DO EXOPLANETS LISTEN TO THE MUSIC 2018 HAVE MOONS? p. 30 OF THE HEAVENS p. 46 BONUS! JANUARY 2018 Guide to the Night Sky

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THE LATEST NEWS ON • Neutron star merger detected • Seven Earth-sized planets

orbiting nearby star Two neutron stars merge in a kilonova, throwing out gravitational waves, • Mysteries of fast radio bursts gamma rays, and other forms of light. • Cassini’s last glory at Saturn www.Astronomy.com AND MORE p. 20

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ON THE COVER Astronomers recently observed gravitational waves from the long- 30 ago crash of two neutron stars. ROBIN DIENEL COURTESY OF THE CARNEGIE INSTITUTION CONTENTS FOR SCIENCE FEATURES

20 COVER STORY BONUS! 56 COLUMNS Top 10 space stories Astronomy’s 2018 Snapshots from Starmus The fourth Starmus Festival, Strange Universe 10 of 2017 Guide to the Night Sky BOB BERMAN Last year, we found a star with This handy four-page insert will a celebration of science and the seven Earth-sized planets, said keep you looking up all year. arts, took place in Trondheim, Observing Basics 64 goodbye to the Cassini mission, Norway, in June 2017. GLENN CHAPLE and watched a total solar eclipse DAVID J. EICHER race across America. LIZ KRUESI 44 Secret Sky 66 Ask Astro 60 STEPHEN JAMES O’MEARA 30 Celestial motion. Explore Scientific’s Binocular Universe 68 Do exoplanets 12-inch Truss Tube PHIL HARRINGTON have moons? 46 Dobsonian Our solar system harbors at least The real music This telescope offers top-notch QUANTUM GRAVITY 180 moons. Now astronomers of the spheres construction and high-quality Snapshot 8 have launched a quest to find The sky is an endless source optics, and is easy to set up and satellites in another system. of inspiration for artists and use, as well. MIKE REYNOLDS Astro News 12 NOLA TAYLOR REDD composers. Here’s a look back at how the stars have influenced 62 IN EVERY ISSUE JOEL DAVIS 36 music. Starmus awards 2017 From the Editor 6 Sky This Month 52 Stephen Hawking medals Astro Letters 11 Totality over America. MARTIN The prestigious prize recognizes RATCLIFFE AND ALISTER LING Explore Auriga’s popularizers of science from New Products 63 deep-sky wonders around the world. JAKE PARKS Advertiser Index 69 38 Bright star clusters, challenging Reader Gallery 70 StarDome and nebulae, and even a distant globular cluster await you in one Breakthrough 74 Path of the Planets of winter’s great constellations. RICHARD TALCOTT; STEPHEN JAMES O’MEARA ILLUSTRATIONS BY ROEN KELLY

Astronomy (ISSN 0091-6358, USPS 531-350) is ONLINE published monthly by Kalmbach Publishing Co., 21027 Crossroads Circle, P. O. Box 1612, Waukesha, WI 53187–1612. Periodicals post- FAVORITES age paid at Waukesha, WI, and additional offices. POSTMASTER: Send address changes to Astronomy, P.O. Box 62320, Tampa, Fla. 33662-2320. Go to www.Astronomy.com My Science Picture of Ask Astro News Canada Publication Mail Agreement #40010760. for info on the biggest news and Shop the Day Archive The latest observing events, stunning photos, Perfect gifts for Gorgeous Answers to all updates from your favorite photos from your cosmic the science and informative videos, and more. science geeks. our readers. questions. the hobby.

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$60 $80 $100 $200 $225 $250 $450 Don’t forget to follow us on Facebook, Twitter and Instagram! and Twitter Facebook, on us follow to forget Don’t www.skywatcherusa.com . FROM THE EDITOR BY DAVID J. EICHER Editor David J. Eicher Art Director LuAnn Williams Belter EDITORIAL Managing Editor Kathi Kube Senior Editors Michael E. Bakich, Richard Talcott Associate Editors Alison Klesman, Jake Parks 45 years of Copy Editors Dave Lee, Elisa R. Neckar Editorial Assistant Nicole Kiefert ART Graphic Designer Kelly Katlaps Illustrator Roen Kelly Production Specialist Jodi Jeranek Astronomy CONTRIBUTING EDITORS Bob Berman, Adam Block, Glenn F. Chaple, Jr., Martin George, Tony Hallas, Phil Harrington, Korey Haynes, Jeff Hester, Liz Kruesi, Ray Jayawardhana, Alister Ling, Steve Nadis, Stephen James O’Meara, Tom Polakis, Martin Ratcliffe, Mike D. Reynolds, Sheldon Reynolds, Erika Rix, Raymond Shubinski EDITORIAL ADVISORY BOARD Buzz Aldrin, Marcia Bartusiak, Timothy Ferris, Alex Filippenko, Adam Frank, John S. Gallagher lll, Daniel W. E. Green, William K. Hartmann, Paul Hodge, Edward Kolb, Stephen P. Maran, Brian his year, our maga- in the history of modern staff as the most junior of its May, S. Alan Stern, James Trefil zine marks an anni- astronomy, covering the members. In the mid-1980s, versary — 45 years Voyager missions to the plan- Kalmbach Publishing Co., Kalmbach Publishing Co. of publication, and ets in spectacular detail. They famous for Model Railroader CEO Dan Hickey Senior Vice President, Sales & Marketing Daniel R. Lance still going strong. guided the magazine through and Trains magazines, pur- Vice President, Content Stephen C. George Vice President, Consumer Marketing Nicole McGuire TIn August 1973, the title’s the period in which it became chased AstroMedia. We left Art and Production Manager Michael Soliday founder, Steve Walther, the largest-circulation our building for another part Corporate Advertising Director Ann E. Smith Circulation Director Liz Runyon produced the first issue, astronomy publication in of town, ramping up for the New Business Manager Cathy Daniels Retention Manager Kathy Steele which offered 48 pages and the world — larger than the appearance of Halley’s Single Copy Specialist Kim Redmond five feature articles, Comet and living ADVERTISING DEPARTMENT plus information through the Phone (888) 558-1544 Advertising Sales Manager Steve Meni about what to see in Challenger disaster. Advertising Sales Representative Dina Johnston, [email protected] the night sky that Ever since those Ad Services Representative month. As the ’70s early days, the Christa Burbank, [email protected] transformed into the magazine has RETAIL TRADE ORDERS AND INQUIRIES Selling Astronomy magazine or products in your store: ’80s, and the Voyager continued furiously, Phone (800) 558-1544 Outside U.S. and Canada (262) 796-8776, ext. 818 spacecraft began and it now boasts Fax (262) 798-6592 exploring Jupiter and a print circulation Email [email protected] Website www.Retailers.Kalmbach.com Saturn, Astronomy of 100,000, three- CUSTOMER SALES AND SERVICE became the world’s quarters of a million Phone (877) 246-4835 Outside U.S. and Canada (813) 910-3616 largest publication on visitors to our website Customer Service [email protected] the subject, a status it each month, and a Digital [email protected] Back Issues [email protected] has not relinquished. social media following CONTACT US Walther died in of 1.4 million. Ad Sales [email protected] Ask Astro [email protected] 1977, but the company Together, this Books [email protected] he started — comprises the largest Letters [email protected] Products [email protected] AstroMedia Corp. — community of Reader Gallery [email protected] brought in Richard astronomy enthusiasts Editorial Phone (262) 796-8776

Berry to become editor on the planet. Copyright © 2018 Kalmbach Publishing Co., all rights reserved. This pub- lication may not be reproduced in any form without permission. Printed and Bob Maas to take August 1973: The first issue We plan to celebrate in the U.S.A. Allow 6 to 8 weeks for new subscriptions and address changes. Subscription rate: single copy: $5.99; U.S.: 1 year (12 issues) the publisher’s helm. this community with you in $42.95; 2 years (24 issues) $79.95; 3 years (36 issues) $114.95. Canadian: Add $12.00 postage per year. Canadian price includes GST, payable in Together, Berry and Maas long-established, conserva- this anniversary year. Stay U.S. funds. All other international subscriptions: Add $16.00 postage per year, payable in U.S. funds, drawn on a U.S. bank. BN 12271 3209 RT. Not forged Astronomy into a solid, tive Sky & Telescope; larger tuned for some surprises. responsible for unsolicited materials. respectable, and exhilarating than the Japanese leader, I think Steve Walther package showcasing the best Tenmon Gaido. would be proud of what the astronomy had to offer When Berry hired me magazine has become. I throughout the late 1970s and in 1982, I brought my know that I am. early 1980s. Berry and his magazine, Deep Sky, now Follow Astronomy co-workers lorded over one relaunched as a quarterly, Yours truly, of the most exciting periods and joined the Astronomy www.twitter.com/ www.facebook.com/ plus.google.com/ AstronomyMag AstronomyMagazine +astronomymagazine Follow the Dave’s Universe blog: www.Astronomy.com/davesuniverse David J. Eicher Follow Dave Eicher on Twitter: @deicherstar Editor

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WWW.ASTRONOMY.COM 7 QUANTUM QG GRAVITY EVERYTHING YOU NEED TO KNOW ABOUT THE UNIVERSE THIS MONTH . . .

LIKE CLOCKWORK RESTING PLACE NONE MORE HOT BYTES >> An all-mechanical Venus Lunar probe SMART-1’s BLACK rover could operate 2006 crash site was The exoplanet WASP- TRENDING without succumbing to recently discovered in 12b’s atmosphere traps TO THE TOP instrument degradation data from the Lunar so much light that the as quickly as previous Reconnaissance Orbiter. planet is blisteringly hot landers. and appears pitch black. TERRY HANCOCK; TOP FROM LEFT: NASA/JPL-CALTECH; P STOOKE/B FOING ET AL.2017/NASA/GSFC/ARIZONA UNIVERSITY; STATE NASA, ESA, AND G. BACON (STScI) The immense sea of nebulosity surrounding the southern portion of Orion appears when the gas lies close to hot stars that excite it to glow. Some dark nebulae, dust grains that block light from behind, are also visible.

SNAPSHOT Go under a really dark sky, in the ongoing cosmic recycling We see the brightest parts of and you can see a vast array of program, these clouds of gas play this complex, including the Orion glowing clouds of gas littering a major role in how galaxies Nebula and the nebulosity sur- The beauty the Milky Way Galaxy. Some work. They are difficult to gauge; rounding and backlighting the are visible with the naked eye, their distances are hard to deter- famous dark nebula called the of nebulous others in binoculars, and most mine, unless bright stars happen Horsehead, because bright stars require a telescope and a moon- to be lodged conveniently within energize those parts of the cloud. less night for visibility. The most them. Astronomers know the But large amounts of gas, as well space famous nebula of all, the Orion Orion Nebula is about 1,500 as the dust that makes up dark Nebula, stands as a case study in light-years away, but that’s an nebulae, mostly go unnoticed. The Orion Nebula and its what the cosmos shows us. estimate. The whole region of the This area serves to remind us neighbors reveal much Nebulae can be nebulous to constellation Orion is swamped that what we see in the sky is but about what we see — and understand. Glowing clouds of in what’s known as the Orion the tip of an iceberg. So much don’t see — in the cosmos. gas that are collapsing into new- Molecular Cloud, a vast bubble more lies in the quiet darkness born stars, the death shrouds of stretching several hundred light- that we cannot yet tease out of aged suns, or simply the detritus years across. space. — David J. Eicher

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WWW.ASTRONOMY.COM 9 STRANGEUNIVERSE BY BOB BERMAN Earth’s gravity: A downer?

Gravity’s pull influences life — and the potential for death — on the planet.

very seashore demon- disparity in lunar strength act- Boats sit directly on the exposed ocean floor during low tide in Gorey Harbour, Jersey. strates the influence ing on Earth’s hemispheres. But Water levels around Jersey, an island between England and France, can differ by more of celestial bodies. the Sun’s great distance yields than 40 feet (12 m) between low and high tide. FOXYORANGE ON WIKIPEDIA It’s vivid but old only a 0.018 percent variation in news: Ancient cul- its pull on opposite hemispheres. further energy to the job. The atmosphere at 72,000 mph Etures knew that tides are That’s less than one-twentieth of concept that a speed greater (115,873 km/h) hit rooftops at mainly controlled by the Moon, a percent. Result: comparatively than the escape velocity is just 250 to 300 mph (402 to 483 not the Sun. Yet nowadays, wimpy solar tides. needed is only valid in a one- km/h), and penetrate no far- many are mystified by this sup- Even more fun is dealing shot deal, after which your ther than one or two floors. posed disparity. with Earth’s own gravity. rocket then coasts on its own. Ignoring air resistance, you Ask your smartest friends, Especially in ways often misun- What’s cool is that escape can find your final falling “The Sun’s gravity is much derstood, like escape velocity: velocity equals the impact speed by multiplying your greater than the Moon’s — we It’s 7 miles per second. That’s speed if you fell to the ground height in feet times 64.4 and even orbit it, right? Yet the the speed you’d need, after from a great distance. If you then hitting the square root Moon controls the tides, so it being shot from a cannon, to toss an orange up, it comes button. The result is in feet per boasts a greater tidal influence keep going and never be pulled back to strike your palm at second, which very nearly on us. This means tidal and back, ignoring air resistance. exactly the same speed you equals kilometers per hour. For gravitational pulls are different Many imagine that if a rocket happened to hurl it upward. Up miles per hour, multiply again animals. But how?” failed to achieve that speed, it equals down. by 0.68. This equation reveals You’ll find no one who can could never escape the planet. Schools teach that falling that jumping from 1 foot tell you. Maybe you yourself In the ’90s, I had that debate bodies accelerate by 32 feet (9.8 (times 64 is still 64, whose know, since you’re into astron- square root is 8) makes you omy. Yes, the Sun pulls on strike the ground at 8 km/h or Earth about 175 times more A little change in nearness 8 fps. That’s 5 mph. From 5 feet forcefully than the Moon. But yields a big shift in power. up, you’d land at 12 mph. its effect on the oceans isn’t These are typical impact even half that of the Moon. speeds after slipping on ice. That’s because gravity alone with the astrophysics chair at meters) per second squared. But From 10 feet, a single house won’t make water move. What Columbia University. That oth- most people grasp that more story, you hit at 17 mph. From does the job is the difference in erwise brilliant man insisted easily if we instead say a rock two stories it’s 24.4 mph, and the gravitational pull on vari- that if a rocket headed upward tossed off a cliff falls 22 miles now you’d better land on some- ous parts of the ocean. at only, say, 2 miles per second, (35.4 kilometers) an hour faster thing very soft to avoid serious The Moon’s extreme near- its path would invariably curve after each passing second. If it injury. Fatal impacts become ness is the key. Since gravity’s back down. “That’s not true,” I falls for two seconds, it hits the more likely than not at around grip falls quickly with distance, told him, in what was surely the ground at 44 mph. Three sec- 35 mph, which corresponds to a little change in nearness only instance of me being right onds, and it’s 66 mph. Simple. four stories. An old insurance yields a big shift in power. The and him being wrong about Air resistance stops the table says the chance of death Moon hovering 3.4 percent anything. “You could keep speed gain at some point, which increases by 1 percent for each closer to one side of Earth heading upward at even 2 miles is why rain falls at just 22 mph. additional foot you fall. yields a 7 percent inequality in an hour, and as long as the And why squirrels have no Enlightening, perhaps, but its gravitational influence engines kept firing, you could lethal terminal velocity. It’s why we’re now getting morbid. across the globe. This differ- go clear across the universe.” an arms-and-legs-out base Let’s stop. ence doesn’t produce the tidal He disagreed because he’d jumper leaping from any height effect; it is the tidal effect. apparently forgotten that above 49 stories remains falling Contact me about So a tidal effect is a gravity escape velocity simply doesn’t at 120 mph. It explains why my strange universe by visiting http://skymanbob.com. difference. There’s a 7 percent apply if you’re supplying meteoroids screaming into our

BROWSE THE “STRANGE UNIVERSE” ARCHIVE AT www.Astronomy.com/Berman.

10 ASTRONOMY • JANUARY 2018 ASTROLETTERS TOM OLSON TOM

Beautiful cloudshine fluorescent pink with orange tints), the I read Stephen James O’Meara’s article diamond rings before and after totality, about cloudshine in Astronomy’s July the view of solar prominences, and the 2017 issue. I witnessed the phenomenon brightly glowing extended corona went one evening leaving the gliderport at together to produce a jaw-dropping, Harris Hill near Elmira, New York. I heart-stopping, otherworldly naked-eye snapped this photo, but it pales in com- view! This incredible view was so colorful, parison to reality. A rainbow was forming brilliant, and crisp, it looked unreal. It was in the glare of the reflection, and the as if Hollywood had taken an actual total under-cloud landscape stretched into the solar eclipse image, enhanced it beyond all horizon. I thought I’d send this image reason, and projected it on an overhead and let you know how much I appreciate screen. Each time I think about it, talk the observation of planetary science all about it, read about it, or watch a TV around us. I’ve been learning soaring the program about it, my heart starts racing, past three summers at the gliderport. It’s my hands start shaking, and I get a lump been said that weather and wind patterns in my throat. I guess it’s time to start are fingerprints of Earth’s primordial planning for 2024! — Larry Russell, atmosphere after the planet’s formation. Germantown Hills, IL Learning to sail on these wind currents is fascinating and thrilling, and a direct connection to the forces of the universe. The magnificent eclipse — Tom Olson, Ithaca, NY I traveled to Hopkinsville, Kentucky, to view the total solar eclipse August 21. It was magnificent, beautiful, awe-inspiring, Ready for the next eclipse and eerie. I almost felt like I was on an I was fortunate enough to witness my extrasolar planet viewing something that first total solar eclipse August 21, and I was normal there. Being alive at this time have to say that it was better than I to view this rare and spectacular event dreamed it could be! The sight of that was special and very memorable. I feel pitch-black hole in the sky where the Sun fortunate that I was able to witness it! should be, the amazing and indescribable — Tom Bryant, Danville, KY colors around the edges of the eclipsed Sun (something like a hot, reddish, The amazing Moon House We welcome your comments at Kudos to Mark Boslough for his Moon Astronomy Letters, P. O. Box 1612, House piece, a brilliant exposition of Waukesha, WI 53187; or email to letters@ celestial phenomena through the eyes astronomy.com. Please include your of an ancient Anasazi culture with the name, city, state, and country. Letters time, energy, and incentive to watch the may be edited for space and clarity. sky very closely, very closely indeed. — Kenneth Roberts, Tucson, AZ

WWW.ASTRONOMY.COM 11 CHIMING IN. The new Canadian Hydrogen Intensity Mapping Experiment (CHIME) will probe nearly ASTRONEWS the entire observable universe in 3-D while studying dark energy and gravitational waves. YOUNG GALAXIES MAY HAVE OLD MAGNETIC FIELDS BRIEFCASE rom prompting star forma- MAGNETIC FINGERPRINTS. NEIGHBORHOOD WATCH tion to driving accretion Lensed images of The Hubble Space Telescope Coryn Bailer-Jones of the Max captured two gravitationally around supermassive black CLASS B1152+199 Planck Institute for Astronomy F lensed images of a distant quasar has published the first system- holes, magnetic fields behind a young foreground galaxy. atic estimate of how often influence nearly every astro- The two images are light that other stars wander into our physical process. However, one has traveled through opposite solar neighborhood. Using ends of the galaxy, picking up data from the European Space of the biggest hurdles in study- information about its magnetic field Agency satellite Gaia, Bailer- ing the magnetic fields that along the way. MAO ET AL., NASA Jones found that every million pervade galaxies is their lack of years, between 490 and 600 stars typically pass within strength. Millions of times The light passing through 5 parsecs (16.3 light-years) of weaker than Earth’s magnetic Foreground the galaxy’s edges is further the Sun. Astronomers are inter- field, galactic magnetic fields galaxy affected by any local mag- ested in these close stellar are difficult to measure at great netic fields, which can encounters because they can nudge comets out of the Oort distances. change the light’s polariza- Cloud and into the inner solar But in an August 28 paper in tion, or the direction of its system, potentially wreaking Nature Astronomy, a team of researchers reported vibration. This effect is called Faraday rotation, and havoc on unsuspecting planets like Earth. the best measurements yet of a magnetic field in a the stronger the magnetic field, the more the light’s • galaxy located a record-breaking 4.6 billion light- polarization is rotated. TURBULENCE AHEAD years away. The team, led by Sui Ann Mao of the By measuring this rotation in the light received Researchers once thought Max Planck Institute for Radio Astronomy, from the background quasar, the researchers deter- Jupiter’s aurorae were created the same way as Earth’s, where detected a magnetic field similar to the Milky mined the young galaxy’s magnetic field is similar energetic particles are acceler- Way’s in a host nearly 5 billion years younger, pro- in size and strength to those found in the Milky ated by differences in strength viding new insight into how these fields have Way and other nearby, older galaxies. between atmospheric mag- netic fields, called electric evolved in the universe over cosmic timescales. One of the leading theories on the evolution of potentials. But the strongest The scientists investigated the galaxy using a phe- galactic magnetic fields is that they begin scrawny aurorae on Jupiter are not nomenon called gravitational lensing, which occurs and tangled, then strengthen and organize over always associated with the big- when a massive object — the galaxy in this study time. But that doesn’t seem to be the case here. gest electric potentials, as on Earth. Instead, it appears a dif- — lines up between Earth and a distant object — in “By catching magnetic fields when they’re so young, ferent cause is responsible for this case, a quasar (CLASS B1152+199). As divergent we can rule out some of the theories of where they the most powerful displays. “At light rays from the quasar pass by the intervening come from,” Ellen Zweibel, a co-author on the Jupiter, the brightest aurorae — Jake Parks are caused by some kind of tur- galaxy, the galaxy’s gravity bends their path. to 8000 study, said in a press release. bulent acceleration process that we do not understand very well,” Johns Hopkins University Applied Physics Deneb Laboratory researcher Barry 9600 to FUTURE Mauk said in a press release. At 10300 high energies, he said, “a new CYGNUS CEPHEUS NORTH STARS acceleration process takes over,” which Juno scientists are 10000 POLAR EXPRESS. Because of Delta now working to understand. 11000 to gravitational influences from the Sun and Moon, our planet • 12000 5000 Alderamin wobbles like a top with a period MIDDLE GROUND 6800 to 8000 LYRA of 25,772 years. That means the In a paper published Alrai Nature Iota 3000 to 5200 point above the North Pole September 4 in 5200 to 6800 Astronomy (the North Celestial Pole, or , a team of astrono- Vega NCP) traces a circle in that mers led by Tomoharu Oka of 13100 to span. Currently, the closest Keio University in Yokohama, 15000 Polaris bright star to the NCP is Japan, shows evidence that a DRACO URSA gas cloud called CO-0.40-0.22 MINOR 500 to 3000 Polaris, the brightest star in the constellation Ursa Minor near our galaxy’s center may 15000 North harbor an intermediate-mass Celestial Pole the Bear Cub. But 10 other 2017 relatively bright stars will black hole. Gas particles inside lie closer to the NCP before CO-0.40-0.22 have motions Polaris once again assumes consistent with an object Tau 0 100,000 times the Sun’s mass. 18500 to 21700 the mantle of North Star. Edasich — Michael E. Bakich Radio emission measured from 21700 to 22300 Kochab 24100 to 26500 the cloud also bears striking HERCULES similarities to the radio source Thuban FAST associated with our galaxy’s 20000 22300 to 24100 4 million-solar-mass supermas- FACT sive black hole, Sagittarius A*, BIG though 500 times fainter, sug-

: ROEN KELLY ROEN : DIPPER Polaris, currently 0.77° from gesting a black hole a few hun- dred times smaller. — J.P., the North Celestial Pole, will John Wenz, Alison Klesman

ASTRONOMY be closest to that point in 2102, when it will lie 0.46° away.

12 ASTRONOMY • JANUARY 2018 NOT SO WINDY. New ALMA observations of young galaxies indicate that the winds generated by new stars aren’t ASTRONEWS strong enough to blow away material and stop star formation. QUICK TAKES

TAKING AIM NASA plans to use the James Webb Space Telescope to study plume activity on the icy solar system worlds Europa and Enceladus.

MOON• PILEUP Uranus’ satellites Desdemona and Cressida are on a future collision course as Cressida destabilizes its sister moon’s orbit.

REFLECTION• PERFECTION Gradually applying atom- THE ULTIMATE BREAKUP. Cassini disappeared into Saturn on September 15, ending its 13-year-long mission at the ringed planet. thin coatings could improve Before breaking up, the spacecraft beamed back valuable data from within the planet’s atmosphere. NASA/JPL-CALTECH silver-based telescope mir- rors by preventing corrosion.

