Will a killer asteroid Behind the scenes at the impact Earth? p. 28 Kennedy Space Center p. 44

JULY 2016

The world’s best-selling astronomy magazine

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28 COLUMNS CONTENTS Strange Universe 6 FEATURES BOB BERMAN For Your Consideration 10 22 COVER STORY 38 56 JEFF HESTER The Milky Way StarDome and Explore Earth’s Observing Basics 14 through thick and thin Path of the Planets big impacts GLENN CHAPLE Astronomers studying our gal- RICHARD TALCOTT; Earth has a long history of aster- Secret Sky 18 axy’s vertical structure are teasing ILLUSTRATIONS BY ROEN KELLY oid strikes, and some intriguing STEPHEN JAMES O’MEARA out details about how our home scars remain. MIKE REYNOLDS system evolved. BRUCE DORMINEY 44 Binocular Universe 20 Behind the scenes at 60 PHIL HARRINGTON 28 Kennedy Space Center Seek exoplanets Astro Sketching 66 Falling behind on he home of American from your backyard ERIKA RIX asteroid follow-ups space light is bursting with Learn how amateur astronomers Powerful surveys are discovering memories — and ready to host can help professionals study QUANTUM GRAVITY asteroids at a faster rate than ever the launches of today and worlds outside our solar system. Snapshot 5 before, but most of these Earth- tomorrow. DAVID J. EICHER DENNIS CONTI approaching asteroids never get Astro News 8 a second glance. ILIMA LOOMIS 50 64 Target our galaxy’s The quest for IN EVERY ISSUE 34 dark nebulae distant Pluto From the Editor 4 Ask Astro Pull up a chair, and spend some his newly revealed world at Letters 6, 14, 18, 20 time away from the light. the solar system’s edge makes a New Products 68 36 RICHARD P. WILDS tempting target through amateur The Sky this Month telescopes as it reaches peak Advertiser Index 69 MARTIN RATCLIFFE AND visibility early this summer. Reader Gallery 70 ALISTER LING RICHARD TALCOTT Breakthrough 74

Astronomy (ISSN 0091-6358, USPS 531-350) is ONLINE published monthly by Kalmbach Publishing Co., 21027 Crossroads Circle, P. O. Box 1612, Waukesha, WI 53187–1612. Periodicals post- FAVORITES age paid at Waukesha, WI, and additional offices. POSTMASTER: Send address changes to Astronomy, P.O. Box 62320, Tampa, Fla. 33662-2320. Go to www.Astronomy.com Dave’s Trips & Tours Seasonal Interactive Canada Publication Mail Agreement #40010760. for info on the biggest news and Universe Travel the Observing Star Atlas observing events, stunning photos, The inside world with Find great Pan and zoom scoop from the staff of targets in your through the informative videos, and more. the editor Astronomy summer sky night sky

WWW.ASTRONOMY.COM 3 FROM THE EDITOR BY DAVID J. EICHER Editor David J. Eicher Art Director LuAnn Williams Belter EDITORIAL Managing Editor Kathi Kube Senior Editors Michael E. Bakich, Richard Talcott Associate Editor Korey Haynes Copy Editors Dave Lee, Elisa R. Neckar Join us for Editorial Associate Valerie Penton ART Graphic Designer Kelly Katlaps Illustrator Roen Kelly the 2017 Production Coordinator Jodi Jeranek CONTRIBUTING EDITORS Bob Berman, Adam Block, Glenn F. Chaple, Jr., Martin George, Tony Hallas, Phil Harrington, Jeff Hester, Liz Kruesi, Ray Jayawardhana, Alister Ling, Steve Nadis, Stephen James O’Meara, Tom Polakis, Martin Ratcliffe, Mike D. Reynolds, eclipse! 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, Anne L. 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In 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

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4 ASTRONOMY • JULY 2016 QUANTUM GRAVITY QGEVERYTHING YOU NEED TO KNOW ABOUT THE UNIVERSE THIS MONTH . . .

JUNO ARRIVES EXTREME PLANET BLACK HOLE SPIN HOT BYTES >> The Juno mission arrives Exoplanet HD 80606 b Astronomers measured a July 4 at Jupiter, where has a nearly cometlike distant, 18-billion-solar- TRENDING it will peer deep into the orbit, spending 20 hours mass black hole’s rota- TO THE TOP planet’s cloudy depths roasting close to its star tion rate to be one-third and decipher its power- and then 110 days travel- the maximum spin gen- ful magnetic field. ing a cold loop far away. eral relativity allows.

SNAPSHOT

When galaxies HOLE SPIN) CK Gravity brings them collide together frequently, building monsters from blebs and blobs.

Ever since the 1920s, we’ve known that the universe is expanding — at large scales, everything is moving away from everything else. But at smaller scales, gravity can be the dominant force. This leads to some of the (EXTREME COLLEGE TECH/MIT/PRINCIPIA PLANET); (BLA NASA most interesting aspects of galaxies as we see them in Earth’s sky: collisions. Like cars on an overcrowded, fast-moving freeway, galax- ies sometimes lunge headlong into each other, often with exciting and transformative results. Now face it: As anti-humanistic as it may be, everyone driving along on a freeway slows down to see a car wreck. That curiosity of seeing the unusual, the tangled up, the dra- matic, is part of the human psyche. Of course with humans driving cars, we hope for no injuries. But with galaxies coming together, the more fireworks, the better. Collisions between galaxies are important for several reasons. They are probably the (JUNO NASA/JPL-CAL ARRIVES); NASA/ESA/L. NASA/JPL-CALTECH FRATTARE/STScI; This Hubble Space Telescope image of the galaxy Perseus A, the central object in the Perseus Cluster of galaxies, reveals major way in which numerous protogalaxies an object undergoing immense galactic trauma. The galaxy’s bloated size is the result of numerous absorptions of in the early universe built themselves up into smaller objects, and its center is powered by a supermassive black hole. the normal galaxies we now see around us. The Milky Way, for example, may consist of That’s what galaxies do — they eat their American astronomer Herbert J. Rood first as many as 100 protogalaxies that came friends, and the closer the better. Galactic proposed this explanation in 1965, and can- together by galactic mergers. As we’ve seen, cannibalism results in the largest, most nibalism among galaxies has been observed the Milky Way continues to “eat” several incredible, and most energetic galaxies we in many clusters since. Examples of cD gal- small dwarf galaxies that orbit near it, most know of, cD galaxies. These are supergiant axies include Perseus A (NGC 1275) in the prominently at the present time, the elliptical galaxies often lying at the centers Perseus Cluster of galaxies; M87, the domi- Sagittarius Dwarf Spheroidal Galaxy, which of rich galaxy clusters, and they have grown nant member of the Virgo Cluster; and NGC will be shredded and incorporated into the enormously by swallowing many of the 4889, the brightest object in the Coma Milky Way in the future. smaller galaxies that surrounded them. Cluster of galaxies. — David J. Eicher

WWW.ASTRONOMY.COM 5 STRANGEUNIVERSE FROM OUR INBOX BY BOB BERMAN Young viewers needed It was with great interest that I read David J. Eicher’s “Whither the astronomy hobby?” — p. 6, April 2016. I agree totally that avid enthusiasts are aging. I’m 65 now, but I can remember the Feel the force awe and excitement that I felt on first seeing Saturn through What’s the universe’s greatest power? my 2.4-inch refractor. It took my breath away, and I hardly slept that night — I was just 12 years old. I maintain that all this generation needs is one look through a telescope, and it o you love fire- U.S. explosion yielded will transform them in ways that will be life-changing. works shows that 15 megatons and surprised To those of us who have telescopes, PLEASE share a view let you get very scientists, whose incorrect with a kid! They will remember it forever. — Richard Dodge, close? At such calculations made them expect New Prague, Minnesota pyrotechnics “only” a 6-megaton blast. Ddisplays, the delay between But no matter how big our We welcome your comments at Astronomy Letters, P. O. Box 1612, each flash and the earsplit- explosions get, the stars will Waukesha, WI 53187; or email to [email protected]. Please ting boom can be just a half- overpower us every time. include your name, city, state, and country. Letters may be edited for second, meaning you’re only Ultra-high core pressure boosts space and clarity. two blocks from the detona- the fusion process in winter’s tions. My hometown display is Rigel and summer’s Deneb. like that, with glowing debris These overcaffeinated stars sign of positrons (antielec- minute. Sounds like a lot, per- virtually raining down on the release the energy of 200,000 trons) meeting electrons. It’s haps, but when mated with pos- crowd, which must strangely Suns. Calling them stars is to the 100 percent conversion of itrons it would then still take not include any attorneys. underappreciate their nonstop matter to energy. 100 billion years to manufacture These annual boom-fests bring explosions. Yet they’re still the A single gram of mozzarella a single gram of antihydrogen. up the topic of power. minor leagues compared with cheese, fully converted, could NASA estimates a gram of anti- Where is the universe’s most supernovae. When the Crab power a 100-watt bulb for matter would cost $62 trillion. awesome energy? And can we exploded on the 4th of July 30,000 years. Any material is as Buying generic doesn’t help. grab some of it? in 1054, it was as bright as a good as any other. A dollar bill Is any power greater? Right now, when days are half-billion Suns. Even now, weighs a gram. A twenty would Yes. Vacuum energy, also longest, our impulse might flow long after the crowds have gone work, too, but why go crazy? called zero-point energy. This in sync with the ancient Greeks home, the crazy whirling of its Squeezing the energy from a unseen power fills all of space. and Egyptians, who’d say it’s tiny collapsed pulsar still man- single paper currency note Some believe a vacant pickle jar the Sun. It’s a good first guess. ages to continuously emit the could run a 1-horsepower of empty space could boil away We’re talking nuclear fusion. In energy of 75,000 Suns. motor from 1500 B.C. right all our oceans in 3 seconds. 1920, when Arthur Eddington Unfortunately, the disparity explained how the Sun shines, between its theoretical energy it seemed astonishing. At SOME BELIEVE A VACANT PICKLE JAR and what little hard data we high enough temperatures, OF EMPTY SPACE COULD BOIL AWAY ALL have differs by 100 orders four ordinary, plain-vanilla OUR OCEANS IN 3 SECONDS. of magnitude. The Z-point hydrogen atoms fuse into one power discrepancy is so huge, of helium. The Sun relies on it’s called the “vacuum this conversion to power its Yet even the Sun’s fusion through this Election Day. No catastrophe.” astounding 96 billion-megaton- process converts only 0.7 per- wonder Geordi La Forge grew And catastrophe might per-second output. That’s cent of its four hydrogen atoms’ nervous every time the starship indeed follow if we could fig- 96 billion H-bombs going off mass into energy, leaving the Enterprise’s warp core was ure out how to capture and continuously in the solar core. rest behind mostly as disap- about to lose its antimatter exploit vacuum energy. So Amazingly, we humans fig- pointing helium. We can’t stop containment. when we watch Independence ured out how to do the same there. We want tales of insane Given our proclivity toward Day fireworks, we might atomic consolidation. The first explosiveness. misadventure, it’s probably remember that, yes, Homo time was in 1952, with a colos- For that we must seek per- good that we can’t get our hands bewilderus has learned how to sus the size of a building. Mike, fect efficiency, the total con- on much antimatter. It is make ever-bigger booms. But as the device was known, held version of mass to energy. That insanely expensive. Although they’re baby burps compared supercold liquid deuterium requires colliding matter and an Amazon search leads to the with what the universe has hid- (hydrogen’s heavier cousin) for antimatter. It’s not science fic- optimistic link “antimatter in ing in reserve in each bit of fuel and a fission bomb to light tion. Antimatter fountains all departments,” the problem is seeming emptiness. the fuse. Our next H-bomb spew like geysers from our the unavailability of antipro- blast, in 1954, was named own Milky Way. We observe tons. Europe’s CERN thinks it Contact me about my Castle Bravo and used a solid its telltale energy signature in should be able to produce strange universe by visiting http://skymanbob.com. fuel instead. This largest-ever effusive gamma rays, the sure 10 million antiprotons per

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

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WWW.ASTRONOMY.COM 7 SOLAR TWIN. Star Kappa Ceti has a stellar wind 50 times stronger than our Sun’s and may experience “superflares.” Otherwise ASTRONEWS it’s a close match for our Sun and, at only 400 million to 600 million years old, may provide insights about the early solar system. HOT AND COLD. BRIEFCASE This artist’s concep- tion of 55 Cancri e shows pools of lava SEEKING ALIENS THAT CAN SEE US and dust streaming Just as the Kepler Space Telescope spots planets by detect- off the colder areas of ing a dip in light as they pass in front of their stars, there’s a the planet’s surface. sizable region of our cosmic neighborhood where alien NASA/JPL-CALTECH astronomers could similarly detect Earth thanks to this edge-on view. A group of astronomers from Germany’s Max Planck Institute for Solar System Research compiled a list, published in the April issue of Astrobiology, of 82 nearby Sun-like stars that might already know about us. The team reasons that such aliens might already be trying to make contact, making the search for E.T. that much easier. EARTH’S CLOAKING• DEVICE Humanity has some hope of hiding from potentially hostile aliens, according to a paper published online March 30 in the Monthly Notices of the Royal Astronomical Society. The Columbia University astronomers suggest blasting laser light toward extraterrestrials just as Earth transits the Sun from the aliens’ point of view. The laser emission would counteract a dip in visible light like the one the Kepler tele- LAVA PLANET SURPRISES ASTRONOMERS scope uses to detect alien planets. Blocking all wavelengths of light would require a network of lasers, but the research- ecently, astronomers using NASA’s said, “These observations helped us build ers say specific frequencies of lasers could be used to cloak infrared Spitzer Space Telescope a map of the planet. This map informs us Earth’s oxygen, giving the appearance of a dead planet. created the first temperature map of which regions are hot on the planet.” • R SETI TURNS SEARCH TO RED DWARFS a “super-Earth.” Researchers found an enormous tem- Astronomers looking to contact aliens have tended to The planet, dubbed 55 Cancri e, lies perature difference comparing one side of ignore red dwarf stars because their planets would need about 40 light-years away and has a diame- the planet with the other. The hottest side dangerously close orbits to support liquid water. But evolv- ter twice that of Earth and a mass roughly is nearly 4,400° F (2,427° C), and the cool- ing research gives hope for the existence of life in such sys- tems. That prompted the Search for Extraterrestrial eight times larger. The planet orbits its est is 2,060° F (1,127° C). Their prevailing Intelligence (SETI) to begin a targeted red dwarf hunt using star every 18 hours and is “locked” to it in idea about the two hemispheres is that the its Allen Telescope Array. Red dwarfs are the most common the same way our Moon is tidally locked planet has a slight atmosphere that does stars in the Milky Way, so the closest 20,000 red dwarfs that they’ll search are just half the distance of the nearest 20,000 to Earth. So, 55 Cancri e always keeps the not conduct heat well, with possible lava Sun-like stars. That improves their chances of detection. same face toward its star. flows covering the surface. And red dwarfs also live much longer, potentially giving “Spitzer observed the phases of “The day side could possibly have riv- aliens more time to advance technologically. — Eric Betz 55 Cancri e. . . . We were able to observe the ers of lava and big pools of extremely hot first [and] last quarter, new, and full phases magma, but we think the night side would of this small exoplanet,” said Brice Olivier have solidified lava flows like those found Demory of the University of Cambridge in in Hawaii,” said co-author Michael Gillon Calling out imposter England. Demory, lead author of the study of the University of Liège in Belgium. published in the March 30 issue of Nature, — Michael E. Bakich biosignatures Oxygen is often thought of as the hallmark of life, a prime biosignature. Earth’s atmosphere under- MARTIAN DRIVING RECORDS went a major renovation when its first living creatures dramatically altered their environment RED PLANET ROVERS. Four Mars rovers make up the Red Planet’s robotic population, and two of them with oxygenated exhalations. But researchers at are still active. Opportunity holds the distance record by far, having roved more than a marathon length in its the University of Washington’s Virtual Planetary more than 12 years exploring an alien world. Curiosity has a lot of driving to do to catch up. Laboratory have proven that abiotic reactions Opportunity between sunlight and water or carbon dioxide in 2004–present a planet’s atmosphere can also produce oxygen. 26.6 miles (42.8 kilometers) So how can observers tell the difference between Curiosity (as of April 14, 2016) true biosignatures and imposter oxygen? 2012–present In research published February 26 in 7.9 miles (12.7 km) (as of April 1, 2016) Astrophysical Journal Letters, the Virtual Planetary Spirit Laboratory team studied how sunlight breaking 2004–2010 4.8 miles (7.7 km) down carbon dioxide would also yield high lev- els of carbon monoxide, a compound research- Sojourner ers could measure at the same time as the 1997 NASA/JPL-CALTECH AFTER JOHNSON RICK : 330 feet (100.6 meters) oxygen. In the case of sunlight breaking down Miles 0 5 10 15 20 25 water in the atmosphere, they found that when

ASTRONOMY this process occurs, it creates such huge stores of 0 5 10 15 20 25 30 35 40 45 oxygen (O2) that it collides to form O4 in larger Kilometers quantities than can be attributed to living organ- isms. The ability to identify true signposts of life The Mars Exploration Rovers, Spirit and Opportunity, had a planned mission FAST from false signatures will be invaluable as more lifetime of 90 sols (martian days). Spirit sent its last communication on sol 2,210, and Opportunity continues trekking at well over 4,000 sols. FACT sensitive telescopes like James Webb come online to hunt signs of E.T. — Korey Haynes

8 ASTRONOMY • JULY 2016 50 kilometers

North on Titan Elevation 2,807 meters

Elevation 3,337 meters

ICY PEAKS. DEEP SCARS. Titan’s Mithrim Montes is a triple chain of mountains Many of Saturn’s moons bear massive scars likely caused home to the moon’s tallest peak. NASA/JPL-CALTECH/ASI by tidal stresses, such as Ithaca Chasma on Tethys. NASA SATURN’S MOONS ARE YOUNG AND ACTIVE

Saturn’s rings and most of its icy moons force. Such a small world can remain active tallest peak in a chain called the Mithrim may not be the permanent fixtures we only if Saturn’s tug warms its interior, con- Montes. The mountain rises 10,948 feet usually assume they are. Astronomers tinuously melting what should have turned (3,337 meters). “As explorers, we’re moti- have suspected this since at least 2012, to solid ice long ago. But here lies another vated to find the highest or deepest places, when they noticed that the complicated mystery, because Enceladus’ eruptions partly because it’s exciting. But Titan’s tidal push and pull between Saturn and occur roughly five hours after the peak of extremes also tell us important things about its inner moons are moving the moons to tidal strain. A different research team sug- forces affecting its evolution,” said Jani wider orbits with surprising speed. And the gested a novel “plumbing system,” where Radebaugh, a Cassini radar team associate moons are taking the rings with them. vertical cracks stretch from the moon’s sur- at Brigham Young University, who led the Now, research published March 24 in face down to its underground ocean. The research. Her team presented the findings The Astrophysical Journal shows that the cracks are wide enough to allow the water’s at the 47th Lunar and Planetary Science rings and icy moons, like Tethys, Dione, and passage, but narrow enough to delay Conference at The Woodlands, Texas, on Rhea, might be only 100 million years old. its travel. This research appeared online March 24. Because Titan’s surface and man- This means that if a Stegosaurus had a tele- March 28 in the Proceedings of the National tle are made of softer, icier materials than scope, it might have seen a ringless Saturn. Academy of Sciences. Earth’s, scientists expected its mountains to Enceladus, one of Saturn’s more famous Farther out, Saturn’s largest moon is be smaller as well; its tall peaks indicate that moons thanks to its erupting geysers, also yielding surprises. Scientists using the some tectonic forces must be at work to helped astronomers measure Saturn’s tidal latest Cassini data have identified Titan’s raise the mountains so high. — K. H.

BRIGHT BURSTS. Enceladus’ plumes tell a story of ongoing tidal stress from its parent planet that keeps the moon’s inner ocean liquid and its geysers erupting. NASA/JPL-CALTECH/SPACE SCIENCE INSTITUTE FORYOURCONSIDERATION BY JEFF HESTER Pulsars and neutrinos The history that LIGO forgot.

