded what with pretty pictures by the end counts. So, if I take enough sure that are not in the average could be accomplished with of a night! As I used Photo- exposures and average them image. Most of these are cosmic film in the same period of time. shop’s “Clone” tool (and later together, the resulting value rays, which represent values we More experienced imagers the “Healing” brush), visitors will be a good approximation of do not want to include when combined RGB-filtered images. often would be concerned that I the intensity. Unfortunately, we calculating the mean of a set of However, the exposure times might erase a galaxy rather never know what this average measurements. and number of frames collected than a cosmic ray. value should be beforehand. In Image #3, a cosmic ray (a remained small. Interestingly, Nowadays, guests who visit That’s why we need to make white pixel) was part of the imagers often would buy larger me at the Mount Lemmon many measurements to find the fifth measurement. It contami- instruments and more sensitive SkyCenter have a much better average (or mean) value. nated the resulting mean value cameras before increasing the experience joining me in the Image #1 graphically shows for that pixel, and it degrades exposure duration and number. processing of images. The an analog to these fluctuations. the image quality. What we Later, the seemingly esoteric tedium of removing cosmic In Photoshop, I took a simple want to do is identify such out- practices of image processing, rays is a thing of the past. In column of six pixels that dis- lying values and not use them done by professional astrono- order to understand how this play a low-contrast pattern (a when calculating the mean. mers, trickled down to the happened, you must under- mere two shades of gray) and This means that for the 20 amateur realm through the stand the nature of light and applied “Add Noise” to imitate values measured at a particular inclusion of utilities in popular the power of statistics. Every fluctuations. After generating pixel in the WeBo 1 image, if a software. One such area is the time we take an exposure, each 11 pseudo-measurements, I cosmic ray activated that pixel, statistical analysis of data, pixel of the detector is making then created the column labeled we should reject that value and which permits the identifica- a measurement. When I take a “Average.” Note that you would calculate the mean from the tion and management of 20-minute exposure, the pic- be hard-pressed to identify the remaining 19 values. This unwanted sources of noise and ture that results has a single expected pattern from any indi- greatly improves the image signals. Before imaging soft- value for each pixel. vidual row. Only after averag- quality and eliminates transient ware included these tools, it Because of the particle ing the results does it start to signals in our images. was extremely difficult to elim- nature of light, the number of approximate the “Ideal” form. In my next column, we will inate satellite trails, defects on photons a CCD chip detects Image #2 shows a real-world look at how to measure the chips, and cosmic rays. fluctuates with each exposure. example. The left side is a single average amount of fluctuation When I accommodated visi- If the average intensity of a star measurement, and the right and then identify these outlying tors at Kitt Peak National on a specific pixel is 1,000 half is the average of 20 values values.

Image #1. Each column is a picture of a low-contrast gray Image #2. The left image is a single 30-minute exposure of Image #3. Identical to the first image, but here a white object. Because of the random fluctuations in values, we planetary nebula WeBo 1 through a Hydrogen-alpha filter. square, representing a cosmic-ray strike, degrades the can’t discern the pattern until we know the average value. The right image is the average of 20 exposures (for the image quality by affecting the mean value at that pixel. To The author has shown the ideal value in the right column. mean value at each pixel). Note how it reveals more of the view an online version of WeBo 1, go to http://skycenter. ALL IMAGES: ADAM BLOCK/MOUNT LEMMON SKYCENTER/UNIVERSITY OF ARIZONA galaxy’s structures. arizona.edu/gallery/nebulae/WeBo1. BROWSE THE “COSMIC IMAGING” ARCHIVE AND WorldMags.netFIND VIDEO TUTORIALS AT www.Astronomy.com/Block. 70 ASTRONOMY • APRIL 2015 NEW Attention, manufacturers: To submit a product PRODUCTSWorldMags.netfor this page, email [email protected].

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This past autumn, a unique reminiscent of when, in when the two were approxi- Hubble event in solar system history 1994, the 21 pieces of Comet mately 149 million miles (240 took place when Comet Siding Shoemaker-Levy 9’s nucleus million km) from Earth. captures Spring (C/2013 A1) passed with- bombarded Jupiter’s cloud tops. Astronomers assembled the in about 87,000 miles (140,000 The Hubble Space Telescope two images to accurately depict a unique kilometers) of Mars. Such a captured a splendid composite the angular separation between close encounter had not been image of Comet Siding Spring Mars and the comet at closest moment observed before, and it was and Mars on October 19, 2014, approach. WorldMags.net 74 ASTRONOMY • APRIL 2015 WorldMags.net ONE HALF OF THIS THE OTHER WAS TAKEN IMAGE WAS TAKEN WITH A SCOPE THAT WITH A $2,499 ESPRIT COST TWICE AS MUCH