LARGE •SURVEY Cassini probe sends its last regards The Karl Jansky Very Large After an amazing 20 years in space — global subsurface ocean, elevating The spacecraft’s signal went out at Array in New Mexico is undertaking its biggest-ever 13 of those years at Saturn — NASA’s the moon to one of the more likely 4:55:46 A.M. PDT, to a standing venerable Cassini spacecraft met its places in the solar system to find ovation. Shortly after, Cassini observing campaign, search- ing the sky for high-energy fiery death in the upper atmosphere alien life. The spacecraft also discov- program manager Earl Maize told his events over the next 7 years. of the ringed planet September 15. ered circumstantial evidence of team, “I hope you’re all deeply proud The craft was launched October 15, oceans and cryovolcanism on Dione, of this amazing accomplishment.” FAST AND• FURIOUS 1997. Gravity assists from Venus, as well as inexplicable red streaks on Linda Spilker, a Cassini project Astronomers estimate that Earth, and Jupiter sent it on to Saturn, Tethys that might be due to outgas- scientist who has been with the one or more mysterious where it arrived in June 2004. From sing, fracturing, or perhaps some mission since it was first planned in fast radio bursts may pop off there, the craft wrote the book on our other process entirely. 1982, said, “It felt so much like losing every second somewhere understanding of the Saturn system. In its final months, Cassini skimmed a friend, a spacecraft I got to know in the universe. It provided incredible views of Saturn’s rings and traversed the space so well.” Saturn’s largest moon, Titan, showing between the rings and the planet itself. NASA is now reviewing proposals SLEEPING• BEAUTY ever-shifting seas of hydrocarbons Using a last gravity assist from Titan, for future missions that could return NASA’s New Horizons awoke and revealing a subsurface ocean NASA set Cassini on a destruction us to Titan, Enceladus, or Saturn. In from a five-month slumber much like Europa’s. course to disintegrate within minutes in the meantime, there are several September 12, en route Cassini also followed up on tenta- Saturn’s atmosphere. The decision was hundred gigabytes of data for to MU69 — a primordial tive evidence from the Voyager made out of concern that extreme present and future generations to Kuiper Belt object. probes of watery activity on the small bacterial life from Earth could survive sort through to make amazing • moon Enceladus, ultimately discover- deep inside the craft and contaminate discoveries about the Saturn system. SPIN DOCTORS ing geysers shooting water hundreds one of the system’s habitable moons Thanks for everything, Cassini. Researchers seeking to understand galaxy shapes of miles into space. Their source is a if an accident were ever to occur. — J.W. now believe a galaxy’s rotation speed plays a big role in its appearance.

Revealing Pluto’s first officially named features SEVEN •SISTERS Voyager Terra The Pleiades’ seven recog- Djanggawul Hayabusa Terra nizable stars are all variable, Fossae Al-Idrisi Montes according to evidence from the Kepler telescope. Burney Sputnik Sleipnir Fossae crater • Planitia ALIEN AGENTS Tartarus Comets and asteroids of Dorsa interstellar origin may have Hillary Elliot crater Montes brought the building blocks of DNA to Earth. — J.W. Virgil Fossae Adlivun Tenzing Cavus Tombaugh Montes Regio BEYER RI/ROSS W 42 The number of NASA/JHUAPL/S MAPMAKING. New Horizons gave us our first and only up-close look at the Pluto system in 2015. In September, the International spacecraft that Astronomical Union (IAU) announced the first 14 officially named features on the dwarf planet. The names highlight individuals whose ended their work has contributed to our understanding of Pluto, including Clyde Tombaugh and James Elliot. Some names also pay homage to missions on famous explorers and space missions, such as Sir Edmund Hillary and Sputnik 1. Additional regions bear the names of figures or places associated with the underworld in Norse, Australian, Inuit, and Greek mythology. The IAU will continue to consider proposals to name another planet, more features on Pluto and its five moons. — A.K. excluding moons.

WWW.ASTRONOMY.COM 13 GAINING WEIGHT. Astronomers bumped white dwarf 40 Eridani B’s mass from 0.42 to 0.57 solar mass ASTRONEWS after carefully watching it interact with its red dwarf binary companion. The fastest pulsar in the Milky Way discovered Even the fastest heavy metal drummers have nothing on the pulsar PSR J0952–0607. One of two rapidly rotating pulsars recently discovered with the Low-Frequency Array (LOFAR) telescope, PSR J0952-0607 emits more than 700 “beats” (or radio pulses) per second. That makes it the fastest pulsar in the Milky Way and the second-fastest pulsar ever discov- ered, after PSR J1748–2446ad in the Terzan 5 globular cluster. (See page 17 for more on Terzan 5.) And the other newly discovered pul- sar, PSR J1552+5437, is no slouch itself. It rotates 412 times per second. Pulsars are a subclass of neutron stars, which are objects left behind when a star goes KELLY ROEN : supernova but isn’t massive enough to form a

black hole. They emit radiation from their poles ASTRONOMY as they spin, making them a sort of metronome RAPID FIRE. Pulsars such as PSR J0952–0607 are believed to spin so fast because they steal material from a for the universe. These pulsars were discovered binary companion to boost their spin rates. Such rapidly rotating pulsars beam powerful radio and gamma-ray jets using a new technique on the LOFAR telescope, from their poles, destroying those companions over time. which looks in lower-frequency light than tra- ditional pulsar searches. instruments to filter out noise from any matter higher frequencies, where traditional pulsar Although it’s difficult to search for pulsars between the telescope and the observing tar- searches occur — perhaps hinting at a at low frequencies because their light is dis- get. PSR J0952–0607 and PSR J1552+5437 are previously unseen population that could tell rupted by intervening gas and dust, LOFAR has both bright at low frequencies but dim at us more about these extreme objects. — J.W.

The number of asteroids the proposed Asteroid Touring 300 Nanosat Fleet could visit, using 50 tiny spacecraft.

AS GOOD AS IT GETS Aug. 1 June 1 Oct. 1 Feb. 1 April 1 Dec. 1

Magnitude 1.18 0.28 –1.21 – 2.77 –1.32 –0.04 Angular size 5.60" 8.45" 15.30" 24.33" 15.81" 9.28"

30" 25" 20" 15" 10"

Angular size 5"

–3 –2 –1 0 : ROEN KELLY ROEN :

Magnitude 1 2 NASA/SDO/GODDARD ASTRONOMY

Jan. 1 July 1 Oct. 1 Feb. 1 April 1 May 1 June 1 Aug. 1 Sept. 1 Nov. 1 Dec. 1 NASA catches a huge solar flare March 1 Date IN A FLASH. In early September, the Sun released its largest solar flare RED PLANET REVIVAL. Mars puts on its best since 2006. NASA’s Solar Dynamics Observatory easily spotted it, shown FAST At its peak in August show in 15 years during 2018. At its peak in late July, here in the extreme ultraviolet (304 angstroms, or about 30 nanometers). FACT 2003, Mars shone it will shine at magnitude –2.8 — brighter than Solar flares typically erupt from or near sunspots — cooler areas on the at magnitude –2.9 any other point of light in the sky besides Venus surface of the Sun that are associated with localized buildups in the star’s and appeared 25.1" — and swell to an apparent diameter of 24.3". But powerful magnetic field. The magnetic field can become twisted and in diameter. Mars will exceed magnitude –1.0 from late May to looped as the Sun rotates, until finally these lines “snap” and trigger a mid-October and span more than 10" from late April massive eruption of energy in many wavelengths across the spectrum, until mid-November. — Richard Talcott including X-rays. — A.K.

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WWW.ASTRONOMY.COM 15 MERCURIAL ICE. A review of MESSENGER data indicates there’s enough water ice at Mercury’s poles to cover ASTRONEWS the state of Rhode Island. Shocks boost nova brightness Novae occur when a white dwarf, the rem- white dwarf, controlling how much light and nant of a Sun-like star, collects material from energy are emitted,” co-author Laura a nearby donor star. The resulting runaway Chomiuk of Michigan State University nuclear reaction causes a powerful explosion explained in a press release. “What we discov- visible from vast distances. ered, however, was a completely different But some novae seem too bright. Now, source of energy — shock waves that can astronomers have shown that such explosions dominate the entire explosion.” don’t defy the laws of physics, but result from “This event shows that shocks are the main amplification making them appear brighter. event,” added Metzger. The findings, published September 4 in Nature White dwarfs in binary systems can pull Astronomy, prove a theory developed by Brian material from companion stars, and it slowly Metzger, an astronomer at Columbia builds on the stellar remnant’s surface. Once a University and co-author on the paper. tipping point is reached, a nuclear reaction “Astronomers have long thought the begins. A wave of material is ejected from the energy from novae was dominated by the white dwarf, with another wave right after it. The second wave, hotter and faster than the SHOCKING DEVELOPMENT. Material ejected first, collides with the cooler, slower-moving during a nova, colored yellow in this artist’s concept, material to produce heat and light that boost gives off gamma rays as shock waves travel through it. the appearance of the nova. “The bigger the Observing optical light and gamma rays from a recent shock, the brighter the nova,” said Chomiuk. nova helped astronomers to determine the role shocks “We believe it’s the speed of the second wave play in a nova’s brightness. BILL SAXTON, NRAO/AUI/NSF that influences the explosion.” — A.K. Supermassive black holes can form tight pairs TIPPING THE SCALES PARTNER DANCE. Located at the center Black holes come in many sizes. of galaxy NGC 7674, How are they categorized, and Stellar-mass these two compact black holes radio sources are how does each class measure up? 2 to 100 solar masses less than a light-year apart and correspond Intermediate-mass black holes These black holes form after the death to two accreting of a massive star (≥8 M 100 to 10,000 solar masses? black holes can grow by accreting nearby supermassive Sun). Stellar-mass black holes orbiting Intermediate-mass black holes could matter or by merging with other black holes, causing gravitational waves that TIFR-NCRA AND RIT, USA RIT, AND TIFR-NCRA each other. provide a link between stellar-mass and or more. can be seen by the Laser Interferometer supermassive black holes, withSun masses Like their smaller counterparts, supermassive between 100 and 10,000 M Gravitational-wave Observatory (LIGO). black holes weighing in at over 1 million times No intermediate-mass black holes the mass of the Sun can exist in binary pairs. have been definitively discovered yet, Scientists believe such pairs most commonly form but several candidates have been Example: when galaxies merge — over time, each galaxy’s identified for further study. Cygnus X-1: 14.8 M supermassive black hole falls to the center of the Sun resulting larger galaxy, eventually orbiting and Example: merging with each other. But just how closely Possible black hole in 47 Tucanae: can two gargantuan black holes orbit each other 2,300 MSun before they collide? In September 18’s Nature Astronomy, an Black Black hole international team of astronomers reported the hole discovery of the tightest-ever orbiting supermas- sive black hole system. Located 400 million light- years away near the center of the spiral galaxy NGC 7674, the two black holes are separated by less than 1 light-year. The previous record holder has a separation of nearly 25 light-years. Supermassive black holes To resolve such a tiny separation from such a 1 million to several billion solar masses large distance, the team took advantage of a Supermassive black holes reside in the centers of galaxies. technique called very-long baseline interferome- They are the engines that power quasars and jets spanning try, which uses multiple radio telescopes net- hundreds of light-years. Astronomers still aren’t sure how worked together to function as one massive these huge black holes form, but they, too, telescope. This provided an angular resolution can merge and grow when their host about 10 million times better than the human galaxies collide. — A.K. eye, enough to resolve the two black holes. The combined mass of the black holes is about Example: 40 million times the mass of the Sun. Though they Milky Way’s supermassive : ROEN KELLY ROEN : are tightly bound, their orbital period is a sluggish black hole (Sagittarius A*): 100,000 years, meaning it will be a while yet 4 million MSun Black hole before they merge to create a single object. — J.P. ASTRONOMY

16 ASTRONOMY • JANUARY 2018 TWEET AWAY. University of Kansas researchers found that social media can help, rather than hinder, ASTRONEWS young students’ ability to argue scientific theories. Pulsars reveal origin of a globular cluster The motions of stars inside globular clusters can help Pulsar Pulsar moving astronomers better understand the cluster’s origin to moving away from determine whether it originated within the Milky Way, toward Earth Earth or is the leftover core of a dwarf galaxy that our galaxy gobbled up. Though optical studies are often thwarted by galactic dust, astronomers have now used radio observa- tions to track pulsars in the Terzan 5 globular cluster, find- ing evidence that it came from within our galaxy. Terzan 5 has 37 known pulsars, more than any other globular cluster. Brian Prager at the University of Virginia in Charlottesville and his collaborators observed 36 of those pulsars with the 100-meter Green Bank Telescope (GBT) in West Virginia. They watched as the pulsars’ regu- lar radio pulses were Doppler shifted (stretched or squished in frequency) by their motion relative to Earth, allowing precise mapping of the cluster’s interior. The work was published August 21 in The Astrophysical Journal. “Pulsars are amazingly precise cosmic clocks,” co-author Scott Ransom of the National Radio Astronomy Observatory said in a press release. “With the GBT, our team was able to essentially measure how each of these clocks is falling through space toward regions of higher mass. Once we have that information, we can translate it into a very pre- cise map of the density of the cluster, showing us where the bulk of the ‘stuff’ in the cluster resides.” If Terzan 5 used to be a dwarf galaxy, it might still har- bor a central supermassive black hole or show signs that it warped as the Milky Way gobbled most of its stars. The team saw no sign of either, instead finding “better evi- dence that Terzan 5 is a true globular cluster born in the IN MOTION. Astronomers measured the motion of 36 pulsars in the Terzan 5 globular cluster Milky Way rather than the remains of a dwarf galaxy,” said to map the location of its mass. Blue markers indicate pulsars moving toward Earth, while red Ransom. — A.K. markers show those moving away. B. SAXTON (NRAO/AUI/NSF); GBO/AUI/NSF; NASA/ESA HUBBLE, F. FERRARO Hubble spies asteroid pair sporting a tail A group of German-led astronomers used the Hubble Space Telescope to study main belt asteroid 288P as it passed Earth in September 2016 on its clos- est approach to the Sun. The team was surprised to discover the asteroid was actually two asteroids, orbiting each other with a separation of about 60 miles (100 kilometers). Astronomers can easily measure the mass of a

binary system by watching KERSCHBAUM (ESO/NAOJ/NRAO)/F. ALMA the objects orbit each TWO IN ONE. 288P is not one asteroid, but two, orbiting each other, and the researchers other as a wide binary pair. This artist’s impression shows not only ALMA sees a star blow a bubble found that the two aster- the asteroids’ elliptical orbit outlined in blue, but also the diffuse SURROUNDED. U Antliae is a carbon star — a luminous oids are not only roughly cometary tail spotted by Hubble. ESA/HUBBLE, L. CALÇADA the same size, but also red giant with an atmosphere composed of more carbon about the same mass. Their Jessica Agarwal of the Max which can’t survive long on than oxygen. With binoculars, the red star is visible in the Southern Hemisphere constellation Antlia the Air Pump. work was published in Planck Institute for Solar the surface of an object in The Atacama Large Millimeter/submillimeter Array (ALMA) Nature on September 20. System Research said the the asteroid belt, is a sign recently found that this star is quite unusual: It has a very Wide asteroid binary observations showed indi- this binary system was thin shell of material around it. Only ALMA’s ability to take pairs are already rare, but cations of water ice, a fea- likely once a single object sharp images at multiple wavelengths allows astronomers 288P appears to be unique. ture that sublimates (turns with ice buried just to see the thin, round shell of material and the wispy clouds, The pair was caught sport- directly from a solid to a beneath the surface. The called filamentary substructures, that comprise it. The shell ing a cometlike tail, making gas) when the comet parent asteroid may have was created when the star ejected the material at high 288P the first binary aster- comes close to the Sun, broken up to produce the speeds over a brief period 2,700 years ago. Researchers can oid also classified as a main creating a tail. pair as little as 5,000 years now use this data to better understand how carbon stars belt comet. Team leader The presence of ice, ago. — Nicole Kiefert evolve and form these shells. — N.K.

WWW.ASTRONOMY.COM 17 WORKING BACKWARD. Australian National University scientists created the best estimate of Earth’s composition, ASTRONEWS which can now be used to improve solar system formation models. Hot Jupiter’s skies contain titanium oxide Research into the exoplanet WASP-19b, classified as a hot Jupiter because of its size and proximity to its star, revealed something star- tling: It has titanium oxide scattered throughout its upper atmosphere. Astronomers studied WASP-19b’s atmosphere, which is measured at 3,600 degrees Fahrenheit (2,000 degrees Celsius), using the FORS2 instrument on the European Southern Observatory’s Very Large Telescope. As the planet passed in front of its star, background light filtered through its atmosphere, highlighting some of the molecules and elements present. FORS2 is a spectrograph, which splits light into its constituent parts to identify the signatures of ele- REVERSE THINKING. Astronomers think the titanium oxide in the hot Jupiter WASP-19b’s atmosphere leads to a situation ments and molecules. Using this tech- called temperature inversion: The upper atmosphere is hot, with cooler temperatures deeper down. ESO/M. KORNMESSER nique, researchers found titanium oxide, water, and sodium. titanium oxide may act as a heat our slowly increasing under- larger, hotter worlds, but Previously, titanium oxide was absorber, creating a thermal blanket standing of exoplanet atmo- upcoming instruments may be largely associated with cool stars. But around the planet that traps heat spheres, as we often find that able to finally study Earth-sized as we learn more about exoplanet mostly in the upper atmosphere and they’re vastly different from planets in distant solar systems atmospheres, we are discovering keeps lower areas cool. those of our solar system’s plan- enough to detect a holy grail: compounds like titanium oxide The research, published ets. So far, all the information water vapor on worlds with are also found there. In this case, September 13 in Nature, highlights we’ve gathered has been on Earth-like temperatures. — J.W. Birthing stars makes galaxies swell

RISE AND SHINE. Infrared light from the Hubble Space Telescope (right) emphasizes the large galactic disk of a young galaxy. Optical light (middle) highlights three young star clusters packed full of freshly formed stars near its center. Submillimeter waves from the Atacama Large Millimeter/submillimeter Array (left) show a dense, star-forming cloud of material in the galactic core. ALMA (ESO/NAOJ/NRAO), NASA/ESA HUBBLE SPACE TELESCOPE, TADAKI ET AL.

The prevailing theory in galactic like yeast helps bread rise — morph- evolution is that massive elliptical ing them into ellipticals without the galaxies are formed when smaller help of collisions. The researchers disk galaxies collide and merge. used the Hubble Space Telescope However, an international team and the Atacama Large Millimeter/ of astronomers led by Ken-ichi submillimeter Array to investigate 25 Tadaki of the National Astronomical galaxies about 11 billion light-years Observatory of Japan (NAOJ) away, observing them just 3 billion UNIVERSITY STATE NASA/GSFC/ARIZONA recently found that this is not years after the Big Bang, at a time always the case. when most galaxies were in their What did totality look like “Massive elliptical galaxies are infancy. They looked at both the believed to be formed from colli- number of stars already shining and from the Moon? sions of disk galaxies,” said Tadaki in the amount of gas and dust available LUNAR VIEWPOINT. During the August 21 total solar eclipse, NASA’s a press release. “But, it is uncertain to form more stars. The team saw a Lunar Reconnaissance Orbiter (LRO) took an image of the eclipse as seen whether all the elliptical galaxies huge available reservoir of gas and from the Moon. LRO completed a slow 180° turn shortly after passing over have experienced galaxy collision. dust in the centers of these galaxies, the Moon’s south pole, allowing it to look back toward Earth and snap a There may be an alternative path.” indicating that over time, star forma- photo as the shadow sped just north of Nashville, Tennessee, moving at Tadaki and his team discovered tion in the core will dominate the 1,500 mph (670 m/s). LRO’s Narrow Angle Camera, which is actually two that possible path. They found that galaxy’s appearance — “puffing up” high-resolution cameras, began imaging Earth at 2:25 P.M. EDT and took 18 intense bursts of star formation can these galaxies and turning them into seconds to complete the image, building it up line by line. The final picture swell disk-shaped galaxies — much ellipticals from within. — J.P. shows the eclipse near the longest duration of totality. — N.K.

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WWW.ASTRONOMY.COM 19 NASA/JPL-CALTECH; NASA/AUBREY GEMIGNANI Last year, we found a star with seven Earth-sized planets, said goodbye to the Cassini mission, and watched a total solar eclipse race across America. by Liz Kruesi

Each year, Astronomy ranks the top 10 astronomical discoveries and space stories. Choosing 2017’s top stories wasn’t easy, as it was a year full of exciting discoveries and unexpected findings. In the end, the detection of a neutron star merger tops the list. For the first time, astronomers spotted a pair of neutron stars spiraling inward and colliding, throwing off gravitational waves, gamma rays, and many other forms of light. Coming in a close second was the discovery of seven likely terrestrial planets crammed into their star’s habitable zone. The global network of astronomers who pinpointed the location of a weird, mysterious blast of radio waves also makes our top 10. Not all of the past year’s biggest space stories came from outside our solar system. Cassini’s final goodbye after 13 years of incredible discoveries brought tears to the eyes of the scientists who have worked with the craft, as well as those who have followed the mission from the sidelines. And closer to home, millions watched as the Moon blocked the Sun and its shadow raced across the continental United States. Here’s how these and the rest of the top 10 stories stack up.

WWW.ASTRONOMY.COM 21 Cassini’s high- A perfectly positioned resolution camera penetrated the standard candle haze around Titan and spotted some On September 5, 2016, the 48-inch telescope at Palomar of the moon’s largest seas and Observatory captured a stellar explosion, dubbed iPTF16geu. lakes of liquid Astronomers published the discovery April 21 in Science. hydrocarbons. This isn’t just any type of explosion — it’s one that’s used as These seas could a ruler to measure cosmic distances, called a type Ia supernova sustain life: Researchers found (or type Ia SN). Each of these blasts has a nearly identical light a signal from curve, which measures brightness over time. The fainter the vinyl cyanide, explosion, the farther it must lie from us. Astronomers can cal- a molecule that could act as a culate distances to high precision by comparing these blasts cell membrane. because of their similarities. Scientists used this type of mea- NASA/JPL-CALTECH/SPACE surement in the late 1990s to show the universe’s expansion is SCIENCE INSTITUTE speeding up, as some type Ia SN explosions are fainter than expected, meaning they are farther than expected. Titan’s complex chemistry But iPTF16geu is more than just a type Ia supernova. — and astrobiology? Astronomers found four images of that same blast at the site of a galaxy lying about 2 billion light-years away. It turns out Saturn’s largest moon, Titan, is lipid bilayer membrane, a the supernova lay directly behind that galaxy as viewed from one of the solar system’s most structure that separates and Earth. When objects line up like this, background light is bent intriguing worlds. It hosts a protects a cell’s innards from around the foreground object — in this case, the massive gal- thick atmosphere denser than its environment. All living axy. (Think of putting a straw into a glass of water; the straw Earth’s and harbors lakes and organisms on Earth have such looks like it bends.) As a result, the light from the blast took rivers of a methane-ethane cell membranes. four separate paths around the galaxy, leading to four images of mixture on its surface. The Palmer and her colleagues the same stellar explosion. And with four images, there’s more saturnian satellite even has looked through several science that can be done. That’s because the light in each image a complex weather system months of ALMA observations traveled a slightly different path around the intervening galaxy. that circulates this liquid, of Titan and found three Slightly different paths equate to different distances and differ- which evaporates into the spectral lines associated ent amounts of time. “If you measure the arrival times of the atmosphere, condenses into with vinyl cyanide. Each of different images, that turns out to be a good way to measure the clouds, and then rains back these lines is produced as expansion rate of the universe,” lead author Ariel Goobar said to the surface. Could Titan an energized vinyl cyanide in a press release. even harbor some form of life molecule settles to a lower Astronomers expect this is the first of many similar discov- that relies on hydrocarbons in energy state, giving off a eries, as new surveys come online and software better under- the way Earth organisms rely photon. The brightness of stands how to pick out multiply lensed explosions. Not only will on water? Perhaps. Scientists each spectral line relates to finding more lensed supernovae improve our ability to measure continue to find more the number of photons ALMA the expansion rate of the universe, new gravitational lenses will complex chemistry at the received. “And the number of also allow astronomers to more accurately map the distribution satellite (although, no aliens). photons is dependent on how of normal and dark matter throughout the cosmos. A July 28 paper in many molecules are changing Science Advances shows energy levels and releasing Titan is astrobiologically these photons,” adds Palmer. interesting. While looking The researchers modeled for the molecule acetonitrile different scenarios to estimate isotopolog in archived the overall abundance of vinyl observations taken with the cyanide at Titan, but their Atacama Large Millimeter/ data weren’t sensitive enough submillimeter Array (ALMA), to create a map of where in researchers found a signal the atmosphere the molecule from vinyl cyanide, “a more is most abundant. They’ve exciting molecule,” says taken more observations Maureen Palmer of NASA’s of Titan with ALMA and are Goddard Space Flight Center currently analyzing them. and lead author of the This type of work — discovery paper. Laboratory hunting for biologically experiments and computer important chemistry — can simulations suggest that this begin to address how life A distant supernova, iPTF16geu lit up the sky not once, but four times, thanks to the phenomenon of gravitational lensing. The Hubble Space particular molecule would be forms, at other locales and Telescope caught this image of the lensed supernova, which appears as a stable material from which here on Earth. Perhaps soon, four bright spots surrounding a blue foreground galaxy. The supernova to form something called a we’ll find out we’re not alone. itself occurred at a distance of 4.3 billion light-years. ESA/HUBBLE, NASA

22 ASTRONOMY • JANUARY 2018 Earth rises just over the lunar horizon in this image taken by the Apollo 17 crew. When SpaceX sends humans back to the Moon, they’ll enjoy

similar views. NASA

A trip around the Moon SpaceX certainly has big goals. In 2012, the aerospace company was the first private corporation to dock with the International Space Station. And in 2015, SpaceX was the first organization, government agencies included, to bring a rocket safely back to Earth after sending a payload of supplies to the space station. Yet the goal SpaceX announced in February 2017 could be even more difficult to reach, because it involves the safety of human lives. The aerospace giant announced its plans to send two private citizens — who will likely pay an enormous sum of money — on a trip around the Moon. At the time, the company set a date of late 2018, but that Pad 39A at the Kennedy Space Center will become the home of SpaceX Falcon Heavy launches. goal is hard to believe, considering SpaceX The rocket, shown in this artist’s rendition, is the company’s chosen vehicle to transport two hasn’t sent humans into space yet. In its humans around the Moon in early 2018. SPACEX February announcement, SpaceX said its first crewed flight will take place in late has launched its Falcon 9 dozens of times, humans and supplies to the Moon before spring of 2018. In July 2017, the company but that rocket’s payload goes into orbit to returning to Earth. For a crewed trip announced via social media that its heavy- rendezvous with the ISS — a target only around the Moon to occur, there’s still lift rocket, the Falcon Heavy, would have about 250 miles (400 kilometers) above technology that must be fully developed. its first test flight in November. Earth’s surface. The Moon is much farther Many doubt it can happen by the end of A mission around the Moon will cer- away (238,900 miles [384,500 km]). 2018, but if it does, SpaceX will see itself in tainly need that powerful rocket. SpaceX It’ll take a lot more power to launch our top 10 again.