Russell Hulse and Joseph Taylor were wo black holes spi- Taylor were awarded the 1993 moment. Believe me, I get it. I the first to measure the energy loss from a binary pulsar system, a loss raled together in a Nobel Prize in Physics for their was among those who that was well-predicted by Einstein’s cataclysmic event work. Isaac Newton famously addressed the American theory of relativity. MPIFR/M. KRAMER that converted three said, “If I have seen further Astronomical Society in times the mass than others it is by standing on January 1994, celebrating the science itself and instead attack Tof the Sun into pure energy. the shoulders of giants.” For successful repair of the Hubble the credibility of scientists. That energy traveled outward LIGO, those giants included Space Telescope. Sometimes “There are a substantial num- through space as ripples in Hulse, Taylor, and Weisberg. you have to shout “we’re num- ber of scientists who have the very fabric of the universe. During the gravitational ber one!” and spike the ball in manipulated data so that they More than a billion years later, waves press conference, Rainer the end zone. will have dollars rolling into those gravitational waves swept Weiss, a LIGO co-founder, Certainly stretching the their projects,” he claimed in a past Earth and were detected seemed about to tell that story. truth a bit at a press conference speech to New Hampshire vot- by the most extraordinary He set it up beautifully, talking is nothing new. A few years ers in 2011. measuring device humankind about the rapid orbital decays after Hubble was repaired I Those attacks were had ever built. of collapsed objects like black attended a colloquium about unfounded, but a lot of people By directly detecting gravita- holes and neutron stars. The some lovely ground-based were (and are) predisposed to tional waves, LIGO has given us next words out of his mouth observations of elliptical galax- believe them anyway. Perry a whole new way of observing should have been “Hulse and ies. The speaker closed with was tapping into and reinforc- the universe. That extraordi- Taylor.” Instead it was as if a a tongue-in-cheek remark. ing a common perception that nary technical accomplishment chapter had been eliminated “Just remember, when Hubble scientists routinely gild the lily and the discoveries it promises from a book. In the narrative, discovers this, you saw it here in their all-consuming quest are awe-inspiring. We had been suddenly it was 2015 and LIGO first!” The room roared with for publicity and funding. He blind, but now we can see! was confirming Einstein’s pre- laughter! marginalized solid and impor- Of course, astrophysi- dictions for the first time. Then there is realpolitik. tant research by painting scien- cists had already known that Another surprising omission Back in the day, then Hubble tists as hucksters. gravitational waves exist for came later. When Kip Thorne, project scientist Ed Weiler had Over the years I’ve heard four decades before the LIGO black hole expert and fellow a favorite saying: “Congress that sentiment more times than announcement. LIGO scien- LIGO co-founder, took his turn doesn’t read The Astrophysical I can count. “Hey Jeff, what’s tists recount that history in the at the mic, he enthused, “All of Journal. Congress reads The this new thing? What’s the opening paragraphs of their our previous windows through New York Times.” He was right. spin? How much of it is real?” own 2016 paper in Physical which astronomers have looked As the most expensive proj- Is the LIGO press conference to Review Letters: “The discovery are electromagnetic!” In the ect ever supported by the blame for that perception? Of of the binary pulsar system process he ignored not one but National Science Foundation, course not! But, if only in small PSR B1913+16 by Hulse and two Nobel Prizes. The 2002 and LIGO faces that same reality. ways, LIGO did play that game. Taylor and subsequent obser- 2015 prizes both recognized Press conferences are impor- The detection of gravita- vations of its energy loss by neutrino astronomy, which not tant. They are scripted and tional waves from merging Taylor and Weisberg demon- only confirmed our fundamen- rehearsed, with PR types black holes was a truly pro- strated the existence of gravita- tal understanding of the work- directing the show. That’s fine. found and triumphant event. tional waves.” ings of stars and core-collapse But when crucial things like the A few spoken sentences placing In 1974, the binary pulsar supernova explosions, but also binary pulsar and neutrino LIGO in its proper historical was the test of Einstein’s theory provided the first hard evi- astronomy aren’t mentioned, it and scientific context would that everyone had been waiting dence of a failure of the is usually because someone only have added to the celebra- for. Had the orbit of the binary Standard Model of particle worried they would “detract tion of such an extraordinary pulsar not decayed as pre- physics — neutrinos were sup- from the story.” That’s not OK. accomplishment. dicted, the headlines would posed to be massless. Maybe an example best illus- have read, “Einstein wrong! Maybe I’m just being a cur- trates my concerns. When then Jeff Hester is a keynote speaker, Gravitational waves don’t mudgeon. Events like the LIGO presidential candidate Rick coach, and astrophysicist. exist!” And LIGO would never press conference are about Perry ridiculed climate science, Follow his thoughts at jeff-hester.com. have been built. Hulse and sharing the excitement of a he would typically sidestep the

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10 ASTRONOMY • JULY 2016 MOON TILT. By studying ice placement on the Moon, astronomers ascertained that our partner world’s rotation axis ASTRONEWS shifted by about 5 degrees 3 billion years ago, meaning the Moon’s face was once tilted farther down. QUICK TAKES Fast radio burst RED FLASH V404 Cygni, a nearby black hole in the Milky Way, has source is a bust been blasting out flashes of Fast radio bursts (FRBs) are cosmic enigmas. red light, indicating the black They are short, bright, and usually found in hole’s powerful jets are flicker- ing off and on as it consumes data long after their light has died away. We nearby material. know little about them. In February, scientists announced that they had, for the first time, MILKY• WAY identified the source of one of these elusive POWERHOUSE events, FRB 150418, in a galaxy 6 billion light- Astronomers used a gamma- years away. (See June news story, “Fast radio ray observatory to trace pow- burst reveals missing matter.”) erful cosmic rays to the central But a follow-up study, accepted for publica- 33 light-years of the Milky Way. tion in The Astrophysical Journal Letters, proves that the fading radio “afterglow” used to pin PRESERVED• COLLISION down the source of FRB 150418 is, in fact, a per- An abundance of heavy sistent source that brightens and dims over time: elements in the nearby dwarf the active black hole at the center of the distant galaxy Reticulum II indicates galaxy. And its erratic but ongoing radio emis- that massive neutron stars sion is unassociated with the one-time FRB must have merged there in event, re-mystifying the burst’s origins. powerful collisions in the Meanwhile, an unrelated study published distant past. online March 2 in Nature details the first repeat- SUPERNOVA• SHOCK ing radio burst, which sent out multiple signals The Kepler Space Telescope in less than a minute. These new bursts, caught caught the burst of light from by the Arecibo telescope in Puerto Rico, match a supernova’s shock wave for the profile and position of an FRB from 2012, the first time in visible light, indicating that this source has been sending out an event that lasts only signals for a while. The finding upends what sci- 20 minutes. entists had believed about FRB sources, namely PLAY IT AGAIN. An artist’s interpretation shows the radio signals that they are cataclysmic events — such as racing toward the Arecibo telescope’s enormous dish. Arecibo found FARTHEST• GALAXY supernovae or collapsing neutron stars — that the first repeating fast radio burst. DANIELLE FUTSELAAR Astronomers push the cannot repeat because the event destroys its distance record for a galaxy a source. The repeating FRB might instead ema- little farther back by using the nate from an extreme pulsar, the rapidly rotat- Spitzer Space Telescope to ing core of an expired star, and perhaps pinpoint GN-z11 at a distance indicates that multiple types of FRBs exist. million mph (200M km/h) of 13.4 billion light-years. What is clear, at least for now, is that FRBs will speed of material measured around HEAT• WAVE remain one of space’s mysteries. — K. H. a supermassive black hole. 120 Bright quasar 3C 273 has a temperature over 10 trillion degrees, according to new observations from Galaxy’s a worldwide collection of radio telescopes. missing gas BABY BLANKET• The ALMA radio observatory spotted imaged both the gas disk FALLING BEHIND. surrounding a still-growing Galaxy NGC 4569 (center) protostar and its gas was long known to be low envelope. The envelope flows onto the disk, and the disk on hydrogen, the fuel for star formation. But astrono- feeds the star. mers didn’t know how or DUSTY• DISK to where the material had vanished. New observations The Very Large Telescope using the Canada-France- Interferometer revealed a Hawaii Telescope revealed detailed look at the ring of the gas streaming behind material around aging double the galaxy in a tail 300,000 star RAS 08544–4431, inform- light-years across (red mate- ing astronomers about older rial). NGC 4569 is charging star systems. through the nearby Virgo COOPERATIVE• cluster of galaxies at 750 PLANET HUNTING miles (1,200 kilometers) per second, and scientists say NASA and the National Science the resulting radiation pres- Foundation are teaming up sure, like wind in a runner’s with Pennsylvania State face, has stripped out the University to build NEID, a gas and left it to trail in the next-gen exoplanet instru- ment slated for 2019. — K. H.

CFHT/COELUM galaxy’s wake. — K. H.

WWW.ASTRONOMY.COM 11 EARLY MERGERS. Using the Subaru Telescope, astronomers studied 80 galaxies from the early universe and discov- ASTRONEWS ered signatures of collisions and gravitational interactions, indicating that the young universe was an active place. Jupiter’s eerie northern lights Solar storms are generating extremely powerful aurorae on Jupiter that are “hundreds of times” more energetic than the northern lights, say astronomers. A study in the March 22 issue of the Journal of Geophysical Research: Space Physics presents images and data from a massive storm in 2011, when coronal mass ejections — powerful bursts of material from the Sun’s surface — encountered the giant planet. The research team, led by William Dunn of University College, studied jovian aurorae in X-rays using the Chandra X-ray Observatory. They tracked the interaction of solar particles with Jupiter’s magnetosphere during two 11-hour observation periods. The arrival of a blast of energy from the Sun triggers the X-rays emitted in jovian aurorae, which sprawl over a surface area larger than Earth. — David J. Eicher

October 2, 2011

October 4, 2011 NASA/JPL-CALTECH/UCLA/MPS/DLR/IDA/PSI/LPI A window into Ceres’ salty heart Dawn first saw Ceres’ chemical fingerprints of Instead of one white spot, strange cluster of white a kind of salt. The find- Occator actually holds a spots on approach in ing backs up scientists’ network of crisscrossing early 2015. From more suspicion that Ceres has fractures and bright areas than 100,000 miles a complex mixture of surrounding a large (160,000 kilometers) volatiles and ices sitting dome. “The intricate away, the bright region just below its surface. The geometry of the crater provided the only sign of constant bombardment interior suggests geologic action on an otherwise of space rocks pushes activity in the recent past, drab and crater-covered the ice onto the surface, but we will need to com- world. But as NASA’s where it can evaporate plete detailed geologic spacecraft lowered its and leave behind salts. mapping of the crater in orbit to within a few hun- But a close-up view of order to test hypotheses dred miles of the surface, the bright region that for its formation,” says LIGHT IT UP. Composite images show Jupiter and its aurora whitish material glistened Dawn first spotted, now Dawn co-investigator Ralf during and after the arrival of a coronal mass ejection (CME) in across the dwarf planet. called Occator Crater, Jaumann of the German October 2011. The top image depicts the X-ray activity when the Dawn’s instruments shows a more compli- Aerospace Center in CME reached Jupiter, and the view above shows the planet two showed it carries the cated process at work. Berlin. — E. B. days later. NASA/CXC/UCL/W. DUNN ET AL. (X-RAY), NASA/STSCI (OPTICAL)

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OBSERVINGBASICS ε ζ BY GLENN CHAPLE β

Lounging in Lyra γ The Harp is home to more than one famous object. η

o your telescopic The two, designated as Epsilon1 2 1 2 excursions into the and Epsilon (ε and ε ) Lyrae Although Lyra the Harp is a small constellation in the northern sky, it offers a wide constellation Lyra and of magnitudes 4.7 and 4.6, range of objects for deep-sky and double-star observers. BILL AND SALLY FLETCHER involve a cursory respectively, are separated by glance at the Ring just 206" (about 1⁄9 of the Full separated by 14", while STF Albireo (Beta Cygni), slightly DNebula (M57) and then a quick Moon’s diameter) — right at 2474 is composed of magnitude closer to the latter. departure for the bounty of the resolving limit of the 6.8 and 7.9 stars 16" apart. Now you can set your sight the summer Milky Way? This human eye. Folks like me with Three more worthy doubles on the Ring. M57 is one of the slam-bang approach is a big ordinary vision see one star and are Zeta (ζ) Lyrae (magnitudes sky’s most visited destinations mistake! This month, take time have to use binoculars. 4.3 and 5.6; separation 44"), Eta for two reasons: It’s a bright to smell the roses and devote an Now that your scope is accli- (η) Lyrae (4.4 and 8.6; 28"), and planetary nebula, and it’s easy evening to the celestial Harp. mated, let’s get an up-close look SHJ 282 (6.1 and 7.6; 45"). to find. If you’ve never seen it, While your scope is adjust- at this trio of stars. The brighter English astronomers James aim your scope between Sheliak ing to the outdoor temperature, component of Vega has a mag- South (S) and John Herschel and Sulafat and scan the area make a naked-eye survey of nitude 9.5 companion 82" to its (HJ) cataloged the last one in using a magnification between Lyra. At magnitude 0.0, Vega south. Look carefully. The sec- the mid-1820s during a collab- 30x and 50x. If your focus is on, (Alpha [α] Lyrae) is exceeded in ondary isn’t easy to see through orative search. Like Sheliak and you should spot a small, hazy brightness tonight only by small scopes because it’s more Epsilon, all are easy to split with puffball among a field of stellar Arcturus (Alpha Boötis), cur- than 6,000 times fainter than a 2.4-inch refractor. specks. A switch to an eyepiece rently shining high in the west. the primary. More great double stars pop- that yields 100x or more will A glance from one to the other Sheliak A has a magnitude ulate Lyra, but let’s go truly reveal the nebula’s oval shape reveals an obvious color differ- 6.7 partner 45" away and, on “deep space” and check out and dark center. ence. Vega, of spectral class A0, the opposite side at distances M56 (that’s 56, not 57). This is Most backyard astronomers appears white; the cooler of 67" and 86", two 10th- the often-overlooked globular visit Lyra only for a glimpse of K0-type giant Arcturus is dis- magnitude companions, the cluster that I spotlighted in this the Ring Nebula. If you’re among tinctly ruddy. quartet forming a lopsided let- column in August 2014. The that group, spend a July evening Now turn your attention to ter Y. Epsilon Lyrae is a double 8th-magnitude object may pale broadening your horizons and Sheliak (Beta [β] Lyrae) and its star masterpiece. Each of the in comparison to larger and really getting to know this won- neighbor Sulafat (Gamma [γ] two is a close binary, as any brighter examples like Omega derful little constellation. Lyrae). Sheliak shines at magni- telescope and a magnification Centauri (NGC 5139) and the Questions, comments, or tude 3.5 — sometimes. It’s an of 100x will reveal. Epsilon1 Hercules Cluster (M13), but it suggestions? Email me at amazing edge-on pair of stars combines magnitude 5.2 and still deserves a look. Find M56 [email protected]. Next that eclipse each other during a 6.2 components separated by by making a low-power scan of month: some late summer 13-day orbit. During that time, 2.2", while Epsilon2 features the area between Sulafat and asterisms. Clear skies! Sheliak steadily fades to magni- magnitude 5.3 and 5.4 members tude 4.3, returns to normal, 2.5" apart. To me, all four stars dips again to magnitude 3.8, of the double-double seem pure FROM OUR INBOX and then rebounds to begin a white. What’s your impression? new cycle. You can detect these Lyra is home to another Bedinis changes by comparing Sheliak double-double, made up of the I enjoyed Stephen James O’Meara’s column about Benjamin to Sulafat from night to night. pairs STF 2470 and STF 2474, Banneker — p. 18, April 2016 — where you quote from the late When Sheliak is at maximum, both cataloged by Russian Silvio Bedini, whom I met in the early 1970s and later spoke with the two seem nearly equal in astronomer Friedrich Georg by phone a few times. I wonder if you were aware of Silvio’s other brightness. But during an Wilhelm von Struve during the cosmic connection? He is the father of Peter Bedini of the Johns eclipse, Sulafat is the brighter. 1830s. This twin twosome is Hopkins University Applied Physics Laboratory, who was the How keen is your eyesight? less spectacular than Epsilon project manager of MESSENGER and deputy project manager Take a hard look at Epsilon (ε) (the two are three times farther of New Horizons. I enjoyed meeting Peter and seeing him Lyrae. If you can see two stars apart with fainter and wider repeatedly during July when I came out of retirement to work incredibly close to each other, components) but still visually as an embedded science writer on the New Horizons team. consider yourself a charter appealing. STF 2470 combines — Stephen P. Maran, Chevy Chase, Maryland member of the Eagle-eye Club. magnitude 7.0 and 8.4 stars

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14 ASTRONOMY • JULY 2016 ASTRONEWS JPL scientists make case for ice giant mission An armada of spacecraft currently keeps a constant watch on the Red Planet. Meanwhile, the ice giants — Uranus and Neptune — were collectively explored close up for less than 48 hours. Mark Hofstader of NASA’s Jet Propulsion Laboratory hopes to change that. He’s been tasked with studying the merits and engineer- ing requirements for a major mission to study these outer solar system worlds. In the decades since Voyager 2 made humanity’s only visit to each planet, these outer worlds have taken on increased signifi- cance. NASA’s Kepler Space Telescope has now shown Neptune-like worlds are abundant in the Milky Way. “We want to understand how our solar sys- tem formed and evolved, and we want to DECADES IN THE MAKING. The Voyager 2 team understand how other solar systems formed crowds around images of Neptune’s moon Triton fol- and evolved,” Hofstader says. “Ice giants hold lowing the flyby on August 25, 1989. Half a century important clues.” will have passed before the next mission. NASA/JPL-CALTECH And yet, mysteries abound. Astronomers still don’t fully understand the ice giants’ struc- provide the space agency with an initial game ture. Jupiter and Saturn are mostly gas. Earth plan for what such a mission would look like. and the terrestrial planets are mostly rock. The mission would compete to be NASA’s next Neptune and Uranus consist of about one-third flagship-class, the biggest and most expensive rock, one-third ice, and one-third gas. But that kind, and — if it won — would fly sometime material doesn’t seem to be fully segregated. between 2023 and 2035. What astronomers do know is that both “You cannot fly a single vehicle from Uranus planets have planetary rings and moons that and then to Neptune,” he says. “The planets are are unique. Neptune’s moon Triton is the only not aligned properly to do that with a single large satellite in the solar system with a retro- launch vehicle.” grade orbit — one that runs opposite from the Instead, his team is studying how they other moons. This and other evidence indicates might use one rocket to send two spacecraft that Triton is a captured Kuiper Belt object like — one for each ice giant — something that’s Pluto. Its strange cantaloupe terrain and never been tried before. They’re also studying smokestack plumes also hint at an active world the merits of a single spacecraft sent to study and possibly a subterranean ocean. either only Uranus or only Neptune. By the end of this year, Hofstader’s NASA- Whatever the final architecture, NASA’s funded team will create a list of science goals plans to visit an ice giant should crystallize by for a mission to Uranus and/or Neptune, and year’s end. — E. B.

WHY DOES TOTALITY VARY IN LENGTH?

Sun

Size of Sun

Moon Moon

FAST FACT

The next total solar eclipse will cross TIMING TOTALITY. During total solar eclipses, the length of totality can range from an instant the United to some 7½ minutes. This is because Earth’s distance from the Sun changes, as does the Moon’s States on from Earth. The Earth-Sun distance varies by 3 percent, while the Moon-Earth distance can August 21, change by 14 percent. The result is that while the Moon doesn’t actually change size, the Moon’s 2017. apparent diameter — that is, the disk that we see — can range from 7 percent larger than the Sun to 10 percent smaller than the Sun. JOHN CHUMACK (SUN AND MOON); ASTRONOMY ILLUSTRATION: RICK JOHNSON

WWW.ASTRONOMY.COM 15 RECORDBREAKERS. Astronomers identified galaxies with 100 trillion times the Sun’s brightness, which places them ASTRONEWS beyond “ultra-luminous” or “hyper-luminous,” leading scientists to call them “outrageously luminous” instead. SATURN’S CHANGING FACE Frigid surprise hiding at Venus’ poles Thanks to its thick atmo- sphere, Venus is the hottest March 21, 2010 planet in our solar system, Magnitude: 0.5 with temperatures boil- Ring diameter: 44.4" ing over at 850 degrees Ring tilt: 3.2° Fahrenheit (454 C). But in a study published April 11 in April 3, 2011 Nature Physics, the European Magnitude: 0.4 Space Agency (ESA) found Ring diameter: 43.8" something surprising at the Ring tilt: 8.9° planet’s poles: temperatures more frigid than anywhere April 15, 2012 on Earth. Magnitude: 0.2 Even though ESA lost con- Ring diameter: 43.3" tact with the Venus Express Ring tilt: 13.7° probe two years ago after it ran out of fuel, the agency is May 10, 2014 still working through the data Magnitude: 0.1 it returned. As the first space- Ring diameter: 42.4" craft to explore our nearest POLAR PLUNGE. Venus Express plummeted into the planet’s Ring tilt: 21.7° neighbor since 1989’s atmosphere in 2014. ESA/C. CARREAU Magellan mission, the probe June 3, 2016 revealed much about that not captured by models.” NASA is mulling several mis- Magnitude: 0.0 world. Many of the observa- This marks the first time sions as part of its Discovery Ring diameter: 41.8" tions were made by plunging the poles of Venus have been program, one of which, : RICHARD TALCOTT AND RICK JOHNSON RICK AND TALCOTT RICHARD : Ring tilt: 26.0° the craft into the atmosphere directly studied, owing to VERITAS, will map the entire above the poles, where the Venus Express’ circumpolar surface of the planet, and

ASTRONOMY probe encountered an atmo- orbit, which also allowed a could tell us more about the RINGED PLANET ROUNDUP. Although Saturn sphere thinner than previously global view. By crashing geology of the poles. and its rings always look spectacular when viewed modeled, and filled with through these winds on its Müller-Wodarg adds that through a telescope, its appearance changes notice- choppy atmospheric gravity final descent, the probe made there may be some relation ably as it orbits the Sun. Here we show the planet’s waves, ripples caused by trans- the first ever in-situ observa- between the choppy gravity FAST changing façade at selected oppositions since the fers of momentum between tions of polar climates on waves (which are a separate FACT last time Earth passed through the ring plane in layers in the atmosphere. Venus. phenomenon from the much- September 2009. Notice how it has grown brighter “Concerning uniformity, The Japanese Aerospace heralded LIGO study) and over the years despite shrink- models are mostly rather Exploration Agency has a geologic activity on the ing in size. That’s because the Earth will next cross smooth while the reality is probe in orbit around Venus ground near the poles, but it rings reflect more sunlight than Saturn’s ring plane much more complex and called Akatsuki, but it will will require further investiga- in March 2025. Saturn itself, so their tilt drives the planet’s overall luminosity. structured,” says ESA scientist mostly study the climate tion to determine that. and lead author Ingo Müller- closer to the planet’s equator, “We can make observa- Wodarg of Imperial College hoping to determine what tions from the ground — and London. “We found enor- caused the runaway green- these are continuously being mous variability in the atmo- house effect. Müller-Wodarg done — but the real motiva- amount of light spheric densities that is points out that previous tion would be to launch a reflected by Comet explained by a combination atmospheric models relied new spacecraft to Venus over C/2011 L4 PANSTARRS, of local (horizontal) day-night on equatorial data from the the coming decade which making it darker than density variations, but above Pioneer Venus mission, which could explore the polar atmo- 3 all by strong periodicities, led to incorrect uniformity sphere in-situ,” Müller- percent fresh asphalt. atmospheric waves. These are modeling of the atmosphere. Wodarg says. — John Wenz Hubble spies a sleeping giant QUIET MONSTER. The bright elliptical galaxy that dominates this new Hubble image may appear tranquil, but a dormant monster lurks at its center. NGC 4889, which sits some 300 million light-years away in the Coma Cluster, contains perhaps the larg- est supermassive black hole ever found. Humanity’s fastest spacecraft, Voyager 1, would take more than 200 years to travel the width of its event horizon — the region from which no light can escape. NGC 4899 stopped feeding on its neighbors at some point in its past, and the rapid orbits of its central stars are the only sign of its true nature. — E. B. NASA/ESA

16 ASTRONOMY • JULY 2016

SECRETSKY BY STEPHEN JAMES O’MEARA

Pitatus The Nubium A Rima Hesiodus Whisker Hesiodus View another scratch on the Moon’s feature-filled face.

he Moon’s Mare Grasping Nubium (the Sea the graben of Clouds) is most Unlike the Straight Wall, which noted for its Straight is an individual fault, Rima