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Few night-sky scenes can rival background stars, which slip Mercury becomes a morn- Eighteenth-century French the proximity of two bright lower in the west each evening, ing object during the second astronomer Nicolas Louis de planets. And June brings one to Venus is the one on the march. half of June. The innermost Lacaille created the constella- remember when Venus encoun- It travels from eastern Gemini planet reaches greatest western tion to commemorate the air ters Jupiter in the northwestern across Cancer and into western elongation June 24, when it lies pump’s invention a century ear- sky after sunset. Leo during June. In contrast, 22° from the Sun and stands lier. He first depicted it as a sim- Venus, the brighter of the Jupiter drifts slowly from east- nearly 10° high in the east- ple single-cylinder device on a two, has adorned the evening ern Cancer to just across the northeast an hour before sun- planisphere he created in 1756. sky since the start of 2015. It border into Leo. rise. Mercury then shines at Lacaille originally named has been pulling away from the Jupiter is always worth a magnitude 0.5 and appears the constellation la Machine Sun ever since and, on June 6, look through a telescope. This against the Hyades star cluster Pneumatique, but he later reaches greatest elongation. It month, its 34"-diameter disk in Taurus. Through a telescope, changed it to Antlia Pneu- then lies 45° east of our star should show plenty of detail. the world appears 8" across and matica. Later astronomers and appears 20° above the Pay particular attention to the about one-third lit. shortened it to Antlia. horizon at the end of twilight. alternating series of light zones Mars remains out of sight NGC 2997 is a spiral galaxy Venus continues to brighten all and darker belts. Also keep an all month, passing behind the located in western Antlia at a month, however, climbing from eye on the planet’s four bright Sun from our point of view distance of roughly 50 million magnitude –4.4 to –4.6. moons, which change positions June 14. It will return to view light-years. Glowing at 10th As Venus’ orbital motion from night to night and often before dawn in August. magnitude, it’s not hard to spot carries it closer to Earth, the hour to hour. in a 20-centimeter telescope on inner planet grows larger while As if Venus and Jupiter The starry sky a dark night. its phase diminishes. These weren’t enough, the evening sky In my early days in the plane- Although several fainter changes show up through any boasts a third planetary won- tarium profession, I often galaxies call Antlia home, I telescope. If you target the der. Saturn reached opposition wowed audiences by showing want to highlight two nice dou- world June 1, you’ll see a and peak visibility in late May, them a gorgeous image of the ble stars. Delta (δ) Antliae has 22"-diameter disk that’s a touch and June sees the ringed planet galaxy NGC 2997 taken by magnitude 5.5 and 9.8 compo- over half-lit. By the 30th, Venus high in the eastern sky after renowned astrophotographer nents separated by a relatively appears 32" across and barely darkness falls. It resides among David Malin. This image easy 11". And Zeta1 (ζ1) Ant is one-third lit. the background stars of eastern helped introduce many astron- the western member of a pair Although Venus gleams Libra, close to that constella- omy enthusiasts to the spiral’s of 6th-magnitude stars near about 10 times brighter than tion’s border with Scorpius. rather inconspicuous host con- Antlia’s western border with Jupiter, the solar system’s larg- Saturn shines at magnitude 0.1, stellation, Antlia the Air Pump. Pyxis. Focus in on Zeta1 and est planet outshines every star. a full magnitude brighter than Antlia appears high in the you’ll discover it is an attractive You can find Jupiter to Venus’ the Scorpion’s brightest star, west after darkness falls these double whose stars glow at upper right. About 20° separate Antares, which lies roughly June evenings. It lies immedi- magnitude 6.2 and 6.8 across the two June 1, but the gap 10° to the planet’s southeast. ately south of Hydra the Water a divide of 8". closes significantly as the Don’t let the beautiful pair Snake, but it is easiest to find No matter how hard you try, month progresses. On the 30th, of planets in the northwest keep by looking approximately mid- you won’t find stars labeled the divide has dropped to 0.5° you from pointing your tele- way between Sirius, the night Beta (β) or Gamma (γ) in this — the Full Moon’s apparent scope toward Saturn. The plan- sky’s brightest star, and Spica constellation. When the diameter. The scene takes on et’s disk measures 18" across at in Virgo. Although Antlia’s International Astronomical added allure the evenings of midmonth while the rings span brightest stars glow only at 4th Union defined the constellation June 20 and 21 when the wax- 42" and tilt 24° to our line of magnitude, the constellation’s borders in 1928, Beta and ing crescent Moon slides by. sight. The rings’ angle makes it roughly triangular shape shows Gamma ended up in neighbor- If you compare the positions relatively easy to see the Cassini up under a dark sky. ing Hydra. Although Delta, of Venus and Jupiter to the Division, the dark gap that sep- Many constellations bear also cataloged as SAO 178771, horizon each night, you’d think arates the outer A ring from the little resemblance to the object lurks just over the border, Beta that Jupiter is the one making brighter B ring, even through or creature they’re named after, (SAO 202901) lies several the big move. But relative to the small instruments.WorldMags.netand Antlia is no exception. degrees inside Hydra. STAR S