WWW.ASTRONOMY.COM 23 Spying When the universe came into existence Antihydrogen 13.8 billion years ago, equal amounts of n = 3 light from matter and antimatter should have been cre- ated. Look around the cosmos now, and it’s n = 2 Positron antimatter obvious matter stuck around, and antimat- n = 1 ter didn’t. While scientists don’t know why Photon When electrons transition between there’s a preference for matter, learning more energy levels in an atom, they either about antimatter will help reveal the answer. absorb or release specific wavelengths But it’s not easy. Whenever antimatter Positron of light. The ALPHA collaboration encounters its matter match, the two annihi- energy has measured a positron transition in levels antihydrogen, and found its wavelength late. (For example, when an electron encoun-

identical to hydrogen. ASTRONOMY: ROEN KELLY ters an antielectron, called a positron, they are converted into a burst of radiation.) So Nucleus (antiproton) scientists have to find a way to isolate anti- matter from matter.

Juno and its outreach camera

Swirls and waves of red-tinged clouds, white oval-shaped storms processing team. “Our concept was that the public would be mixed with tan-toned vortices — these are some of the incred- our virtual imaging team,” says Candice Hansen, the scientist ible details that the JunoCam instrument is capturing at Jupiter. responsible for planning and operating JunoCam. That means The images made a splash across the news and social media in the public recommends imaging targets, then discusses and 2017, and for good reason: Never before have human eyes seen votes on which ones to study — all via the internet. Once the features JunoCam is revealing. And it’s all because of a late JunoCam captures the images, members of the public process decision to add this public outreach instrument. them. The entire concept has been successful “beyond our wild- Like all NASA space missions, Juno has a set of science objec- est dreams,” says Hansen. tives, but none of those objectives requires a visible-light cam- JunoCam has received the most attention, but Juno’s other era. The craft is equipped with seven other instruments to reveal instruments have also been hard at work. In May, the mission the deep layers of Jupiter’s atmosphere, map the planet’s mag- team released the first science results. Scientists knew Jupiter netic and gravitational fields, and study its aurorae. However, has a strong magnetic field — that’s why Juno’s electronics have those instruments and their collected data don’t always reso- to be well-shielded to protect against radiation damage — but nate with the public. A chart showing the abundance of water at Juno has found it is twice as strong as expected. The magnetic different depths of Jupiter’s atmosphere doesn’t have the same field is also “lumpy” — it’s stronger in some places than others. impact on non-scientists as a stunning photograph of Jupiter’s Researchers think that could mean the field is generated not at Great Red Spot. the very center of the planet, but closer to the surface. The mission leader, Scott Bolton, recognized that fact. Prior Juno flies by Jupiter every 53 days, skimming a few thousand to launch, Juno got one more instrument: a small camera to miles above the cloud tops at each pass. Its primary mission engage the public. JunoCam has fewer resources than the includes 12 of these 53-day orbits and continues through July science instruments. There’s no large dedicated planning or 2018. NASA could then opt to extend the mission.

24 ASTRONOMY • JANUARY 2018 In 2011, physicists with the ALPHA atom. Conversely, if the electron is at one of The ALPHA group is working on experiment at Europe’s CERN laboratory those higher energy levels and falls down, detecting all the different colors at which were able to create and trap antihydrogen it releases that same color of light. (For antihydrogen glows. In December 2016, — consisting of an antiproton and a posi- example, the red color of hydrogen-alpha they announced they’ve observed one. The tron — for 16 minutes, long enough to radiation, commonly observed by astrono- light the atom emits when its positron study the material. And in December mers, corresponds to an electron in a bounces between two specific energy levels 2016, that same group announced it had hydrogen atom moving between the third is the same as the light emitted from a reg- measured the glow of antihydrogen for the and second energy levels.) Understanding ular hydrogen atom, meaning so far, matter first time. the colors each element glows at is crucial and antimatter appear to give off identical Every chemical element — whether it’s to identifying the material and learning colors. This agreement shows that antimat- hydrogen, carbon, or copper — glows at about its physics. Scientists know every ter does indeed appear to be matter’s exact specific colors when energized. Each spe- color that a hydrogen atom gives off. Does but opposite twin, confirming predictions cific color corresponds to the amount of antihydrogen differ? And if it does, what made by the current Standard Model of energy that an electron needs to absorb to does it mean about the reason our universe particle physics — and special relativity jump to another energy level within an picked matter over antimatter? — so far.

On May 19, Juno zipped past Jupiter. The spacecraft’s two-hour close approach is captured in this sequence of 14 color-enhanced JunoCam images, beginning with the planet’s north pole (left), then crossing the equator (middle images), and ending with the south pole

(right). NASA/SWRI/MSSS/ GERALD EICHSTÄDT/SEÁN DORAN

Juno achieved another first when JunoCam snapped the closest-ever pictures of the planet’s turbulent Great Red Spot from a distance of 6,130 miles (nearly 9,900 kilometers)

July 10. NASA/SWRI/MSSS/ GERALD EICHSTÄDT/SEÁN DORAN

WWW.ASTRONOMY.COM 25 During its plunge into Saturn on September 15, the Cassini spacecraft kept its antenna pointed at Earth until 4:55 A.M. PDT. Shortly after its signal was lost, the spacecraft ended its mission as a meteor streaking across

Saturn’s sky. NASA/ JPL-CALTECH

Cassini’s kiss goodbye

On September 15, the Cassini tweaked the spacecraft’s orbit. spacecraft took its last bow. It As a result, four days later grazed Saturn’s atmosphere, Cassini dove between Saturn’s burned up due to friction, and inner rings and its upper atmo- became part of the planet it sphere. After that close flyby, had spent 13 years exploring. the spacecraft followed a six- The craft arrived at the day elliptical orbit to its far- ringed planet in summer 2004 thest point before swinging after a seven-year journey. back through that gap again Since then, Cassini has revealed May 2. In total, Cassini passed NASA/JPL-CALTECH/SPACE SCIENCE INSTITUTE SCIENCE NASA/JPL-CALTECH/SPACE not just the planet itself in between Saturn’s inner rings In one of the last few photos taken Cassini imaged its impact site in more detail than ever before, and its atmosphere 22 times by Cassini, the moon Enceladus monochrome just hours before its but also has shown Saturn’s before finally diving into the sinks behind Saturn September 13. 13-year mission at Saturn ended. NASA/JPL-CALTECH/SPACE SCIENCE INSTITUTE This is the last image taken by the moons as a diverse bunch, with ringed planet’s upper atmo- spacecraft’s cameras, recorded a few possibly capable of sup- sphere and disintegrating. at 19:59 UTC (spacecraft time) porting life. “We’ve changed During each close crossing, September 14. how you look at the Saturn Cassini was between about pole, and features in the rings. system,” says Linda Spilker, 1,000 miles and 2,400 miles Crossing inside the rings also Cassini’s project scientist. “I’m (1,700 km and 3,900 km) above meant that Cassini could mea- After those 22 orbits, Cassini just so proud of Cassini and all the planet’s cloud tops. The sure precisely the mass of the completed a final half orbit. its wonderful discoveries.” spacecraft’s imaging camera rings and even sample a few On the night of September 14 The end of this historic mis- continued to take incredible ring particles, something never and into the early hours of sion went precisely as planned. photographs, while its other 11 done before. And by flying so September 15, scientists and The primary mission took four instruments also recorded close to the planet, the space- engineers gathered at NASA’s years, but after two mission data. The craft was traveling craft’s magnetometer was able Jet Propulsion Laboratory and extensions, the spacecraft was too fast at each orbit’s closest to take detailed measurements held a vigil. “I think of Cassini running out of fuel. The approach — some 75,000 mph of the strength and direction of almost like a person,” says Cassini team decided to make — to snap photos at those pre- the planet’s magnetic field. Spilker. On September 15, the final few months memo- cise moments, but the camera Scientists can use that informa- Cassini plunged into Saturn’s rable via a mission plan they system could focus well enough tion to learn about the rotation atmosphere; the final signals named the Grand Finale. to take images at other times in and size of Saturn’s core, plus arrived at 4:55 A.M. local time. On April 22, as Cassini flew the orbit. It captured atmo- determine how fast the cloud And then the Cassini mission by Saturn’s largest moon, spheric vortices, the great tops are moving with respect to team said goodbye to a friend Titan, the moon’s mass hexagon at the planet’s north the core. of nearly 20 years.

26 ASTRONOMY • JANUARY 2018 The case of the mysterious radio waves One of the most mysterious Berkeley, during a January 4, signals encountered in modern 2017, press conference announc- astrophysics is a blast of radio ing the observations. The scien- waves lasting only milliseconds. tists found a varying source of The first of these fast radio radio waves at that rough loca- bursts (FRBs) was discovered tion. Was that source connected about a decade ago, but several to the FRB signals? years elapsed before astronomers Astronomers used additional detected another. Now, they know radio instruments to zoom in on of around 20 FRBs, and yet these the suspected sky site. The bizarre signals remained mysteri- European Very-Long-Baseline ous because astronomers couldn’t Interferometry Network, which figure out precisely where any of connects 21 radio telescopes scat- them were originating. tered mostly across Europe, iso- What scientists needed was to lated the location further. The pinpoint a signal’s location on FRB signal was originating just the sky with enough precision to 130 light-years away from Totality crosses find out how far away the source another source of both radio America was. In the past year and a half, waves and optical light. It looked the universe has obliged. like the two might be related. One of nature’s greatest spectacles August 21 marked It all hinged on a discovery Next, scientists used an optical arrived at the Oregon shore at the first time a total made a few years ago. Scientists solar eclipse crossed telescope to identify where in 10:16 A.M. PDT on August 21. The the continental found an FRB that actually three-dimensional space the signal midmorning light turned to dark- United States in seemed to repeat, though not was coming from. They learned ness as the Moon blocked the Sun’s nearly 100 years. with any noticeable pattern. Now that a small, faint galaxy hosts this As millions of people disk from view. The Sun’s million- watched the Moon they knew a rough location in the FRB. This dwarf galaxy has 1,000 degree outer atmosphere, the solar blot out the disk sky. A coordinated effort of sev- times less mass than the Milky corona, then took center stage. And of the Sun, the eral radio telescopes across the Way and is physically 10 times for the millions of people in that brilliant solar corona globe followed. Using the Very smaller than our home galaxy. It appeared. 70-mile-wide (115 km) shadow, the NASA/AUBREY Large Array (VLA) to take 83 GEMIGNANI lies so far away that the radio corona looked like fire sprouting hours of observations in 2015 waves traveled some 2.4 billion from a gray disk. The shadow then and 2016, astronomers figured light-years to reach our telescopes. continued across 13 more states before the South out roughly where the blast Now that astronomers have Carolina coast ushered it into the Atlantic Ocean. — called FRB 121102 — is located pinpointed the precise location, There was nothing surprising about the August 21 on the sky. The VLA captured the next step is to figure out what solar eclipse. Astronomers understand eclipse geom- the repeating signal nine times. process is producing this repeat- etry very well, and they can predict these events “The FRB was extremely gen- ing radio signal. For that, astron- millennia in advance. But this eclipse was historic for erous to us,” said Casey Law of omers may need the universe to other reasons. It crossed the entire continental United University of California, cooperate again. States, the first eclipse to do so in almost a century. More than 12 million people lived along the path of the 2017 eclipse. An additional 20 million people traveled to get a better view, according to the University of Minnesota’s Jon Miller. Talk of traffic nightmares, like gridlock on interstates, began cir- cling months beforehand. Some hotels and camping sites were booked several years in advance. Twenty- one national park units and seven scenic national trails lay in the path of totality — including Grand FRB 121102 Teton in Wyoming and Great Smoky Mountains in Tennessee and North Carolina — and some of them experienced full capacity that August day. Whether people made their observing plans years out or waited until the day before, August 21, 2017, presented an act of beautiful celestial geometry to those along the Moon’s umbral path. It’s likely no The fast radio burst FRB 121102 is the only known repeating FRB. Astronomers other astronomical observing event in history has used this property to track down the burst’s host galaxy: an unassuming garnered so much attention. dwarf galaxy nearly 3 billion light-years away. GEMINI OBSERVATORY/AURA/NRC/NSF/NRAO

WWW.ASTRONOMY.COM 27 Terrestrial planet plethora

One of humanity’s greatest discov- world, which orbits farthest from The TRAPPIST-1 system contains at least eries will be the confirmation that the star, came in May. And there seven planets circling life exists elsewhere in our uni- could even be more exoplanets in an M-dwarf star. All verse. We haven’t made this dis- the system. seven appear Earth- covery yet, but each year, astrono- sized and terrestrial From the amount of light each in nature, prompting mers move closer to that goal. This exoplanet blocked, the astrono- astronomers to past year was no exception. mers could calculate its diameter. wonder whether they In February, a team of planetary By analyzing the amount of time might also host life. scientists announced — both at a that passed between subsequent NASA/JPL-CALTECH press conference and in a Nature transits of the same exoplanet, article — that it had found seven and comparing the six different Earth-sized planets orbiting a inner worlds’ orbits, the scien- nearby star. All seven were within tists could also estimate those the so-called habitable zone. exoplanets’ masses. With diam- Inside this region, the amount of eter and mass, you can calculate starlight the exoplanets receive density. The calculations suggest could lead to ideal temperatures the six inner worlds are rocky like for liquid water on those worlds’ Earth, Mars, Venus, and Mercury, • BepiColombo, the European- surfaces. (Though just because although the numbers are still Japanese collaborative mis- a planet is in the habitable zone highly uncertain. (The seventh sion to Mercury, is set to doesn’t mean there’s water.) The exoplanet’s density has even launch in October. researchers also ran computer greater uncertainty.) • SpaceX is still hoping for models and estimated that three While the exoplanets might be crewed missions to start up of those exoplanets could harbor rocky and Earth-sized, their star is in 2018. water oceans on their surfaces, nothing like the Sun. TRAPPIST-1 provided those worlds also have holds only 8 percent of the Sun’s • NASA’s next space-based Earth-like atmospheres. mass and is about 12 percent of exoplanet observatory, the To find these seven worlds, the width of our star. It is also Transiting Exoplanet Survey astronomers used several much cooler, giving off a red glow Satellite (TESS), launches in ground-based telescopes in instead of our Sun’s yellow-white early 2018. addition to the infrared Spitzer light. This planetary system is • The agency’s InSight Space Telescope to focus on the also far more condensed than (Interior Exploration using star known as TRAPPIST-1. They our solar system. The innermost Seismic Investigations, watched as its starlight flickered. planet completes an orbit around Geodesy and Heat From their hours of data, the TRAPPIST-1 in 1.5 days, whereas Transport) mission to Mars researchers determined the flick- the most distant one takes 18.8 has a launch window begin- ering was due to multiple planets days. Even though astronomers ning May 5, and a landing crossing in front of the star, block- haven’t found an exact solar date of November 26. ing a tiny amount of starlight at system analogue, the discovery each crossing. As of February, of seven likely terrestrial planets • The X-ray satellite they could confirm six exoplan- orbiting a star only 40 light-years Spectrum-Roentgen- ets in orbit around TRAPPIST-1. away is a good indication that an Gamma (SRG) will launch Confirmation of the seventh Earth twin may be out there. in 2018. This Russian and German collaboration proj- ect will scan the entire sky and is expected to discover millions of supermassive black holes. — L.K. 28 ASTRONOMY • JANUARY 2018 Astronomers spotted gravitational waves, gamma rays, and several other forms of light from a pair of merging neutron stars August 17. The event, called a kilonova, produced heavy elements such as gold

and platinum. ESO/ L. CALÇADA/M. KORNMESSER

The day multi-messenger astronomy burst forth

August 17, 2017, began like any other day. and had come online just weeks before, but Las Campanas Observatory in Chile. It But at 8:41 A.M. EDT, everything changed. it couldn’t make out the August 17 event spied a new source of light in the outskirts For 100 seconds, ripples in the fabric of even though the signal should have been of galaxy NGC 4993. Several other tele- space-time stretched and squished Earth’s visible. “The event happened in one of the scopes confirmed the find. extremely precise gravitational wave very few areas on the sky that they have By spreading out the received optical telescopes. A bright flash of gamma rays low sensitivity to,” says LIGO team mem- and infrared light by wavelength, astrono- followed shortly afterward. And so began ber Amber Stuver of Villanova University. mers found chemical fingerprints of heavy weeks of intense analysis by 3,500 astrono- “That gave us information that made us elements, including those heavier than iron mers and physicists using 70 observatories better able to pinpoint where on the sky the — elements like gold. While researchers scattered across all seven continents and source could have come from.” know that stellar explosions called super- in space. While gravitational wave scientists were novae produce these elements, which then Scientists announced the results of that alerting their colleagues, gamma-ray diffuse throughout the cosmos and provide analysis October 16 during several press astronomers were processing a signal that material for new stars and planets, super- conferences and in more than three dozen arrived at the Fermi gamma-ray space nova blasts account for only part of the papers. They had spotted gravitational observatory. “We were absolutely sure we universe’s heavy element content. Neutron waves from a source never before detected: had a gamma-ray burst,” says Eric Burns, a star collisions, it turns out, create the rest. two neutron stars spiraling together and team member with Fermi’s Gamma-ray Plenty of questions remain. This round merging. The collision also let out a Burst Monitor (GBM). The GRB arrived of analysis was just the first, says Burns. gamma-ray burst (GRB), thus proving a 1.74 seconds after the gravitational wave “Now it’s time for the community to long-held assumption that neutron star signal ended. Once the LIGO/Virgo scien- come in and figure out what really hap- mergers cause at least one type of GRB. But tists narrowed the location of their source pened by combining all of this informa- this event also emitted other forms of light: on the sky, it lined up with the GBM’s sig- tion, hopefully into a single coherent visible light, infrared radiation, radio nal. “That’s when all of us were certain it picture,” he says. Perhaps the neutron star waves, ultraviolet light, and X-rays, all of was the same thing,” says Burns. merger marks the beginning of multi- which astronomers examined for details. The observatories had seen two neutron messenger gravitational-wave astronomy On the morning of August 17, the gravi- stars spiraling toward one another, circling and the future of the field, in which the tational waves reached Earth first. The some 1,500 times before merging. And they entire astronomical community studies all Laser Interferometer Gravitational-wave saw the resulting energetic light. What else forms of light and gravitational waves Observatory (LIGO) in Louisiana — com- could we learn about this incredible event? together to reveal how the universe’s most posed of fine-tuned lasers, mirrors, and That region of sky hosts some 50 galax- energetic events work. detectors — saw a strong signal, as did its ies. Pinpointing the signal’s origin required twin in Washington state just milliseconds other forms of light. Eleven hours after Liz Kruesi, a contributing editor to Astronomy, later. The European gravitational wave the LIGO and Fermi events, the area writes about our universe from the sunny locale observatory, Virgo, uses similar technology came into view of the Swope Telescope at of Austin, Texas.

WWW.ASTRONOMY.COM 29 Do exoplanets have moons? Our solar system harbors at least 180 moons. Now astronomers have launched a quest to find satellites in another system. by Nola Taylor Redd n the African savanna, a tiny telescope with owl-like eyes peers at the heavens. Amid OAntarctic ice, a larger instru- ment stares at the same slice of sky. The two are part of an international hunt to discover the first moon beyond the solar system. In 2017, a slew of telescopes turned their eyes toward Beta Pictoris, a modest star in the southern sky just 6° from brilliant Canopus. More specifically, astronomers are scrutinizing Beta Pictoris b, one of the few exoworlds discovered through imaging. The star’s massive planet barely avoids passing directly between its sun and our planet from April 2017 to January 2018. The near miss opens up a rare opportunity to study any material surrounding the planet, which could boast rings visible from Earth. With a little luck, it may also reveal an exomoon, a plan- etary satellite beyond the solar system.

Astronomers are hunting for possible moons and rings around the gas giant planet Beta Pictoris b. Beta Pic itself, enveloped in a dusty disk, lurks in the background. RON MILLER FOR ASTRONOMY

WWW.ASTRONOMY.COM 31 The young star Beta Pictoris boasts a huge, flat disk of dust and gas. The disk glows brightly thanks to its edge-on orientation and vast amounts of starlight-scattering dust. The Hubble Space

Telescope captured this view by blocking Beta Pic’s light. NASA/ESA/D. APAI AND G. SCHNEIDER (UNIVERSITY OF ARIZONA)

The gas giant planet Beta Pictoris b appears as a faint blip to the upper left of center in this 2003 image, though confirmation did not come until 2009. Astronomers carefully subtracted the light of Beta Pic itself to reveal the planet’s glow. ESO/A.-M. LAGRANGE ET AL.