Wall, a 75-mile-long Hesiodus is a geologic feature KINGSLEY A. BRUCE T(121 kilometers) cliff face that known as a graben, where a This image shows Hesiodus Crater and the graben known as Rima Hesiodus. casts a remarkable shadow block of land has subsided about a week after New Moon. between two normal faults; through a patch of rugged ridge the terminator, allowing a view Visible as a “cat scratch” in Africa’s Great Rift Valley and of lunar highland, before it ends of the rille’s full length. eastern Mare Nubium, the Valles Marineris on Mars are north of Capuanus Crater in However, the segment in Palus Straight Wall is the youngest fine examples of grabens linked Palus Epidemiarum (the Marsh Epidemiarum (being closest to large-scale fault on the Moon to volcanic processes. of Epidemics). You’ll see it best the terminator) was now the visible through small tele- The Hesiodus Rille appears through small telescopes nine darkest and most prominent scopes. But Mare Nubium has to originate near the crater or 10 days after New Moon. section. The remainder of the other hidden treasures, includ- Hesiodus (a small lava-flooded graben appeared broader and ing a longer rille known as plain in southern Mare Whispering fainter with the two parallel Rima Hesiodus, a great visual Nubium). It stretches south- darkness faults running across Mare challenge for small-scope users. west across that sea, slicing On the evening of February 17, Nubium like a set of ghostly 2016, I observed the Hesiodus train tracks. Rille through my 3⅓-inch FROM OUR INBOX refractor at 150x. At a glance, More to ponder it appeared merely as a fine Just west of Hesiodus is a rare Starry sky thread of darkness (like a cat’s double crater, Hesiodus A, whisker), hardly noticeable created most likely by twin I read your column “The face of beauty?” — p. 22, February against the lunar sea. The rille asteroid impacts. The craters 2016. I ordered Richard Powers’ novel, Orfeo, and I thoroughly was darkest near the termina- are concentric, and I’ve spied enjoyed it. tor, where it appeared to emerge them through a 3-inch scope I grew up in a little town in South Texas, sleeping on the from a tadpole-shaped patch with an eyepiece that yielded a porch with the beauty of the southern sky right in front of me. of lunar highland northwest of magnification of 150x. I would have been an astronomer, but alas, I am no mathemati- Weiss Crater’s broken wall. The Hesiodus has long been con- cian. I became a biologist. remainder of the rille was more sidered a fascinating feature. In The stars stay with me here in Athens, Georgia. I seek them of a visual whisper, especially an 1899 volume of Memoirs of every night; they console me. They tie me to my childhood, to near the northern flanks of the British Astronomical my grandmothers who taught me the constellations, to a sense the ejecta blanket surrounding Association, the Lunar Section of belonging to something larger than myself. Hesiodus. reports that on May 14, 1894, Yes, some of my friends turn away from the stars at night. I The rille all but vanished at Captain Molesworth made a believe it’s because they find them an unknown. The panorama, lower magnifications because “beautiful drawing” of when you can see it here, makes them uneasy. If you can’t see the brightness of the surround- Hesiodus that shows the “well- familiar constellations or recognize the Milky Way, the night ing landscape created too much known central crater [Hesiodus sky can be scary. glare to see it comfortably. With D] missed by Madler, which is Keep the “Secret Sky” coming. — Dac Crossley, Athens, Georgia time, I could make out a bright very strange unless it has “negative” flow of light parallel- become more conspicuous Correction ing the rille’s shadow to the since.” It may be worth keeping In the June issue’s “Target gems of Scorpius,” pp. 62–63, we north, which flowed along its your eye on this curious mislabeled M6 and M7 as globular clusters. They are, of course, full length, making the rille feature. two of the finest open clusters in the sky. — Astronomy editors appear out of focus. As always, send your lunar On the following night, Palus imaginings to sjomeara31@ Epidemiarum emerged from gmail.com.

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

18 ASTRONOMY • JULY 2016 STARS COLLIDE. Supernova G1.9+0.3 exploded 110 years ago within the Milky Way, and astronomers ASTRONEWS recently identified the cause as two white dwarf stars — the remnants of Sun-like stars — colliding. NASA/ESA/HUBBLE HERITAGE TEAM HERITAGE NASA/ESA/HUBBLE Hot star blows a massive bubble

BIRTHDAY BUBBLE. To celebrate the Hubble Space Telescope’s 26th birthday in April, NASA released the spacecraft’s new view of the Bubble Nebula (NGC 7635). The bright star at left center sends out powerful winds that carve out the symmetric shape, though how it does this from its non-central location still puzzles astronomers. What they can tell from this and other images is that the expanding shell, already 10 light-years across, is still inflating at a speed of 62,000 mph (100,000 km/h). — K. H. Astrobabble 3,000 Class L From asterisms to Thorne-Żytkow objects, Brown dwarfs we turn gibberish into English.

Air blast Brown dwarf desert >> Planets The wind gust that follows after The strange lack of failed stars an asteroid strikes land or found by astronomers, despite theo- 2,000 Stars explodes in Earth’s atmosphere. ries that predict their abundance. An impact like the one at New research by the Sloan Digital Arizona’s Meteor Crater can send Sky Survey indicates many of these 900 mph (1,500 km/h) winds in overstuffed Jupiters are actually in all directions for several miles. orbit around much larger stars, Deuterium Hydrogen implying a potential oasis waits. 1,000 fusion begins Class T fusion begins Hydrogen cyanide A gas detected in the atmosphere Zvezda Surface temperature (kelvins) Surface temperature of super-Earth 55 Cancri e, the Formal name (Russian for “star”) for Class Y so-called “diamond planet,” Russia’s International Space Station Jupiter which is larger than our own module, which NASA funds and sup- 200 world but smaller than Neptune. plies with power. It houses cosmonauts KELLY ROEN : The substance would likely poi- and serves as a tugboat for the entire son any inhabitants, but it sup- structure in the case of emergency ASTRONOMY ports the idea of a carbon-rich space-debris evasive maneuvers. 110 13 2030405060707580 and exotic world. — Eric Betz, [email protected] Mass (Jupiter masses)

WWW.ASTRONOMY.COM 19 BINOCULARUNIVERSE FROM OUR INBOX BY PHIL HARRINGTON Fantastic writing I’ve subscribed to Astronomy magazine on and off since I was a kid in 1987. In 2001, I visited my university library in northern Michigan and found a column by a guy named Bob Berman Exploring and renewed my subscription based solely on his wonderful article. I kept it up for a few years, but with moves, kids, and new jobs, I let it lapse. Hercules I recently bought my 10-year-old son a telescope and renewed my subscription. I picked up the April issue and Welcome to my binocular uni- of four moderately bright stars flipped to a random article, “April Fool’s” (p. 10), and read it verse. It’s good to be back. Each about two-thirds of the way without noticing whose column it was, and I was instantly cap- month, you and I are going from Arcturus (Alpha [α] tivated. I thought this guy is as good as Bob Berman used to be! to venture outside, binoculars Boötis) to Vega (Alpha Lyrae). Then I looked up and saw it was Bob Berman. Fantastic writ- in hand, to explore the sky. M13 lies between Eta [η] and ing. I will keep my subscription going. Thanks for a terrific While many view binoculars as Zeta [ζ] Herculis along the magazine filled with great articles and columns. stepping-stones on the way to western side of the Keystone. — Carl Schell, Waterford, Michigan a telescope, I see them as fine You may even spot it with- instruments in their own right. out optical aid under a dark The low power and wide fields sky. hrough binoculars, M13 a binocular ield north of Pi [π] look like a star — a distinctly of view make binoculars ideal looks like a tut of celestial cot- Herculis, the northeastern star blue-green star. hat color for both a casual scan as well as ton. Standing to either side are in the Keystone. should help set it apart. NGC for many sophisticated observ- two faint “sentry stars,” as if M92 shines at magnitude 6.5, 6210 has been nicknamed the ing programs. guarding a vault of diamonds. roughly half a magnitude fainter Turtle Nebula for the four leg- Most of the targets that I’ll It’s hard to believe, but that than M13, and appears only half like protrusions extending feature will be visible through little puf is actually a collec- as large. But since M92 lies from its shell-shaped disk seen common size binoculars. But tion of some 300,000 stars. about the same distance from in photographs. just to mix it up a little, we will Unfortunately, they lie 25,000 us, at 26,000 light-years, it’s fun NGC 6210 lies 8° south of also feature at least one “chal- light-years away and are so to see just how diferent two Zeta Herculis. hat’s a little lenge object” that may only be tightly packed that we can’t globulars can appear. more than a typical binocular visible through 10x70 and hope to resolve them through Our inal stop in this great ield of view. here are two larger models. binoculars. We are in good constellation is at the planetary 7th-magnitude stars nearby, his irst column kicks of company, because neither nebula NGC 6210, this month’s one to its south and another to with a survey of the sky’s leg- could Charles Messier (1730– binocular challenge. Planetary its southeast. Remember to endary strongman, Hercules. 1817) when he added it to his nebulae are expanding gas look for a bluish-green star; While the stars in Hercules are burgeoning catalog of counter- clouds expelled by aging, pul- that will be NGC 6210. comparatively faint, they hold feit comets. sating stars. hey almost always Join me next month as we some notable targets for bin- Most observers are so capti- appear small when seen from delve deep into the center of ocular stargazers. vated by M13 that they forget Earth, which makes identifying our galaxy. Until then, remem- First and foremost is the the second globular cluster in even the brightest through bin- ber my mantra: Two eyes are Hercules Cluster, M13. No Hercules that is also a Messier oculars a real challenge. better than one. other globular cluster north of object. M92 may not stand out NGC 6210 rates 9th magni- the celestial equator puts on like its more lamboyant tude, just within the brightness Phil Harrington is a longtime such a grand display. To ind it, neighbor, but it is still easily barrier of 50mm binoculars. observer and contributing irst ind the constellation’s visible through properly aimed Of course, with its disk only editor of Astronomy. Keystone asterism, a trapezoid binoculars. You’ll ind it about measuring 15" across, it will

The Hercules Cluster, M13, is one of the finest globular Globular cluster M92 lies 26,000 light-years away and Planetary nebula NGC 6210 appears as a bluish-green clusters visible from the Northern Hemisphere. R. JAY GABANY is visible as a fuzzy haze through binoculars. NEIL FLEMING “star” when viewed with good binoculars. CHRIS SCHUR

20 ASTRONOMY • JULY 2016 MONSTER STARS. Nine enormous stars with over 100 solar masses each reside in the star cluster R136, ASTRONEWS according to Hubble scientists. The cluster also houses dozens of stars with over 50 solar masses.

C F S /G T S S E R -C C B M /U IT M

Gravity helps probe beneath Mars’ surface NEW MARS MAP. Planetary scientists have confirmed that molten rock pervades Mars’ outer core and that some 3 million to 4 million tons of carbon dioxide freeze out of the planet’s atmosphere onto the north and south polar regions each winter. They reached these conclusions by studying how Mars’ changing gravitational pull caused minute changes in the orbits of the Mars Global Surveyor (whose nine-year mission ended after a battery failure in November 2006), Mars Odyssey, and Mars Reconnaissance Orbiter spacecraft over a 16-year period. The researchers also used these observations to create the most accurate map yet of the planet’s gravity. In this view, white and red colors signify regions with the greatest gravitational pull while purple and blue represent the weakest attraction. — Richard Talcott

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WWW.ASTRONOMY.COM 21 Galactic astronomy The Milky Way through thick and thin Astronomers studying our galaxy’s vertical structure are teasing out details about how our home system evolved. by Bruce Dorminey

asking in the faint glow of the the galaxy’s thin disk. Luckily, we’re far Milky Way, it’s hard to realize that enough from the galactic center that we our home planet is just an infini- can look north and south of the galactic tesimal part of one of the cosmos’ poles and see deep into the outer fringes grandest spiral galaxies — one that of the Milky Way’s vertical structure. Bastronomers are only now coming to Images of the cosmic microwave back- fully understand. The “You Are Here” ground radiation also help. NASA’s Cosmic T-shirts — typically emblazoned Background Explorer satellite first recorded with a nearly face-on depiction of this glow in detail, and more recently the Milky Way Galaxy’s grand spi- NASA’s Wilkinson Microwave Anisotropy ral structure — present a textbook Probe and the European Space Agency’s view of our home galaxy. But to (ESA) Planck satellite have done even bet- truly appreciate how it formed and ter. Such images capture the Milky Way’s evolved, you need to imagine the foreground dust and give astronomers a Milky Way’s vertical structure as it pretty good edge-on view of our galaxy. would appear edge-on. “You get an idea for what it looks like That’s kind of hard to do because, to look at a galaxy like the Milky Way not unlike a plastic fishing cork, our from an edge-on perspective,” says Stacy solar system is bobbing up and down in McGaugh, a longtime galactic astronomer at Case Western Reserve University in Cleveland. “Right now, most of what you Viewed face-on from afar, the Milky Way see is a very thin disk of stars.” probably looks like UGC 12158. This barred spiral galaxy, which spans about 140,000 light-years, In the past decade, the main observa- lies some 400 million light-years away in the tional tool for studying the evolution of the constellation Pegasus. ESA/HUBBLE AND NASA Milky Way’s vertical structure has been the

22 ASTRONOMY • JULY 2016 The Two-Micron All-Sky Survey revealed what the Milky Way looks like edge-on. Clearly visible are the thin disk, which harbors most of the galaxy’s gas and dust, as well as a thicker disk and a central bulge. Also visible at lower right are two satellite galaxies: the Large and Small Magellanic Clouds. 2MASS/IPAC/CALTECH

Sloan Digital Sky Survey (SDSS). But to from ESA’s Gaia satellite, which is targeting England. It is this young thin disk, with an measure how this structure evolved with more than a billion stars, only one thing is estimated height of just 300 light-years, that time, astronomers ultimately have to mea- certain: Our current models of the Milky he says contains all the visually stunning sure the ages of distant stars, as well as Way’s vertical structure, in particular, will molecular clouds that produce new stars. their chemical compositions and move- get even more complicated. But by tracing Gilmore says that this thin disk includes ments through the galaxy. how the vertical structure differs for stars a dominant thin central bar and three or With comprehensive wide-field ground- of different types, theorists can sketch in four spiral arms, which probably start at based surveys like SDSS, astronomers have broad terms how the Milky Way must have the end of the bar. However, he adds that a been forced to reshuffle their theoretical evolved over time. majority of the galaxy’s stars, including the decks to accommodate a much more com- According to Hans-Walter Rix, an Sun, remains in an old thin disk about plicated picture of galactic disk structure. astronomer at Germany’s Max Planck 1,000 light-years thick. This, in turn, has obliged theorists to Institute for Astronomy in Heidelberg, This is a puzzle because standard improve on astronomer Walter Baade’s most of the Milky Way’s stars have galaxy-formation models say that mergers classic idea from 1944, that in broad terms remained in either the galaxy’s disk or with other galaxies in the Milky Way’s the Milky Way is made up of two main bulge, wherever they happened to form. youth should have wrecked the thin disk. populations of stars: Population I and He adds that the Sun still appears to be Gilmore notes that all big spirals seem to Population II. The former lurk in the disk on the same nearly circular orbit of the have extended old thin disks, however, so of the galaxy, where the Sun resides, and galactic center on which it was born. astronomers still have much to learn about are relatively young and enriched in metals this topic. (the term astronomers use for all elements A trio of disks The galaxy’s thick disk, which Gilmore heavier than hydrogen and helium). The The galaxy as we know it includes “a visual- co-discovered, is some 3,000 light-years latter are much older, metal-poor stars that ly dominant young thin disk of young star- thick and contains stars both older and with generally reside in the galaxy’s halo. forming regions, dust, and gas,” says Gerry systematically lower abundances of heavy Yet as the whole galactic astronomy Gilmore, another longtime galactic astrono- elements than those in the thin disks. At the community awaits the first data analysis mer at the University of Cambridge in center of it all is Sagittarius A* (pronounced

WWW.ASTRONOMY.COM 23 Thick disk Old thin disk Mostly older stars Mostly stars Height: 3,000 light-years Height: 1,000 light-years Orion spur

Sun Young thin disk Molecular gas clouds Height: 300 light-years

Hovering beyond all an astronomer at the University of Virginia this galactic structure in Charlottesville and the principal investi- is a huge halo of dark gator for the Apache Point Observatory matter, a still-mysterious Galaxy Evolution Experiment (APOGEE). form of matter that interacts The model couldn’t explain stars revolving with other material only around the galaxy in the opposite direc- through gravity. This approxi- tion from the Sun, he says. How can you mately spherical dark matter halo produce that from a collapsing cloud in remains concealed except for its gravita- which everything is spinning in the same Our galaxy already has started to pull in the tional influence. It spans some 600,000 direction? Large Magellanic Cloud. The Milky Way grows and evolves by swallowing smaller galaxies like light-years, or some four times the diam- You can’t. Theorists now think the gal- this one. C. SMITH/S. POINTS/THE MCELS TEAM/NOAO/AURA/NSF eter of the visible Milky Way, and holds axy formed hierarchically through con- about a trillion solar masses of material. tinual mergers with dwarf galaxies and dark matter filaments and halos. Primor- “A-star”), a largely quiescent supermassive Building a galaxy dial gas clouds that already existed in black hole that likely was an active galactic How did all this structure come together? the Local Group environment probably nucleus early in the galaxy’s history. The first modern idea of the Milky Way’s accreted and merged with one another, says Finally, a galactic halo envelops the formation dates to a 1962 paper in The Denilso Camargo, an astronomer at the inner part of the galaxy. The oldest, most Astrophysical Journal by Olin Eggen, David Brazilian Ministry of Defense’s Military metal-poor stars reside in this region, Lynden-Bell, and Allan Sandage. They pro- College in Porto Alegre. Majewski agrees. which doesn’t rotate. The outer halo holds posed a model in which the galaxy began “We now believe galaxies form inside out,” maybe 100 small satellite galaxies, includ- as a big blob of protogalactic gas that set- he says, “and that as we accrete more stuff, ing the southern sky’s Magellanic Clouds tled down and started to form stars. the disk of the Milky Way grows outward.” and others being tidally destroyed by the This idea started having problems after But if this hierarchical model is correct, Milky Way’s gravity. a couple of decades, says Steve Majewski, says McGaugh, the Milky Way should still

A hungry Milky Way Ursa Major II 60° Stellar debris floods the northern sky as the Milky Way can- nibalizes numerous dwarf galaxies. The smaller galaxies’ self-gravity proves 40° no match for our galaxy’s potent Canes tidal forces. The Venatici I Canes longest debris Venatici II ) g arm m stream, which forks ailin a (tr e into at least two r Declination B Coma ius t r s tta segments, belongs Berenices agi s 20° S o to the Sagittarius r rm) Leo T e ading a c Dwarf Spheroidal s A (le o tariu n Galaxy. In this por- Hercules Boötes agit o S M trayal, blue objects lie closest to Earth while red ones are Leo IV Orphan stream far away. ASTRONOMY: 0° ROEN KELLY, AFTER VASILY BELOKUROV AND THE SDSS-II 16h00m 12h00m 8h00m COLLABORATION Right ascension The Milky Way Galaxy consists of a young thin disk roughly 300 light-years thick, an old thin disk some The Milky Way’s 1,000 light-years wide, and a thick disk some three times broader than that. The galaxy’s oldest stars vertical structure reside in the galactic bulge and halo around the Milky Way’s nucleus. ASTRONOMY: ROEN KELLY

Galactic bulge

Central bar

Globular cluster Nucleus Halo be getting bombarded by tiny satellite galaxies — or at least by more than it is. So, the question in his mind is whether hierar- chical models have a fundamental problem. In fact, Gilmore says the early galaxy was a messy splotch of accumulating small galaxies and dark matter, with some of the dark matter belonging to protogalaxies and some just flowing along dark matter fila- ments. He says this process quickly formed the early halo stars and soon after gener- ated a large turbulent disk with lots of gas and star formation. Some 10 billion years ago, a satellite gal- axy with as much mass as our neighboring Large Magellanic Cloud dumped itself onto the Milky Way, creating the galaxy’s thick disk. Gilmore says that star-forming regions then settled into a large thin disk about 300 light-years in height. Subsequently, starting about 8 billion years ago, this disk grew fat- ter as stars “diffused out,” leaving a thick- ness of about 1,000 light-years. “After a billion years, the thick disk stopped getting any thicker,” says Gilmore. “The disk quickly became spiral, with the structure and numbers of arms coming then become and going, [and] the inner bar growing and unstable and buckling vertically.” collapse and eventu- ally form stars.” This gas Massive globular star cluster Omega Centauri On and on and on disk, he says, probably assembled likely is the relic core of a dwarf galaxy that the But because infalling matter continues to around 10 billion to 12 billion years ago Milky Way devoured long ago. ESO/INAF-VST/OMEGACAM influence the Milky Way, Camargo says it and has been forming stars ever since. is crucial for astronomers to better under- This jibes with Majewski’s timing for stand the interaction between our galaxy star formation. “Most stars are in the thin 10-billion-year-old stars are born in a thick and the neighborhood environment. As disk, [which] is embedded in the thick layer of gas,” he says. “The gas gradually he notes, dwarf galaxies and high-velocity disk,” he says. “But thick-disk stars get becomes thinner over time and newly born clouds continue falling into the halo. up to higher altitudes above the galactic stars start out in thinner and thinner dis- Among the objects still being accreted are plane and they all seem to be 8 or 9 billion tributions, until we get the situation we dwarf galaxies like the Sagittarius Dwarf years old.” have today where the gas layer is very thin.” Spheroidal Galaxy, clouds of dark matter The stars get kicked around through But in McGaugh’s mind, the current such as the Smith Cloud, and clouds of interactions with material in the spiral influx of stellar material and gas from satel- ordinary gas. arms and encounters with massive molec- lite galaxies and the like still doesn’t add up “The dark matter halo forms first and ular gas clouds, which is also where new to much. “Whatever made the thick disk gas then aggregates into the dark matter stars form, explains Bovy. As a result, their had a mass a tenth of the Milky Way,” he and cools into a gas disk,” says Jo Bovy, distribution becomes more random and says. “The satellites coming in now make all a longtime researcher into the galaxy’s less ordered. these streams, but they add up to nothing.” vertical structure from the University of “The picture for the evolution of the What remains of the Sagittarius Dwarf Toronto in Canada. “Parts of the gas disk ver tical structure then becomes one where Spheroidal Galaxy is a case in point. “The