DOME

TUCANA

RETICULUM WorldMags.netDORADO SMC

THE ALLSKY MAP 104 NGC

SHOWS HOW THE LMC

PICTOR SKY LOOKS AT: HYDRUS 9 P.M. June 1

8 P.M. June 15

2070

OCTANS

P.M. Canopus 7 June 30 NGC MENSA

Planets are shown _ VOLANS

at midmonth CHAMAELEON

SCP

2516 PAVO CARINA

NGC

APUS

MAJOR

PUPPIS CANIS

AUSTRALE

TRIANGULUM

NGC 3372 NGC

ESCOPIUM

2477

NGC

EL

NGC 6397 NGC ARA

CIRCINUS

_

NGC 4755 NGC

b

VELA

`

_

CRUX `

a CENTAURUS

NORMA PYXIS

5139 ANTLIA

NGC NGC

5128

NGC 6231 NGC M6

NGC

SCORPIUS

LUPUS

Antares

_ M4

Alphard

W M83

CORVUS

_

CRATER LIBRA SEXTANS Saturn HYDRA

M104 Spica _

CANCER VIRGO M5

ic) (eclipt he Sun _ Path of t Regulus M65 M66 SERPENS CAPUT Jupiter ` Venus Denebola

LEO a _ M64 Arcturus

NGP CORONA BOREALIS COMA BERENICES MAGNITUDES BOÖTES Sirius Open cluster 0.0 Globular cluster CANES VENATICI 1.0 Diffuse nebula 2.0 M51 3.0 Planetary nebula 4.0 5.0 Galaxy URSA MAJOR

WorldMags.net N WorldMags.net HOW TO USE THIS MAP: This map portrays the sky as seen near 30° south latitude. JUNE 2015 Located inside the border are the four directions: north, south, east, and

west. To find stars, hold the map Calendar of events INDUS overhead and orient it so a direction label matches the 1 The Moon passes 1.9° north of 15 The Moon passes 0.04° south of direction you’re facing. Saturn, 20h UT Mercury, 2 UT The stars above the map’s horizon now 2 Full Moon occurs at 16h19m UT The Moon passes 1.0° north of match what’s Aldebaran, 12h UT 6 Venus is at greatest eastern in the sky. elongation (45°), 18h UT 16 New Moon occurs at 14h05m UT Asteroid Ceres is stationary, 20 The Moon passes 6° south of 22h UT Venus, 11h UT

9 The Moon passes 3° north of 21 The Moon passes 5° south of

EL T Neptune, 3h UT Jupiter, 0h UT

SAGITTARIUS Last Quarter Moon occurs at Winter solstice occurs at

AUSTRALIS CORONA 15h42m UT 16h38m UT

10 The Moon is at perigee 23 The Moon is at apogee M7 (369,711 kilometers from Earth), (404,132 kilometers from Earth),

4h44m UT 17h00m UT

M22 M6

M8 11 Mercury is stationary, 20h UT 24 Mercury passes 2° north of

Aldebaran, 8h UT M17 The Moon passes 0.5° south of

M20 Uranus, 20h UT First Quarter Moon occurs at SCUTUM 11h03m UT M11 12 Asteroid Pallas is at opposition,

M16 E 1h UT Mercury is at greatest western elongation (22°), 17h UT Neptune is stationary, 20h UT 29 The Moon passes 2° north of 14 Mars is in conjunction with the Saturn, 1h UT Sun, 16h UT

OPHIUCHUS

STAR COLORS: Stars’ true colors depend on surface temperature. Hot stars glow blue; slight- ly cooler ones, white; intermediate stars (like the Sun), yellow; followed M13 by orange and, ulti mately, red. Fainter stars can’t excite our eyes’

HERCULES color receptors, and so appear white without optical aid.

Illustrations by Astronomy: Roen Kelly

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