Astronomers confirmed the presence of Beta transit, Wang, a graduate student at the Pictoris b with this 2009 image. The massive University of California, Berkeley, calcu- planet’s faint glow appears on the opposite side of Beta Pic (indicated by the star symbol lated the planet’s path. at center) than it did in observations taken To his disappointment, Wang learned six years earlier. ESO/A.-M. LAGRANGE that Beta Pic b dances just outside our line of sight to the star. But he quickly realized Among the Sun’s family, moons are Even more important, the region that its Hill sphere — the region where a abundant. Only two planets — Mercury around the planet where any rings or planet’s gravity dominates that of its host and Venus — lack orbiting companions. moons could exist is passing between star and where any rings or moons could It’s not unreasonable to think that moons Beta Pic and Earth over the course of orbit — would cross. If the planet carries might be plentiful around exoplanets. So 10 months, with its closest brush in late a massive ring system tilted with respect far, however, they’ve dodged detection. Part August 2017. Any moons or rings hiding to Earth, it could be visible, as could a of the trouble is technological. Small rocky around the gas giant may well be revealed. massive moon. worlds are barely discernible, and tinier But it can be spotted only if astrono- moons present even greater challenges. A limited opportunity mers are looking. Luck also plays a role. Although scientists When Jason Wang turned his eye toward are hunting for exomoons using a variety of Beta Pictoris in 2016, he was far from the Moons near and far techniques, each requires a specific align- first astronomer to find it intriguing. Since The solar system’s moons play an impor- ment between the candidate object and scientists discovered a disk of gas and dust tant role in helping scientists understand Earth. And even then, the largest search orbiting the young star in the 1980s, it has how planets form and evolve. For example, has targeted hot Jupiters, massive gas giants garnered plenty of attention. In the 1990s, Jupiter’s four big moons — Io, Europa, that circle their host stars in days or even astronomers detected a warp in this disk Ganymede, and Callisto — help track hours. If these giants traveled inward from that suggested an unseen planet. But it was how water surrounded the gas giant when the outskirts of their system, as many sci- not until 2009 that Anne-Marie Lagrange it was young. entists suspect, they may have shed their of Grenoble Observatory and her col- “These four moons, they serve as tracers moons along the way or lost them in a leagues confirmed Beta Pic b through — or records — of the water or tempera- gravitational tug-of-war with their star. direct imaging. The gas giant holds about ture distribution in the circumplanetary For Beta Pic, however, the stars — and 10 times the mass of Jupiter. accretion disk, which has long gone today,” planets — seem to be aligned. The system Later photos revealed the world drawing says René Heller of the Max Planck boasts a gas giant orbiting at about Saturn’s closer to our line of sight to Beta Pic. If the Institute for Solar System Research in distance from the Sun, far enough away planet should cross in front of its sun, the Germany. To Heller, these objects could that it should be able to hold on to any light that it blocked would reveal more reveal similar characteristics about other satellites. Also, the star is only about information about the world. NASA’s planetary systems. Scientists still aren’t sure 20 million years old, so even if the violent Kepler space telescope used this technique, just how planets form; exomoons could interactions common to adolescent systems known as the transit method, to discover help clarify the process. “We can take these wind up stripping its moons, there’s a good thousands of exoplanets. With the hope moons as yardsticks to calibrate our models chance they’re still orbiting today. that Beta Pic b would make a similar of giant planet formation,” he says.

32 ASTRONOMY • JANUARY 2018 A ring system that spans some 200 times the diameter of Saturn’s rings circles the exoplanet J1407 b. Astronomers suspect that undetected moons may create the observed gaps. This artist’s depiction shows the rings blocking light from the

host star, J1407. RON MILLER

An exomoon alone could be a challenge lifetime is much shorter than the age of of exomoons in much the same way that to detect. While Beta Pic b’s entire Hill the solar system, says Heller. Fragments Saturn’s moons sculpt its rings. sphere will take from early April 2017 to from colliding moons are one possible Ironically, although the rings are visible, late January 2018 to transit, a massive source, and exoplanets presumably could the planet has yet to be discovered. The moon detectable from Earth would zip by host similar systems. And a young planet moons also have evaded direct detection; in two days, says Wang. And it may make like Beta Pic b may still possess a dazzling, the evidence for them remains circumstan- only a single transit. To confirm an exo- pristine ring system that could put tial. Nor have the strange rings eclipsed planet, scientists typically have to view at Saturn’s to shame. J1407 again, although Kenworthy and his least three transits to rule out other possi- Matthew Kenworthy of Leiden colleagues are keeping their eyes on the bilities. Since Beta Pic b takes more than Observatory in the Netherlands knows star. But without seeing a planet, there’s no 20 years to orbit its star — and the moon about rings. In 2007, he and his colleague, way to determine an orbit to know when may not be visible during some transits, Eric Mamajek of the University of the geometry might repeat. according to Heller — it could take a Rochester, spotted a massive ring system “We think that the same thing may century to confirm a moon this way. around a planet circling another star, happen with Beta Pic and its planet,” says Massive rings could be quite a bit easier J1407, only a few million years younger Kenworthy. And this world might provide to spot. Saturn boasts the solar system’s than Beta Pic. The enormous rings stretch even better signs of its rings than J1407 did. most massive ring system, but all the giant nearly 200 times farther than Saturn’s, and “The difference is that we know when the planets have rings. Saturn’s set remains an they have gaps that the researchers tenta- planet is moving between us and its star.” enigma, however, because its expected tively identify with the gravitational pull There’s another reason Kenworthy is mildly optimistic about finding rings. Because Beta Pic is reasonably bright — Rings around an at 4th magnitude, it’s easily visible to the naked eye from a dark site — astronomers exoplanet have long used it as a standard star to help calibrate observations of other objects. In J1407 b 1981, a strange fluctuation changed the star’s usually steady light over a two-week Track of J1407 period, creating a pattern that puzzled astronomers. According to Wang’s calcula- tions, there’s a good chance that Beta Pic b’s Hill sphere transited the star at that time, suggesting that something associated with Astronomers deduced the presence of the planet blocked the star’s light. So when J1407 b’s ring system from the rapid brightness variations it caused as the Kenworthy heard that the planet itself rings passed in front of the Sun-like star J1407 in 2007. In this plot, the intensity of the red color corresponds to how much light each ring blocked. wasn’t going to transit, he began wonder- ASTRONOMY: ROEN KELLY, AFTER KENWORTHY AND MAMAJEK ing if perhaps a set of massive rings could produce a signal.

WWW.ASTRONOMY.COM 33 The Antarctic Search for Transiting Exoplanets researcher at France’s National Center for observed Beta Pictoris under pristine skies Scientific Research, is using the instrument throughout the long southern winter. This to study the makeup of comets around the view shows the Milky Way rising above the distant star. His project searches for the telescope’s dome. EOIN MACDONALD/IPEV/PNRA absorption signatures of exocomets imprinted in the spectrum of Beta Pic. Wilson is intrigued to see if the amount of water and other ingredients varies within the Hill sphere, much as lighter compounds in Earth’s atmosphere drift higher above our planet’s surface. To spot atoms like hydrogen, nitrogen, carbon, and oxygen, Wilson must probe at far- ultraviolet wavelengths, which are visible only from space because Earth’s atmo- sphere absorbs them. Wilson and his col- leagues also hope to study the motion of gas and dust around Beta Pic b. If a moon orbits this planet, the team could help determine its natal material. Far smaller than Hubble is the Bright Target Explorer Constellation (BRITE- Constellation), an array of nanosatellites studying the brightest stars in the sky. The first of the five 8-inch (20 centimeters) tele- scopes launched in February 2013 to study stellar quakes. Just like earthquakes help reveal the internal structure of our planet, starquakes can reveal what’s happening inside a star. Konstanze Zwintz, a stellar scientist at Austria’s University of Innsbruck, previ- ously studied Beta Pic with BRITE- Constellation. Now she has the star in her sights again. Her goal was to map its oscil- lations precisely before the transit began. Observations of the Hill sphere need to account for Beta Pic’s pulsations. Zwintz’s models should help other researchers remove the variations of light that come from the star, leaving behind only traces of a ring or moon. Although she won’t actu- ally study the star during the transit, the oscillations should remain constant over the short period. “In principle, the mecha- Beta Pic b’s Hill sphere stretches roughly the search to space. Working with his nism acts like a clock for a very long time,” the distance between the Sun and Earth. adviser, Paul Kalas, also from UC Berkeley, says Zwintz. Any rings would have to be enormous for Wang has targeted the transit with the Although Hubble could catch a glimpse astronomers to spot them from our world. Hubble Space Telescope several times. of a moon as large as Io or Ganymede, two And if any gaps like those seen in the rings Hubble got its first glimpse in mid-June, of Jupiter’s largest satellites, the odds are around J1407’s planet show up, they could when it searched for material orbiting the against it. Astronomers would have to be be clues to the presence of exomoons. “The infant planet. The space observatory took incredibly fortunate to spot a two-day tran- potential for seeing exomoons by seeing the its second look in early August. Wang says sit while the space telescope is pointed at path they cleared is very exciting and very their initial analysis of the data shows noth- Beta Pic b. plausible,” says Kenworthy. ing. But the team has three more observa- And ground-based observatories tions scheduled between early October and couldn’t provide a lot of help, particularly A worldwide hunt late November (after this issue went to during the transit’s early stages. Beta Pic Beta Pic’s southern location limits observa- press), and Wang remains optimistic about climbs highest in the Southern Hemisphere tions because the Southern Hemisphere finding material around Beta Pic b. sky late in the calendar year, so it was houses far fewer telescopes than its north- Wang isn’t the only one studying the essentially beyond the reach of earthly ern counterpart. So Wang decided to take planet with Hubble. Paul Wilson, a instruments until August.

34 ASTRONOMY • JANUARY 2018 View from a frozen desert There is one place on Earth where the star remains visible throughout the Southern Hemisphere winter: Antarctica. The winter season keeps the frozen continent shroud- ed in darkness, so from May to July, it is the only land on Earth where the transit can be viewed. Kalas reached out to Chinese astronomers, who run a handful of modest telescopes in Antarctica, and they planned to observe the transit. He also spoke with Tristan Guillot at the Observatoire de la Côte d’Azur in Nice, France, about a telescope that had only Above: The owl-like eyes of the Beta Pic b ring recently left the continent. camera stare toward the southern sky, where The Antarctic Search for Transiting scientists hope they will pick up the telltale Exoplanets spent four years hunting for signs of exomoons or exorings around the massive planet. exoplanets as they transited their faint host MATTHEW KENWORTHY (LEIDEN OBSERVATORY) stars before the telescope came home at the Left: The Beta Pic b ring camera operates from end of 2013. But when asked, the French the South African Astronomical Observatory. group responsible for the 16-inch (40 cm) Astronomers built the camera, which takes an image every six seconds, to record any instrument was willing to return it to the moons or rings of the gas giant planet as southern continent. they pass in front of their host star. “This system being so extraordinary, MATTHEW KENWORTHY (LEIDEN OBSERVATORY) IPEV, the French Polar Institute, was will- ing to make a really important effort to technical problems must be resolved from he installed the Beta Pic b ring camera — allow this telescope to be flown back to a distance. Only about a dozen people bRing for short — on the African savanna Antarctica,” says Guillot. “This is some- remain on the base over the winter, and at the South African Astronomical thing really special.” they aren’t astronomers; they can fix any Observatory. About the size of a mini- Operating in Antarctica isn’t without mechanical issues, but they can’t address fridge, the telescope sits off to the side of its challenges. Standard electric cables scientific concerns. larger instruments, its camera eyes peering become as fragile as glass once tempera- “It’s not easy, but once you overcome toward the south. The scope takes an tures plunge to –58 degrees Fahrenheit all that, then you have the reward of a image every six seconds, and three com- (–50 degrees Celsius), says Guillot, so you night that can be really, really nice with puters inside the instrument crunch the have to be extremely careful with connec- extremely good conditions,” Guillot says. data before transmitting it back home. A tions. And electronics and parts built to While Antarctica was the only conti- second bRing, supervised by Mamajek, withstand –4 F (–20 C) begin to have prob- nent where Beta Pic was well placed has been set up in Australia, and the two lems when they reach –112 F (–80 C), even throughout the southern winter, it won’t should provide nearly continuous coverage when heated. be the only site viewing the transit’s latter of the night sky. If a large series of exorings While it rarely snows on the continent, stages. Telescopes in Chile and South exists within Beta Pic b’s Hill sphere, the ice can form. The base sits on a plateau at Africa were set to peer at the star after bRing team should know pretty quickly. an elevation of 10,000 feet (3,000 meters), August, once it put some distance between “We’re pretty sure we’ll see something, and when the wind blows, it can carry ice itself and the Sun. but we’re not sure when we’ll see it or how to cover the instruments. Frost and con- Kenworthy has built a ground-based big the signal will be,” says Kenworthy. densation are concerns, too. And any telescope just for the event. In January 2017, This loose-knit band of astronomers The 16-inch telescope of the Antarctic Search for Transiting Exoplanets is working together, each on their own and its dome rest on the frozen desert of Earth’s southernmost continent. individual projects, to reveal the secrets of This December 2016 view shows the instrument before it began its Beta Beta Pictoris. “This is a worldwide effort,” Pictoris observing campaign. DJAMEL MEKARNIA AND ABDELKRIM AGABI/IPEV/PNRA Kalas says. If one of the teams spots some- thing unusual, it will immediately share the news with everyone else, including other astronomers who don’t have their eyes trained on the bright young star. They hope any find will galvanize even more astronomers to turn their attention to Beta Pic. “It’s quite an exciting and unusual time,” says Kenworthy.

Nola Taylor Redd is a freelance science writer who writes about space and astronomy while home schooling her four kids.

WWW.ASTRONOMY.COM 35 SKYTHIS Visible to the naked eye MARTIN RATCLIFFE and ALISTER LING describe the Visible with binoculars MONTH solar system’s changing landscape as it appears in Earth’s sky. Visible with a telescope January 2018: Totality over America

on casting its shadow all the Totality occurs at the month’s way to its only natural satellite. second Full Moon, so it also Those in the continent’s earns recognition as a Blue western two-thirds can view Moon. Our satellite reaches at least some of totality, which its first Full phase on New gets underway at 6:52 a.m. CST Year’s Night. This is the clos- (4:52 a.m. PST). Totality lasts est Full Moon of 2018, so it is 76 minutes and can be seen in also the biggest (33.5' across), its entirety west of a line that and many people will feel runs from central North compelled to label it a Dakota to New Mexico. The “Super Moon.” eclipsed Moon hangs among Although no planet rises the stars of Cancer the Crab to the level of “super” this with the Beehive star cluster month, most will reward your (M44) 4° to its northwest. viewing efforts. The evening Observers in Northern sky offers the two outermost California, Oregon, and and dimmest members of the Washington get to witness solar system’s family. Despite the concluding partial phases, their faintness, both Uranus which wrap up at 7:11 a.m. PST. and Neptune are within range Fortunately, we don’t have long of binoculars. Neptune lies to wait for the next total lunar lower and should be your first eclipse. Earth will cast its target. In early January, the On October 8, 2014, the Full Moon passed into Earth’s umbral shadow and shadow on the Moon on July 27 ice giant stands 30° above the created this stunning total lunar eclipse. On January 31, observers across (though this time the eclipse southwestern horizon at the more than half the globe can witness a similar event. DAMIAN PEACH won’t be visible from North end of twilight. America), and again the night Neptune glows at magni- ll of January’s naked-eye From North America, the of January 20/21, 2019. tude 7.9 among the back- planets congregate in eclipse occurs before dawn The eclipse isn’t Luna’s only ground stars of Aquarius. the morning sky. Mars and delivers better views to distinction during January. You can find it near and Jupiter lead the those who live farther west. way, and they provide East of a line that runs from A great view of totality Athe month’s planetary high- the Ohio-Indiana border to light when they pass within 1° New Orleans, the eclipse of each other during the New starts after the onset of twi- LEO Year’s first week. The pair light and the Moon sets before makes a stunning backdrop totality begins. The Full Regulus for the Moon when it slides Moon enters Earth’s umbral by a few days later. Mercury shadow at 6:48 a.m. EST and Saturn also shine brightly (3:48 a.m. PST). Within Eclipsed Moon from their positions lower in 10 minutes, the lunar orb Pollux the predawn sky. looks like a giant sugar cookie CANCER Castor But the Moon deserves top with a bite taken out of it. HYDRA billing in January’s sky show. The geometry of the Sun, Alphard GEMINI On the 31st, our satellite dives the Moon, and Earth drives completely into Earth’s umbral itself home during lunar shadow, bringing a total lunar eclipses in twilight. With the 10° eclipse to viewers in much of Sun just below the eastern North America, the Pacific horizon before dawn and the January 31, 5:30 A.M. PST Looking west Ocean, Asia, and Australia. eclipsed Moon hanging low in This is the first total eclipse the west, you can almost feel Viewers in western North America won’t want to miss the spectacular total since September 2015. the giant rock you’re standing lunar eclipse in January 31’s predawn sky. ALL ILLUSTRATIONS: ASTRONOMY: ROEN KELLY

36 ASTRONOMY • JANUARY 2018 RISINGMOON Reading ages from a crater’s structure Theophilus, Cyrillus, and Catharina

If there’s a best face to the Moon, size as Theophilus, its softer edges the thick waxing crescent phase imply an older age. has to be it. Large waves seem to Still farther south rests ancient swell across smooth seas, big cra- Catharina. Its lower, rounded rim ters take your breath away, and signifies a longer history of pum- Torricelli small impacts stand out by casting meling. The impact that created long shadows. On the evening of Theophilus spread a rugged January 22, the Serpentine Ridge debris apron north into the Sea grabs your attention as a couplet of of Tranquility. Selenographers Sinus Asperitatis light and darkness snaking across named this bleak landscape Sinus Theophilus Mare Serenitatis (Sea of Serenity) Asperitatis (Bay of Roughness). north of the equator. Although it The unusual double crater looks like a frozen wave rippling Torricelli lies in this bay. Planetary Cyrillus through the lava, it’s actually a scientists think its weird shape compression feature formed when arose from a single glancing blow the mare lavas contracted. instead of two unrelated events. Scanning southward, you’ll A fraction of a second after the cross Mare Tranquillitatis (Sea of initial impact, what was left of the Catharina Tranquility) before running into projectile blasted through the the crater Theophilus. This back wall of the developing main N 60-mile-wide, sharp-edged impact crater. Torricelli — named after feature presents a complex jumble the Italian scientist who invented E of central peaks and slumped ter- the mercury barometer — sits races on the rim’s inside slopes. off-center in a low-profile, bat- This trio of lunar craters on the waxing crescent Moon tells a tale Just to its south lies Cyrillus. tered bowl filled to the brim with of advancing age, from Theophilus in the north to Catharina in Although this crater is the same solidified lava. the south. CONSOLIDATED LUNAR ATLAS/UA/LPL; INSET: NASA/GSFC/ASU

4th-magnitude Lambda (λ) Aquarii. On the 1st, the planet METEORWATCH lies 0.5° southeast of Lambda. By the 31st, Neptune stands The Super Moon’s Quadrantid meteor shower 1.1° due east of the star. While URSA MINOR binoculars reveal the world as unwelcome impact URSA MAJOR a dim pinpoint, a telescope shows the planet’s blue-gray Although the Quadrantids rank BOÖTES disk, which spans 2.2". among the year’s strongest show- Radiant Arcturus Uranus shines brighter ers, the 2018 edition likely won’t and lies farther east, against be memorable because of the the backdrop of eastern January 1 Super Moon. At the peak CORONA before dawn on the 4th, bright BOREALIS Pisces. Although the planet moonlight will wash out faint is an easy binocular object at DRACO meteors and make the brighter magnitude 5.8, Pisces has few HERCULES ones less impressive. The hourly Vega bright stars to guide you. Your rate can top 100 meteors in good best bet is to home in on 5th- years, but observers may be lucky 10° magnitude Mu (μ) Piscium. to see 20 this year. Quadrantid meteors Uranus remains nearly sta- Observers shouldn’t give up, January 4, 4 A.M. Active Dates: tionary during January some however. Bright meteors still show Looking east-northeast Dec. 28–Jan. 12 Peak: January 3/4 3° north of the star. And no up through moonlight, and the Bright moonlight mars the peak Moon at peak: Full Moon other object in the area shines nice planet grouping before dawn of January’s best meteor shower, Maximum rate at peak: so brightly. makes an early morning observing rendering it less impressive than 110 meteors/hour Uranus stands nearly 60° session all the more worthwhile. in most years. above the southern horizon as darkness falls. That’s the best time to target the distant OBSERVING The Full Moon on January 31 slides deep into Earth’s shadow, HIGHLIGHT — Continued on page 42 bringing a total eclipse to observers from North America to Asia.

WWW.ASTRONOMY.COM 37 N

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HOROLOGIUM

38 ASTRONOMY • JANUARY 2018 S Note: Moon phases in the calendar vary in size due to the distance from Earth JANUARY 2018 and are shown at 0h Universal Time. SUN. MON. TUES. WED. THURS. FRI. SAT. MAP SYMBOLS

Open cluster 123456

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: ROEN KELLY ROEN :

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C 21 22 23 24 25 26 27 ASTRONOMY

b

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28 29 30 31

_ BY ILLUSTRATIONS LACERTA Calendar of events

1 Mercury is at greatest western 11 The Moon passes 0.4° south d elongation (23°), 3 P.M. EST of asteroid Vesta, 11 P.M. EST

The Moon is at perigee (221,559 13 Mercury passes 0.6° south of `

+

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_ c W 1 P.M. EST (252,565 miles from Earth), P.M. _ 9:10 EST Uranus is stationary, 4 P.M. EST

a 15 The Moon passes 3° north of 3 Earth is at perihelion Mercury, 2 A.M. EST

a d (91.4 million miles from PISCES the Sun), 1 A.M. EST 16 New Moon occurs at Uranus Pa 9:17 P.M. EST th of the Su n (ecliptic) AQUARIUS Quadrantid meteor shower peaks 20 The Moon passes 1.6° south of Neptune, 3 P.M. EST 5 The Moon passes 0.9° north of Regulus, 3 A.M. EST 23 The Moon passes 5° south of b Uranus, 8 P.M. EST SPECIAL OBSERVING DATE 24 d 7 Mars passes 0.2° south of First Quarter Moon Jupiter before dawn. occurs at 5:20 P.M. EST CETUS 27 o The Moon passes 0.7° north ` 8 Last Quarter Moon of Aldebaran, 6 A.M. EST occurs at 5:25 P.M. EST 30 The Moon is at perigee 9 Venus is in superior (223,068 miles from Earth), NGC 253 A.M. A.M. SGP conjunction, 2 EST 4:57 EST _ SW Pluto is in conjunction with the 31 Dwarf planet Ceres is at Sun, 5 A.M. EST opposition, 8 A.M. EST SCULPTOR 11 The Moon passes 4° north of Full Moon occurs at Jupiter, 1 A.M. EST 8:27 A.M. EST; total lunar eclipse The Moon passes 5° north of Mars, 5 A.M. EST PHOENIX

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

WWW.ASTRONOMY.COM 39 PATH OF THE PLANETS The planets in January 2018

DRA Objects visible before dawn UMa LYN Dwarf planet Ceres reaches AUR CYG HER CVn opposition January 31 BOÖ Asteroid Flora reaches LYR opposition January 2 CrB VUL COM CNC Path of the

DEL LEO SGE Massalia SER ORI AQL CMi

EQU Celestial equator AQR A total lunar eclipse occurs VIR SEX January 31 across most of OPH LIB Mercury appears bright North America, Australia, before dawn in early January and Asia. Vesta Jupiter CRT Pluto SCT Mars CRV CMA CAP Sun Saturn LEP Mars passes 0.2° south HYA PYX SGR of Jupiter on January 6/7 ANT PUP MIC LUP COL SCO TEL VEL

Moon phases Dawn Midnight

18 17 16 15 14 13 12 11 78910 6 5 4 3 2 1

31 30 29

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

Mercury Uranus Mars

S

WE Pluto N Saturn Venus Ceres Neptune 10" Jupiter

Planets MERCURY VENUS MARS CERES JUPITER SATURN URANUS NEPTUNE PLUTO Date Jan. 1 Jan. 15 Jan. 15 Jan. 15 Jan. 15 Jan. 15 Jan. 15 Jan. 15 Jan. 15 Magnitude –0.3 –4.0 1.4 7.1 –1.9 0.5 5.8 7.9 14.3 Angular size 6.7" 9.8" 5.1" 0.8" 34.2" 15.1" 3.5" 2.2" 0.1" Illumination 62% 100% 92% 99% 99% 100% 100% 100% 100% Distance (AU) from Earth 0.999 1.711 1.830 1.645 5.761 10.972 19.879 30.601 34.464 Distance (AU) from Sun 0.389 0.728 1.619 2.576 5.430 10.065 19.901 29.945 33.485 Right ascension (2000.0) 17h07.4m 19h52.3m 15h21.8m 9h26.0m 15h06.9m 18h11.9m 1h31.2m 22h55.0m 19h22.1m Declination (2000.0) –20°52' –21°54' –17°39' 28°00' –16°24' –22°31' 8°56' –7°54' –21°40'

40 ASTRONOMY • JANUARY 2018 This map unfolds the entire night sky from sunset (at right) until sunrise (at left). Arrows and colored dots show motions and locations of solar system objects during the month.