WWW.ASTRONOMY.COM 25 Sagittarius galaxy formed stars all through within one of its spiral arms is more its life but only started being shredded by than daunting. But a Brazilian-led team the tidal forces of the Milky Way in the last recently made a breakthrough. Using 3 billion years,” says Majewski. “Older stel- data from NASA’s Wide-field Infrared lar streams have been so pulled apart and Survey Explorer spacecraft, the researchers are so tenuous, they are not visible to us.” tracked some 400 embedded star clusters. To fine-tune their models, theorists Most lie in the Perseus spiral arm at dis- need multidimensional data on stellar pop- tances roughly 30,000 light-years from the ulations so they can learn not only a star’s galaxy’s center. precise 3-D position and motion, but also “Since most newly found clusters are its chemical composition. And they need embedded clusters, which have not had this information for stars throughout the enough time to move far from their birth- Milky Way’s disks and spiral arms. Only places, we use them to trace the Milky with such observations will they be able to Way’s spiral pattern,” says Camargo. “Our determine how the galaxy’s structure grew map favors a four-spiral-arm structure for and evolved over cosmic time. the Milky Way.” “Chemically tagging a stellar popula- Camargo says he and his colleagues tion will not only tell you where a star is, also discovered two embedded clusters at but what other stars are associated with it, high galactic latitudes, which surprised and then how they are moving and where them because astronomers previously The aptly named “Nessie” is the dark filamentary they are going,” says McGaugh. thought that high-latitude clouds would nebula that meanders through the center of this infrared image. The dense molecular gas that The goal, says Majewski, is to figure not form stars. Presumably more star- forms Nessie resides entirely within the Milky out where such stars came from based on forming material accretes out there Way’s young thin disk. NASA/JPL-CALTECH/SSC multidimensional data that includes the than expected. relative compositions of different elements Although space-based observations in their stellar atmospheres. continue to open up fainter and more changed over time,” says Bovy. This way, distant regions of the galaxy to analysis, astronomers can look at how the structure Sketching spiral structure theorists still rely on ground-based tele- changes closer to and farther from the gal- In truth, the task of tracing the galaxy’s scopes for data to hone their ever-evolving axy’s center. APOGEE’s first such measure- spiral structure from our vantage point Milky Way models. ment showed that many stellar populations In fact, the ongoing APOGEE survey is formed less than 8 billion years ago and do the only comprehensive survey of the gal- not have a constant thickness, but become axy taking spectra at near-infrared thicker the farther they are from the galac- wavelengths. The survey started tic center. This is a telltale sign, says Bovy, in the spring of 2011 using the that these stars do not remain at the same 2.5-meter wide-field Sloan distance from the center but migrate over Telescope at Apache Point, large distances with enough time. New Mexico. APOGEE’s Because red giants — stars that no lon- high-resolution spectro- ger fuse hydrogen into helium in their graph provides astrono- cores and thus have expanded greatly — mers with the chemical are so bright, they make perfect targets. abundances of each tar- “We are focusing on red giants because get star. The data will they give you the largest distance at an shed more light on the apparent magnitude,” says Majewski. evolution of the Milky Months in advance of observations, a Way’s central bar and milling machine drills fiber-optic plug spiral arms as well as holes in nine 40-inch-wide (100 centi- the galaxy’s history of meters) aluminum plates in order to star formation and chem- match exactly the relative positions of 300 ical enrichment. stars in each patch of sky APOGEE sur- Beginning this year, veys. “[Individual] fiber-optic cables then the survey is expanding to channel the light of the stars we want to include the 2.5-meter Irénée sample into our spectrograph,” says du Pont Telescope at Las Cam- Majewski. “And every time we point the panas Observatory in Chile. The telescope, we’re looking at a field of view addition will help the project wrap up that is six Moon diameters across.” by 2020, when it will have surveyed some As a result of these observations, Tendrils of hydrogen in the Smith Cloud belie its 500,000 stars. Majewski says he and APOGEE team true nature. The cloud spans some 10,000 light- “APOGEE will let us measure individ- members have made the first-ever large- years and holds more than a million times the Sun’s mass. Astronomers think that dark matter ual stellar ages, so we can directly map scale map of the relative chemical compo- contributes most of this heft. BILL SAXTON (NRAO/AUI/NSF) how the vertical distribution of stars has sition of stars all the way from the middle

26 ASTRONOMY • JULY 2016 of the galaxy out to the disk’s edge both the largest protogalactic clouds north and south of the galactic poles. when they exploded as super- novae,” says Howes. In search of more data She adds that of The Gaia mission, which is now taking the 14,000 stars they a census of the Milky Way in six dimen- observed, some 500 sions, will provide direct distances to more are metal-poor and than a billion stars. These observations likely extremely old. will allow galactic astronomers to get a In a paper published much better idea about the Milky Way’s in Nature in 2015, dark matter component and thus its for- Howes and her col- mation, history, and evolution. But signifi- leagues identified cant new results on the galaxy’s structure 23 stars as the most likely won’t come before 2017 when the ancient, with ages Gaia team will have positions, distances, of at least 13.5 billion and motions for a large fraction of its years. stellar targets. Longevity does Even so, data from ongoing ground- appear to be a hallmark based surveys continue to surprise. of the Milky Way. After all, The Australian National University’s astronomers project that some SkyMapper Telescope recently detected the of our low-mass red dwarf neigh- Milky Way’s oldest known Population II bors could live another trillion years. stars in the galaxy’s central bulge. Formed But that doesn’t mean the Milky Way’s University of Arizona optical engineer Paul Maseman checks the alignment of the APOGEE only 300 million years after the Big Bang, structure will remain intact for the rest of instrument. Researchers use it to gather spectra or more than 13 billion years ago, the stars their extended lives. on hundreds of objects at a time to understand predate the Milky Way itself. They are The biggest changes likely will come our galaxy’s star-formation history. THE APOGEE TEAM extremely metal-poor and have composi- roughly 4 billion years from now when tions just barely enriched by an even earlier the Milky Way collides with our large supernova. One star in particular had no spiral neighbor, the Andromeda Galaxy most important source of high-resolution detectable carbon and an iron abundance (M31). Well before these two behemoths galactic data. 10,000 times lower than what the Sun has. start merging, however, gravitational As Rix puts it: “The Milky Way is the “The stars we observed are [red] giants forces should destroy both galaxies’ cur- Toledo, Ohio, of the galaxy world. So it with masses about 0.8 times that of the rent spiral structure. makes for a good ‘model organism’ for Sun,” says team member Louise Howes, a Still, at this point in the early 21st cen- understanding how galaxies form in postdoctoral researcher at Sweden’s Lund tury, our galaxy seems to fit the norm for general.” University. The scientists think these stars its mass and classification. For some rea- are metal-poor Population II stars formed son, though, it appears that M31 has had Science journalist Bruce Dorminey is author out of the gas ejected from the cosmos’ a much more violent merger history than of Distant Wanderers: The Search for Planets very first so-called population III stars. the Milky Way. So for the foreseeable Beyond the Solar System (Springer, 2001). “[Models] suggest that they were in one of future, our home will continue to be the Follow him on twitter: @bdorminey.

WWW.ASTRONOMY.COM 27

Characterizing NEOs

Falling behind on asteroid follow-ups Powerful surveys are discovering asteroids at a faster rate than ever before, but most of these Earth-approaching asteroids never get a second glance. by Ilima Loomis

WWW.ASTRONOMY.COM 29 NASA’s Infrared Telescope Facility on Hawaii’s Mauna Kea can help scientists characterize asteroids from its perch high above the Pacific Ocean. ERNIE MASTROIANNI

didn’t take long for Vishnu Reddy to signifi- population of objects, according to a paper Galache cantly lower the price tag of the so-called co-authored last year in the journal Planetary and “trillion-dollar asteroid.” This giant space Space Science. rock loaded with precious metals made Planetary defense is one big reason to study more headlines last July, but all it took was a quick asteroids. Astronomers already have found the vast peek with NASA’s Infrared Telescope Facility majority of large asteroids, but smaller objects — those (IRTF) on Mauna Kea to show it was just a with diameters less than 0.6 mile (1 kilometer) — run-of-the-mill, ordinary chondrite. remain a significant blind spot. Powerful sky surveys “It turned out to be completely bogus,” Reddy, an like Pan-STARRS, the Panoramic Survey Telescope Itassociate research scientist at the Planetary Science and Rapid Response System, are on a mission to dis- Institute, said hours after observing the asteroid in cover such asteroids that could strike Earth. This fast- August. “It’s not made of platinum, like the press moving behemoth on Hawaii’s Haleakalā volcano uses release claimed.” the world’s largest digital camera to catalog near-Earth The lure of space mining is just one reason why asteroids as small as 1,000 feet (300 meters) wide. many asteroid researchers are itching to get a closer look However, even Pan-STARRS doesn’t reveal much at the objects zooming past Earth. But not many information about the kind of threats those objects asteroids get the same treatment as that faux- actually pose. Knowing whether an Earth- platinum behemoth. In fact, even though threatening asteroid is likely to be solid astronomers are now finding more space rock or a pile of rubble would make a rocks than ever before, most are never Planetary big difference in how governments studied further. and civil defense agencies prepare, “We can’t keep up,” says José Luis defense is one says Reddy. Galache, acting deputy director of the “It helps us better know our Minor Planet Center at the Harvard- big reason to study adversary, for lack of a better word,” Smithsonian Center for Astrophysics, he adds. “If something is going to “not because it’s impossible, but because more asteroids. impact us, we want to know as much there are no dedicated programs to char- as possible about this object.” acterize [near-Earth asteroids], unlike how Studying asteroids that pass by Earth there are dedicated programs to look for them.” can also reveal tantalizing clues about how the Astronomers have cataloged more than 12,000 solar system formed. These objects give scientists a asteroids orbiting close to Earth, but only about 1,000 close-up look at the building blocks of the solar system,

: ROEN KELLY have been characterized — studied to determine notes planetary astronomer Andy Rivkin of the Johns their composition, size, shape, rotation speed, and Hopkins University Applied Physics Laboratory. They

ASTRONOMY other data. Of the more than 1,000 new asteroids dis- allow scientists to study objects smaller than they can covered every year, less than 10 percent are ever char- see in the main asteroid belt between Mars and Jupiter. acterized. At the current rate of follow-up, it would “Each one is a piece of this bigger puzzle,” Rivkin take another 100 years to do so for just the known says. “They’re the leftovers from the formation of the inner planets, and because they haven’t experienced Ilima Loomis is a freelance writer based in Hawaii. She tweets wind, erosion, water, or volcanoes, they’re all pretty

ARTWORK PREVIOUS TWO PAGES about science and the Aloha State from @iloomis. much as they were.”

30 The fragments of Comet Shoemaker-Levy 9 stretch a distance three times that between Earth and the Moon, as the space rocks progress on their collision course with Jupiter in this 1994 Hubble Space Telescope image. NASA/ESA/H. WEAVER AND E. SMITH (STSCI)

Space exploration is another reason to push for better asteroid characterization. Knowing whether an object is likely to contain water or precious minerals would help private companies select targets for mining. And scien- tific missions to redirect or place a rover on asteroids might want to avoid trying to land on fast spinners, for example. “For all these things, you want to know a little bit more than just the orbit of the asteroid,” Reddy says. A widening gap So why are so few asteroids ever investigated? Part of the reason is simply that it’s easier to spot new asteroids than Earth-based radar to study them in depth. “Doing characterization takes a Galache says dedicating a telescope to that mission tracked asteroid 2014 HQ as it lot more effort,” Reddy says. In the same way, “it’s easier full time — or preferably one each in the Northern and 124 passed within to count a group of people than to find out about each Southern hemispheres — is what’s needed to keep up 776,000 miles person’s genetic history or research their heritage.” with discovery. “There are several telescopes that per- (1.25 million But the gap between discovery and characterization is form a few nights of characterization a month, but that’s kilometers) of our getting wider. Not only are survey telescopes now cata- not enough,” he says. “The funding agencies just don’t planet June 8, 2014. The images loging more new asteroids than ever before, says Martin see this as a priority.” revealed a rapidly Elvis, an astrophysicist at the Harvard-Smithsonian From a planetary defense point of view, Galache says rotating and Center for Astrophysics, “they’re going fainter, and he understands why NASA’s focus has been on discovery. peanut-shaped they’re also finding smaller objects.” “They feel as long as they’re discovering as many as space rock — a binary trait shared Many of those smaller objects become visible only possible, if we do find one that’s dangerous, resources by as many as one when they are close to Earth, often within days of their will come in to study that one in depth, and that will be in six asteroids. closest approach. That means there’s a small window to enough,” he says. NASA/JPL-CALTECH/ARECIBO OBSERVATORY/USRA/NSF observe them, typically around two weeks, before they But with surveys now spotting smaller, closer objects move away again and become too faint. Large asteroids than ever before, there may not always be time to perform that were once astronomers’ main target tend to make a a full characterization on an asteroid found to be heading return trip past Earth after a year or two, giving scien- toward Earth, Rivkin notes. Getting a statistical sample of tists a second look. But the smaller objects now being NEOs could provide critical information to help the found either get lost altogether or are too faint to see on planet prepare for impact on short notice, he says. their return trip. “You either get it the first time, or not Galache is quick to note he’s not arguing for 100 per- at all,” says Elvis. cent characterization, but he says he’d be happy if Characterizing 100 near-Earth objects (NEOs) a year researchers could sample 2,000 to 3,000 large asteroids used to be enough to satisfy scientists, but that’s no lon- and several hundred smaller asteroids. “In order to say ger the case now that surveys are discovering as many as something scientifically about the distribution of com- 1,400 new objects a year, Elvis says. positions at various sizes and within a range of orbits, we “It’s like going from artisanal production to indus- do need a larger sample than we have now,” he says. trial,” he says. “They’re finding objects at such a rate — There’s a particular need to better understand smaller and they disappear so quickly, and don’t come back for a objects, says Cristina Thomas, a planetary astronomer long time — that we’ve got to up our game and keep up at NASA’s Goddard Space Flight Center employed by with discovery.” the Planetary Science Institute and Universities Space Finally, there’s the matter of policy. While NASA Research Association. Some of the work now being received a congressional mandate in 2005 to identify done has revealed that small asteroids differ from the 90 percent of large NEOs by 2020, no similar mission population of larger bodies in important ways, including exists to perform follow-up observations. composition and rotation speed.

WWW.ASTRONOMY.COM 31 Where do NEOs come from?

Mercury Vesta Earth Mars Asteroid belt 2–5 AU

Venus Jupiter Ceres

Jupiter’s gravity bumps rocks from the asteroid belt, setting them on paths that can cross Earth’s orbit and create so-called near-Earth asteroids. ASTRONOMY: ROEN KELLY

“We certainly don’t need spectra or light curves of AMATEUR EYES ON THE SKY every NEO — that would be excessive,” she says. “For the largest objects in the population, I think we kind of have a As the asteroid community struggles to step up handle on what’s going on. But I think we’re really not characterization efforts, some researchers are getting an assist from amateur astronomers. very good at understanding the objects that are less than a Asteroid researcher Vishnu Reddy of the Planetary couple of kilometers [across].” Science Institute has partnered with a network of The explosion of the Chelyabinsk meteorite over dedicated amateurs to make light-curve observations Russia in 2013, which caused tens of millions of dollars in that help to determine asteroid rotation speed. damage and injured more than 1,500 people, was a wake- “They’re simply invaluable,” he says. “They can make up call that more study of small objects was needed, good observations, and they have all the telescope time Galache adds. “What this showed is that even something they want because it’s their own personal telescope.” Bruce Gary, a retired Jet Propulsion Laboratory (JPL) as small as 17 meters [56 feet] across can be dangerous,” scientist and consultant and an amateur astronomer, got he says. “You can’t just ignore it.” involved after Reddy spoke to his astronomy club in Arizona. He was excited to take on the challenge. Rapid response “He said, ‘Can you do near-Earth asteroids? We want One program working to help close the characteriza- to characterize as many as possible,’ ” Gary recalls. “The tion gap is the Mission Accessible Near-Earth Object goal was to do several a month.” On a typical observing Survey (MANOS). The project is designed to make “rapid night, Gary would check a list of near-Earth objects maintained by JPL and find out which ones were passing response” follow-up observations of newly discovered close to Earth that evening, and would select a likely near-Earth asteroids, with observing time on 4-meter and target based on Reddy’s parameters. Around sunset, larger telescopes. he’d open the domed observatory in his backyard and “We’re using some of the largest telescopes in the get his telescope ready. world to study this population,” says principal investigator After making his calibrations, he’d settle in for a night Nick Moskovitz, an astronomer at Lowell Observatory in of observing, repointing his telescope every half-hour to track the asteroid, and shooting 200 to 300 images on a Flagstaff, Arizona. good night. Of the approximately 100 new NEOs discovered by “The next morning I’d wake up, filled with survey telescopes each month, MANOS follows up anticipation. Could this be a binary? on about 10 percent of them, gathering spectra Could it be a fast rotator? Because and light curves to determine size, composi- those are rare, everybody wants to tion, rotation speed, and other informa- catch a fast rotator,” Gary says. tion. Moskovitz expects to complete He observed 28 asteroids for “Even some- Reddy over nine months observations of several hundred aster- before moving on to other thing as small as oids by the end of the project. interests in June 2015. MANOS started in 2013 with Gary says he enjoyed 17 meters [56 feet] across observing time awarded by the working on the project. “It’s National Optical Astronomy like going out on the beach can be dangerous. Observatory, and it went on to get looking for shells. You never funding time from NASA and the know what you’re going to You can’t just stumble across,” he says. — I. L. National Science Foundation, as well as ignore it.” observing time on other telescopes,

32 This six-image mosaic of asteroid Eros was captured by NASA’s NEAR Shoemaker mission in 2000. For scale, the crater at the top of the image NASA’s IRTF is part of an asteroid-observing network. Their research shows meteorites and large near- is 3.3 miles (5.3 kilometers) wide. NASA/JPL/JHUAPL Earth objects come from distinct populations. HARUN MEHMEDINOVIC/WWW.SKYGLOWPROJECT.COM including Gemini, NASA’s IRTF, Lowell’s Discovery “Unfortunately, the count is still Channel Telescope, and others. quite small.” “We’re slowly growing, slowly adding telescopes to Moskovitz agrees. “Yes, we our network,” Moskovitz says, adding that the program’s have a lot of resources. Yes, results to date have helped his team of about 20 scien- we’re building a nice statistical tists leverage more funds and observing time. sample,” he says. “But there’s still “Because we’re studying a population that hasn’t been 90 percent of the population that isn’t studied much before, we’re continuing to find new and being studied, and not much is being done about it.” Scientists still know relatively little interesting things,” he says. With so much potential benefit to commercial min- about the makeup Those surprises include more asteroids with rota- ing operations, is private funding for asteroid character- of most small aster- tional periods faster than what scientists had predicted. ization on the horizon? Galache, Reddy, and Moskovitz oids, like the one MANOS recently identified the fastest-spinning aster- all say they’ve been informally approached by wannabe that exploded over Chelyabinsk, Russia, oid yet, a 20-meter object with a rotational period of space mining companies, but haven’t seen them demon- in 2013. These just 16 seconds. “We’re finding some that are very, strate any serious interest in getting involved for the chondrite fragments very fast,” says Thomas, who’s also a co-investigator time being. (shown actual size) were found in a field on MANOS. “There haven’t been any offers of money,” Galache between two nearby Knowing the rotation speed of an asteroid provides says. “There have certainly been conversations about small villages. important clues about its composition, notes Moskovitz. [characterization], but at the moment, they’re not in the DIDIER DESCOUENS/WIKIMEDIA A fast spinner is likely to have a solid, dense interior position to start prospecting. So I think they consider this COMMONS because centrifugal force would pull apart a clump of as something they need to do a bit further down the line.” boulders or rubble. “That’s one of the holy grails in So far, most of the firms that have contacted understanding asteroids — what are their internal Moskovitz seem to be working toward doing their properties,” he says. research in-house, he says. “It’s still early for many of MANOS’ research is also raising some intriguing these companies,” he says. questions about where meteorites come from. Scientists Meanwhile, 2013’s Chelyabinsk meteorite has rekin- had long believed that most came from small asteroids dled interest in asteroid research in general, and scien- because meteorites recovered on Earth are composition- tists like Galache and Thomas hope some of that ally different from the large-NEO population. But attention and funding will find their way past discovery Moskovitz says based on recent studies of small NEOs, and trickle down to characterization. that doesn’t seem to be the case. “I’m sad people got hurt — don’t get me wrong — but “We’re finding that their composition looks nothing for us, it was a big ‘wow,’ moment,” Thomas says. “We like the meteorite population,” he says. were all completely floored that we didn’t see it coming, Galache and Reddy say MANOS has yielded impor- and then all of a sudden, everyone was like, ‘Oh my tant results and is a big step toward a more coordinated God, we need you so much.’ It really put the attention effort. It approaches the characterization problem sys- back on us.” tematically rather than leaving follow-up to individual She predicts the event will be a key talking point for scientists looking at a handful of objects at a time. asteroid scientists explaining the importance of their “It’s the only project that has attempted to do rapid work for years to come. “You can only make so many follow-up of newly discovered asteroids, with the sole Armageddon references,” she says, “before people don’t purpose of characterization,” Galache says. know what you’re talking about anymore.”