Objects visible in the evening Jupiter’s moons Dots display positions PER AND LAC Io of Galilean satellites at 6 A.M. EST on the date Europa CYG TRI shown. South is at the LYR ARI top to match S e Sun (eE VUL cliptic) the view PEG WE Ganymede DEL through a Path Iris of th SGE telescope. N Callisto e Mo PSC TAU on Uranus EQU AQL SER 1

Neptune AQR 2 3 SCT CET 4 Callisto Sun Pallas Venus 5 Io SCL CAP ERI FOR PsA SGR 6 MIC 7 CAE PHE GRU 8

Early evening 9 Europa 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. 10 11

12 28 27 26 25 24 23 22 21 20 19 18 17 16 13 Jupiter

14 Ceres Earth Opposition Perihelion is 15 Ganymede is January 31 January 2/3 16

17 Mercury 18 Greatest western elongation 19 is January 1 Mars 20

21 Venus 22 Superior conjunction Jupiter is January 8/9 23

24

25

26 Uranus The planets 27

in their orbits Jupiter 28 : ROEN KELLY ROEN : Neptune Arrows show the inner planets’ 29 monthly motions and dots depict Saturn the outer planets’ positions at mid- Pluto 30 ASTRONOMY month from high above their orbits. Solar conjunction is January 9 31 ILLUSTRATIONS BY BY ILLUSTRATIONS

WWW.ASTRONOMY.COM 41 — Continued from page 37 Jupiter’s moons on the verge of eclipse WHEN TO VIEW THE PLANETS S Jupiter EVENING SKY MIDNIGHT MORNING SKY Uranus (south) Uranus (west) Mercury (southeast) Neptune (southwest) Mars (southeast) Jupiter (south) W Saturn (southeast) Europa

Io world through a telescope. A pair rises more than four view at medium power reveals hours before the Sun. Mars 15" Uranus’ 3.5"-diameter disk and shines at magnitude 1.5 while January 10, 5:25 A.M. EST distinct blue-green color. Jupiter dazzles at magnitude The rest of the visible plan- –1.8. The two straddle Libra’s On January 10, Io and Europa simultaneously disappear into Jupiter’s ets congregate in the morning second-brightest star, magni- shadow just a few minutes after the scene depicted here. sky. Mars already has begun its tude 2.8 Zubenelgenubi long trek toward an outstand- (Alpha [α] Librae), which from the Sun and invisible. Jupiter lies 2.1° west of the ing opposition in July. Or, more itself is a fine double. They haven’t been this close Red Planet. Use binoculars accurately, Earth has started to The planets shift eastward and visible since January 1998. for a close-up view or just catch up to Mars as our planet relative to the background A telescope shows both enjoy the scene with your speeds around the Sun a bit stars during January, with planets in a single low-power naked eye. more quickly than its outer Mars moving faster in its inner field of view. Mars spans 5" Although the planets rise neighbor. The Red Planet will orbit. Watch every morning as compared with Jupiter’s 34". earlier with each passing linger in the morning sky for their positions change relative Yet Jupiter lies three times far- morning, the gap between the several months, at first growing to Zubenelgenubi and to each ther away, a testament to its two grows wider. Slowpoke slowly in brightness and appar- other. On the 2nd, Mars passes status as a giant planet. Jupiter remains in Libra all ent size as Earth draws closer. 0.6° north of Alpha. And on Just four mornings after month, while Mars speeds The snail’s pace will pick up the 7th, the two solar system this fine conjunction, a waning across that constellation and this spring as Mars gets ready worlds stand just 16' apart. crescent Moon joins the two in enters Scorpius on the 31st. for a spectacular summer show. This is the closest they’ve been a stunning predawn display. Having brightened to magni- On January 1, Mars stands since September 2004, but they On January 11, Mars stands tude 1.2, the Red Planet 2.6° west of Jupiter and the were then just a few degrees 4.6° south of the Moon while stands 9° northwest of the COMETSEARCH A snowball in the winter sky Comet PANSTARRS (C/2016 R2) N Comet PANSTARRS (C/2016 R2) C/2016 R2 should be within shares the sky with dozens of reach of 4-inch telescopes under Pleiades deep-sky gems sprinkled across a dark sky. From the suburbs, 31 the winter Milky Way. It glides you’ll likely need a 10-inch scope past the head of Taurus the to spot it. On a positive note, it 26 Bull during January as it heads should be compact and well- north, and it remains on view for defined, making it a good target E 21 most of the night. at medium or high power. Path of ¡ Comet PANSTARRS A small ball of dust and ice, Astroimagers will want to 16 PANSTARRS simultaneously is out capture PANSTARRS in this pho- Aldebaran of place and at home. Visually it togenic region near the Hyades Hyades 11 appears much like a 10- or 11th- and Pleiades (M45) star clusters. TAURUS 6 magnitude elliptical galaxy, at Deeper exposures also will record a odds with the sparkling open the wisps of galactic dust and gas star clusters and amorphous gas that thread through the Milky Jan 1 2° clouds in this area. Yet the fin- Way’s outer spiral arm. Imagers This first-time visitor to the inner solar system should glow around 10th gers of obscuring dust and gas in should skip the first few days of magnitude as it travels between the Hyades and Pleiades star clusters. the background are every bit like January and the month’s final the nursery that gave birth to our week when the Moon interferes. much promise for bright com- hold, Comet 46P/Wirtanen solar system and its shell of com- Although the first few ets, things should pick up this could become visible to the ets, the Oort Cloud. months of 2018 don’t show summer. And if predictions naked eye next autumn.

42 ASTRONOMY • JANUARY 2018 The Moon slides past Mars and Jupiter LOCATINGASTEROIDS VIRGO Spica Out of darkness comes the light

Asteroid 20 Massalia reached of the month when the Full Moon opposition in mid-December, Moon lies nearby. Start at 3rd- Jupiter Mars which places it high in January’s magnitude Zeta (ζ) Tauri, the evening sky and not far from its star that marks the tip of the OPHIUCHUS LIBRA peak brightness. Massalia glows Bull’s southern horn. at 9th magnitude this month as Take a quick look at the Crab Antares it treks across eastern Taurus. Nebula (M1) 1° to the northwest CENTAURUS Although you might think before targeting 5th-magnitude SCORPIUS 10° the asteroid would be difficult 114 Tau 1.6° farther west. Just to locate among the swarms of three stars matching Massalia’s January 11, 6 A.M. faint Milky Way stars, it fortu- brightness reside near the path Looking southeast itously passes in front of the to 5th-magnitude 109 Tau, dark clouds of dust and gas which lies 2° west of 114. Your A waning crescent Moon stands above Mars and Jupiter in the predawn sky January 11. Brilliant Jupiter shines 20 times brighter than ruddy Mars. in this region. Only a relative best bet for seeing Massalia handful of stars shines through, move during a single observing leaving the 90-mile-wide aster- session comes the evenings of Scorpion’s brightest star, mag- You can find Mercury to oid in the open. January 10 and 11, when the nitude 1.1 Antares. The star’s the lower left of Mars and Avoid looking for it on the asteroid slides 0.2° south of name literally means “rival of Jupiter during January’s first first few and last few nights 109 Tau. Mars,” and the similarities three weeks. The innermost between their brightnesses planet reaches greatest elonga- Massalia horns in on Taurus the Bull and hues this month will tion on the 1st, when it lies 23° help you understand why west of the Sun and stands 11° N ancient astronomers made high in the southeast 30 min- the comparison. utes before sunrise. It shines at 121 This new season of Jupiter magnitude –0.3, more than a TAURUS observations promises some full magnitude brighter than splendid views through a tele- ruddy Antares 11° to its right. Path of Massalia scope. The best observing A view through a telescope 108 M1 Jan 1 109 E 31 comes shortly before twilight reveals the planet’s disk, 114 26 starts to paint the sky. In mid- which spans 6.7" and appears 6 11 16 21 January, the giant planet 62 percent lit. stands some 30° high in the Mercury loses altitude c southeast at that time, and its each morning. On January 10, 34"-diameter disk should look it’s still a decent 8° high a half- 1° impressive through any tele- hour before sunup, but that scope. Notice the two dark drops to just 4° by the 20th. equatorial belts that sandwich Although the planet remains This 9th-magnitude asteroid should be easy to find during January a brighter zone coinciding with at magnitude –0.3 throughout as it moves slowly against the backdrop of eastern Taurus. Jupiter’s equator. this period, it becomes pro- The jovian satellites are also gressively harder to see in worth a look. You’ll typically bright twilight. Its disk also each passing day. By the end of out of sight all month. Venus see the four brightest — Io, shrinks and becomes more the month, the planet appears reaches superior conjunction Europa, Ganymede, and fully illuminated, making tele- 10° high in the southeast an January 8/9, when it passes on Callisto — arrayed beside the scopic views less appealing. hour before sunrise. You the opposite side of the Sun planet’s disk, though occasion- But you’ll want to be should be able to spot it easily from Earth. Look for it to ally one or more will hide in sure to look for Mercury on among the background stars of reappear low in the evening front of or behind Jupiter. A January 13 because Saturn Sagittarius. Unfortunately, sky in late winter. good example of vanishing then lies just 0.6° north of the Saturn’s low altitude means it moons comes January 10. At inner world. You’ll probably won’t look that great through Martin Ratcliffe provides plane- 5:28 a.m. EST, Io and Europa need binoculars to spot the a telescope. You’re better off tarium development for Sky-Skan, simultaneously disappear into magnitude 0.5 ringed world waiting a month or two for it Inc., from his home in Wichita, the giant planet’s shadow. in the bright twilight. to return to glory. Kansas. Meteorologist Alister Track the two moons for the But unlike its neighbor, The last of the solar sys- Ling works for Environment half-hour leading up to the Saturn climbs higher with tem’s major planets remains Canada in Edmonton, Alberta. eclipse and then watch them fade over several minutes. GET DAILY UPDATES ON YOUR NIGHT SKY AT www.Astronomy.com/skythisweek.

WWW.ASTRONOMY.COM 43 ASKASTR0 Astronomy’s experts from around the globe answer your cosmic questions.

CELESTIAL Low tide

Direction of MOTION Moon’s motion High tide Earth High tide Moon Q: I SAW A PROGRAM THAT SHOWED THE MOON REVOLVING AROUND EARTH, CAUSING THE OCEANS TO SWELL ON Direction of Earth’s rotation BOTH SIDES OF THE PLANET. SHOULDN’T Low tide THE OCEAN OPPOSITE THE MOON BE The ocean nearest the Moon bulges outward in a high tide because of SHALLOWER THAN THE SIDE FACING IT? increased gravitational attraction. On the other side of Earth, the ocean bulges outward as the rest of the planet is pulled toward the Moon. Low Michael Gamble, New Berlin, Illinois tide occurs at the two points on Earth between the bulges. ASTRONOMY: ROEN KELLY

A: Tides occur because of the the water to pile up and bulge each other. This gives us the attraction, with a nearly spheri- uneven pull of the Moon’s away from the planet. Earth’s highest high tides and lowest cal distribution and high den- gravity on different parts of rotation causes most locations low tides (called spring tides). sity in the center. Our own Earth. Portions closer to the to experience these two bulges During the First and Last galaxy has approximately 170 Moon are pulled more strongly each day, approximately 12 Quarter Moon, the tidal forces globular clusters separated into than those farther away. As the hours apart. from the Sun and Moon are two subsystems associated with Moon pulls on the portion of The Sun also influences working in different directions, the galactic disk and halo. The the planet nearest its location, tides on Earth, though its effect leading to smaller tidal bulges movement of halo star clusters the water deforms and bulges is slightly less than half as (neap tides). traces the galactic gravitational toward the Moon more easily strong as the Moon, due to its Tides are even more com- field at large scales, and their than the seafloor beneath. On greater distance. During the plex than this; not all places on spatial distribution provides the far side of Earth, the water Full and New Moon phases Earth have two equal high and stringent constraints for mod- is “left behind” as the rest of when Earth, the Moon, and the low tides per day (called semi- els of dark matter distribution the Earth feels a stronger Sun are aligned, these gravita- diurnal tides). Some places, in the outer parts of the galaxy. attraction to the Moon, causing tional interactions reinforce such as the Gulf of Mexico, In a globular cluster, star only have one high and one low motions are determined by the tide per day because the sur- sum of the mass of all stars rounding landmasses prevent within the cluster. The cluster’s the free flow of water through- internal dynamics are also out the globe. As a result, more affected by its “relaxation complex patterns occur in par- time,” which is the time it takes ticular regions. for random encounters April Russell between stars to erase informa- Visiting Professor, Siena College, tion about their initial orienta- Loudonville, New York tion. For globular clusters, the average relaxation time is shorter than their age, so it can Q: WHAT ARE THE MOTIONS be argued that they are close to OF STARS RELATIVE TO a relaxed state, like air mol- EACH OTHER IN A GLOBU- ecules at room temperature. LAR OR OPEN CLUSTER? This is the physical reason why DOES THE CLUSTER MOVE the orbits of member stars do AS A UNIT OVER TIME? not have a preferential orienta- George Haskins tion (i.e., their distribution is Auburn, Washington “isotropic”) around the center of mass of the cluster itself. A: Globular clusters are com- This is even more pronounced ESA/HUBBLE AND NASA AND ESA/HUBBLE The globular cluster Messier 68 is 33,000 light-years from Earth and spans pact groups of up to a million in open clusters, which are about 100 light-years. At least 2,000 bright stars are easily visible, but this or so stars held together by typically smaller systems of cluster likely contains several tens of thousands more. their mutual gravitational only a few thousand stars.

44 ASTRONOMY • JANUARY 2018 Measuring the motions of But the universe is a busy the stars in a given globular place, and our Milky Way cluster is beyond the capabili- alone contains more than ties of small telescopes. The 100 billion stars moving European Space Agency’s Gaia around its center. A very wide observatory is currently mea- binary has a very weak gravita- suring the positions and veloci- tional bond, so if another star ties of thousands of star passes near the binary, the pair clusters in our galaxy with can break apart. Eighty years Barnard 68 is a nearby molecular cloud with higher density than the unprecedented accuracy. This ago, Armenian astronomer space around it. Left: The cloud absorbs light from the stars behind it at data, coupled with decades- Victor Ambartsumian calcu- optical (short) wavelengths, appearing dark. Right: At infrared (longer) long observational campaigns lated that a wide binary rarely wavelengths, background stars become visible through the cloud. ESO by the Hubble Space Telescope breaks apart as the result of a and other surveys (e.g., the single close encounter with atoms) every 0.6 cubic inch apparent lack of stars in certain Gaia-ESO survey, conducted another star, but rather (10 cubic centimeters). Amid directions back in the 18th with the Very Large Telescope through numerous distant pas- this gas is a smattering of dust century, and may be the dis- in Chile), will soon enable us to sages that each gently tug on grains; on average, 1 percent of coverer of dark nebulae study the distribution of globu- the binary until it impercepti- the interstellar mass is in the (although he didn’t understand lar clusters’ individual stars in bly passes from being bound to form of solid silicate or carbon- what they were). These dark, or position and velocity space. being unbound. ate grains. Astronomer Robert absorption, nebulae are local- Stay tuned for the many inter- For a very long time, the two Trumpler showed in 1930 that ized enhancements in the den- esting discoveries that will stars will still travel together interstellar gas and dust sity of the interstellar medium surely emerge! through space until eventually absorbs light at a typical rate of by factors of 1,000 to 100,000. Anna Lisa Varri they part ways. An ultrawide 2 magnitudes per kiloparsec A density enhancement of Marie Skłodowska-Curie Research binary with a separation of 0.5 (3,262 light-years). 10,000 means a 1-magnitude Fellow, Institute for Astronomy, parsec (1.6 light-years) is statis- All gas and dust in the inter- attenuation occurs over a frac- University of Edinburgh, Scotland tically likely to break up within stellar medium absorbs (or tion of a light-year. just 100 million years, while a scatters) light that passes To tell which stars are in the slightly less extreme binary through it, resulting in the background, look at their col- Q: HOW FAR CAN A PAIR with separation around 0.1 pc extinction of light from back- ors. Stars whose light passes OF STARS BE SEPARATED (0.3 light-years) may survive ground stars. Most of the through the absorption nebula AND STILL MAINTAIN for more than 1 billion years. extinction at optical wave- will be reddened — their blue A STABLE ORBIT AROUND In summary, there is no lengths is due to dust grains, light will be preferentially EACH OTHER? known fixed upper limit for which have typical sizes of 0.01 absorbed and scattered. Be care- Robert Bobo binary separations, but the to 1 micron. A photon with a ful though — some stars are McKenzie, Tennessee wider a binary is, the more wavelength smaller than the naturally red. You really need to difficult it will be to find. size of the dust grain can be have a spectrum (or spectral A: There are two issues here: Bo Reipurth physically absorbed by the type) that will tell you what the First, how far apart can two Institute for Astronomy, grain, heating the grain up. colors of the star should be. stars form and remain bound? University of Hawaii Longer wavelengths of light Frederick Walter And second, once formed, how can diffract (which causes the Professor of Physics and Astronomy, far apart can they survive as a light to bend or spread) around Stony Brook University, pair? There are a number of Q: HOW DO WE KNOW the grain. Stony Brook, New York ideas being debated for how WHAT STARS ARE BEHIND Optical light (about 400 to very wide binaries can form. DARK NEBULAE (IF THEY 700 nanometer wavelengths) is The Gaia satellite will, with its ABSORB THE LIGHT FROM strongly dimmed by these dust Send us your precision measurements, iden- BACKGROUND STARS)? grains. The amount of dim- questions tify many thousands of ultra- Margaret Lucero ming is proportional to the Send your astronomy wide binaries that we can Baldwinsville, New York cross sectional area of the questions via email to study, and their properties will grains times the number of [email protected], help astronomers to determine A: You’ve actually answered grains in the line of sight. The or write to Ask Astro, the most likely formation your own question here. The size of the grain affects the P. O. Box 1612, Waukesha, mechanism behind them. key word is “absorption.” wavelength of light that will be WI 53187. Be sure to tell us The second issue is better Interstellar space is not a dimmed. Extinction is stron- your full name and where understood. If the two stars in perfect vacuum. The mean gest at short wavelengths and you live. Unfortunately, we a very wide binary were the density in interstellar space in its effects decrease with cannot answer all questions only stars in the universe, the our part of the galaxy is about increasing wavelength. submitted. pairing could survive forever. 1 particle (mostly hydrogen William Herschel noted the

WWW.ASTRONOMY.COM 45 MUSICOF THE The sky is an endless source of inspiration for artists and composers. Here’s a look back at how the stars have influenced music. by Joel Davis

DO THE MOON AND THE PLANETS SING as they move through the sky? The idea falls. Totality lasts only a few minutes for of the “music of the spheres” is at least observers along the path. For example, at 2,500 years old. The Greek philosopher its longest, the total eclipse of August 21, Pythagoras of Samos (ca. 570–490 B.C.) 2017, lasted for 2 minutes, 41.6 seconds noticed that simple mathematical ratios near Carbondale, Illinois. For most of exist among harmonious frequencies. He human history, solar eclipses were mysteri- proposed that the Moon, Sun and planētes ous, terrifying events, omens of disaster. asters (“wandering stars”) all produced But they also might have been sources of a kind of metaphysical “hum” as they artistic inspiration — it is quite possible George Frideric Handel is one of many artists moved in their paths around Earth. These that a solar eclipse (or maybe two!) influ- struck by inspiration upon viewing a total solar eclipse. The composer likely witnessed at least sounds, the “music of the spheres,” were enced one of the greatest Baroque compos- one, if not both, of the total solar eclipses that undetectable by the human ear, but influ- ers and one of his most famous works. crossed England in 1715 and 1724. THOMAS HUDSON; enced the quality of all life on Earth. On May 3, 1715, a solar eclipse traced a WIKIMEDIA COMMONS: PHROOD Today, the music of the spheres is noth- path of totality in England from Cornwall ing more than a fascinating piece of archaic across London to Norfolk. Totality lasted philosophy. But another kind of celestial for 3 minutes, 33 seconds in London. On Handel was born in 1685 in Germany, music has been around for centuries: songs May 22, 1724, another total solar eclipse and while still a boy he showed great musi- and other music about or inspired by astro- was visible at sunset from southern Wales cal talent. After attending university, he nomical objects or events. They include to Sussex. The path of totality ran south of took positions as a cathedral organist, a classical oratorios, jazz standards, folk London. At the time both eclipses occurred, violinist and harpsichordist, and later a songs, and even a few rock ’n’ roll tunes. George Frideric Handel was among composer and performer for Catholic car- London’s citizens. dinals in Italy. Handel moved to England Handel’s total eclipse in 1710, and by 1713 he was living in A total solar eclipse occurs when the Moon Barnes, about 6 miles (10 kilometers) passes in front of the Sun as seen from southwest of central London. Earth, and completely blocks the Sun’s Four years later, he had moved disk. The dark inner lunar shadow races to the northwest part of across Earth’s surface, cutting a narrow London, and in 1723, he bought path of totality in which night briefly a mansion in the exclusive Mayfair district of central Left: The Leonid meteor storm of April 1833 London, where he lived for the produced hundreds of thousands of meteors rest of his life. and struck awe and wonder into all who saw it. It was in London that Handel Among them was Joseph Harvey Waggoner, whose account inspired artist Karl Jauslin became famous, and his magnifi- to paint the storm. This image, in turn, is cent Messiah sealed his fame for an engraving produced by Adolf Vollmy, the ages. When Handel finished based on Jauslin’s painting. ADOLF VOLLMY Messiah in 1741, he immediately Right: In 1619, Johannes Kepler published began another project. Like Harmonices Mundi (Harmony of the Worlds). Messiah, this would be an oratorio, In it, he looks for “harmonies” analogous a large musical composition for to those between musical notes in the orchestra, choir, and soloists, with distances and speeds of planets in the solar system. While no such harmonies identifiable characters and arias. appeared to exist with regard to planetary He titled the new project Samson. distances, he did discover a pattern The text (by Irish writer Newburgh governing a planet’s speed with respect to its position in its orbit — this would Hamilton) was based on John become Kepler’s third law. JOHANNES KEPLER: Milton’s dramatic poem Samson HARMONICES MUNDI, LINZ 1619; WIKIMEDIA COMMONS: URS WERRA Agonistes, a retelling of the famous

WWW.ASTRONOMY.COM 47 Bible story of a super-strong Israelite hero Samson was a favorite of audiences dust. Older meteoroid trails are fairly brought low by the treacherous Dalila. throughout Handel’s life, and it remains sparse and produce few meteors per hour, Samson’s first act begins with Samson popular to this day. while newer trails are denser and the mete- blinded and in chains, a prisoner of the In his later years, “Total Eclipse” would or showers are more impressive. Outbursts hated Philistines. He bemoans his fate in often bring the composer to tears as he sat greater than 1,000 meteors per hour are an aria that uses the image of a total solar listening to the performance, but unable to called meteor storms. eclipse to symbolize his loss of sight. see it. For the last 10 years of his life, The Leonid meteor shower graces the Samson premiered in February 1743 at Handel himself was blind, trapped in the night sky every November. Named for the London’s Covent Garden Theatre, and it shadowy path of his own “total eclipse.” constellation Leo, from which it appears to was a smash hit. radiate, the Leonids are famous for their Why a solar eclipse as a metaphor for Stars fell occasional spectacular outbursts. The blindness? Did Handel witness the total Comets eject gas and dust as they approach Leonid meteor storm of November 1833 eclipse of 1715? It’s more likely than not the Sun and their surfaces heat up. They was truly epic. For nine hours on the night that he did. After all, he lived near or in leave a meteoroid stream of dust particles of Thursday, November 12, people across London from 1713 onward. He could have in their wake, with some areas denser eastern North America saw thousands of easily made the journey to see both the than others. The gravitational influence meteors streaking through the sky each 1715 and 1724 eclipses. Both were wit- of the planets — especially Jupiter — as minute. Observers later estimated the nessed by thousands of people, and their well as the pressure of sunlight perturb the number of meteors from 100,000 to nearly memories of the events would have been streams, so the orbits of the particle trails 240,000 per hour. Newspapers and maga- vivid when Samson and its dramatic aria, are not quite the same as their comets of zines around the country ran stories about “Total Eclipse,” premiered in 1743. Talk origin. Meteor showers occur when Earth the event, complete with illustrations based about a gripping opening, a dramatic hook! moves through these clouds of cometary on observers’ reports.