WWW.ASTRONOMY.COM 33 ASKASTR0 Astronomy’s experts from around the globe answer your cosmic questions. INNER TURMOIL Q: ARE IMPACTORS MORE PREVALENT IN THE OUTER SOLAR SYSTEM THAN THEY ARE IN THE INNER SOLAR SYSTEM? DOES THIS AFFECT HOW SURFACE AGES ARE ESTIMATED? David Kaiser, Thornton, Colorado

A: Determining surface ages are small main-belt asteroids. throughout the solar system Remarkably, considering that helps explain the evolution of the asteroids are much closer Pluto’s surface is strangely lacking in craters. These craters on the dwarf planetary bodies. To estimate than objects in the outer solar planet show signs of layering, an implication that the surface has changed the surface age, you need to system, here too the census of since the terrain first formed. NASA/JHUAPL/SWRI know the number of craters impactors is only approximately and the number of impactors known. In both cases, we have There are lots of 1-kilometer- uncombined with other ele- near that body. The former can estimates of bodies larger than size Kuiper Belt objects, but ments. This free oxygen has not be measured through space- about 0.6 mile (1 kilometer). they are spread out over a vast been detected in appreciable craft images, but what about But even if you know the volume. In the inner solar sys- amounts in our solar system or the latter? number of craters and the tem, the potential impactors on exoplanets. In the outer solar system number of potential impactors, are crammed into a much Meanwhile, in our solar sys- — for example, near Pluto — the last remaining factor is the smaller area. So the impact rate tem we do see a phenomenon the impactors are small Kuiper impact probability. If the density is much higher in the main called a “fire fountain,” which Belt objects. Their census is of impactors is high — many asteroid belt than in the outer strongly resembles fire. Fire known through telescope sur- impactors per cubic kilometer of solar system. Vesta and Ceres fountains occur when heated veys, but some uncertainty space — then the cratering rate get hit much more frequently material in a volcano erupts remains. In the inner solar is high. If the density is low, then than Pluto because they orbit rapidly. We see fire fountains on system — for example, near the cratering rate is low. Herein in a relatively dense swarm of Earth and believe they also Ceres or Vesta — the impactors lies the answer to your question. potential impactors, whereas occur on Jupiter’s volcanic Pluto orbits in a relatively moon Io. Our team is devising a impactor-free environment, way to look for fountain-like and therefore has a lower structures in eruptions on Io impact rate. using a new technique we’ve David Trilling already used to detect unrelated Northern Arizona University lava features. Fire fountains are Flagsta, Arizona beautiful and fascinating phe- nomena, but they are not, strictly speaking, fire. Q: PLENTY OF REALLY Will we see extraterrestrial HOT THINGS EXIST IN THE fire in the future? The chances UNIVERSE. BUT DO WE of detection in our solar system KNOW OF FIRE ANYWHERE are small, but with the effort BESIDES ON OUR PLANET? being put into detecting another Tom Malkoch Earth, we could see an exo- Plymouth Meeting, Pennsylvania planet with the right ingredients for fire (free oxygen, heat, and A: Fire has occurred here on combustible material — the Earth for millions of years and “fire triangle”) in this century. was harnessed by humans more Finally, let’s consider man- NASA’s Galileo spacecraft saw shimmering, fresh lava in Io’s Tvashtar than 100,000 years ago. But like made fire. Will we have astro- Catena back in 2000. Jupiter’s volcano moon holds the closest thing to humans, fire requires free oxy- nauts, like Mark Watney in The earthly fire in our solar system. NASA/JPL/UNIVERSITY OF ARIZONA gen — molecular oxygen Martian, making fire soon?

34 ASTRONOMY • JULY 2016 The modular build of Meade’s LightBridge telescope — and other That is likely. In fact, we ability. Don’t be afraid to call Dobsonians — makes for have already seen fire off Earth ahead and ask if anyone has simple setup and take- if you consider the near disaster access to tactile graphics of down, a key concern for on Apollo 13. And NASA is some of the observing targets. observers with mobility issues. ASTRONOMY: WILLIAM now studying fire in micro- If you are lucky, someone at ZUBACK gravity on the International a star party will be using an Space Station. off-the-shelf webcam mounted Al Conrad to a scope to view targets on a Large Binocular Telescope Observatory monitor, providing you many Tucson, Arizona more options for enlarging and maximizing the display for your needs. You may want to Q: I AM STRUGGLING TO pursue a system like this for FIND A SYSTEM FOR TELE- yourself. Many amateurs take SCOPIC OBSERVATIONS OF very good planetary images THE PLANETS AND THEIR using this method. Coupling a MAJOR MOONS WORTHY OF small go-to telescope with a PHOTOGRAPHING. ONE webcam may let you explore WRINKLE: I AM IN A WHEEL- objects too dim for you to see CHAIR AND ALMOST BLIND. while giving you maximum Robert Parisi independence. Elizabethtown, Kentucky Another area to explore is the world of robotic telescopes A: Every amateur astronomer accessible via the Internet. Slooh faces the delightful challenge of and New Mexico Skies provide choosing equipment to match telescope time to the public on a his or her lifestyle, seeing con- fee basis. You can use their ditions, and schedule. Your online interfaces to request biggest considerations when images of your choice while choosing equipment will be controlling exposure time and maximizing the light-gathering filters. When the images are power of your scope while returned to you, you can then keeping the system within your use whatever optimizations you The simple formula is: changes the focal length of your ability to set up and maneuver typically use with your monitor Magnification = Focal eyepiece to 11.2mm (28 ÷ 2.5). efficiently. to view your work. length of telescope ÷ focal Said another way, this Yerkes Observatory has Kate Meredith length of eyepiece. Barlow lens increases the helped make skies accessible to Director of Education Outreach For this to work, both must magnification of any eyepiece the visually impaired for many Yerkes Observatory be in millimeters. In your case, used with it by 2.5 times. years. We’ve found that the Williams Bay, Wisconsin we need to calculate the focal Finally, the magnification of best way to start is to get length of your telescope. this optical system is 441 ÷ 11.2 comfortable with eyepiece We do that with another = 39.375, or 39x. observing options and then Q: HOW DOES ONE DETER- really simple formula: Michael Bakich explore the robotic telescopes MINE MAGNIFICATION? Focal length = Aperture x Senior Editor available online. Another good I HAVE AN EDMUND focal ratio. first step is to contact a local SCIENTIFIC ASTROSCAN, First, let’s change the aper- amateur astronomy club. They 41⁄8-INCH APERTURE, F/4.2 ture to millimeters: 4.125 Send us your are typically knowledgeable REFLECTING TELESCOPE, inches = 104.775mm, which questions and welcoming. Go to a few USED WITH A 2.5X BARLOW we’ll call 105mm. Send your astronomy events. LENS AND A 28MM PLOSSL So, the focal length of your questions via email to Dobsonian telescopes also EYEPIECE. scope = 105mm x 4.2 = 441mm. [email protected], provide good first experiences Pete Condon This is the first thing we need or write to Ask Astro, for amateurs and are common Girard, Ohio to know for our magnification P. O. Box 1612, Waukesha, at astronomy clubs. You should formula. WI 53187. Be sure to tell us be able to roll right up to an A: The magnification (or If you were using only the your full name and where 8-inch Dob for a firsthand view power) you will see through eyepiece, the magnification you live. Unfortunately, we of the Moon and planets. Expe- a given optical system depends would be 441 ÷ 28 = 15.75, or cannot answer all questions rience moving and pointing a on the telescope and the 16x. But you’re using a 2.5x submitted. telescope to the best of your eyepiece. Barlow lens, which effectively

WWW.ASTRONOMY.COM 35 THIS SKY Visible to the naked eye MARTIN RATCLIFFE ALISTER LING and describe the Visible with binoculars solar system’s changing landscape as it appears in Earth’s sky. MONTH Visible with a telescope July 2016: Mercury and Venus return west an hour after sunset and doesn’t set until midnight local daylight time. Gleaming at magnitude –1.9, Jupiter is unmistakable. Its altitude drops during July, and by month’s end it appears just 10° high an hour after sundown. The best time to view Jupiter through a telescope is when it lies high in the sky in early July. Its slightly flattened disk then measures 34" across and should show a wealth of atmospheric features. Jupiter’s four bright moons also put on a good show. Venus and its fainter cousin, innermost Mercury, hovered near each other after sunset in January 2015. The pair You’ll typically see all of them puts on a repeat performance in late July. ALAN DYER strung out in line with the planet’s equator, though occa- t’s not often you can see eight Mercury and Venus are Your first realistic chance sionally one or more will be worlds in one evening, but if among the more challenging to find the duo comes July 21. passing in front of or behind skies are clear after sunset in of the solar system objects. Although Venus then lies just the giant’s disk. Perhaps the late July, you should be able Both scrape the western hori- 2° high a half-hour after sun- best such event this month to observe from Mercury to zon during twilight in the set, it shines brilliantly at mag- occurs on the 1st when Gany- IPluto. The Moon isn’t shy this latter half of July. Mercury nitude –3.9. Mercury stands mede crosses Jupiter’s north- month either, passing directly passes behind the Sun on 3° to Venus’ upper left, but is ern hemisphere. The transit in front of Neptune and Taurus July 6 and then climbs slowly harder to see because it glows begins at 10:48 p. . EDT (best the Bull’s brightest star, Aldeb- into view. It slides 0.5° north more faintly, at magnitude for eastern North America) aran. It all makes for an action- of Venus on the 16th, but the –0.6. Binoculars will help pull and lasts for more than three packed viewing season despite two are hopelessly lost in the them out of the twilight. hours (allowing western the short summer nights. Sun’s glare. As Mercury ascends during observers good views). the next 10 days, it also fades. You’ll find Mars due south Mercury and Venus at dusk On the 31st, it glows at magni- and about one-third of the tude –0.2 and stands 6° high 30 way to the zenith as darkness minutes after sundown. Bright Denebola falls in early July. The planet VIRGO Venus remains easier to see shines brightly at magnitude despite lying deeper in twilight. –1.4, but stands out nearly as By the time Mercury and much for its distinctive Jupiter Venus slip below the horizon, orange-red hue. You can find Jupiter comes to the fore. it among the background LEO Unlike its siblings, however, stars of southern Libra, the giant planet is an evening though Mars makes a better fixture throughout July. On guide to the constellation’s Mercury the 1st, it lies 25° high in the faint outline than vice-versa. Regulus The Red Planet reached Martin Ratcliffe provides plane- opposition and peak visibility Venus 5° tarium development for Sky-Skan, in late May and now is mov- July 31, 30 minutes after sunset Inc., from his home in Wichita, Looking west ing away from Earth. As a Kansas. Meteorologist Alister result, it fades by nearly 40 The two inner planets appear together in evening twilight late this month Ling works for Environment percent (to a still-bright mag- under the watchful eye of distant Jupiter. ALL ILLUSTRATIONS: ASTRONOMY: ROEN KELLY Canada in Edmonton, Alberta. nitude –0.8) during July.

36 ASTRONOMY • JULY 2016 RISINGMOON Young and old enjoy a northern exposure Goldschmidt and Anaxagoras N Anaxagoras Reminiscent of seasonal changes Return to the area one eve- in Earth’s polar regions, the lunar ning later when sunlight has E north transforms every month advanced to the sharp-rimmed from creeping cratered shadows Anaxagoras. This crater’s deep to a sprawling reflective domain floor remains in shadow on both Goldschmidt and back again. On July 19, the the 13th and 14th (the top photo high Sun at Full Moon reveals approximates the second day). a zone with gray patches and Notice how this 32-mile-wide white rays that converge toward feature cuts into the edge of the youthful crater Anaxagoras. sprawling Goldschmidt. As Full The progression begins on Moon approaches, watch Anax- the 12th, an evening after First agoras turn into the brightest Anaxagoras Quarter phase. First locate Gold- splotch of rays in the north. schmidt, a 75-mile-wide crater The younger crater, named that sports a freckled floor and after a Greek philosopher, and a low rim. Relentless bombard- Tycho, in the south, are of a ment from solar system debris similar age. If Anaxagoras were Goldschmidt has worn down its once-steep closer to the equator, it would be walls and left rounded shadows just as famous as Tycho. The rays that extend across the shallow spread evenly and are beautifully floor. The crater got its name defined at Full Moon when the Bright rays emanate from Anaxagoras at Full Moon (above); at other from a 19th-century German debris apron almost obscures its times, the youthful crater appears as a sharp-rimmed blemish on amateur astronomer. older neighbor, Goldschmidt. Goldschmidt’s aged walls (top). CONSOLIDATED LUNAR ATLAS/UA/LPL; INSET: NASA/GSFC/ASU

Mars’ increasing distance METEOR also reveals itself in the plan- WATCH et’s dwindling size. Point your telescope at Mars in early Fiery debris from Southern Delta Aquariid meteor shower July and you’ll see a disk that spans an impressive 16". Do the water’s source Enif the same thing at month’s PISCES end and you’ll encounter a In terms of volume, few meteor DELPHINUS 13"-diameter disk. But don’t showers can compete with the AQUARIUS Southern Delta Aquariids. Unfor- fret: That’s plenty big enough CETUS to show subtle surface features tunately, the shower’s peak is so if you view when Mars lies broad that a viewer typically sees Radiant highest in the sky an hour or only a modest number of “shoot- ing stars.” The shower peaks the two after sunset. The greater Fomalhaut CAPRICORNUS altitude means you’ll be look- night of July 29/30, though you’ll ing through less of Earth’s probably see just as many meteors a day or two on either side. image-distorting atmosphere. The streaks of light appear to GRUS Summer ends in Mars’ 10° radiate from near 3rd-magnitude northern hemisphere in early Delta (δ) Aquarii, which climbs Late July, 4 A.M. July, so the north polar ice cap A.M. Looking south Southern Delta Aquariid highest around 3 local daylight meteors should be near its minimum time. From the Southern Hemi- The waning crescent Moon Active dates: July 12–Aug. 23 extent. Look for a patch of sphere, where the radiant passes white — the permanent cap of produces little interference Peak: July 29 nearly overhead, observers can see for July’s best meteor display, water ice — near the planet’s Moon at peak: Waning crescent up to 16 meteors per hour. Those which rules the predawn sky Maximum rate at peak: northern limb. This region at mid-northern latitudes will be for several days around its 16 meteors/hour remains on view all month lucky to see half that number. July 29 peak. because the planet’s north pole currently tilts about 15° OBSERVING Pluto reaches opposition and peak visibility July 7, when it glows at toward Earth. More subtle HIGHLIGHT — Continued on page 42 magnitude 14.1 among the background stars of northern Sagittarius.

WWW.ASTRONOMY.COM 37 STAR N

DOME

NGC 884 NGC How to use this map: This map portrays the 869 NGC

sky as seen near 35° north latitude. Located CAMELOPARDALIS inside the border are the cardinal directions and their intermediate points. To find

stars, hold the map overhead and M81

CASSIOPEIA orient it so one of the labels matches NE M82 the direction you’re facing. The

stars above the map’s horizon M31

Polaris ANDROMEDA

now match what’s in the sky. NCP

MINOR

CEPHEUS The all-sky map shows URSA how the sky looks at: midnight July 1 11 P.M. July 15

10 P.M. July 31

izar LACERTA

M Planets are shown PEGASUS

at midmonth

DRACO

Deneb

CYGNUS

Vega M13

LYRA HERCULES

E M27

M57 M15

Enif VULPECULA

DELPHINUS

CORONA SAGITTA BOREALIS EQUULEUS

AQUARIUS Altair SERPENS CAUDA SERPENS CAPUT STAR MAGNITUDES AQUILA OPHIUCHUS Sirius 0.0 M11 3.0 SCUTUM 1.0 4.0 CAPRICORNUS M16 2.0 5.0 M17 Saturn STAR COLORS M22 M20 A star’s color depends Antares on its surface temperature. M8 SAGITTARIUS M4 • The hottest stars shine blue SE M6 • Slightly cooler stars appear white • Intermediate stars (like the Sun) glow yellow M7 Lower-temperature stars appear orange CORONA • LU AUSTRALIS • The coolest stars glow red SCORPIUS NGC 6231 • Fainter stars can’t excite our eyes’ color receptors, so they appear white unless you TELESCOPIUM use optical aid to gather more light

38 ASTRONOMY • JULY 2016 S Note: Moon phases in the calendar vary in size due to the distance from Earth JULY 2016 and are shown at 0h Universal Time.

SUN. MON. TUES. WED. THURS. FRI. SAT. MAP SYMBOLS

Open cluster 12 Globular cluster

Diffuse nebula 3456789 NW Planetary nebula

Galaxy URSA MAJOR URSA 10 11 12 13 14 15 16

17 18 19 20 21 22 23 LEO MINOR LEO : ROEN KELLY ROEN :

24 25 26 27 28 29 30 ASTRONOMY M

31

M51 BY ILLUSTRATIONS

LEO CANES VENATICI CANES

Calendar of events Denebola

NGP 1 The Moon is at perigee (227,411 19 Full Moon occurs at

miles from Earth), 2:40 A.M. EDT 6:57 P.M. EDT

M64

BERENICES 23 COMA The Moon passes 0.4° north of The Moon passes 1.1° north of BOÖTES W Aldebaran, midnight EDT Neptune, 2 A.M. EDT 4 New Moon occurs at 25 The Moon passes 3° south of 7:01 A.M. EDT Uranus, midnight EDT ) c ti p li Earth is at aphelion (94.5 26 Last Quarter Moon c e ( million miles from the Sun), occurs at 7:00 P.M. EDT Arcturus n u S noon EDT e 27 th The Moon is at perigee f o 6 h Mercury is in superior (229,698 miles from Earth), VIRGO t Pa conjunction, 11 P.M. EDT 7:37 A.M. EDT

M104 7 Pluto is at opposition, SPECIAL OBSERVING DATE M5 6 P.M. EDT 29 A crescent Moon passes in front of 1st-magnitude Spica 9 The Moon passes 0.9° south Aldebaran for observers of Jupiter, 6 A.M. EDT in the eastern and southern United States. 11 First Quarter Moon occurs at 8:52 P.M. EDT 29 LIBRA The Moon passes 0.3° north of 13 Aldebaran, 7 A.M. EDT HYDRA The Moon is at apogee (251,201 A.M. miles from Earth), 1:24 EDT Southern Delta Aquariid Mars 14 The Moon passes 8° north of meteor shower peaks P.M. Mars, 2 EDT Uranus is stationary, 10 P.M. EDT SW 16 The Moon passes 3° north of 30 Mercury passes 0.3° north of A.M. Saturn, 1 EDT Regulus, 1 P.M. EDT Mercury passes 0.5° north of PUS U Venus, 2 P.M. EDT

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 July 2016

DRA Objects visible before dawn LYN AND AUR LAC LYR PER CYG

GEM The Moon occults TRI CNC Aldebaran on July 29 ARI VUL Sun Pa PEG th of P the S DEL ath of un ( PSC SGE the M eclip Pallas ORI oon tic) EQU TAU Uranus CMi AQL Melpomen Celestial equator Ceres e Neptune AQR MON SCT CET SER

CMa LEP ERI FOR PYX PsA CAP SGR PUP COL SCL Pluto appears at its best MIC for the year in July CAE GRU

Moon phases Dawn Midnight

6 5 4 3 2 1

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17

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

Mercury Uranus

S Mars

WE Pluto N Saturn Venus Ceres Jupiter Neptune 10"

Planets MERCURY VENUS MARS CERES JUPITER SATURN URANUS NEPTUNE PLUTO Date July 31 July 31 July 15 July 15 July 15 July 15 July 15 July 15 July 15 Magnitude –0.2 –3.9 –1.1 9.0 –1.8 0.2 5.8 7.8 14.1 Angular size 5.9" 10.1" 14.7" 0.5" 33.2" 17.9" 3.5" 2.3" 0.1" Illumination 73% 97% 90% 97% 99% 100% 100% 100% 100% Distance (AU) from Earth 1.143 1.651 0.635 2.868 5.944 9.261 19.957 29.277 32.127 Distance (AU) from Sun 0.433 0.719 1.454 2.933 5.445 10.033 19.957 29.955 33.136 Right ascension (2000.0) 10h10.0m 9h42.7m 15h24.9m 2h03.4m 11h21.1m 16h35.4m 1h30.5m 22h53.3m 19h07.9m Declination (2000.0) 12°07' 15°18' –21°34' 1°35' 5°27' –20°17' 8°49' –8°01' –21°09'

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

UMA Objects visible in the evening Jupiter’s moons LYN Dots display positions Io HER CVn of Galilean satellites at LMi 11 P.M. EDT on the date Europa BOÖ GEM CB shown. South is at the COM top to match LEO CNC S the view WE Ganymede y Sun through a cur er us N M Ven telescope. Callisto SER CMi 1

Jupiter 2 OPH VIR SEX LIB MON 3

Flora CRV CRT 4 HYA CMa 5 Mars ANT PYX 6 Saturn PUP LUP 7 SCO VEL 8 Jupiter

Early evening 9 To locate the Moon in the sky, draw a line from the phase shown for the day straight up to the curved blue line. 10 Io Note: Moons vary in size due to the distance from Earth and are shown at 0h Universal Time. 11 Callisto

12 16 15 14 13 12 11 10 9 8 7 6 5 4 13

14

15 Mercury Superior conjunction 16 is July 6 17

18

Venus Ceres 19 Europa Jupiter 20

21 Mars 22 Earth Aphelion is July 4 23 Ganymede 24

25 Jupiter 26

The planets Uranus 27 in their orbits 28 : ROEN KELLY ROEN : Neptune Arrows show the inner planets’ 29 monthly motions and dots depict Saturn the outer planets’ positions at mid- 30 ASTRONOMY month from high above their orbits. Pluto 31 Opposition is July 7 ILLUSTRATIONS BY BY ILLUSTRATIONS

WWW.ASTRONOMY.COM 41 — Continued from page 37 The ins and outs of Saturn’s moons WHEN TO VIEW THE PLANETS S Enceladus Saturn Titan EVENING SKY MIDNIGHT MORNING SKY Mercury (west) Mars (southwest) Uranus (southeast) Dione Venus (west) Saturn (southwest) Neptune (south) Tethys Mars (south) Neptune (southeast) Rhea Jupiter (west) W Saturn (south) dark markings come and go bright stars of northern as Mars rotates. The most con- Scorpius. Saturn stands 6° spicuous such feature — Syrtis north of that constellation’s 30" Major — appears near the cen- luminary, 1st-magnitude Iapetus July 11, 11:30 P.M. EDT ter of the planet’s disk during Antares. This region lies the evening hours in late July nearly due south and at peak The night of July 11/12 offers observers fine views of inner Enceladus near for North American observers. altitude as night falls and greatest elongation and far-flung Iapetus due north of the ringed planet. Trailing about an hour stays on view past midnight. behind Mars, Saturn also daz- Any telescope reveals moons than mighty Jupiter, July 11/12, when it shines at zles. The ringed planet reached Saturn’s globe, which mea- though none glows as brightly. 11th magnitude. By month’s opposition in early June and, sures 18" across in mid-July, The most obvious saturnian end, it lies 8.4' east of Saturn like Mars, recedes from Earth surrounded by a stunning satellite is 8th-magnitude and its darker hemisphere during July. But unlike its ring system that spans 41". Titan. It takes 16 days to circle faces Earth, so it glows dimly closer cousin, Saturn shows The rings tilt 26° to our line the planet, so you can see at 12th magnitude. little ill effect. Because the gas of sight, just 1° less than the nearly two complete orbits dur- Three 10th-magnitude giant lies more than 10 times maximum they’ll achieve next ing July. You’ll find this moon moons hover near Saturn like farther away, the percentage year. Can you spot the outer due north of Saturn on July 7 fireflies next to a bright light. change doesn’t amount to A ring peeking above Saturn’s and 23 and due south of the All circle the planet in less much. Saturn dims from mag- north pole? Or what about planet July 15 and 31. It retreats than a week — Tethys in 1.9 nitude 0.1 to 0.3 during July, a Saturn’s disk shining through up to 3.2' away at greatest east- days, Dione in 2.7 days, and barely noticeable difference. the Cassini Division — the ern and western elongation. Rhea in 4.5 days — and none Saturn resides in southwest- dark gap that separates the A Outermost Iapetus spends strays more than 1' from the ern Ophiuchus. Although the ring from the brighter B ring? most of its 79-day orbit far edge of the rings. planet calls the Serpent-bearer For small telescope owners, from Saturn. It slides 2.2' due Inner Enceladus proves home, it appears closer to the Saturn boasts more visible north of the planet the night of more challenging because it COMETSEARCH

Look low for PANSTARRS’ glow Comet PANSTARRS (C/2013 X1)

July’s brightest comet lurks low northern Centaurus, passing N in the south during early eve- 0.6° west of magnitude 4.1 c1 31 CENTAURUS ning. To avoid bright moonlight, Centauri on the 23rd. C/2013 X1 29 hunt down Comet PANSTARRS should be visible through bin- (C/2013 X1) either at the begin- oculars then, though barely, and 27 ning or end of the month. The a nice target for small telescopes. dirty snowball should glow at The comet should appear as E 25 6th magnitude in early July, one an out-of-round gray fuzzball. c1 or two magnitudes brighter To see more detail, bump up the 23 than it will be by month’s end. power. Notice that the north- c2 It should be easier to see late in western edge looks sharper Path of the month, however, because it because that’s where the solar 21 Comet PANSTARRS lies higher in the sky. wind of charged particles flows For observers in the north- past the comet. Large scopes ern United States and Canada, may show a hint of green from July 19 1° PANSTARRS will be hard to see escaping gases. And if PAN- as it skims south of Scorpius in STARRS ejects a decent amount early July. In the month’s final 10 of dust, you might see a stubby This first-time visitor from the Oort Cloud should glow around 8th days, it makes its way through tail pointing to the southeast. magnitude in late July as it swings northward through Centaurus.