Left: Edmond Halley’s map of the predicted path of the 1715 eclipse visible over England was printed and sold as a broadside (a type of advertisement or poster). Its widespread availability and affordable price created excitement and encouraged people

to view the event; one of them may have been Handel. UNIVERSITY OF CAMBRIDGE, INSTITUTE OF ASTRONOMY LIBRARY

Below: Handel’s Samson included an eclipse-inspired piece, aptly named “Total Eclipse.” The oratorio premiered in 1743 to great success and remained hugely popular. This playbill advertises a performance in San Francisco in 1863. MARGARET BLAKE ALVERSON: SIXTY YEARS OF CALIFORNIA SONG, 1913 Through the end of the 18th century, 3C 273, a quasar located in an elliptical meteors had been commonly considered a galaxy 2.5 billion purely atmospheric phenomenon, like light-years away, lies lightning. The 1833 Leonid storm changed in the constellation all that, and kick-started the scientific Virgo. While some once believed quasars study of meteors. Shortly after the storm, might be generated astronomer Denison Olmsted proposed a by alien civilizations, cosmic origin of meteors, suggesting they astronomers now know they are the accretion came from a cloud in space. The Leonids disks surrounding returned the following November, though supermassive black not at “storm” levels. Astronomer Heinrich holes. ESA/HUBBLE AND NASA Olbers predicted in 1837 that the Leonids would have especially large displays every 33 or 34 years. Sure enough, the November 13–14, 1866, display was spec- tacular. At about the same time, astrono- mers Wilhelm Tempel and Horace Parnell Tuttle independently discovered the comet that bears their name. Giovanni Schiaparelli soon determined that Comet Tempel-Tuttle was the source of the Leonids. In 1934, American writer Carl Carmer published an autobiographical account of the six years he spent living and teaching in Alabama. He included stories of the 1833 Leonid meteor storm based on both old newspaper accounts and stories he heard from children and grandchildren of eyewitnesses. “Many an Alabamian to this day reckons dates from the year the stars “Radio-loud” quasars (about 10 percent of fell,” Carmer wrote, “though he and his all known quasars) emit radio waves and neighbor frequently disagree as to what visible light up to a hundred times as bright year of our Lord may be so designated. All as our entire Milky Way Galaxy. are sure, however, that once upon a time In 1959, no one had a clue what these stars fell on Alabama.” Folks would recall mysterious cosmic radio sources were. that their son or daughter was born “about Their measured redshifts implied they the time the stars fell,” or that they got were billions of light-years distant, but that married “a week after the stars fell.” The 1833 night when “stars fell on Alabama” meant their energy output was gargantuan. and the song it later inspired were so memorable Carmer’s book, Stars Fell on Alabama, that the phrase was featured on the state’s Perhaps the objects were much closer, and quickly became a best-seller. license plate between 2002 and 2009. the large redshifts were caused by light One of the book’s fans was music pub- WIKIMEDIA COMMONS: ROGUE FALCONER escaping from a deep gravitational well. lisher Irving Mills. He was sure there was a That year, radio astronomers from the song in it, something that could be based musical sky like, well, a meteor — a meteor California Institute of Technology found on or inspired by the meteor shower story. that’s never stopped blazing. More than a one they named CTA-102 — the 102nd Mills turned to Frank Perkins to write the hundred artists have covered the song, entry in the Caltech Survey, Part A. tune and Mitchell Parish to write the lyr- including Guy Lombardo, Bing Crosby, In 1963, Russian astrophysicist ics. Perkins was a solid but otherwise Ella Fitzgerald and Louis Armstrong, Nikolai Kardashev offered a novel sugges- undistinguished composer. Parish, though, Cannonball Adderley and John Coltrane, tion: CTA-102 could be the product of a was one of jazz’s great lyricists. Among Billie Holiday, Anita O’Day, Stan Getz, highly advanced extraterrestrial civiliza- other classics, Parish wrote “Sophisticated Dean Martin, Frank Sinatra, Doris Day, tion. Two years later, Gennady Sholomitskii Lady” (Duke Ellington), “Moonlight Kate Smith, Mel Torme, Ricky Nelson, and found its radio emissions were variable. Serenade” (Glenn Miller), and “Stardust” even Jimmy Buffett. Perhaps this strange celestial object (Hoagy Carmichael). The lyricist turned was the powerful radio beacon of an the shared memories of the 1833 meteor A quasar for The Byrds advanced alien race. This was a wondrous storm into a song about romance: Boy fell Quasars, short for “quasi-stellar objects,” suggestion — with nothing to support it. for girl the night the stars fell on them are regions immediately surrounding The “ET hypothesis” was still making both. “We lived our little drama / We supermassive black holes at the centers the rounds in 1966 when it captured the kissed in a field of white / And stars fell on of distant galaxies. Their gravitational fancy of a 24-year-old musician named Alabama / Last night …” fields suck surrounding matter onto Roger McGuinn. Like so many of Parish’s other pieces, their accretion disks, releasing enormous McGuinn is the guitarist, singer, and “Stars Fell on Alabama” streaked across the amounts of electromagnetic energy. songwriter who founded The Byrds, one of

WWW.ASTRONOMY.COM 49 An account of a comet 1P/Halley is arguably the most famous comet of all time. Its regular visits to the inner solar system have been reli- ably recorded since at least 240 B.C. In 1066, the comet was seen in England and its appearance recorded in the famed Bayeux Tapestry, a 230-foot (70 meters) textile depicting the Norman conquest of England. None of its apparitions were identified contemporaneously as the same comet, however, until its appearance in 1682, when English astronomer Edmond Halley successfully predicted its return in 1758. Halley’s Comet returned again in 1835, and then again in 1910. That was actually a year of two great comets. Halley’s was one, and people around the world were eagerly awaiting its return to our cosmic neighborhood after 75 The Great January Comet of 1910 (pictured) grew brighter than Venus and dazzled viewers with a long, arcing tail visible in daylight; Halley’s Comet would appear just months later. The close timing years. But C/1910 A1, better known as the of the comets could have confused people’s later recollections — including those of John S. Stewart. Great January Comet of 1910 or the UNIVERSITY OF CHICAGO PHOTOGRAPHIC ARCHIVE, [APF6-02103], SPECIAL COLLECTIONS RESEARCH CENTER, UNIVERSITY OF CHICAGO LIBRARY Daylight Comet, dazzled the world first. It was already a magnitude 1 naked-eye object when it was spotted January 12. The the most influential bands of the 1960s. with their fists, and nonsense sounds comet was visible in broad daylight in the He’s also an enthusiastic — if not always laid down on audiotape that was speeded Southern Hemisphere, and by February it well-informed — astronomy fan. With col- up or played backward to achieve the was visible at twilight in the Northern laborator Bob Hippard, McGuinn wrote desired effect. As McGuinn later said, Hemisphere as a spectacular object with a “C.T.A.-102.” The space-themed song “That was a big fad at the time, to play long, curved tail. appeared on the group’s early 1967 album things backwards.” Two months later, Halley’s Comet was a Younger Than Yesterday. A 1968 paper published in The naked-eye object in the night sky, reaching In a 1973 interview, McGuinn said Astrophysical Journal (“Quasi-Stellar Radio perihelion April 20. It then passed within of the inspiration for the song, “At the Sources: 88 GHz Flux Measurements”) 0.15 AU (13.9 million miles [22.4 million time we wrote it, I thought it might be actually referenced McGuinn and The km]) of Earth. So while not quite as possible to make contact Byrds. Referring to aspects with quasars.” It was not of CTA-102’s spectrum, the until later, he added, authors wrote: “The spec- that he learned they trum … [gives] no indica- “were stars which are tion of an upturn at short imploding at a tremen- wavelengths. … [W]e have dous velocity … sending been unable to detect it.” In out tremendous a wry reference to the rock amounts of radiation.” band’s song they added, He mistakenly thought “Therefore we are unable to that the signals were comment on the discussion audible as an electronic by McGuinn, Clark, Crosby, impulse detected by Clarke and Hillman.” radio telescopes “in “C.T.A.-102” isn’t the only rhythmic patterns.” science- or science-fiction- The song’s tune is inspired rock song. David jaunty, the lyrics upbeat: Bowie’s 1969 “Space Oddity,” “We’re over here receiving you / Signals Elton John and Bernie Taupin’s 1972 tell us that you’re there … on a radio tele- “Rocket Man,” Brian May and Queen’s 1975 scope / Science tells us that there’s hope.” space-travel folk song “ ’39,” and Rush’s And the group went to considerable lengths 1977–78 two-part “Cygnus X-1” are other to produce some spacey sound effects. At a examples. But “C.T.A.-102” is the first song time when computers weren’t yet available, inspired by a quasar, the first to reference a they got creative. They used audio feed- radio telescope in music — and possibly the back, an oscillator connected to a telegraph first to garner a rock band a mention in a key, a piano keyboard repeatedly pounded refereed scientific journal.

50 ASTRONOMY • JANUARY 2018 awesome as the Great January Comet, Halley was still a spectacular sight. It certainly made an impression on a boy named John S. Stewart, who was living with his parents near Lexington, Kentucky, at the Transylvania Inn, where his father was a horse trainer. The young boy’s expe- rience seeing Halley’s Comet remained with him the rest of his life. Some 60 years later, his son tape-recorded his memories of that long-ago spring in 1910. His son was John C. Stewart, a folk singer and songwriter probably best known as a member of the Kingston Trio and the composer of the Monkees’ hit “Daydream Believer.” But Stewart also had a successful solo career that stretched from the late 1960s to his death in 2008. He was an acknowledged and continuing influence on contemporary folk music’s so-called The Byrds (pictured in 1970; from left are Roger McGuinn, Skip Battin, Clarence White, and “Americana” sound. An enthusiastic sup- Gene Parsons) found musical inspiration in the radio-loud quasar CTA-102. Their song of the same porter of the U.S. space program, Stewart name communicates a positive message of hope that the quasar is an alien beacon. JOOST EVERS/ANEFO; wrote “Armstrong,” a tribute to the first COURTESY OF THE NATIONAAL ARCHIEF, THE DUTCH NATIONAL ARCHIVES, AND SPAARNESTAD PHOTO lunar landing with not-so-subtle references to troubling social issues still with us today. His song about his father and a comet, or early summer, my mother came to me His father continues his story, recalling though, is particularly touching, both for and said, ‘Let’s go upstairs on the veranda.’ how the comet got larger and brighter until its subject matter and its lyrics. She said, ‘I want you to see Haley’s one night “it was over the Tattersall’s barn. Stewart began with his father’s tape- Comet.’ ” At first it looked like a bright star, … The horses were restless … [and] my recorded recollections. To them he added a but as it came closer to Earth, it “started to father … went to the barn to try and quiet” musical arrangement with a string section take on the look of a ball of fire with a tail them. The young John S. runs to his and a simple but driving chorus. The result behind it.” John C. and several backup mother and tells her he’s afraid, and she was “An Account of Haley’s [sic] Comet.” It singers then sing the refrain: “Kentucky replies, “So am I.” He describes the light opens with John S. narrating his personal light shine / Will it fall from the sky? / as “eerie” and so bright the eaves of the story. “It must have been in the late spring Kentucky light shine / Stranger in the sky.” barn cast shadows. The refrain cuts back in: “Kentucky light shine / Will it fall from the sky?” Some of the senior Stewart’s memories may have been colored by the passing years. He may have confused the spectacular twilight sight of the Great Comet a few months earlier with his experience of Halley. In the end, though, it doesn’t matter much. In 1910, John S. Stewart saw Halley’s Comet during one of its most impressive appearances. Sixty years later, his folk singer son turned his memories into a moving “music of the spheres” account of an astronomical experience most of us will have only once in a lifetime. We’ve been singing songs about the awe- inspiring worlds of the night sky for a long Halley’s Comet also time, maybe as long as we’ve been human. lit up the sky in 1910, From meteor storms to comets, from solar during an especially close pass to Earth; eclipses to quasars — and much more — in fact, Earth passed the night sky continues to inspire us to through the comet’s make celestial music right here on Earth. extensive tail in May that year. This photo was taken during the Joel Davis has worked as a technical writer comet’s subsequent at Microsoft and WideOrbit. He blogs regularly apparition in March at notjustminorplanets.blogspot.com. 1986. NASA/W. LILLER WWW.ASTRONOMY.COM 51 EXPLORE AURIGA’s DEEP-SKY WONDERS

52 ASTRONOMY • JANUARY 2018 Open cluster M36

Bright star clusters, challenging nebulae, and even a distant globular cluster await you in one of winter’s great constellations. by Stephen James O’Meara

uriga, a wreath of stars within the larger wreath of the Winter Hexagon, possesses some of the most disparate deep-sky objects in the heavens — from dazzling Capella (the most northern 1st-magnitude star) to the dim and distant globular cluster A Palomar 2 (among the most visually demanding deep-sky objects). Beyond the bright showpiece trick is to resolve the 5th-magnitude pri- open star clusters M36, M37, and M38 mary, which also has a 10th-magnitude — which all observers should admire for “companion” 12" to the north; I put their rich diversity in visual splendor — “companion” in quotes because the two Auriga has a cache of objects that can sat- are not physically related, being most likely isfy your desires. a chance line-of-sight pairing. Now return to the leaping minnow and FOLLOW THE look immediately northwest of 19 Aurigae “LEAPING MINNOW” for a naked-eye star at the edge of visibil- Beyond Capella and its Kids — Epsilon (ε), ity: AE Aurigae. This variable star fluctu- Zeta (ζ), and Eta (η) Aurigae — the first ates erratically between magnitudes 5.8 object to catch my eye in this constellation and 6.1. Born in a binary system some under a dark sky is the tight and “hazy” 200 million years ago in the Trapezium ellipse of starlight east of Iota (ι) Aurigae star cluster in the Orion Nebula (M42), on the western bank of the Milky Way; AE Aurigae was ejected to its present loca- it may be among the most unsung naked- tion after its system had a close encounter eye objects in the night sky. Binoculars with another binary star system. will show this delightful grouping as what Today we still see AE Aurigae “running Sky & Telescope’s Alan M. MacRobert away” to the north, only now it is passing likens to a “leaping minnow.” The bright- through and illuminating an interstellar est minnows are 5th-magnitude 16, 19, cloud of dust and gas known as the and IQ Aurigae. Flaming Star Nebula (IC 405). Under Flaming Star Nebula (IC 405) About 1˚ southwest of the leaping min- dark Hawaiian skies, I’ve spied AE Aurigae now you’ll find 14 Aurigae. This wide and the brightest part of IC 405 that sur- double star is visible through small tele- rounds the star, using averted vision scopes. The pale white pair consists of a through 10x50 binoculars. Small telescope

GERALD RHEMANN. UPPER RIGHT: BERNHARD HUBL BERNHARD RIGHT: UPPER RHEMANN. GERALD 5th-magnitude primary and a magnitude users should try low power first, and plan

LEFT: LEFT: 7.5 secondary 14.6" to the southwest. The to gently sweep in a general north-south

WWW.ASTRONOMY.COM 53 Open cluster M37 Open cluster M38

Emission nebula IC 417 Emission nebula NGC 1931

direction along the nebula’s 30'-by-20' of starlight that seem to connect the two nebulous cluster NGC 1931 (about 5' to the length while keeping your eyes relaxed and clusters to 5th-magnitude Phi (φ) Aurigae, east-southeast) — “The Fly.” your mind alert. The nebula’s most promi- an orange K-class giant flanked by two NGC 1931 is a beautiful little cluster nent portion is a kite-shaped wedge 6th-magnitude attendants. As a whole, this that’s easily seen through small scopes. extending southeast from AE, followed by star-and-cluster stream forms an open V Only 10 million years old, the cluster is a long, thin streamer that runs along the asterism that New York City skywatcher 7,000 light-years distant — or about five nebula’s northeastern edge. Ben Cacace refers to as the Cheshire times farther away than the Orion Nebula, If you are under a dark sky, use 10x50 Cat (an allusion to Alice’s Adventures in of which it is a remarkable miniature. binoculars to scan about 1˚ southeast of Wonderland). Telescopically, at low power and with the leaping minnow, and see if you can Now peer at Phi Aurigae through a direct vision, NGC 1931 is so dense that it detect the soft and tiny (12') glow of the larger looking-glass — your telescope. That appears like a fuzzy star. With averted magnitude 7.5 cluster NGC 1893 that illu- crisp, golden star has numerous fainter vision, however, it immediately swells minates the surrounding 20'-wide diffuse stars sprinkled around it from northeast to into a distinct nebulous knot. The trick emission nebula IC 410. I mention this southwest, while a smaller collection of to seeing the cluster within is to use high latter object specifically for astroimagers jewels hugs Phi to the southeast. magnification (start with 165x and work because the nebula reminds me of a little All these stellar gems belong to the your way up) to resolve its central triad of Rosette Nebula and is part of the larger largely “silent” Stock 8 — a 2 million-year- suns. Concentration will bring out several one that lies at the core of the Auriga OB2 young cluster embedded in its nascent neb- other fainter jewels. But these may swim association. The embedded cluster has ula IC 417, which washes through the in and out of view as you move your eye about 20 members, the brightest of which entire region. Wide-field imaging reveals while using averted vision and pass over shine around 9th magnitude and dip down that IC 417 is a vast cloud of glowing the nebulosity, which is brightest on the to about 13th. hydrogen with long, spindly legs that southern side. The stars appear to be HANSON; MARK AYIOMAMITIS; ANTHONY ARIZONA; OF SKYCENTER/UNIVERSITY LEMMON BLOCK/MOUNT ADAM stretch across 1½° of sky. When Boston embedded in knots or nebulous folds, SAID THE SPIDER amateur astronomer Steve Cannistra from which thinner tendrils stream — TO THE FLY . . . scanned one of his wide-field images of the including a graceful sweep of reflection If you’re out admiring M36 and M38 with region, he nicknamed IC 417 “The Spider,” nebulosity stretching southward from CLOCKWISE FROM UPPER LEFT: binoculars, look for two curious threads and our next target — the tiny (4') the main nebula. BLOCK/NOAO/AURA/NSF ADAM BLOCK/NOAO/AURA/NSF; FERAYORNI/ADAM ANDY AND AL GERMANO; MARTIN C.

54 ASTRONOMY • JANUARY 2018 southern skirt of an even larger (18'-wide) EXTRAGALACTIC and much more discrete cluster, Czernik 20. DENIZENS Telescopes 12 inches (30.5 centimeters) and If you’d like a galaxy challenge, Auriga larger may show up to four dozen roughly has two “visually reasonable” island uni- magnitude 13.5 stars within NGC 1857, verses for you to seek out: NGC 2208 and transforming it into a blizzard of faint NGC 2303. The magnitudes are faint and starlight. The alignment of NGC 1857 and both are small, but they are highly con- Czernik 20 appears to be by chance because densed, making them decent targets. So recent estimates place NGC 1857 about when you look for them, search for a “star” 3,000 light-years farther away. in the right position and use high power Heading farther “upstream” toward the and averted vision to see their diffuse disks. northwest border of Auriga and Perseus, American astronomer Lewis Swift dis- we arrive at the magnitude 7.6 open star covered both galaxies visually in 1886 IC 410 and NGC 1893 cluster NGC 1664. This little explosion of using the 16-inch refractor at Warner about 100 stars sprays outward to the Observatory in Rochester, New York. northwest for about 20' from a magnitude Today, however, a telescope as small as a 7.5 star about 2˚ west of Epsilon Aurigae. I 4-inch will show them from a dark site, Open cluster NGC 1664 find the cluster most appealing at low with time and patience. NGC 2303 is a power as it seems to play with the Milky round (1.5' across) magnitude 12.6 elliptical Way, appearing as if it were the cloudy galaxy 270 million light-years distant that aftermath of an oblique meteorite strike has a starlike appearance. NGC 2208 is a into that milky river. Higher powers show round (1.6' by 1.1') magnitude 12.8 lenticu- its irregular loop and tail of starlight as a lar galaxy 265 million light-years distant. stingray swimming, or an earring dangling under moonlight. TWO VISUAL Now we’ve nearly hit rock bottom PECULIARITIES in the magnitude range for decent cluster IC 2149 is an unusual planetary nebula in viewing. NGC 2126 lies in the remote northeastern Auriga, just 40' west-north- regions of far northern Auriga and shines west of 4th-magnitude Pi (π) Aurigae. A at a dismal magnitude 10.2. Fortunately, longtime enigma, IC 2149 defied classifica- not only is the cluster compact (6') but it tion until 2002. In images, the compact has an unrelated 6th-magnitude star super- 8"-wide ellipsoidal nebula surrounding imposed on its northeastern flank. an 11th-magnitude central star (visible in Through small telescopes, the cluster large binoculars) appears to be a bipolar About midway between Phi and Nu (ν) appears simply as an elliptical fog of faint planetary nebula still in the process of Aurigae is a great visual challenge object: light oriented northeast to southwest. With forming. I got the best view between 165x the collision site of two giant molecular averted vision and high power, it appears and 180x, though powers of 300x and clouds, Sharpless 2–235. If you’re a granular — like an unresolved globular greater will start to show it more and a skilled observer using a 5-inch or larger cluster. For those using larger instruments, trivial bit of “fuzz.” telescope, try to visually swallow this kid- the cluster contains 40 stars of 13th-magni- Hopping far to the southwestern corner ney bean-shaped emission nebula; a deep- tude and fainter. of the constellation, we come to our final sky or ultra-high-contrast filter will help We’ll end our cluster scan on a high challenge. Palomar 2 is an incredibly dim show this 10'-wide pale oval glow. The note, with the bright (5th-magnitude) open (magnitude 13) and distant (90,000 light- challenge for large telescope users is to not cluster NGC 2281. It’s a largely overlooked years) denizen of our galaxy’s outer halo, a only resolve the dark band that separates treasure hiding in the remote far-eastern distant globular cluster. First, you’ll need the nebula’s bright northern half from its corridor of Auriga, in one of the seven precise coordinates to find it (R.A. dimmer southern portion, but also the lashes of the Charioteer. Yet the cluster is 4h46m06s, Dec. 31°22'51"); next, you’ll two “knots” of nebulosity immediately to bright enough to blossom forth in 7x50 need perhaps a 12-inch or larger telescope its south: Sharpless 2–235A and B. How binoculars as a diffuse glow nestled to see it; and third, you’ll need to use small a telescope will show them? between a 7th- and an 8th-magnitude star; averted vision and tube-tapping tech- both have dramatic golden hues, so the niques, and eat lots of carrots. But don’t let HIDDEN CLUSTERS binocular scene is quite pleasing. this dissuade you. You’ll be looking for a Auriga sports some of the brightest (M36, Telescopically, the cluster looks like a tor- 2'-wide amorphous round glow, which, as M37, and M38) open star clusters, and tured stellar system, one that’s been the 17th-century comet hunter Charles also some of the faintest. The latter group “stretched on the rack,” in all four direc- Messier would have said (if he were using a includes 7th-magnitude NGC 1857, a tions, creating Gumby-like arms in the 24-inch Dobsonian at 170x), “resembles a 5' cluster centered on a 7.5-magnitude process. NGC 2281 has about 120 members comet, just beginning to shine.” star about 45' south-southeast of Lambda of 8th magnitude and fainter, with many of (λ) Aurigae. Through a small telescope, the the dimmest stars hovering around 13th Stephen James O’Meara is a contributing cluster is a little polygon of about a half- magnitude. The question is, can you spy it editor of Astronomy and an author of many dozen dim stars — which itself lies on the without optical aid? books on observing.

WWW.ASTRONOMY.COM 55 A panel of 11 Nobel Prize laureates discusses the future of science. Pictured from left are Edvard Moser, Adam Riess, Chris Pissarides, Finn Kydland, George Smoot, May-Britt Moser, moderator Adam Smith, Tim Hunt, Robert Wilson, Stefan Hell, Susumu Tonegawa, and

Torsten Wiesel. MAX ALEXANDER/STARMUS

SnapshotsSnapshots fromfrom TheThf fourth thSt Starmus FtilFestival, a celebration lbti of fi science and dth the arts, t took place in Trondheim, Norway, in June 2017. by David J. Eicher

FOUR STARMUS FESTIVALS HAVE In 2017, the event showcased 11 Nobel Prize winners, taken place since 2011. The international science cel- an astronaut panel of moonwalkers (Buzz Aldrin, ebration, the creation of astronomer Garik Israelian, Charlie Duke, and Harrison Schmitt), talks by Larry grew out of his friendship with astrophysicist Brian King and Oliver Stone, many important scientific lec- May, also the founding guitarist of the rock group tures, and a Sonic Universe Concert led by the amazing Queen. The festival is dedicated to stars and music, guitarist Steve Vai. Starmus was hosted in Trondheim thus the name, but has expanded to highlight impor- by the Norwegian University of Science and Technology, tant scientists from all disciplines. and occurred June 18–23. The following pages present postcards from Starmus, David J. Eicher is editor of Astronomy and a member of the glimpses of what the 2,500 attendees experienced. For Starmus Festival Board of Directors. more information, visit www.starmus.com.

56 ASTRONOMY • JANUARY 2018 1. Garik Israelian, Starmus’ founder and director, describes the effort that went into assembling Starmus

IV. THOR NIELSEN/NTNU

2. May-Britt Moser, who helped to bring Starmus to Trondheim, talks about her neurological research during a multimedia show. StarmusStarmus THOR NIELSEN/NTNU 3. Well-known TV and radio host Larry King commands a discussion on post-truth and fake news. MAX ALEXANDER/STARMUS

3

2 1 4

5

7

8

6 12 4. Emmanuelle Charpentier describes her groundbreaking work on CRISPR-Cas9, gene editing technology that will revolutionize the life

sciences. MAX ALEXANDER/STARMUS

5. Edvard Moser talks about his amazing research on how the brain maps space, which happens in the hippocampus. MAX ALEXANDER/STARMUS

6. Jill Tarter delivers a landmark “state of the union” address on where we stand with the search for life in the universe.