42 ASTRONOMY • JULY 2016 Luna plays hide-and-seek with Aldebaran LOCATINGASTEROIDS Iris claws its way through the Scorpion

Luck plays into our hands this brightness nearby, particularly month because asteroid 7 Iris in July’s last 10 days. On the lies just about midway between month’s final night, the asteroid Mars and Saturn. Before you approaches within 5' of magni- track down Iris, however, take tude 5.0 Lambda (λ) Librae. a moment to enjoy the easy If you’re a stickler for proof, double star Beta (β) Scorpii. Iris itself provides confirmation Even the smallest scope at low by moving slowly relative to the power will split the pretty blue- background stars from night to white components, which shine night. Make a sketch of the field at magnitudes 2.6 and 4.9 with of view about a Moon-diameter On the morning of July 29, a waning crescent Moon passes in front of 1st- a separation of 14". Iris lies 2° to across, placing a half-dozen dots magnitude Aldebaran. In this view from September 5, 2015, the same star reappears from behind the Last Quarter Moon’s dark limb. PHILIPPE MOUSSETTE 3° west-southwest of the star, a as best as you can. Remember pale white dot in comparison. to note which edge of your To track down the 10th- sketch is north by nudging the glows dimly (12th magnitude) the month 29' (about a Full magnitude asteroid, use the scope up toward Polaris and and stays close to the bright Moon’s diameter) southeast brighter stars to create a memo- seeing where new stars appear rings. It scoots around Saturn of Lambda and tracks slowly rable pattern in your mind and in the field. Then come back a in 33 hours, so once you’ve southwest. It passes 31' due then zero in on the spot where night or two later and see which spotted it, you can see it move south of the star July 24/25. the map below shows Iris to be. of the dots has shifted position noticeably in a few hours. A telescope shows Neptune’s There’s not much of similar — that will be Iris. Search for Enceladus near 2.3"-diameter disk and dis- greatest elongation. A good tinct blue-gray color. Looping through the Scorpion’s pincers opportunity comes the evening On the night of July 22/23, N of July 11 when it lies 35" west the waning gibbous Moon of Saturn and appears in a passes in front of (occults) ` tight triangle with Tethys and Neptune for those in most of 31 26 Dione. Coincidentally, this is eastern North America. The SCORPIUS h 21 the same night Iapetus passes faint planet will be hard to see Path of Iris t1 16 north of the ringed world. 2 11 when it disappears behind our t Last July, our view of Pluto satellite’s bright limb, but E 6 changed forever. The nimble, much easier when it reappears July 1 piano-sized New Horizons next to the dark limb. For loca- spacecraft sped past the distant tions south and east of north- world then and has spent the ern New Mexico, the Moon year since returning stunning also occults Lambda Aquarii. images and scientific data. On Exact times depend on your 0.5° July 7, Pluto reaches its first location. For specifics, go to b opposition since this historic www.lunar-occultations.com. A number of bright stars in northern Scorpius make it relatively easy to flyby. The dwarf planet won’t Uranus rises about 90 min- track down the 10th-magnitude asteroid Iris during July. be easy to spot (after all, it utes after Neptune, so by July’s glows at magnitude 14.1), but final week, it pokes above the its proximity to 3rd-magnitude horizon before midnight and brightest and northernmost of crescent Moon occults Aldeb- Pi (π) Sagittarii makes this a completes our tally of eight this quartet. The planet doesn’t aran. With the Moon just realistic challenge. For com- evening worlds. Uranus resides move much relative to the 23 percent lit and the star plete instructions and detailed among the background stars background stars during July, shining at 1st magnitude, even finder charts, see “The quest of Pisces the Fish, southeast of remaining some 2.7° north of Aldebaran’s disappearance for distant Pluto” on p. 64. the Great Square of Pegasus. Mu. To confirm a sighting, behind Luna’s bright limb Neptune rises shortly To find the planet through point your telescope at what should be easy to view. Obser- before midnight July 1 and two binoculars, first center magni- you think is Uranus. Only the vers south of a line running hours earlier by month’s close. tude 4.8 Mu (μ) Piscium in planet will show a distinctive from southern New Mexico It has a convenient guide star the field of view. Some 2° to 3° blue-green disk spanning 3.5". to northern Maine should see in 4th-magnitude Lambda (λ) north of Mu lies a group of The last major event this the event while those to the Aquarii. Once you locate this four 6th-magnitude objects. month occurs the morning north will see the Moon and star with binoculars, magni- Magnitude 5.8 Uranus is the of July 29 when the waning star just miss. tude 7.8 Neptune will be in view as well. The planet begins GET DAILY UPDATES ON YOUR NIGHT SKY AT www.Astronomy.com/skythisweek.

WWW.ASTRONOMY.COM 43 Behind the scenes at

Kennedy is home to Atlantis, which flew the last space shuttle mission July 8–21, 2011.

44 ASTRONOMY • JULY 2016 Space history

The home of American space flight is bursting with memories — and ready to host the launches of today and tomorrow.

Text and images by David J. Eicher The scenes are emblazoned in our tours of the magnificently outfitted minds: Apollo 11 lifts off the launch Visitor Complex, which boasts an pad, carrying astronauts on their array of magnificent space treasures. way to the Moon; John Glenn blasts Toff on his way to becoming the first Visiting KSC American in Earth orbit; or, tragi- I was privileged to go to Florida for a 1. Astronauts cally, the space shuttle Challenger behind-the-scenes tour of Kennedy used this Lunar Module Simulator shockingly explodes only 73 seconds last December. I hadn’t been to the for training dur- after leaving the pad. KSC complex since I was on my ing the Apollo So much American space pro- Florida honeymoon, some 26 years era. Formerly displayed simply gram history is intertwined with earlier, and I was astonished at the with a cockpit sec- one place: Kennedy Space Center differences from what I remembered. tion, the exhibit (KSC). And with the conclusion of KSC stands on a swampy plot on now includes the the Space Shuttle Program, many Merritt Island, some 45 miles (72 engineering sec- tion. Astronauts might believe NASA’s human space- kilometers) east of Orlando, along a stood at the flight efforts are on hiatus. Private promontory called Cape Canaveral. controls in the space companies now dominate the The area has hosted humans cockpit. news, sending cargo into orbit and for at least 12,000 years; only in 2. Completed in preparing for crewed future trips. 1949 did the U.S. Department of 1966, the Vehicle We hear a lot about European mis- Defense establish a Assembly Building sions, about Russian space activities missile-launching is the world’s larg- est single-story and the developing Chinese pro- base on the cape that building. Built to gram. We also know that India and would evolve into allow vertical con- Japan are active. America’s platform struction of the But the wonderful folks at KSC for the space race. Saturn V rocket, the structure want you to know that American KSC now sprawls has since housed space exploration is alive and well. over 144,000 acres construction and And they have a strong way of and contains more maintenance efforts for the reinforcing the notion with their than 700 structures. space shuttles and other vehicles.

3. The “Forever Remembered” exhibit, which opened in 2015, contains tributes to and personal items of astronauts who lost their lives during a mission. NASA recov- ered this haunting side panel following the 1986 space shuttle Challenger explosion. 4. One of the two crawler-transporters 1 at Kennedy Space Center stands waiting for its next job; when in use, it transports rockets from the Vehicle Assembly Building to one of the launch pads at a snail’s pace of 1 mph (1.6 km/h). The famous crawler- transporters are now 50 years old.

2 3 4 One of three surviving Saturn V rockets lies on its side within Kennedy Space Center was established as a missile launch site in 1949. the mammoth Apollo/Saturn V Center. The rocket Visitors arrive at a huge park- launch astronauts are present to The launch complex spans nearly the ing lot whose design seems influ- view as well, including the More impressive yet is the driving entire length of enced by Disney World, just a short Mercury-Redstone, Mercury-Atlas, tour one can take to see facilities the building and drive to the west. The KSC Visitor and Titan II. spread over the launch complex. stretches 363 feet (111 meters), with Complex sprang up in the 1960s but A Saturn IB rocket, designated Passing by numerous 1960s-era the various stages was relatively primitive for years, for use as a Skylab Rescue Mission buildings from the center’s most and sections re-establishing itself in 1995 with vehicle, is also present, gently expansive days, the bus carries slightly separated for maximum an outside partnership that does not placed on its side. Nearby, visitors visitors past the mammoth Vehicle viewing ability. use tax dollars. The complex today can traipse across the same Launch Assembly Building (VAB), the hosts 700 employees and more than Pad 39A gangway that Apollo astro- largest single-story building in the 1.5 million visitors annually. nauts strode across when they world. This giant structure stands I first walked through KSC’s entered their spacecraft on the way 526 feet tall (160 meters) and was Rocket Garden, a collection of to the Moon, as well as into a completed in 1966 to have room nearly all the basic launch vehicles “white room” astronauts passed for the Apollo program’s tower- employed by the United States. through to access the Apollo cap- ing Saturn V rockets. Positioned Here are examples of simple sules. Who, whether child or adult, in Launch Complex 39, the VAB satellite-launching rockets such as wouldn’t be impressed by walking hosted repairs of Apollo-era rockets the Juno I, Juno II, Thor-Delta, and along the same steel-frame gangway and later the space shuttles until the Atlas-Agena. And rockets used to used by the crew of Apollo 11? program ceased in 2011.

WWW.ASTRONOMY.COM 47 2

1

1. The Apollo 14 Command Module, on display at Kennedy, was From the use today. They move from this pad. The facility is now nicknamed Kitty Hawk and housed VAB, visitors trek past the historic along a “crawlway” at the snail’s under lease to the private space Stuart Roosa while viewing stands — the location in pace of 1 mph (1.6km/h). The two flight company SpaceX and hosts fellow astronauts many Hollywood movies of awed crawlers are nicknamed “Hanz” and launches of its Falcon 9 and, in the Alan Shepard and Edgar Mitchell spectators watching rockets head “Franz.” future, Falcon Heavy rockets. explored the lunar skyward — and the Launch Control East and slightly north of the Northwest along the coast lies surface. Launched Center, the heart of vehicle opera- VAB, along the coast, visitors see Launch Pad 39B, another historic on January 31, tions at Launch Complex 39 from perhaps the tour’s most meaningful structure. Here, amid the control 1971, the mission completed nine the Apollo era to the present. Next, sites. First they encounter Launch towers, liquid nitrogen, blast deflec- days later. guests pass one of the famous Pad 39A, home to many of the most tors, and steel-and-concrete pad crawler-transporters. These giant famous launches in the history of itself, are memories of the Apollo 10 2. The world’s tracked vehicles, each weighing space flight, from the first success- launch as well as many shuttle most expensive car, this lunar 6 million pounds (2.7 million kilo- ful Apollo launch in 1967 through flights, including the ill-fated rover test unit was grams), inched the Saturn V rockets the final flight of the space shuttle Challenger mission in 1986 that built for Apollo and space shuttles from the VAB to Atlantis in 2011. All but two of the ended shortly after takeoff. Pad 39B program training. The original fleet the launch sites. And they’re still in manned Apollo missions launched has been retooled in recent years to of four operational accommodate the planned Orion vehicles, termed launch vehicle that could send Lunar Roving humans to Mars by the 2030s. Vehicles, were battery-powered NASA also has built a “launch pad cars used for the in a box,” called the Deployable Apollo 15, 16, and Launch System, that will accommo- 17 missions, and cost $38 million date small-class launches at 39B. combined. Space flight treasures In addition to the bus tour, which takes about two hours, visitors to KSC have plenty to explore. The Visitor Complex is really like an amusement park built around hun- dreds of artifacts and memorabilia. It boasts a variety of IMAX and other films, as well as hands-on dis- plays that will delight children and fascinate adults. The spirit of Disney This detailed mock-up allows visitors to relive an Apollo-era launch in a meticulously has definitely leaked to the coast to detailed room that includes an audiovisual performance. make this facility as enticing and

48 ASTRONOMY • JULY 2016 3. The KSC Visitor Center displays, among many other items, the flight suit Capt. James Lovell wore during the perilous Apollo 13 mission (right), which concluded safely on April 17, 1970. Near Lovell’s space-worn suit stands Alan Shepard’s suit that he wore to walk the lunar surface during Apollo 14 in February 1971.

4. Kennedy’s historic Launch Pad 39A hosted numerous famous launches, from Apollo 4 in November 1967 to the final shuttle voyage of Atlantis in July 2011. Except for Apollo 10, every manned Apollo mission launched from this pad. It also sent off the first 24 shuttle flights and those launching in the last four years of the program. The pad is now under lease to the private company SpaceX. 3

immersive as any fan of space explo- complex consists of another huge ration could imagine. building filled with hundreds of Museums highlight the Apollo artifacts. The centerpiece of this and shuttle eras and nearly over- building is of course Atlantis itself, whelm visitors who want to see veteran of 33 missions to low-Earth everything they can. The Apollo/ orbit that cumulatively circled the 4 Saturn V Center contains as its cen- planet 4,848 times for a total of terpiece one of only three Saturn V nearly 126 million miles (203 mil- rockets still extant, and the incredible lion km). It is incredibly impressive minimum of one day — two would size of this behemoth will impress to study a complete space shuttle be better for students of space — anyone. KSC has laid the rocket out from all sides and angles, as the will delight and deepen your under- on its side to stretch 363 feet (111m) multistory building makes possible. standing of America’s space history. across the floor, and labeled and Among the numerous displays in Many of the most convenient hotels slightly separated its components so this building are the most poignant in the area stand a few miles away that visitors can take in each stage. A mind-searing gallery of exhib- its surrounds the Saturn V, includ- Space shuttle Atlantis orbited Earth 4,848 times during its 33 ing the Apollo 14 Command Module (flown by Stuart Roosa), a Lunar Rover test car (an example of the missions before coming home to rest at Kennedy Space Center. world’s most expensive car, at $38 million for four), a Lunar touches one sees at KSC: personal from KSC along the shoreline of Module Simulator (used for test effects of the fallen astronauts of Cocoa Beach, the former playground landings on a simulated lunar sur- Challenger and Columbia. This of astronauts; visitors can stay where face), and an array of flight-carried exhibit also contains the most chill- many of their astronaut heroes lived, equipment, Moon rocks, and astro- ing pieces: a portion of the damaged swam, raced their cars, and dreamed naut uniforms and personal effects left side panel from Challenger, and of worlds away from ours. that would blow anyone’s mind. The the steel cockpit frame recovered NASA wants you to know that famous van that for years carried from the Columbia accident. The a memorable time awaits at the astronauts to the launch pad is also collection, titled “Forever Kennedy Space Center. I can promise there, along with dozens and dozens Remembered” and just opened in you that a visit will not disappoint. of other artifacts. After several 2015, will leave visitors with a deep hours, any space enthusiast comes and personal sense of reflection. Astronomy Editor David J. Eicher away simply punch drunk from A great deal more than what I’ve has been a fan of space exploration looking at such a treasure trove! described also lies in wait at the KSC since before watching the Apollo 11 Continuing the tour, the enor- Visitor Center Complex. A visit to Moon landing in his living room mous space shuttle Atlantis display the eastern coast of Florida and a as an awestruck 8-year-old.

WWW.ASTRONOMY.COM 49 DEEP-SKY OBSERVING Target our galaxy’s DARK NEBULAE

Pull up a chair, and spend some time away from the light. by Richard P. Wilds

ecause astronomy is a science, Emerson Barnard, Bart J. Bok, Beverly T. opportunity to study dark nebulae. At the we must test it on a regular Lynds, Aage Sandqvist, Kaj Peter Lindroos, time, few high-quality descriptions of the basis. Through such means, we and Claes Bernes, to name only a few. Milky Way existed. And Gaposchkin, a understand the universe. One Studying dark nebulae is challenging for trained astronomer and a capable artist, class of objects that illustrates most observers. We know what they are but had the advantage of a superb site. Bthis process is dark nebulae. During a two- still fail to understand the details when we While Gaposchkin was in the dome, he century quest, we have gone from thinking view them with our naked eyes from a decided to spend his free time looking that these areas are long tunnels meant to truly dark site. through the opening and drawing the look through to the stars, to knowing that entire Milky Way in detail in pen and they are clouds of dust and cold gas block- A solo survey India ink on a sheet of paper about 5 feet ing our view of things beyond. The astronomers I mentioned earlier con- (1.5 meters) long. From his southerly loca- History is replete with the names of sci- centrated mainly on the northern part of tion, the central bulge of our galaxy passed entists who have helped us understand the sky. To discuss the southern Milky directly overhead, showing galactic struc- these objects: William Herschel, Edward Way, we should look to the excellent work ture that most northern observers can of Russian-born astrophysicist Sergei never see clearly. The only drawback was Richard P. Wilds is a member of the American Illarionovich Gaposchkin of Harvard that it did not allow a view of the Milky Astronomical Society, Division for Planetary College Observatory. Way from Perseus to Cepheus. This Sciences and Historical Astronomy Division. His He traveled several times during the explains his sketch’s lack of detail there — latest publication is Bright and Dark Nebulae: 1950s and 1960s to Mount Stromlo he had to make his observations for this A Pocket Field Guide (Springer, 2016). Observatory in Australia, where he had an region from Harvard, which is not known

50 ASTRONOMY • JULY 2016 Astronomer Sergei Gaposchkin created a visual representation of the whole Milky Way from Mount Stromlo Observatory in 1956 and 1957. This section shows the most significant part of the 5-foot-wide work. Note that he includes a ringed symbol for Saturn (in Ophiuchus), triangles for Omega Centauri (in Centaurus) and 47 Tucanae (to the left of “Small Magellanic Cloud”), and an X near “S.P,” which shows the position of the South Celestial Pole. RICHARD P. WILDS as a great observing site. Gaposchkin followed the advice of J. Robert Oppenheimer, first director of the Los Alamos National Laboratory and one of the creators of the first plutonium bomb, to simply practice staring at the Milky Way if you wanted to gain some understanding of its structure. A sky full of darkness In his written observations, Gaposchkin stated that the most obvious detail is a This image of NGC 3628 in Leo shows its famous dark region stretching from one end of the galaxy to dark lane that cuts the galaxy almost the other. This feature resembles our Milky Way’s central dust lane. ADAM BLOCK/NOAO/AURO/NSF

WWW.ASTRONOMY.COM 51 directly into two equal sections, northern and southern. The brightest section for the northern part lies in the constellations Carina and Vela, while the southern sec- tion is brightest in Sagittarius. He found that the dark lane close to the bright region in Carina and Vela takes the form of a giant contorted S extending from Avior (Epsilon [ε] Carinae) to Alsuhail (Lambda [λ] Velorum). He saw noticeable extensions of bright and dark lanes out of the northern half of this part of the Milky Way. Gaposchkin also saw a luminous con- nection between the Milky Way and the Magellanic Clouds to the south, which would indicate a recent galactic encounter between all concerned. The S region con- nects to the Coal Tin dark nebula in Carina, which abuts the famous Coalsack in the tiny constellation Crux. The Coalsack then connects to the huge, dark region northeast of Rigil Kentaurus (Alpha [α] Centauri), which he named the Ditch. It cuts through Norma and Lupus all the way to Antares (Alpha Scorpii). Gaposchkin compared the Ditch, seen so well from Australia, to the Sweep, which is easy to spot from the Northern Hemisphere. The Ditch is broader and fills the northern area of the Milky Way in Ophiuchus. It was this region of the Sweep that caught the imaginations of Herschel and Barnard as they spent many years trying to understand what they were seeing. It seems strange that these intrepid observers did not have the conceptual awareness of the galaxy as the spiral structure we know today. Gaposchkin then described the view of the southern half of the bulge, stating that six dense “lakes” of nebulosity in a row, from Centaurus to Ophiuchus, shroud it significantly. There are numerous sinuous angles to the Milky Way’s plane led to the North of the border interconnections between these lakes and idea that something is happening — or has From dark sites throughout the Northern the northern areas of the Ditch and the happened — in this part of the galaxy on a Hemisphere, we can fill in what the Sweep. Gaposchkin mentioned that the truly large scale. Here, then, is significant great Harvard astronomer couldn’t see. brightest part of the bulge lies just below evidence for the disruptive galactic The nearby cosmic layout includes the the largest lake and close to Theta (θ) encounters with the Magellanic Clouds Ophiuchus Dark Cloud on one side of Ophiuchi. He also noticed that the north- mentioned earlier. our solar system, while the Taurus Dark ern half is of much greater extent than the Gaposchkin goes into less detail about Cloud lies on the opposite side. If we start southern half, which indicates that our the rest of the Milky Way — the part that from the Ophiuchus Dark Cloud, we will solar system lies above the central plane of he would have seen from Harvard, which encounter the Aquila Great Rift. the Milky Way (or north of it, in our was hardly a dark site even in his day. He And don’t miss LDN 141, the naked-eye earthly coordinate system). states that Aquila, Cygnus, Cassiopeia, and dark cloud in Hercules. It lies opposite the To Gaposchkin, it was clear that the Perseus with their dark lanes were very bright star Altair (Alpha Aquilae). The central bulge is the center of the Milky similar to those of Puppis, Vela, and abbreviation clues us in to the fact that this Way, but when observing from Mount Carina. He calls the regions of Gemini and object was included in a catalog containing Stromlo, he noticed that the region of Auriga the “backyard” of the Milky Way, some 1,800 dark nebulae compiled by Carina is also significantly wide and meaning that this was the area with the Lynds and published in 1962. This complex bright. The apparent disturbance from the thinnest amount of material between us also includes the LDN 653, LDN 659, variations of bright and dark lanes at odd and the galaxy’s outer edge. LDN 660, LDN 665, and LDN 666.