MAX ALEXANDER/STARMUS

7. Space shuttle and International Space Station astronaut Sandy Magnus recalls her experiences in orbit and the perspective they provide on Earth below. 13 MAX ALEXANDER/STARMUS 8. Apollo 16 astronaut Charlie Duke describes the 9 science he and John Young conducted on the lunar

surface. MAX ALEXANDER/STARMUS

9. Stephen Hawking addresses the Starmus audience remotely from Cambridge, England, carefully weighing the prospects for the future of

humanity. MAX ALEXANDER/STARMUS

10. David Eicher opens the festival with a welcome and an introduction, and 14 commences hosting the first day. THOR NIELSEN/NTNU

11. Climate scientist Katharine Hayhoe gives a spectacular lecture on the 10 realities of global warming. MAX ALEXANDER/STARMUS

12. Harrison “Jack” Schmitt describes his exploration of the lunar surface during Apollo 17 and reflects on being in the last group of explorers to the Moon.

MAX ALEXANDER/STARMUS

13. Columbia University economist Jeffrey Sachs delivers a commanding performance in his exposé on dark money in American politics, garnering a standing ovation from the festival

crowd. MAX ALEXANDER/STARMUS

14. Guitarist Steve Vai, left, jams with Grace Potter and Nuno Bettancourt during 11 the Sonic Universe Concert. MAX ALEXANDER/STARMUS

WWW.ASTRONOMY.COM 59 Explore Scientific’s 12-inch Truss Tube Dobsonian offers a large aperture at a reasonable cost.

This telescope offers top-notch construction and high-quality optics, and is easy to set up and use, as well. text and images by Mike Reynolds Explore Scientific’s 12-inch Truss Tube Dobsonian

he Dobsonian, The basic Dobsonian mount weight. This led to the truss trio features a number of traits John Dobson’s sidewalk carries a Newtonian reflector tube: a set of rigid poles to con- standard to most Dobs along telescope mount design with its concave primary mir- nect the lower part of the Dob with a few surprises. more commonly ror and flat secondary mirror — referred to as the rocker box, The Explore Scientific referred to as a Dob, has mounted at a 45° angle to the which contains the primary 12-inch Truss Tube Dobsonian Tevolved significantly since its primary. As the Dob evolved mirror — to the Dob’s upper arrived in one box. This was first commercial introduction over the years, innovations cage, which holds the second- the first surprise; previously in the 1980s. Many of us such as shorter focal lengths for ary mirror and focuser. This reviewed Dobs have always remember the blue tube Coulter the big scopes, primary mirror design, and the use of innova- needed at least two boxes. I Optical Dobsonian telescopes, cooling fans, equatorial track- tive connectors, means the tele- appreciated that the included the first of which contained a ing tables (an accessory that scope quickly disassembles into user manual was well-written, 13.1-inch primary mirror. serves as a motor drive), and the rocker box, the mirror box, and even contained pictures! Soon, amateur telescope numerous others appeared. the secondary cage assembly, Assembly of the telescope makers and companies began Truss tube Dobs were also and the truss tubes. was easy, and this would hold producing larger and more one of these early innovations, true even for a beginner. I innovative Dobs. The simplicity brought on by need and by Opening it up found the construction solid, of the mount, coupled with a mirror-size evolution. As the Explore Scientific, known for from the mirror box to the sec- large mirror, made them popu- primaries became larger, solid its apochromatic refractors and ondary mirror cage. The fin- lar telescopes. The Dob rage tubes of either cardboard con- wide-field eyepieces, has ishes appear nice and should brought on what many referred crete column tubing or metal entered the market with three last through many an observ- to as “aperture fever.” became impractical due to new Dobsonian telescopes. The ing session. The weight of the

60 ASTRONOMY • JANUARY 2018 PRODUCT INFORMATION

Explore Scientific 12-inch Contact: Truss Tube Dobsonian Explore Scientific Type: Newtonian reflector 1010 S. 48th St. Aperture: 12 inches Springdale, AR 72762 Secondary mirror 866.252.3811 obstruction: 24 percent www.explorescientificusa. Focal length: 1,525mm com Focal ratio: f/5 Weight: 66.2 pounds (30 kg) Price: $1,199.99 The Dob’s focuser accommodates 2" 12-inch components is reason- Taking it for a spin eyepieces and offers two focusing speeds. able, and they easily fit into my Under the night sky, the tele- Camry’s back seat or trunk. scope performed well. It was The next surprise was the easy to move around to its final collimation tool for the mirror. observing spot. Once at the Collimation (the alignment of a eyepiece, I also found it easy telescope’s optics) is usually to adjust the tube’s position tedious or takes two people. while observing. The focuser Explore Scientific has designed works well. I always appreciate a system so the user can the 10-to-1 reduction. It allows employ the collimation tool, a for getting the focus just right, rod that lets you collimate the especially at higher magnifica- scope from the focuser. Usually tions. And the focuser held my you are back and forth to the fairly heavy wide-angle eye- rear of the telescope, or telling piece with no slippage. The secondary cage and focuser someone, “No, the other screw; There are several general fit inside the Dob’s tighten not loosen.” What a observational tests I do on all rocker box for storage great innovation! telescopes. Even though I was and transportation. The focuser is a 2" two- expecting no color issues, I like speed (10-to-1 reduction) to test telescopes on the Full model. The finder included is a Moon. I detected no color Deep-sky objects were excel- many of those subtle deep-sky red dot finder. I prefer an opti- issues, but our satellite was lent, from the brighter ones like object colors, faint wisps, and cal finder scope on my Dobs, overwhelmingly bright, so I the Orion Nebula (M42) to nebulosity, or if you want but the red dot finder is ade- had to use a filter. The Explore some of the season’s dimmer Jupiter to appear like you’ve quate and reduces the second- Dob also performed nicely on and more elusive targets. I also never seen it in smaller scopes, ary mirror cage’s weight. Yet if the waning crescent Moon, spent some time looking at a Dobsonian just might be for that weight becomes an issue, providing a crisp image. double stars. One of my favor- you. And Explore Scientific’s or you want to use one of these On a good night, a contrast ites this time of year is Albireo new trio of Dobsonian truss heavy wide-angle eyepieces, between two telescopes can be (Beta [β] Cygni) because it’s tube telescopes gives you a Explore has included threaded established. My yardstick is a easy to see and colorful. selection with excellent optical counterweights. This was tough one here; I compare performance and great another unexpected surprise. Dobsonians to my personal Conclusions mechanical quality at good You should know that no 18-inch f/6 Dob, a high-quality All in all, I was pleased with the prices, with convenience of eyepieces are included; most one that used to belong to a telescope’s performance. I did setup and use — just know purchasers of scopes this large close friend. The Explore Dob not note any visual issues like that even the largest of these will already have at least one views were excellent; I pushed coma, astigmatism, or other will eventually leave you want- eyepiece. However, if this is the telescope to 90x with a distortions. ing something bigger. In the your first telescope, make cer- 17mm eyepiece and then to Many of us Apollo program- meantime, explore as much of tain you order an eyepiece or 127x with a 12mm with no era kids considered ourselves the night sky as you can with two with it. I would suggest a problems and a great image. I fortunate if we had an opportu- one of Explore Scientific’s fine wide-field 25mm as a starter. did try a 2x Barlow lens, but nity to look through someone’s new telescopes. You might also want an 18mm found my local sky conditions 12.5-inch reflector. And you for a little higher magnifica- were not good enough to give a were quite advanced if you Mike Reynolds is a contributing tion, or a longer focal length fair test. I noted that the image owned an 8-inch Newtonian editor of Astronomy who observes eyepiece for a wider field of of Jupiter was OK, but not as reflector. Today, if you catch through a variety of scopes from view and lower power. good as at 127x. aperture fever and want to see his home in Jacksonville, Florida.

WWW.ASTRONOMY.COM 61 Astrophysicist Neil deGrasse Tyson and composer Jean-Michel Jarre pose with their awards at the 2017 Starmus Festival. The producers of The Big Bang Theory also won an award but were unable to

attend. MAX ALEXANDER Starmus awards 2017 Stephen Hawking

The prestigious prize recognizes popularizers of science Medals from around the world. by Jake Parks

uring the 2017 Starmus Festival, honor those scien- The back of the medal founder Garik Israelian presented tists, artists, musi- combines an image of Russian cosmonaut the Stephen Hawking Medal for cians, and Alexei Leonov’s trail- Science Communication to three filmmakers who blazing spacewalk worthy recipients. Astrophysicist work tirelessly to with Queen guitarist Neil deGrasse Tyson won for science promote science Brian May’s iconic D guitar — the “Red writing, French electronic composer Jean- to the general Special” — to highlight Michel Jarre captured the prize for music public. “I firmly the connection between and arts, and the producers of the CBS believe that if there is science and art. MAX ALEXANDER sitcom The Big Bang Theory were honored one thing for us all to for films and entertainment. strive for,” said Selda Ekiz, that there is a hunger out there for In addition to the medal, each winner host of the award ceremony, “it is to people to continue to learn long into adult- received a uniquely engraved, 18-karat yel- spread our burning desire to understand hood,” Tyson said. “There is a curiosity low gold Speedmaster Moonwatch from the world and the universe that we are a that still burns within us, even if we have Omega — the official watchmaker for part of.” forgotten it is there.” NASA since the 1960s. Tyson, the first American to receive the Encapsulating the spirit of the Starmus award, used his acceptance speech to Jake Parks is an associate editor at Astronomy Festival, the Stephen Hawking Medal was explain that every human being is born who greatly enjoys playing guitar and drums established in 2016 to acknowledge and innately inquisitive. “This is affirmation despite his lack of talent.

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WWW.ASTRONOMY.COM 63 The Full Moon OBSERVINGBASICS has an apparent BY GLENN CHAPLE diameter of about 0.5°, a convenient reference for calculating an What’s my true eyepiece’s true field of view. JOHN CHUMACK Try these three methods to field? determine an eyepiece’s true field of view.

ast summer, I received of view, not its magnification, is fraction of a Moon, I could fit in true field of 1.5°. Calculator in an email from 13-year- the ultimate determining factor. the field. Because this is the hand, I worked out the true old Adriana Baniecki This caused me to do a little most subjective of the three field for each eyepiece. The in Chandler, Arizona. soul-searching. During my methods and I didn’t want to results for all three methods She wrote, “I have just nearly five decades as an avid bias my results, I used this appear in the table below. Lstarted viewing the sky with my backyard astronomer, I’ve method first. Some final thoughts: Because new telescope, which has an become familiar with the mag- My tool for the next method the Moon’s angular size varies aperture of 114mm (4.5 inches) nifying power all my eyepieces was our spinning planet. Because with its distance from Earth and a focal length of 910mm. produce with my various tele- Earth rotates once every 24 (0.49° when farthest away, 0.56° I have 25mm, 12.5mm, and scopes, but I knew next to noth- hours, covering 360° of sky, a when closest), it’s not an ideal 4mm eyepieces, as well as a 3x ing about their true fields of star near the celestial equator measuring tool. Nevertheless, Barlow. I was wondering, given view. With my 10-inch f/5 will drift 1° every 4 minutes. If the ballpark figure you get is my eyepieces, what magnifica- reflector, for example, I nor- you time how many minutes it better than nothing, as my tion would be needed to view mally use three eyepieces: a takes the star to enter the field of results show. Also, by the time the Moon and planets. 32mm (40x), a 16mm (79x), and view, cross the center, and exit this issue reaches the news- “Also, in your January a 6mm (212x). Spurred to action on the opposite side, then divide stands, Sadalmelik won’t be as Astronomy column, ‘January’s easy to use for star-drift tim- top 10 targets,’ I noticed refer- ings. Work instead with 2nd- ences to both the angular size CALCULATING THE FIELD OF VIEW magnitude Mintaka (Delta [δ] of an object and the magnifica- Orionis), the northernmost and Eyepiece Mag. Apparent TRUE FIELD tion needed to view it. [Author’s westernmost of the three stars Field Moons Star-drift Calculation note: I had mentioned that the in Orion’s Belt and just 18' Pleiades star cluster (M45), 32mm 40x 70° 1.7° 1.8° 1.8° south of the celestial equator. which spans 2°, is best viewed 16mm 79x 82° 0.8° 1.0° 1.0° Finally, the AFOV of an eye- with low power.] Given the piece depends on its design. 6mm 212x 60° 0.3° 0.3° 0.3° angular size of any object, Here are approximate AFOVs could you simply calculate the The author calculated the true field of view of three eyepieces when attached to for traditional types: Huygens or magnification needed to view his 10-inch f/5 reflector. The three methods he used — estimating how many Ramsden (labeled “H” or “R” on Moons would fit in the field, star-drift timings, and mathematical calculations — it? If so, how?” gave pretty consistent results. the barrel), 30°; Kellner, achro- I responded by suggesting matized Ramsden, or modified that she always start with the achromat (“K” or “Ke,” “AR,” or 25mm eyepiece, which yields by Adriana’s email, I went out- that time by 4, you have the true “MA”), 40°; orthoscopic (“Or” or 36x with a 910mm focal length side with scope and eyepieces field of view in degrees. If the “Ortho”), 45°; Plössl, 50°; and scope, because its large field of and went to work determining transit time is 6 minutes, for Erfle (ER) or König, 60°. For view makes it easier to key in their true fields of view. example, the true field is 1.5°. My newer designs, especially super- on sky objects. I also recom- star of choice was 3rd-magnitude and ultrawide types, refer to mended this eyepiece for deep- True to your field Sadalmelik (Alpha [α] Aquarii), the manufacturer’s website sky objects wider than 0.5°, There are three basic ways to located just 19' south of the celes- for specifics. such as the Pleiades and the figure out the true field of view tial equator. I ran several trials Questions, comments, or Andromeda Galaxy (M31), add- an eyepiece provides. One is to for each eyepiece. suggestions? Email me at ing that the 12.5mm eyepiece use the Moon, which has an The final method can be done [email protected]. Next (73x) and 25mm eyepiece with apparent diameter of 0.5°, as a mathematically while indoors. month: another 13-year-old and 3x Barlow (109x) would work measuring tool. So if an eye- An eyepiece’s true field of view her eclipse adventure. fine on the Moon and planets. piece captures a chunk of sky equals its apparent field of view What about the magnifica- three Moon diameters across, it (AFOV) divided by the magnify- Glenn Chaple has been an tion needed for an object of has a true field of view of 1.5°. ing power it yields with a given avid observer since a friend given angular size? I pointed With each eyepiece, I measured scope. An eyepiece with a 60° showed him Saturn through a small backyard scope in 1963. out that an eyepiece’s true field how many Moons, or what AFOV that magnifies 40x has a

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64 ASTRONOMY • JANUARY 2018 15th Annual

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The train of sunspots near the center of the Sun was visible even through the smallest The ‘black drop’ telescopes. JOHN CHUMACK effect of Can this well-known phenomenon during planetary transits also be sunspots observed with sunspots?

he Great American A parade phases, observers using tele- of darkness vanished and reap- Eclipse has come of illusions scopes viewed the black drop peared repeatedly before becom- and gone, and many The phenomenon I had effect whenever the dark lunar ing a solid bridge that rapidly observers have mentioned is akin to the limb encountered a sunspot’s melted into the lunar limb. already shared their “black drop” effect that observ- umbral core. Several observers In addition to this phenom- Timpressions of totality with me. ers have reported during saw the effect independently enon, Chuck, Judy, and Deborah And now I’d like to pass those transits of Mercury and Venus. using telescopes with apertures also observed the larger sunspot exciting stories on to you. Torbern Bergman first noticed ranging from 6 to 16 inches. cores transforming into either a it during the 1761 transit of Judy and Chuck Dethloff, pencil-tip or teardrop shape A sunspot train Venus from Uppsala, Sweden, my wife, Deborah Carter, and before the advancing limb cov- Observers using safely filtered reporting that a dark “ligature” Richard Just all saw the effect ered them all. Deborah binoculars and telescopes (resembling a narrow bridge) as the Moon covered the length described the re-emergence of enjoyed views of a sunspot joined the silhouette of Venus of the sunspot train and the the last sunspot core before “train” with roughly a dozen to the inky background of the eastern group before totality, third contact as a mirage. umbral (dark inner) cores sky beyond the Sun. Imagine and uncovered them afterward. “First, the spot appeared stretching some 140,000 miles the black drop as gum on As the Moon passed over the flattened above the dark limb (225,000 kilometers) along the a hot pavement that clings spots, it created a parade of of the Moon separated by a Sun’s equator. Another sunspot to a shoe — until it breaks free illusions mostly near the center narrow gap,” she said. group near the Sun’s eastern as the shoe lifts. of the Sun’s disk — away from “Darkness from the spot then limb joined the train — a Astronomers still debate the any limb darkening. dripped into the lunar limb as pleasant surprise for an eclipse cause of the effect. Theories the spot transformed into a during a solar minimum. include atmospheric turbulence, A black bridge, teardrop before separating At the Oregon Star Party aberrations in optical systems, teardrops, from the lunar limb and (OSP), which lay in the path and eye-brain visual deceptions. and more appearing as a normal spot.” of totality, the plethora of In the Proceedings of the I got to see only one event It’s important to note that spots gave observers several International Astronomical (through Judy’s 16-inch the observers deemed the opportunities to witness an Union Colloquium, No. 196 Dobsonian-mounted reflec- atmosphere steady during optical phenomenon I had pro- (2004), Jay Pasachoff, Glenn tor), but it was dramatic enough many of these events, with posed might be visible during Schneider, and Leon Golub to convince me of the effect’s occasions of imperfect seeing. the partial phases. During a demonstrated how the Sun’s reality. As the Moon’s limb So these effects were observed talk the night before the main limb darkening is a principal approached the core of one under stable air, through siz- event, I had asked observers for culprit. Now observations made spot, a thin ligament appeared able telescopes, and mostly their help searching for it. And at OSP during the 2017 solar like a narrow bridge that joined near the center of the Sun’s on eclipse day, several of them eclipse add yet another dimen- the spot’s core and the Moon’s disk. Is it possible, perhaps, that took on the challenge and sion to the effect. advancing silhouette. Over the a sunspot’s penumbra serves reported success. During the eclipse’s partial course of seconds, this thread equally well as limb darkening to help cause the effect? As always, if you observed similar phenomena, send your reports to sjomeara31@gmail. com.

Stephen James O’Meara is a globe-trotting observer who is always looking for the The photographs at left and right show the approach and disappearance of a sunspot near the lunar limb during the 2017 solar eclipse. next great celestial event. The middle image has been altered with software to show what the author saw visually. STEPHEN JAMES O’MEARA

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• For use with most tripods, DOBs and piers • 10" Pneumatic tires for soft ride * BINOCULARUNIVERSE BY PHIL HARRINGTON Wonders of the Big Dog Canis Major holds the sky’s brightest star and one of the most beautiful open clusters.

blaze of brilliant stars decorates the January sky, The bright star cluster M41 in Canis Major is one of the most sparkling star groups ushering in 2018. when viewed with a good pair of binoculars. ANTHONY AYIOMAMITIS Brightest of all Ais Sirius (Alpha [α] Canis take a look near the bottom collection of stellar pinpoints. Majoris) in Canis Major, the Big (south) for a clump of faint Some 80 stars call M41 home, Dog. Aptly nicknamed the Dog stars. That’s the open cluster with 16 of them breaking the Star, Sirius stands obediently by M41. I think of it as the “Dog 9th-magnitude “binocular bar- its master, Orion the Hunter. Tag Cluster” for its position rier.” The rest blend together to Swing your binoculars near Canis Major’s “neck.” create a soft glow. Sirius’ way, and it puts on an The brightest star in the sky, Sirius, Many astro history buffs The brightest star in M41, harbors a dim companion called Sirius B astonishing show. If you can, just 4" away (below left). It is quite a credit the Greek scientist designated HD 49091, lies catch it as it is just rising above challenge to see visually. DAMIAN PEACH Aristotle (384 b.c.–322 b.c.) nearly dead center in the pack. the southeastern horizon. Since with discovering M41. That A type K3 orange giant, it you look through more of Sirius appears so bright primar- credit is based on his descrip- shines at magnitude 6.9 and Earth’s atmosphere when view- ily because of its distance from tion in Meteorologica (325 b.c.) puts on a fine show through ing near the horizon, tempera- our solar system. Sirius lies in which he writes, “one of the binoculars. Try defocusing the ture layers and intertwining only 8.6 light-years away, while stars of the Dog has a tail, image ever so slightly to accen- wind currents play havoc with Rigel is almost exactly 100 though a dim one; if you looked tuate the color. How many Sirius’ light, bending and times more distant. Were they hard at it, the light used to other red and orange stars can refracting it into a firestorm of to swap places, Sirius would become dim, but to a less intent you count in M41? rapidly changing colors. When shine at only 9th magnitude. glance it became brighter.” Also try your luck at resolving our atmosphere is especially Rigel, however, would blaze at a The first person to associate a double star found northwest of turbulent, resulting in “poor staggering magnitude –10. this statement with M41 was the cluster’s center. Known as seeing,” Sirius’ color shifts are Sirius is accompanied by a John Ellard Gore (1845–1910) in h2341, its component stars stroboscopic. white dwarf companion star an article he authored in the shine at magnitudes 8.3 and 9.1 As it rises higher in the sky, known as Sirius B, or the Pup. August 1902 issue of The and are separated by 45". That’s the colorful show slowly calms Trying to spot Sirius B is one of Observatory. Others have since wide enough to be resolved at down to reveal that the star’s backyard astronomy’s greatest adopted the same interpreta- 10x, but their faintness will true color is a radiant white. challenges. The problem is not tion, although some suggest it likely require you to use a tripod Winter skies often remain tur- that Sirius B is so faint. In fact, it actually points to a trail of faint or other support to steady the bulent through the night, with shines at magnitude 8.5, which stars farther south, near Wezen view. Then, by using Aristotle’s upper-level winds still creating is within reach of most binocu- (Delta [δ] Canis Majoris). There technique of averted vision, they mayhem with distant starlight. lars. No, the problem is Sirius. is no way to know for sure. may just pop into view. The brighter the star, the The same effect that causes stars From Aristotle’s words, how- I’d love to hear about your greater the twinkling effect. In to twinkle — scintillation — ever, there seems little doubt binocular adventures and con- the case of Sirius, the effect can also blurs the view by scattering that whatever he saw, he used quests. Contact me through my be almost hypnotic. their light. Sirius so completely averted vision to see it more website, philharrington.net. Sirius shines at magnitude overwhelms the observer’s eye distinctly. You can, too. But to Until next month, remember –1.4. But while it appears bright that poor Sirius B, some 10,000 see M41 with the unaided eye, that two eyes are better than in our sky, it is not an especially times fainter, is usually obliter- it takes especially dark, trans- one. luminous star. True, it does ated. The two are separated by parent skies. radiate 26 times more energy only 4", which also confounds It’s much easier through bin- Phil Harrington is a longtime than our Sun, but it is not observers. oculars. Swing your binoculars contributor to Astronomy and nearly as powerful as, say, Rigel, Shift Sirius toward the top toward the cluster, and you will the author of many books. seen 27° to the northwest. No, (north) of the field and then immediately see a compact

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1

1. RIGHT PLACE, RIGHT TIME This photographer was on Pensacola Beach, Florida, shooting the Moon setting August 2, 2017, when a brilliant fireball flashed overhead. He called it “the luckiest shot of my life.” • Austin Houser

2. REMEMBER THE CLUSTER M92 is often called the “forgotten” globular cluster in Hercules because its brighter counterpart — the Hercules Cluster (M13) — is so well known. But M92 isn’t that much fainter. It shines with 60 percent of its counterpart’s brilliance. • Georges Chassaigne

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70 ASTRONOMY • JANUARY 2018 3. RED SKY AT NIGHT Sharpless 2–126 in the constellation Lacerta the Lizard is a magnificent section of sky. This large star-forming region lies some 1,200 light-years from Earth. The energy that makes the cloud emit the characteristic reddish color of emission nebulae comes from the blue main sequence star 10 Lacertae (below and left of center). • Richard Sweeney

4. SEVEN ISN’T ENOUGH The Pleiades (M45) is the brightest and closest celestial object on French comet hunter Charles Messier’s list of 109 objects that were not comets. M45 is also known as the Seven Sisters; images push the total number of stars in this open cluster into the hundreds. • Terry Hancock 3 5. STARGAZER This monument in Eretria, Greece, shows a woman viewing the sky overhead. To complement the statue, this photographer captured and stacked seven hundred forty- three 30-second exposures of the background sky, showing how much it appears to move in more than 6 hours. The smallest curved streak belongs to Polaris (Alpha Ursae Minoris). • Anthony Ayiomamitis

6. MAN IN THE CASTLE A skywatcher observes a majestic group of sunspots in this carefully planned single shot taken September 7, 2017, 1.3 miles (2.1 km) from the Castle of Noudar Park, Portugal. On September 6, the Earth-sized sunspot AR2673 — seen at the right side of the man´s silhouette — unleashed an X9.3-class solar flare, the strongest in more than a decade. • Miguel Claro

45

6

WWW.ASTRONOMY.COM 71 7. COAXING OUT DETAILS Spiral galaxy M100 in the constellation Coma Berenices is difficult to photograph because of its wide dynamic range. Its arms are faint while the galaxy’s core is tiny and bright. M100 does lie in a colorful star field. • Rodney Pommier

8. GO FLY A KITE The Kite Cluster (NGC 1664) lies against a rich star field in the constellation Auriga. You’ll find this attractive open cluster 2° west of Epsilon (ε) Aurigae. It lies some 4,000 light-years away. • Jaspal Chadha

9. DISH IT OUT This two-exposure panorama shows one of the antennas of the Very Large Array in New Mexico. The Northern Hemisphere summer Milky Way lies behind it. The brightest star to the right of the dish is Antares (Alpha [α] 78 Scorpii). • John Vermette

9 10

10. I FELL IN LOVE The Heart Nebula (IC 1805, right) pairs with the Soul Nebula (IC 1848) in the Waning Crescent Moon northern constellation Cassiopeia. The pair lies roughly 7,500 light-years away. This image is a combination of 19 hours of exposures through six filters. • Kfir Simon

11. FIVE FOR OBSERVING This photographer captured a lineup of four solar system objects and a bright star at 6:24 A.M. EDT, September 17, 2017, from East Dayton, Ohio. Venus • John Chumack

Regulus

Mars Mercury

Send your images to: Astronomy Reader Gallery, P. O. Box 1612, Waukesha, WI 53187. Please include the date and location of the image and complete photo data: telescope, camera, filters, and expo- sures. Submit images by email to 11 [email protected].