52 ASTRONOMY • JULY 2016 The region of Lynds Dark Nebula 673 in the constellation Aquila the Eagle is a complex of clouds of ultra-cold hydrogen and dust, which block the light from the stars behind them. ADAM BLOCK/MOUNT LEMMON SKYCENTER/UNIVERSITY OF ARIZONA

The spectacular color in the Rho Ophiuchi region makes it one of the most imaged areas of the sky. Don’t look at the varied hues, however, but at the dark lanes that obscure the more distant features. TONY HALLAS

Other large bright and dark nebulae inhabit Auriga and Perseus. But while you’re examining this region, you’ll want to search for the little-known extensions of dark neb- ulae on the northern side of the Milky Way that stretch from Camelopardalis, Cassiopeia, and Cepheus into Cygnus. In fact, dark nebulae extend all the way on this northern side to the famous North Star, Polaris (Alpha Ursae Minoris).

WWW.ASTRONOMY.COM 53 One of the most famous entries in American astronomer Edward Emerson Barnard’s catalog of dark nebulae is the Snake Nebula (Barnard 72). It lies near the Milky Way’s center in the constellation Ophiuchus the Serpent-bearer. GEOFF SMITH

This spectacular mosaic took the imager nearly two years to capture. It combines an amazing 3,150 photos, captures stars as faint as magnitude 14, and measures 36,000 by 18,000 pixels. Astronomy reproduced a much larger version in the May 2010 issue. On it, you can see vast swaths of dark nebulosity intermingled with billions of stars. AXEL MELLINGER

Head south again when he studied Carina, is that all of these the south through Perseus. It then heads into The images accompanying this story will dark lanes come out of the northern side of Taurus, where we find the dark cloud on the help you see the dark nebulae extending the Milky Way. This agrees with his obser- opposite side of the Milky Way from the one from the inky lanes north of Deneb (Alpha vation that our solar system lies above the in Ophiuchus. You can view dark objects in Cygni), northward in an arc along the galactic plane. Decades of modern astro- Auriga as you observe the ones in Perseus western side of Cepheus through the region nomical research at observatories around and Taurus. Then continue south into of the Iris Nebula (NGC 7023). Head past the world also have shown this, but what Orion, which is decidedly an outlier exten- Polaris and then south into the regions of makes it fascinating is that you actually sion off the main plane of the Milky Way. Alrai (Gamma [γ] Cephei), Segin (Epsilon can see it with your own eyes. Our galaxy’s plane gets back on track in Cassiopeiae), and Gamma Camelopardalis. After dallying in Camelopardalis, our Monoceros and continues into Puppis and The thing to note, as Gaposchkin did dark dust lane takes a distinctly sharp dive to Vela. Here we return to where we started in

54 ASTRONOMY • JULY 2016 the southern sky. It is easy to note this ning, this elderly author must note that to comprehend the few photons it receives. location on Axel Mellinger’s image above young eyes certainly have some advantage. In the case of our topic, start by training because it’s clearly marked by the round, However, the author must also note the your eye to see easier targets such as the red plume of the Gum Nebula. equal importance of having a trained eye. Great Rift in Aquila, the Sweep in Of course, observations like these are I have known for decades that when I’m Ophiuchus, and the Pipe Nebula in not particularly easy, or else people would at the telescope looking through the eye- Ophiuchus. That last feature helps form part have discussed this topic more often and in piece, my left eye dominates. There is no of the more recently famous Dark Horse much greater detail long ago. Remember comparison between what I can see seen on so many photographs of the region. that to make such observations, the most through it compared with my right eye. I After that, get ready for the opportunities important prerequisite is to have an have spent an entire lifetime training my you’ll encounter at a dark site on a night extremely dark site. Beyond such a begin- left eye and its respective areas of my brain clear enough to present these fine details.

WWW.ASTRONOMY.COM 55 THINGS THAT GO BUMP

Earth has a long history of asteroid strikes; some intriguing scars remain. Explore Earth’s by Mike Reynolds

ixty-six million years ago, Earth a part in every school kid’s education — it The largest impact in Earth’s got a wake-up call. What appeared was hardly the only one. Major impact history occurred about 4.5 billion years ago when a to be a second Sun hung briefly events on our planet have not only shaped Mars-sized planetesimal, Theia, in the sky and then, suddenly, a Earth’s history, but they also altered the smashed into our forming S planet. The resulting ring of catastrophic impact splattered the course of life itself. Yucatán Peninsula near the present-day The solar system is littered with impact material accreted into the Moon. The moment of impact is shown town of Chicxulub. BAM! The conse- scars, from the rocky planets, including in this artwork. NASA/JPL-CALTECH quences for everything in the region were Earth, to asteroids, comets, and centaurs terrible, and a yearslong nuclear winter — asteroids orbiting between Jupiter and kicked dust into the atmosphere, ignited Neptune. Many early neighbors of the pres- they saw the bluish light, global fires, and played havoc with life ent bodies were responsible for those early observers reported what they on Earth. Among the casualties were the impacts. Plan etary scientists estimate that described as a bright flash and dinosaurs, wiped from the evolutionary 90 percent of those impactors have been artillery-like sounds. record. cleared out of the solar system. But in the Russian scientist Leonid Kulik In the 1970s, Luis Alvarez and a team early days, the solar system was a cosmic spent part of his career investigating of collaborators found evidence for the battlefield. And impacts still do take place the Tunguska event, including search- subsurface scar left from what came to be within our cosmic neighborhood. ing for any meteorites, which he never called the Cretaceous-Paleogene (K-Pg) found. Kulik also interviewed eyewitnesses extinction event. Although this is the most A bad afternoon in Siberia who provided stories of the impact. During famous impact event in Earth’s history — We only have to look back a little over his 1930 expedition, Kulik recorded a tale as it killed the dinosaurs and therefore gets 100 years, to 1908, for evidence of a major told by Siberian local S. Semenov: impact, called the Tunguska event. On “At breakfast time I was sitting by the June 30 of that year, an incredible explo- house at Vanavara Trading Post [40 miles sion occurred over the Stony Tunguska south of the explosion], facing north. I sud- River region of Siberia. The blast happened denly saw that directly to the north, over when an asteroid or comet produced an Onkoul’s Tunguska Road, the sky split in airburst and catastrophically blew up mid- two and fire appeared high and wide over air some 3 to 6 miles (6 to 10 kilometers) the forest. The split in the sky grew larger, in altitude. The incredible release of energy and the entire northern side was covered flattened nearly 800 square miles (2,000 with fire. At that moment I became so hot square kilometers) of forest. that I couldn’t bear it, as if my shirt was on When the first scientific expedition fire; from the northern side, where the fire finally reached the area nearly a decade was, came strong heat.” later (delays were caused by World War I, In 1908, a large object exploded in an airburst the Russian Revolution, and the Russian Splat! Let’s make a moon over the Stony Tunguska River region of Siberia, Civil War), trees were bent over like match- The Tunguska event was a catastrophic Russia, in what came to be known as the Tunguska sticks. Descriptions from inhabitants of the impact for anyone in that region on Earth. event. Energy from the blast flattened more than 800 square miles (2,000 square kilometers) of region noted a moving bluish light as (No humans are known to have been forest. LEONARD KULIK EXPEDITION, WIKIMEDIA COMMONS bright as the Sun. Some 10 minutes after killed, but certainly vast numbers of other

56 ASTRONOMY • JULY 2016 living beings were.) A far larger impact Earth so hard, it created a ring of material examined zinc isotopes found on Earth and happened much longer ago, in the early in Earth’s orbit that eventually accreted the Moon. Scientists found the Moon has days of the solar system. In fact, most plan- into the Moon. The so-called Giant Impact more heavy zinc isotopes, which would be etary scientists believe this impact formed Hypothesis started rolling as a concept in expected of a collision followed by evapora- the Moon some 4.5 billion years ago. 1975 in a paper by planetary scientists tion of lighter zinc isotopes from the newly The scenario goes that a Mars-sized William Hartmann and Donald Davis. formed satellite. Also, lunar rocks from the body, now named Theia, struck either a Hartmann and Davis found evidence for Apollo missions show ratios of oxygen iso- glancing or more or less head-on blow to such an impact both directly and indirectly. topes very similar to those on Earth. And Earth. This planetesimal smashed into Along with other groups of scientists, they the Moon’s small, iron-rich core agrees with

WWW.ASTRONOMY.COM 57 Meteor Crater in northern Arizona is the best- preserved impact crater on Earth, dating back some 50,000 years. TONY ROWELL

The Sudbury Basin, north of Toronto, contains impact scars 1.8 billion years old and betrays an ancient strike that left the region rich in rare metals. The impact stretches over the whole field; the area at upper right is Wanapitei Lake. The frame width is about 50 miles (80km). NASA

the 110-mile-diameter (180km) of Chicxulub. The Sudbury impact basin is 9.3 miles (15km) deep, although this has mostly been filled in during the 1.8 billion years since the impact. Scientists have found evidence at Sudbury that incudes shocked quartz and shatter cones — rare, geologically stressed rock that forms during a major impact. Debris flung out from the Sudbury Basin has been found as far as 500 miles (800km) away. And of course, unlike some solar system bodies, Earth’s weathering systems largely cover up evidence of impacts over relatively short timescales. the mechanics of such a collision. Not all scales. Far north of Toronto lies an area Just south of Interstate 40, between scientists are convinced the Moon formed of Ontario called the Sudbury Basin. Winslow and Flagstaff, Arizona, sits in this manner, but the concept is the lead- Containing one of Earth’s largest and old- Earth’s most perfectly preserved impact ing explanation for its existence. est impact craters, the region is famous for crater, Meteor Crater. Also called Barringer its rich metal mines, material presumably Crater, this impact scar makes a magnifi- More hits on Earth deposited by the impactor. cent exhibition of a relatively small iron Since those early days, Earth has never The Sudbury feature, sometimes called meteorite collision with Earth. The again had a collision like the Theia event, an astrobleme, stretches about 160 miles 150-foot-diameter (45 meters) chunk of but it has experienced strikes on smaller (260km) in diameter, making it larger than iron-nickel struck Earth about 50,000 years

58 ASTRONOMY • JULY 2016 A network of automatic meteor cameras captured a fireball over California on April 22, 2012. Because scientists had recorded images of the fall, they could track down the resulting meteorites, named for Sutter’s Mill, and find pieces like this An enormous, bright fireball whizzed over the sky of Chelyabinsk, Russia, on February 15, 2013, and one. (The cube measures 1 centimeter on a side.) exploded in an airburst. Nearly 1,500 people were injured by falling building fragments and glass PETER JENNISKENS/SETI INSTITUTE/NASA ARC shattered by the sound wave. ALEX ALISHEVSKIKH/WIKIMEDIA COMMONS ago — a recent time in the history of the enced an airburst and impact in what a project called Cameras for Allsky Meteor solar system! became one of the best-documented Earth- Surveillance. This network of cameras, led If you have not visited Meteor Crater, impact events. On February 15, 2013, a by Project Scientist Peter Jenniskens of the you really should. It stretches just under brilliant bolide brighter than the Sun SETI Institute, employs automated cam- 4,000 feet (1,200m) across and is some moved across the early morning sky, leav- eras in the United States and elsewhere to 570 feet (175m) deep. You could place the ing a wide train in its path. The estimated image meteors. The project has success- Washington Monument, at 555 feet 10,000-ton impactor exploded some fully pinpointed falls that have been ana- (170m), comfortably below the top of the 18 miles (30km) above Earth’s surface in lyzed, such as the 2012 Sutter’s Mill fall crater’s rim. an airburst. Thousands of chondrite mete- in California. When 19th-century explorers trekked orites scattered, and the sonic boom and Earth is not the only solar system the crater, they believed it to be the result of blast injured around 1,500 people, mostly body that has been whacked by an incom- an ancient volcano. Only in 1903 did min- due to broken glass and falling building ing visitor. In July 1994, the astronomy ing engineer Daniel Barringer suggest that fragments in the town of Chelyabinsk. In world held its breath as Comet Shoemaker- a celestial impact might have been respon- terms of energy, the explosion was on the Levy 9 plummeted into Jupiter’s cloudtops. sible. Despite Barringer’s careful research order of the 1908 Tunguska event, about This event provided the first direct obser- and his recovery of some iron meteorites, 20 to 30 times the force of the atomic bomb vations of impacts with a solar system no one believed this at first. Only in 1960, dropped over Hiroshima. object other than Earth. The comet, dis- when astrogeologist Gene Shoemaker stud- covered by Gene and Carolyn Shoemaker ied the crater, did he confirm Barringer’s Searching for space rocks and David Levy in March 1993, broke suspicions of 57 years earlier. Thousands of asteroids and about 100 apart into a string of 23 fragments during Chelyabinsk Oblast in Russia experi- comets are known to orbit relatively near an earlier pass near the gas giant. The larg- us in the inner solar system. These so- est of the fragments spanned 1.2 miles called near-Earth objects pose a threat to (2km); impact features were visible for humanity, of course. Even a small object months, appearing as dark blotches in the like the Chelyabinsk stony meteoroid cloudtops, and some were more prominent would cause devastating destruction and than Jupiter’s famed Great Red Spot. loss of life if it struck a major metropolitan Other jovian impacts occurred in 2009 city. And large impactors like Chicxulub and 2010. and Sudbury would cause a mass extinc- As we contemplate major events that tion that would end human civilization. can affect Earth and its inhabitants, such With a 6-mile-wide (10km) object, it’s not as climate change and pandemic diseases, the initial strike that does the most dam- we should also keep one eye to the sky. The age (though it certainly wouldn’t do you beauty of a meteor shower or a brilliant any good to be in the target area). But what fireball might just be an omen of the next Asteroid Ida and its tiny moon Dactyl typify follows it — the nuclear winter effects, the Chicxulub or Sudbury. space rocks in the main belt, between Mars and dust, smoke, and debris elevated into the Jupiter. Ida spans about 20 miles (32km). Closer atmosphere, the worldwide fires, and so Mike Reynolds is a contributing editor of to Earth, small space rocks sometimes intersect Earth’s orbit, causing impacts on our home forth — pose the biggest danger. Astronomy and has been enamored with space planet. NASA/JPL NASA’s Ames Research Center operates rocks for a very long time.

WWW.ASTRONOMY.COM 59 DIY KEPLER

Seek exoplanets from your back Learn how amateur astronomers can help professionals study worlds outside our solar system. by Dennis Conti Transits, when he question, “Are we alone?” has endured since humans planets cross their stars from our first looked up at the night sky. Indeed, astronomers now point of view, are believebeli that most stars have one or more planets orbiting them. the most common way for amateurs ConsideringCon that the stars we see at night with our naked eyes to study exoplanet are all members of just our home galaxy, and given the billions of systems. ESO/L. CALÇADA otherothe galaxies that we now know exist, the number of exoplanets mustmus be truly stunning! AmateurA astronomers often apply their skills toward producing the “stellar” pictures that grace the pages of this and other publications. TBut is there any role that amateur observers can play in contributing to our knowledge of exoplanets? The answer is a resounding yes!

Finding exoplanets than one that crosses the star’s full diameter, So far, astronomers have confirmed some even if their orbital periods are the same. 1,900 exoplanets, with more than 3,700 While other techniques for detecting others as candidates. The best-known astro- exoplanets exist, the transit method is the nomical instrument for finding exoplanets one most suited for amateur astronomers’ has been the Kepler spacecraft, which uses skills and equipment abilities. an indirect way to detect distant worlds called the transit method. Just as a flea Amateur detections passing in front of a spotlight would cause a Backyard astronomers have been detect- tiny dip in light, so too an exoplanet passing ing exoplanets successfully for more than in front of its host star will cause a similar a decade. In fact, in 2004, collaboration drop that Kepler detects. between professional and amateur observers Astronomers combine individual mea- — the XO Project, led by Peter McCullough surements of the star’s light throughout the from the Space Telescope Science Institute — planet’s transit to create a light curve. They resulted in several new exoplanet discoveries. then use the duration and depth of the light Amateurs also are regular collaborators with curve (and how often it recurs) to calculate the Kilodegree Extremely Little Telescope important characteristics of the exoplanet (KELT) exoplanet search, organized by such as the period of its orbit, the size of the Vanderbilt and Ohio State universities. planet, and, if the orbit’s period is known, Bruce Gary’s 2007 publication of the inclination, or tilt, of the exoplanet’s Exoplanet Observing for Amateurs was the orbit with respect to our line of sight. A first attempt to formalize the best practices planet whose transit just skims the top of its of exoplanet detection. Today, most amateur star, for instance, will have a shorter transit exoplanet hunters post their results online yard The author (fourth from the left) stands with members of the Amateur Astronomers, Inc. club of Cranford, New Jersey, on the night of their first exoplanet observation. They use the club’s telescope at the William Miller Sperry Observatory on the campus of Union County College. DENNIS CONTI

WWW.ASTRONOMY.COM 61 The basic transit light curve Transit of WASP-12b LEFT RIGHT 0.96

0.92

Predicted Predicted

Normalized ux ingress egress 0.88

0h1h 2h 3h 4h UT Time (January 6, 2016)

By fitting a model to a light curve, an observer can learn valuable information about the exoplanet itself and pass that information to research scientists. DENNIS CONTI 1 2 3 How-to

Brightness Amateur astronomers use a technique Time called differential photometry to track the brightness of exoplanet host stars. As the As a planet crosses in front of its star, it blocks some of the light. By plotting the amount of light name implies, this technique measures the against time, astronomers create a light curve. ASTRONOMY: ROEN KELLY relative change in brightness between the host star and one or more nearby compari- son stars. For ground-based observers, this as part of the means that atmospheric effects, such as thin Exoplanet Transit passing clouds, should have a similar effect Database (ETD) on both the host and comparison stars. project, which However, during the exoplanet’s transit, the is sponsored host star’s brightness will change, but not by the Czech the brightness of the comparison stars. Astronomical During image acquisition, the observer Society (http:// measures just a few key stars, which typi- var2.astro.cz/ETD). cally range in brightness from 8th to 13th Astronomers can use the magnitude. The exoplanet observer’s objec- same site to determine tive is to accurately capture the brightness upcoming exoplanet transits at of the host star prior to, during, and after their locations. Exoplanet results will the predicted time of the exoplanet’s tran- also soon be able to be posted to the sit. It is important that the observer’s CCD American Association of Variable Star detector never reaches saturation (its maxi- Observer (AAVSO) International Database. mum detection level), or else changes in the With advances in CCD imaging and host star’s brightness could go unrecorded. the development of supporting software, Although a star’s photons spread out amateurs can now produce exoplanet over multiple pixels of a CCD’s detector, the observations of sufficient quality that pro- majority of them — a star’s so-called full- fessionals can use them to supplement width at half-maximum (FWHM) — fall their own studies. For example, a science on just a small number. Because each pixel team led by noted exoplanet researcher can capture only a small amount of light, it Drake Deming from the University of is important to spread the FWHM over Maryland, College Park, is studying the several of them. So, if the star’s FWHM atmospheres of 15 exoplanets in near- falls on only one or two pixels, the observer infrared wavelengths with the Hubble may actually have to defocus the star so Space Telescope. In order to provide that the FWHM spans a larger number refined timing predictions for the tran- — ideally, three to five. This approach is, of The author’s sits, a worldwide network of amateurs is course, contrary to the sharp pinpoint stars home setup conducting ground-based observations that deep-sky imagers strive for. includes an 11-inch of those same targets in visible bands. After all the raw images are calibrated, Schmidt- Some of the amateurs participating in exoplanet observers can use off-the-shelf Cassegrain this collaboration include members of the software to conduct the differential pho- telescope. AAVSO and the KELT follow-up team. tometry. Two of the more popular packages DENNIS CONTI N

c b

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e XO PROJECTXO d The XO Project, a collaboration between amateur and professional astronomers, discovered five exoplanets using only twin 200mm lenses. DO IT YOURSELF

20 AU A Practical Guide to Exoplanet Observing is available at 0.5" www.astrodennis.com for readers who are interested in exoplanet observing, as well as for veteran observers who want to use Using the largest telescopes on Earth and advanced imaging systems like AstroImageJ as their exoplanet-modeling program. The AAVSO adaptive optics, professional astronomers can directly image exoplanets, also has its Exoplanet Observing Manual, which describes how like this multiple-planet system around HR 8799. For amateur astronomers, AAVSO resources can be of use to exoplanet observers. transits will have to suffice for now. NRC-HIA/CHRISTIAN MAROIS/W.M. KECK OBSERVATORY are AIP4WIN, which comes with the parameters such as the planet’s size and the brightness, exoplanet observers must employ Handbook of Astronomical Image inclination of its orbit. some form of autoguiding and ensure that Processing, by Richard Berry and James their telescope mount is accurately polar Burnell, and AstroImageJ (AIJ), freeware The value of amateur data aligned and they have minimized or cor- maintained by Karen Collins of the KELT The final data from amateur transit model- rected any periodic error. team. AIJ is an all-in-one package that ing is valuable to professional astronomers As stated earlier, a deep-sky imager includes everything from image calibration in at least two ways: First, when profes- wants pinpoint stars, but an exoplanet to exoplanet model fitting. sional astronomers are conducting their observer may desire defocused ones. A deep- Both software choices will produce sev- own studies of exoplanets, they might be sky imager needs multiple filters to obtain a eral data items for each image: a timestamp, missing information such as the midpoint great-looking picture; an exoplanet observer the change in brightness of the host star rel- of the transit or the ratio of the exoplanet’s typically uses only a single filter for an ative to one or more comparison stars, the orbit to the radius of the host star — key observation. A deep-sky imager may spend change in brightness (if any) of each com- measures that amateur astronomers can hours processing images while an exoplanet parison star relative to the other comparison provide. This, in fact, is the case for some observer can typically conduct model fitting stars, and error estimates for these measure- of the exoplanets in the aforementioned in a shorter time period. ments. The observer then fits the data to a Hubble study. Joey Rodriguez of the KELT Will amateur astronomers ever be able model of what an exoplanet transit should team combines multiple amateur observa- to directly image worlds outside our solar look like. Two popular sources for perform- tions into one “global model fit” for the system? This is hard to imagine, though ing such a fit are AIJ and the ETD website. science team’s use. attempts are underway to try. However, The difference between observed data Second, the professional community the precision with which they can conduct and what a model predicts is a measure may rely on amateur observations to con- transit observations will continue to provide of how “good” a particular fit is. The goal firm the existence of an exoplanet candi- professional astronomers with valuable data is to minimize this difference; users can date as well as develop initial orbital to supplement their studies. Beyond con- do so by changing certain inputs to the information about possible transits. tributing to real science, the satisfaction an model. For example, they could eliminate Amateur astronomers participating in the amateur astronomer can take in witnessing comparison stars that are not of the same KELT project are performing this role. a planet transiting across a star light-years magnitude or stellar type as the host star, away is its own reward. or they could make changes to the number Exoplanet observing vs. imaging of pixels used in the differential photom- Exoplanet observing is in some cases more Dennis Conti, chairman of AAVSO’s Exoplanet etry process to determine the star’s inher- challenging than deep-sky imaging, and in Section, is leading a worldwide collaboration ent brightness. The result is a light curve other cases more forgiving. Because even a of amateur astronomers working with a Hubble that delivers the beginning and end times sub-pixel shift of a star on the CCD detec- science team, and is a member of the KELT of the transit, its depth, and a set of key tor might result in an apparent change in exoplanet follow-up team.