WWW.ASTRONOMY.COM 73 BREAK THROUGH A tale of three cities The beauty of the Orion Nebula (M42) belies the firestorm of star birth taking place within its nebulous folds. But this vast stellar nursery shrouds another secret: The young stars within appear to have formed in three separate bursts. Astronomers uncovered these populations by analyzing the data in this image taken through the European Southern Observatory’s VLT Survey Telescope in Chile. The researchers measured the colors and brightnesses of the thousands of stars in the nebula’s core and discovered what appears to be three successive generations born about 2.87 million, 1.88 million, and 1.24 million years ago. ESO/G. BECCARI

74 ASTRONOMY • JANUARY 2018

B&H Photo – 800.947.9970 – bhphotovideo.com OPT Telescopes – 800.483.6287 – opttelescopes.com High Point Scientifi c – 800.266.9590 – highpointscientifi c.com Woodland Hills – 888.427.8766 – telescopes.net Optics Planet – 800.504.5897 – opticsplanet.com Adorama – 800.223.2500 – adorama.com Astronomics – 800.422.7876 – astronomics.com Focus Camera – 800.221.0828 – focuscamera.com SPECIAL Astronomy’s Pull-out section Guide to 2018 the Night Sky MARS remains visible for all of 2018, though it LUNAR PHASES appears most conspicuously from April through November. The Red Planet rises around 2 A.M. in mid-April, but comes up earlier with each passing day. It peaks at opposition in late July, when it shines at magnitude –2.8, swells to an New First Quarter Full Last Quarter apparent diameter of 24", and remains on view all night. Mars hasn’t appeared this bright and big Jan. 1 Jan. 8 since 2003. A telescopic view reveals subtle features that show up Jan. 16 Jan. 24 Jan. 31 Feb. 7 as contrasting shades of orange and brown. NASA/JPL-CALTECH/USGS

Feb. 15 Feb. 23 March 1 March 9 JUPITER always shows a dramatic face. Its March 17 March 24 March 31 April 8 atmosphere displays an alternating series April 15 April 22 April 29 May 7 of bright zones and darker belts pocked by the Great Red Spot. Even through May 15 May 21 May 29 June 6 a small telescope, the planet’s four big moons appear prominent. June 13 June 20 June 28 July 6 You often will see them change July 12 July 19 July 27 Aug. 4 positions noticeably during the course of a single night. Jupiter Aug. 11 Aug. 18 Aug. 26 Sept. 2 reaches its peak in early May, when it Sept. 9 Sept. 16 Sept. 24 Oct. 2 shines brightest (magnitude –2.5) and looms largest (45" across), though it’s a fine Oct. 8 Oct. 16 Oct. 24 Oct. 31 sight through September and again in late

December. NASA/JPL/USGS Nov. 7 Nov. 15 Nov. 23 Nov. 29

Dec. 7 Dec. 15 Dec. 22 Dec. 29 SATURN and its rings provide a spectacular attraction for telescope owners during most of 2018. The ringed planet is All dates are for the Eastern time zone. A Full Moon rises at sunset on display from late January through November, but it and remains visible all night; a New Moon crosses the sky with the appears best around the time of Sun and can’t be seen. opposition in late June. Saturn then shines at magnitude 0.0, and its disk measures 18" THE MOON is Earth’s nearest neighbor and the across while the rings span 42" only celestial object humans have visited. and angle 26° to our line of sight. Because of its changing position relative to Even a small telescope reveals the the Sun and Earth, the Moon appears to dark, broad Cassini Division that separates go through phases, from a slender crescent the outer A ring from the brighter B ring.

to Full Moon and back. The best times to NASA/ESA/E. KARKOSCHKA (UNIVERSITY OF ARIZONA) observe our satellite through a telescope come a few days on either side of its two Quarter phases. For the best detail, look along the terminator — the line separating the sunlit

and dark parts. NASA/GSFC/ARIZONA STATE UNIVERSITY Subscribe today! 1-800-533-6644 Visit our website at www.Astronomy.com 618365 A supplement to Astronomy magazine WINTER N

The sky

DRACO Jan. 1 Winter boasts the brightest stars of any CEPHEUS

season. Orion the Hunter dominates the Mercury is

evening sky this time of year. Its seven MINOR at greatest Mizar

brightest stars form a distinctive hourglass URSA western

Polaris

M51 elongation pattern. The bright blue star marking Orion’s CASSIOPEIA

MAJOR

left foot is Rigel, and the ruddy gem at his URSA ANDROMEDA

M31 Jan. 31

right shoulder is Betelgeuse. The three stars 869 NGC BERENICES NGC 884 NGC of the Hunter’s belt point down to Sirius, COMA Dwarf planet

the brightest star in the night sky, and up Ceres is at PEGASUS

to Aldebaran, the eye of Taurus the Bull. To PERSEUS opposition Capella M33

Orion’s upper left lies the constellation Gemini. Castor

Denebola

Pollux Jan. 31 Total CANCER

LEO

PISCES ARIES

Deep-sky highlights M37 Pleiades

E M44 W lunar eclipse The Pleiades (M45) is the brightest star AURIGA ECLIPTIC cluster in the sky. It looks like a small M35 March 15 Regulus GEMINI Procyon Alde- dipper, but it is not the Little Dipper. baran Mercury is CETUS The Orion Nebula (M42), a region of active Betelgeuse at greatest Mira TAURUS eastern star formation, is a showpiece through NGC 2237-9 ORION telescopes of all sizes. HYDRA M42 elongation Rigel The Rosette Nebula (NGC 2237–9/46), CANIS Sirius located 10° east of Betelgeuse, presents an MAJOR LEPUS April 2 Mars impressive cluster of stars and a nebula. passes 1.3° ERIDANUS south of M35 in Gemini the Twins is a beautiful open COLUMBA cluster best viewed with a telescope. Saturn Castor (Alpha [α] Geminorum) is easy to split PUPPIS April 22 into two components with a small telescope, but the system actually consists of six stars. Lyrid meteor S shower peaks

SPRING May 6 Eta Aquariid The sky meteor The Big Dipper, the most conspicuous part N shower peaks of the constellation Ursa Major the Great Bear, now rides high in the sky. Poke a hole May 8 in the bottom of the Dipper’s bowl, and the Jupiter is at

water would fall on the back of Leo the Lion. CEPHEUS opposition

The two stars at the end of the bowl, called Vega DRACO

LYRA

Polaris June 19

the Pointer Stars, lead you directly to Polaris, Capella MINOR

URSA Asteroid

the North Star: From the bowl’s top, simply go AURIGA HERCULES

five times the distance between the Pointers. Vesta is at M82

MAJOR

Spring is the best time of year to observe URSA opposition

M13 M81

Mizar

a multitude of galaxies. Many of these far- M35 BOREALIS

CORONA June 27 flung island universes, containing hundreds M51

Castor Saturn is at BOÖTES

of billions of stars, congregate in northern TAURUS ORION

COMA Pollux opposition Virgo and Coma Berenices. BERENICES

SERPENS E CAPUT GEMINI W Deep-sky highlights M44 July 12 Arcturus M5 Mercury is The Beehive Cluster (M44) was used to LEO Betelgeuse Denebola CANCER CANIS forecast weather in antiquity. It is a naked- MINOR at greatest VIRGO eastern eye object under a clear, dark sky, but it Regulus Procyon disappears under less optimal conditions. elongation M5 CRATER , a conspicuous globular cluster, lies ECLIPTIC Spica CORVUS between the figures of Virgo the Maiden and Serpens Caput the Serpent’s Head. HYDRA The Whirlpool Galaxy (M51) is a vast spiral about 30 million light-years away. M81 and M82 in Ursa Major form a pair of galaxies that you can spot through a CENTAURUS VELA telescope at low power. S

STAR MAPS BY ASTRONOMY: ROEN KELLY SUMMER N

The sky July 12 PERSEUS High in the sky, the three bright stars known Pluto is at as the Summer Triangle are easy to spot.

opposition These luminaries — Vega in Lyra, Deneb in

CASSIOPEIA

Polaris

M31 Cygnus, and Altair in Aquila — lie near the

CEPHEUS

July 27 MAJOR MINOR URSA starry path of the Milky Way. Following the

Mars is at URSA Milky Way south from Aquila, you’ll find the

opposition

PEGASUS center of our galaxy in the constellation LACERTA

Mizar Sagittarius the Archer. Here lie countless star DRACO Aug. 12 Deneb

M51 clusters and glowing gas clouds. Just west of

Perseid

CYGNUS

Denebola Sagittarius lies Scorpius the Scorpion, which

LEO

meteor Vega HERCULES contains the red supergiant star Antares as

shower peaks

BERENICES well as M6 and M7, two brilliant clusters that BOÖTES COMA M57 LYRA E Enif M13 W look marvelous at low power. Aug. 17 Venus is at Altair Deep-sky highlights AQUARIUS SERPENS The Hercules Cluster greatest VIRGO (M13) contains nearly CAUDA Arcturus eastern AQUILA a million stars and is the finest globular SERPENS elongation M11 CAPUT cluster in the northern sky. Spica SCUTUM CAPRICORNUS The Ring Nebula (M57) looks like a puff of IC Aug. 26 IPT M16 ECL smoke through a medium-sized telescope. M17 OPHIUCHUS Mercury is The Omega Nebula (M17) looks like the LIBRA at greatest Greek letter of its name (Ω) through a western SAGITTARIUS Antares M6 telescope at low power. This object also is elongation M7 LUPUS called the Swan Nebula. The Wild Duck Cluster (M11) is a glorious Sept. 7 SCORPIUS open star cluster. On a moonless night, a Neptune is at small scope will show you some 50 stars. opposition S

Oct. 21 AUTUMN Orionid meteor The sky shower peaks N The Big Dipper swings low this season, and from parts of the southern United States,

Oct. 23 it even sets. With the coming of cooler

MAJOR Uranus is at URSA nights, Pegasus the Winged Horse rides

opposition DRACO

MINOR high in the sky as the rich summer Milky

URSA Way descends in the west. Fomalhaut, a Polaris

Nov. 17 M13 solitary bright star, lies low in the south. The Capella

HERCULES

Leonid M35

CEPHEUS magnificent Andromeda Galaxy reaches its AURIGA

meteor peak nearly overhead on autumn evenings,

shower peaks 884

PERSEUS as does the famous Double Cluster. Both Vega

869 of these objects appear as fuzzy patches to

CASSIOPEIA

Algol Dec. 14 Deneb

ORION

LYRA CYGNUS the naked eye under a dark sky. Geminid M31 Deep-sky highlights meteor ` shower peaks Aldebaran The Andromeda Galaxy (M31) is the brightest E TAURUS ARIES PEGASUS W M33 SAGITTA naked-eye object outside our galaxy visible in Dec. 15 PISCES the northern sky. M15 AQUILA The Double Cluster Mercury is Altair (NGC 869 and NGC 884) at greatest ERIDANUS EC Enif DELPHINUS in Perseus consists of twin open star clusters. LIP western Mira CETUS TIC AQUARIUS It’s a great sight through binoculars. elongation M15 in Pegasus is a globular cluster containing hundreds of thousands of stars, many of which can be glimpsed through a medium-sized telescope. Fomalhaut Albireo β Open cluster CAPRICORNUS (Beta [ ] Cygni), the most beautiful PISCIS double star in the sky, is made up of suns Globular cluster PHOENIX AUSTRINUS colored sapphire and gold. Diffuse nebula GRUS Planetary nebula S Galaxy SOUTHERN MARTIN GEORGE describes the solar system’s changing landscape SKY as it appears in Earth’s southern sky. March 2018: The evening planets return

The early evening sky has been around 10 p.m. local time in might catch a fleeting glimpse most famous double star in the devoid of bright planets all early March and some two of surface detail during southern sky. It is also the near- summer, but that comes to an hours earlier by month’s end. moments of good seeing, when est star system to our own, with end as autumn approaches. The planet appears nearly sta- Earth’s atmosphere steadies faint Proxima Centauri, the Unfortunately, the first two tionary against the backdrop of and the light from celestial system’s third member, the solar system residents to appear central Libra the Scales. Jupiter objects snaps into sharp focus. closest of the three. But it is the at dusk don’t climb very high in brightens from magnitude –2.2 Saturn rises a little more brighter pair that makes a spec- March, particularly from more to –2.4 during March, which than an hour after Mars in tacular telescopic sight. Only southerly latitudes. Blame the makes it 100 times brighter early March, but the gap 4.5" separate the two suns, and shallow angle of the ecliptic — than Libra’s luminary, which shrinks to 10 minutes by the the gap is gradually widening. the apparent path of the Sun glows at magnitude 2.6. 31st. At the end of the month, Next, turn your attention to across the sky that the planets The view of Jupiter through they appear 2° apart and make Orion the Hunter. Center your closely follow — to the western a telescope is no less impres- a fine pair through binoculars. scope on Rigel, the bright, blue- horizon after sunset at this sive. The giant planet’s equato- (The two will pass within 1.3° white star at the upper left of time of year. A planet’s elonga- rial diameter swells from 39" to of each other April 2.) Saturn the constellation these March tion from the Sun translates 43" during March, delivering shines at magnitude 0.5 and evenings. At medium and high more into distance along the exquisite eyepiece images in appears a touch dimmer than magnification, the magnitude horizon and less into altitude. any instrument. Look for an its neighbor. They’ll be easier 6.8 secondary shows up nicely Venus makes the better alternating series of bright to tell apart by their colors: 9" from the primary. Although appearance. In late March, it zones and darker belts, perhaps Mars shines with a distinctive the companion is also a double, lies 20° east of the Sun, and punctuated by the ruddy cloud orange-red hue while Saturn the two stars are a fraction of from mid-southern latitudes, it tops of the Great Red Spot, if it appears golden yellow. an arcsecond apart and invis- appears 4° above the western happens to be on the Earth- It’s always worth exploring ible through backyard scopes. horizon a half-hour after sun- facing hemisphere. Your sharp- Saturn through a telescope, If you want to see a beauti- set. (Conditions improve closer est views will come as Jupiter though your sharpest views ful multiple star system, look to the equator. From Darwin, climbs high after midnight; it will come when it climbs high no further than Sigma (σ) Australia, for example, the reaches a peak altitude of 70° in the east as dawn starts to Orionis. It resides 0.8° south- planet appears twice as high at around the time morning twi- paint the sky. In mid-March, southwest of Zeta (ζ) Ori, the the same time.) Venus shines light commences. the planet shows a 16"-diameter easternmost star in Orion’s brilliantly, at magnitude –3.9, A couple of hours after disk surrounded by a ring sys- Belt. Small scopes reveal four and should show up clearly in Jupiter rises, Mars pokes above tem that spans 37" and tips 26° stars. In addition to the 4th- the twilight if you have an the eastern horizon. The Red to our line of sight. The large magnitude primary, you’ll see unobstructed horizon. Planet moves steadily eastward tilt delivers excellent views of stars of magnitudes 10.3, 7.5, Mercury doesn’t fare as against the background stars the inky-black Cassini Division and 6.5 in order of their increas- well. The best time to look for during March, crossing from that separates the outer A ring ing distance. The primary itself the innermost planet is when it Ophiuchus the Serpent-bearer from the brighter B ring. is a very close double, but you reaches greatest elongation into Sagittarius the Archer in won’t be able to split it. March 15. It then lies 18° east the month’s second week. Mars The starry sky Our final stop these March of the Sun but climbs just 1° brightens by more than 50 per- One of the surprises for many evenings is across Orion’s east- high a half-hour after sundown cent during March, climbing first-time telescope users is ern border into Monoceros the for those at mid-southern lati- from magnitude 0.8 to 0.3, and “discovering” that so many Unicorn. Beta (β) Monocerotis tudes. (Observers in Darwin noticeably outshines the stars stars are double or multiple. is a stunning triple star with see Mercury at an altitude of of its host constellations. The list of such systems is long, components glowing at magni- 5°.) You’ll need binoculars to The rapid brightening goes and includes some of the night tudes 4.7, 5.2, and 6.1. The pick up the planet’s magnitude hand in hand with the planet’s sky’s brightest stars. second-brightest star resides –0.4 glow. increasing diameter. Mars’ disk Probably the first double 7" from the primary, while the If these early evening views spans 6.7" on March 1 and that beginners aim their tele- third-brightest member lies leave you unimpressed, just reaches 8.4" across by the 31st. scopes toward is Alpha (α) another 3" farther away in wait a few hours. Jupiter rises This is big enough that you Centauri, which is arguably the nearly the same direction. SHOP NOW FOR SCIENCE & ASTRONOMY PRODUCTS

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P29014 STAR S

DOME PAVO

THE ALL-SKY MAP TUCANA SHOWS HOW THE ARA SKY LOOKS AT:

10 P.M. March 1 PHOENIX NGC 104 NGC

9 P.M. March 15 AUSTRALE

TRIANGULUM

8 P.M. March 31 OCTANS Achernar

Planets are shown SMC

HYDRUS

_ APUS at midmonth CIRCINUS

SCP

_

CHAMAELEON

`

MUSCA MENSA

S

HOROLOGIUM

RU

RETICULUM

LMC

_

NGC 4755 NGC

DORADO NGC 2070 NGC 39

`

51

b

a

VOLANS

3372

PICTOR

8 NGC NGC

NGC 2561 NGC CRUX

FORNAX

_ CARINA

Canopus

CAELUM

PUPPIS

ERIDANUS

VELA

a

2477 c

NGC

COLUMBA

LEPUS

¡

M41 PYXIS W ANTLIA

CANIS

` MAJOR Rigel

_ ` Sirius MONOCEROS M47 M42

Alphard _

SEXTANS

Aldebaran HYDRA Betelgeuse Procyon ORION _

TAURUS _ ` CANIS MINOR CANCER _ M65 _ Regulus a c LEO M1 a M44 M35 ` ` Pollux GEMINI _ M36 Castor MAGNITUDES M37 LEO MINOR Sirius Open cluster M38 0.0 AURIGA Globular cluster LYNX 1.0 Diffuse nebula 2.0 ` 3.0 Planetary nebula 4.0 URSA MAJOR 5.0 Galaxy

N HOW TO USE THIS MAP: This map portrays the sky as seen near 30° south latitude. MARCH 2018 Located inside the border are the four directions: north, south, east, and west. To find stars, hold the map Calendar of events overhead and orient it so a direction label matches the 1 The Moon passes 0.9° north of 19 The Moon passes 5° south of

NORMA direction you’re facing. Regulus, 6h UT Uranus, 16h UT The stars above the map’s horizon now 2 Full Moon occurs at 0h51m UT 20 March equinox occurs at match what’s 16h15m UT 4 Neptune is in conjunction with in the sky.

the Sun, 14h UT Dwarf planet Ceres is stationary, LUPUS 21h UT

RU 5 Mercury passes 1.4° north of

Venus, 18h UT 22 Mercury is stationary, 17h UT

CENTAU 51 7 The Moon passes 4° north of The Moon passes 0.9° north of

Jupiter, 7h UT Aldebaran, 23h UT NGC NGC

8 9 Jupiter is stationary, 10h UT 24 First Quarter Moon occurs at 15h35m UT Last Quarter Moon occurs at

NGC 512 NGC 11h20m UT 26 The Moon is at perigee M83 (369,106 kilometers from Earth), 10 The Moon passes 4° north of 17h17m UT Mars, 1h UT 28 The Moon passes 1.0° north of 11 The Moon passes 2° north of Regulus, 14h UT Saturn, 2h UT 31 Full Moon occurs at 12h37m UT

The Moon is at apogee (404,678 Spica CORVUS _ E kilometers from Earth), 9h14m UT 15 Mercury is at greatest eastern

M104 elongation (18°), 15h UT

c) ti 17 New Moon occurs at 13h12m UT p CRATER i cl VIRGO (e un 18 Mercury passes 4° north of S he Venus, 1h UT f t o th Pa The Moon passes 8° south of Mercury, 18h UT The Moon passes 4° south of Venus, 19h UT

Denebola M66 `

M64 STAR COLORS:

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

Illustrations by Astronomy: Roen Kelly

BEGINNERS: WATCH A VIDEO ABOUT HOW TO READ A STAR CHART AT www.Astronomy.com/starchart. 5 P.M. 6 P.M. 7 P.M. 8 P.M. 9 P.M. 10 P.M. 11 P.M. Midnight 1 A.M. 2 A.M. 3 A.M. 4 A.M. 5 A.M. 6 A.M. 7 A.M. Jan. 1

M E R URANUS C Jan. 16 U TRANSITS R Y R IS E NEPTUNE SETS S Jan. 31 SIRIUS TRANSITS

Feb. 15

M March 2 ER URANUS SETS CU RY MARS RISES S E

T RISE & SET

March 17 S JUPITER RISES This illustration presents the night sky for 2018, April 1 showing the best times to ES IS observe the planets from R Y April 16 JUPITER TRANSITS R Mercury to Neptune. For each V U E C N R planet, the times when it rises U E S M S SPICA TRANSITS and sets are shown throughout May 1 E T S the year. For Mercury and Venus, SATURN RISES which never stray too far from the May 16 S

U Sun, these times appear as loops

N S coming up from the sunset horizon E May 31 T ANTARES TRANSITS (on the left) or the sunrise horizon (on the right). For Mars, Jupiter, Saturn, M ER C NEPTUNE RISES E Uranus, and Neptune, the times when June 15 U S R I

Y R S they transit — appear highest in E N T SATURN TRANSITS U S S the sky and provide the best view June 30 URANUS RISES through a telescope — also are

JUPITER SETS shown. All the planets lie near the July 15 ecliptic, so you can use this chart in MARS TRANSITS conjunction with the maps on the July 30 previous pages to find a planet’s approximate location. The chart also includes the transit times of Aug. 14 four bright seasonal stars: Sirius, Spica, Antares, and Deneb. This Aug. 29 map shows local times for an DENEB TRANSITS MERCURY observer at 40° north latitude. SATURN SETS Sept. 13 RISES Although exact times will vary depending on your NEPTUNE TRANSITS longitude and latitude (and Sept. 28 don’t forget to add an hour for daylight saving time),

Oct. 13 the relative times and

M E

R approximate positions C

U will stay the same.

Oct. 28 R

Y

S ASTRONOMY: RICK JOHNSON

E

T S Nov. 12 URANUS TRANSITS ES IS NEPTUNE SETS R S U Nov. 27 N MARS SETS E S V ISE SIRIUS TRANSITS Y R UR C R Dec. 12 E

M

Dec. 27 URANUS SETS JUPITER RISES

5 P.M. 6 P.M. 7 P.M. 8 P.M. 9 P.M. 10 P.M. 11 P.M. Midnight 1 A.M. 2 A.M. 3 A.M. 4 A.M. 5 A.M. 6 A.M. 7 A.M.