WWW.ASTRONOMY.COM 63 PLANET HUNT The quest Plutofor dıstant This newly revealed world at the solar system’s edge makes a tempting target Although New Horizons through amateur telescopes as it reaches showed us what Pluto looks like close- peak visibility early this summer. up, it still appears as a mere speck through amateur telescopes. NASA/JHUAPL/SWRI by Richard Talcott

hat a difference a year planet glows dimly at magnitude 14.1 and shines brightly near Pluto’s position, as it makes. In early July 2015, appears as a mere point of light through does around the Full Moons on June 20 Pluto remained a world any telescope, simply knowing that this and July 19. Wshrouded in mystery. Sure, world is more than an inert frozen ball the New Horizons spacecraft brings a fresh perspective. Tea for one had just returned images from only 10 mil- To meet the Pluto challenge, observers The star charts on the opposite page will lion miles (16 million kilometers) away, but need the right equipment, a dark site, and help you to track down Pluto. (Use a dim the mottled terrain they showed was more a detailed star chart. The planet reaches red flashlight to illuminate the maps.) Start tantalizing than revealing. opposition July 7, when it lies opposite the with the naked-eye view at top left and That all changed within a few weeks. Sun in our sky and remains visible all night. locate the triangle of bright stars — Pi (π), On July 14, the robotic probe swept within But the planet’s visibility changes so slowly Omicron (ο), and Xi2 (ξ2) Sagittarii — lurk- 7,700 miles (12,400km) of the dwarf plan- that it remains just as easy to spot for a few ing in northeastern Sagittarius. The group et’s surface. The indistinct dark and bright weeks on either side of this peak date. lies due north of the handle in this constel- markings seen from afar resolved into An 8-inch telescope will gather enough lation’s conspicuous Teapot asterism. breathtaking landscapes. New Horizons light to reveal Pluto, though a larger instru- Use magnitude 2.9 Pi as an anchor to discovered broad canyons, flowing ice, cra- ment will make the task easier. Once you’ve star-hop to Pluto with the help of the tele- ters large and small, towering mountains of got your gear lined up, locate a top-notch scopic view at bottom. (Conveniently, the frozen water, and a Texas-sized glacier no observing site. Not only should it offer a dwarf planet passes just 2.7' south of Pi on more than 10 million years old. The space- dark sky, but it also should deliver good June 26.) We plotted Pluto’s positions dur- craft revealed a geologically active world seeing (atmospheric steadiness). You’ll get ing the evening hours for North America. that may be a tad less mysterious than sharper views if you aim your scope over a The chart shows background stars to mag- before, but still has scientists scrambling grassy field than you will by observing from nitude 14.5, so you should be able to discern to understand its surprising complexity. an area that absorbs the Sun’s heat in day- Pluto. If you can’t tell which point of light it A year has now passed since closest time and reradiates it at night. Plan to reach is, sketch five or six stars near the correct approach, and amateur astronomers have your site by sunset and set up your equip- position and return to the same field a a great opportunity to view Pluto with new ment right away so it can start cooling to night or two later. The “star” that moved is eyes this summer. Although the distant the air temperature. In the hour or so this Pluto. Don’t expect to see the magnificent takes, your eyes will adapt to the darkness. landscapes that New Horizons revealed. Richard Talcott is an Astronomy senior Just as city lights will drown out Pluto’s Instead, simply thrill at your ability to see editor and author of Teach Yourself Visually faint glow, so too will dazzling moonlight. this faint and no longer quite-so-enigmatic Astronomy (Wiley Publishing, 2008). Try to avoid observing when our satellite dot from across the solar system.

64 ASTRONOMY • JULY 2016 This naked-eye view shows the stars of Sagittarius to magnitude 6.2. Pluto This view shows stars to magnitude 8.5 over a typical binocular field of spends the summer in this constellation’s northern sector, within a group view. Use it to pinpoint magnitude 2.9 Pi (π) Sagittarii, the brightest star of 3rd- and 4th-magnitude stars: Pi (π), Omicron (ο), and Xi2 (ξ2) Sagittarii. in Pluto’s vicinity.

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0.05° ASTRONOMY ALL ILLUSTRATIONS: ILLUSTRATIONS: ALL Pluto passes 2.7' south of Pi (π) Sagittarii in late June, then moves westward away from this luminary during July. This chart shows stars to magnitude 14.5.

WWW.ASTRONOMY.COM 65 ASTROSKETCHING BY ERIKA RIX Stellar neighbors

Bright stars can drown out to minimize the star’s glare and nearby faint objects, making make NGC 6144 pop out. them a challenge to see. But When I observed it with when push comes to shove, a 4-inch scope at 125x, the those luminous balls of gas act globular cluster appeared as locating beacons and can as a dim glow with a 12th- provide engaging views when magnitude star on its they pair with their neighbors western edge. When I used through an eyepiece. I’ve cho- averted vision, half a dozen sen two globular clusters in the faint stars flickered in and constellation Scorpius to illus- out of view across its face trate how they do it. with hints of granulation. An Red supergiant Antares 8th-magnitude star floated 14' shines brilliantly at 1st magni- to the south near the edge of tude near the head of the scor- my field of view. Depending on pion. Lying low in the sky, the your latitude, larger telescopes star provides a distinct marker may reveal nearly a dozen to pinpoint the location of resolved stars against the clus- NGC 6144. The 9th-magnitude ter’s hazy backdrop. globular lies just 38' farther I was at a slight advantage Cluster NGC 6144 lurks near Antares in the night sky. For both sketches, the author used northwest, reaching 9' across in that my observing site lies at a 4-inch f/9.8 refractor on a German equatorial mount with an 8mm Plössl for a magni- with a low surface brightness. 31° north latitude. But wherever fication of 125x. She used white printer paper with graphite pencils (2H, 4B, and 8B), a small blending stump, and a kneaded eraser. After scanning the drawings, she added If you find NGC 6144 elusive, your location, take advantage star glow around the brightest stars using Photoshop. Both sketches are oriented so nudge your telescope northwest of clear, dark skies and clean that north is to the top and west is to the right. ALL SKETCHES BY ERIKA RIX until Antares is just out of view optics (which help reduce light scattering) to optimize contrast. 1.5' southwest from its center. While you’re in the area, make Through a 10-inch scope, the sure to grab a view of globular globular takes on a mottled, cluster M4. You can spot it 1° slightly irregular shape, with southwest of NGC 6144. the halo reaching 3' in diameter. Trailing behind the scor- Some optical designs pro- pion’s tail, 3rd-magnitude G duce coma (distortion) near the Scorpii makes a striking pair edge of the lens. Rather than with the second globular clus- nudging G Scorpii out of view ter, NGC 6441. (Note the sub- to reveal more of the cluster’s tle naming distinction from structure, you can block out the previous cluster!) Located the star and reduce its glare by a mere 4' east of its neigh- attaching a thin strip of foil at boring orange-colored star, the focal point of your eyepiece, the cluster shines brightly at creating an occulting bar. magnitude 7.2 and reaches The purpose of my sketch 7.8' in diameter. was to capture both objects as Even through a 4-inch tele- they appeared together with scope, NGC 6441 was an easy their bright neighbor stars. But catch 2.5° south-southwest of another option is to include naked-eye open cluster M7, also any additional details of NGC known as Ptolemy’s Cluster. At 6441 once G Scorpii is hidden 125x, a soft 1' halo surrounded from sight. Whichever method its bright, concentrated core. you choose, be sure to note the The halo extended nearly a view your sketch represents. degree when I moved G Scorpii Questions or suggestions? just outside the field of view. A Feel free to contact me at Cluster NGC 6441 can be found in a pleasing visual pair with star G Scorpii. 10th-magnitude star was visible [email protected].

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1. DARK STAR This sequence shows the progression of 2016’s total solar eclipse, which at this site took 2 hours and 23 minutes from start to finish. Venus shines to the upper right of totality with Mercury halfway between it and the Sun. (Nikon N90, Toking 11–16mm f/2.8 AT-X Pro EX lens set at 11mm and f/8, ISO 200, various shutter speeds, taken March 9, 2016, from Dolo, Palu, Central Sulawesi, Indonesia) • Muhammad Rayhan

2. BILLIONS OF NEW SUNS The flocculent spiral galaxy NGC 3675 floats through Ursa Major some 47 million light-years from Earth. The blue color comes from newly formed stars in the galaxy’s arms. 3 (TEC-140 refractor at f/7, SBIG ST-8300M CCD camera, LRGB image with exposures of 480, 180, 150, and 165 minutes, respectively) Send your images to: • Bernard Miller 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 2 [email protected].

70 ASTRONOMY • JULY 2016 3. STONE COLD BEAUTY The Medusa Nebula (Abell 21) lies in the constellation Gemini. Observers likened it to the mythological figure because of the braided streamers of gas they saw. (20-inch RC Optical Systems Ritchey-Chrétien reflector at f/8.3, Apogee Alta U09000 CCD cam- era, Hα/OIII/RGB image with exposures of 540, 600, 40, 40, and 40 minutes, respectively) • Ken Crawford

4. MIRRORS OF DUST This area just above the belt of Orion the Hunter is full of reflection nebulae, but two stand out. IC 426 is the odd- shaped cloud to the right of center. Then, at center and lit by a triple star, is van den Bergh 48. (3.6-inch Astro- Tech AT90EDT refractor at f/6.7, SBIG ST-8300M CCD camera, LRGB image with exposures of 120, 40, 40, and 40 minutes, respectively) • Dan Crowson

5. ALMOST HEAVEN In October 2015, the Milky Way set behind a tree at Spruce Knob, West Virginia. In addition to bright stars, we also can pick out the vast amount of dark nebulosity, which hides the light from the stars behind it. (Nikon D750, 4 24mm lens at f/1.4, ISO 5000, 10-sec- ond exposure) • Matthew Dieterich

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WWW.ASTRONOMY.COM 71 6

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72 ASTRONOMY • JULY 2016 6. GASEOUS ENVELOPE Reflection nebula IC 2641 (also known as Cederblad 112) is a brilliant blue cloud in the southern constellation Chamaeleon. Look closely to see the partially obscured star whose light is causing the cloud to glow. Nearby, dark nebulae abound. (20-inch PlaneWave corrected Dall-Kirkham reflector at f/6.8, SBIG STX-16803 CCD camera, LRGB image with 7.5 hours of total exposures) • Don Goldman

7. PANORAMIC AURORA On March 25, 2016, this aurora glowed above and around North Pole, Alaska. It varied in intensity throughout the night but was easy to see despite clouds and light from a nearly Full Moon. (Canon 6D, 24mm lens, ISO 3200, three-image panorama, each was a 10-second expo- sure) • John Chumack

8. FULLY FACEON NGC 7424 is a spiral galaxy many 8 astronomers think resembles our Milky Way. It lies some 40 million light-years away within the boundaries of the constellation Grus. Many future star- forming regions are visible as blotches of red nebulosity. (16-inch RC Optical Systems Ritchey-Chrétien reflector at f/11, Apogee U9 CCD camera, LRGB image with exposures of 12, 5, 5, and 5 hours, respectively) • Warren Keller/ Steve Mazlin/Steve Menaker/ Jack Harvey

9. FELLOW TRAVELER Our Moon is easy to photograph because it’s bright. Just about any opti- cal device can record it. But it’s difficult to photograph well because its surface is of such low contrast. Here, the imager combined top-notch optics with careful processing for a “Wow!” result. (7.2-inch Astro-Physics AP-178T StarFire refrac- tor, Canon 70D, taken January 19, 2016, at 19h17m UT, from Flackwell Heath, 910England) • David Tyler

10. DOWNWARD SPIRAL NGC 6118 lies 83 million light-years away in Serpens. Astronomers classify it as a “grand design” spiral — one with large well-defined arms. (32-inch Schulman Telescope by RC Optical Systems, SBIG STX-16803 CCD camera, LRGB image with exposures of 7, 4, 4, and 4 hours, respectively) • Adam Block/Mount Lemmon SkyCenter/University of Arizona

11. PLANETARY TANGO Venus (the brightest object) and Mercury (below and left of Venus) glow low in the western sky early this year. The star to the lower right of Venus is Kaus Boraelis (Lambda [λ] Sagittarii). (Canon 6D, 55mm lens, ISO 400, 5-second exposure, taken January 30, 11 2016, from Warrenton, Virginia) • John Chumack

WWW.ASTRONOMY.COM 73 BREAK THROUGH Pride of Leo the Lion

Many, if not most, spiral galaxies possess a pleas- ing symmetry. But M96 in Leo the Lion breaks the mold. Dark dust lanes and glowing clouds of hydro- gen spread unevenly through its asymmetric spiral arms. Even the core, which harbors a supermassive black hole, doesn’t lie precisely at M96’s center. The galaxy spans about 100,000 light- years, though this Hubble Space Telescope image shows only the inner third. M96 lies some 35 million light-years from Earth and is the brightest member of a group of a dozen or so galaxies. It is the nearest group holding both bright spirals (M95 and M96) and a bright elliptical (M105). ESA/NASA/HUBBLE/THE LEGUS TEAM

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OPT Telescopes – 800.483.6287 – www.opttelescopes.com High Point Scientifi c – 800.266.9590 – www.highpointscientifi c.com B&H Photo – 800.947.9970 – www.bhphotovideo.com Optics Planet – 800.504.5897 – www.opticsplanet.com Astronomics – 800.422.7876 – www.astronomics.com Focus Camera – 800.221.0828 – www.focuscamera.com Adorama – 800.223.2500 – www.adorama.com Woodland Hills – 888.427.8766 – www.telescopes.net DISCOVER MORE AT SOUTHERN MARTIN GEORGE describes the solar system’s changing landscape SKY as it appears in Earth’s southern sky. September 2016: A twilight trio

As darkness settles in during even faster clip than Jupiter. It’s magnitude –0.3 and lies in Way’s hub. The galactic center early September, an attractive still worth the effort to view Scorpius just 6° southeast of lies in the direction of Sagit- trio of planets adorns the west- through a telescope, however. Saturn. That gap grows to 20° tarius the Archer, which holds a ern sky. The grouping of Mer- On the evening of the 1st, the at month’s end, by which time feast of wonderful star clusters cury, Venus, and Jupiter will be innermost planet shows a beau- magnitude 0.1 Mars has crossed and nebulae. sure to draw the attention of tiful crescent that spans 10". southern Ophiuchus and A small patch of the Milky even the most casual observers. Mercury disappears in the entered western Sagittarius. Way here played an outsized The most conspicuous of the twilight glow by September’s Observers who followed role in astronomical history. three is Venus, which shines second week. It then passes Mars through a telescope dur- Called Baade’s Window, this brightest (at magnitude –3.8) between the Sun and Earth on ing its great autumn and winter area spans about 1° and lies 0.6° and appears highest. As Sep- the 13th before re-emerging in show see that spectacle winding northwest of 3rd-magnitude tember progresses, the planet the eastern predawn sky at down in September. The plan- Gamma (γ) Sagittarii. Seventy draws farther from the Sun month’s end. Observers at mid- et’s disk drops below 10" in years ago, while working with and climbs into a darker sky. It southern latitudes will have a diameter on the 8th, so surface the 100-inch Hooker Telescope slides 3° north of 1st-magnitude hard time spotting the planet in features become harder to dis- at Mount Wilson Observatory, Spica on September 17. Despite bright twilight, but those closer cern. It’s still worth a look, how- astronomer Walter Baade noted being Virgo’s brightest star, it to the equator should be able to ever, particularly if you trained that this direction was remark- glows just 1 percent as bright as find its magnitude –0.6 glow. your eye to spot subtle detail ably clear of the interstellar Venus. The planet’s eastward Back in the evening sky, during the past several months. dust that obscures our view of motion carries it into Libra on Saturn continues to put on a The Moon passes directly in the Milky Way’s center. September’s final day. great show. The ringed planet front of the Sun on September 1, Although other such patches Although Venus looks lies high in the west once dark- bringing an annular solar exist, Baade’s Window is the pretty in the twilight sky, the ness falls. You can find it edging eclipse along a narrow corri- most significant. Writing in same can’t be said of its tele- eastward against the backdrop dor that cuts across central and the Publications of the Astro- scopic appearance. Even at the of Ophiuchus the Serpent- southeastern Africa as well as nomical Society of the Pacific end of September, the planet’s bearer. Glowing at magnitude Madagascar. Outside the path in 1946, he announced that his disk measures just 12" across 0.5, it easily outshines the stars of annularity, people in most of observations of the globular star and shows a fat gibbous phase. of its host constellation. Africa and all of Madagascar cluster NGC 6522 and numer- While Venus grows more Of all the planets visible can witness a partial eclipse. ous variable stars in this win- prominent during September, these September nights, Saturn From Cape Town, South Africa, dow yielded a distance to the Jupiter fades away. On the deserves the most scrutiny. the eclipse runs from 7h43m galactic center of about 9 kilo- 1st, the magnitude –1.7 planet The view through a telescope to 9h58m UT and the Moon parsecs (29,000 light-years). stands nearly 10° high 45 min- inspires awe whether you’re blocks 26 percent of the Sun’s NGC 6522 glows at 8th utes after sunset. By midmonth, seeing it for the first or the hun- diameter at maximum. magnitude and is worth view- however, it sets barely a half- dredth time. Even small scopes The month’s second eclipse ing if only because of its his- hour after sundown, and it reveal the planet’s 16"-diameter occurs September 16 when the torical importance. Find it by passes behind the Sun from disk surrounded by a beautiful Moon passes through Earth’s first centering Gamma Sgr in our viewpoint on the 26th. ring system that spans 37" and penumbral shadow. This lunar your field of view and then Needless to say, you’ll tilts 26° to our line of sight. eclipse reaches maximum at nudging the scope 0.6° north- want to get your last evening You’ll also see Saturn’s brightest 18h54m UT when 91 percent west. Even relatively small glimpses of Jupiter in early moon, 8th-magnitude Titan, as of Luna lies in our light outer apertures will reveal a fuzzy September. The giant planet’s it slowly changes position from shadow. Observers in Australia, patch a few arcminutes across, low altitude means you likely night to night. Asia, and Africa should notice but you’ll need a 30cm or larger won’t get crisp views of its You’ll find Mars even higher a slight shading across the instrument to begin resolving 31"-diameter disk, though you and shining brighter in the west northern part of the Moon. it. While you’re in the vicinity, should see its two dark equato- after night falls. The Red Planet check out the 10th-magnitude rial belts and four satellites. passed Saturn late last month The starry sky globular NGC 6528. It lies in Mercury also makes its way and continues to pull away. On September evenings provide the same low-power field, just back toward the Sun, but at an September 1, Mars shines at exquisite views of the Milky 16' to the east.

STAR S

DOME VOLANS

THE ALLSKY MAP CRUX CARINA

SHOWS HOW THE b

a

_ SKY LOOKS AT: CHAMAELEON

10 P.M. September 1 2070 NGC

`

P.M. 4755 NGC

9 September 15 LMC

RETICULUM

8 P.M. September 30 5128 NGC MENSA

Planets are shown 5139 NGC

SCP

`

at midmonth AUSTRALE CENTAURUS

TRIANGULUM

OLOGIUM

HYDRUS

R

_

SMC

OCTANS CIRCINUS

NGC 104 NGC

Achernar

PAVO ARA

TUCANA

NORMA

NGC 6397 NGC

TELESCOPIUM LUPUS

INDUS

NIX

NGC 6231 NGC

OE

LIBRA

GRUS SCORPIUS

AUSTRALIS

Antares

CORONA

M4

M7 M6

SAGITTARIUS

SCULPTOR Mars

Saturn

M8

M20 Fomalhaut W MICROSCOPIUM

M22

M17

M5 PISCIS M16 AUSTRINUS SCUTUM

OPHIUCHUS CAPRICORNUS

SERPENS CAUDA M11 AQUILA

SERPENS CAPUT

AQUARIUS EQUULEUS

Altair Enif

SAGITTA M15 DELPHINUS VULPECULA

HERCULES

MAGNITUDES LYRA Sirius Open cluster LACERTA 0.0 Globular cluster Vega CYGNUS 1.0 Diffuse nebula 2.0 Deneb 3.0 Planetary nebula 4.0 5.0 Galaxy

N HOW TO USE THIS MAP: This map portrays the sky as seen near 30° south latitude. SEPTEMBER 2016 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 New Moon occurs at 9h03m UT; 17 Venus passes 3° north of Spica, direction you’re facing. annular solar eclipse 23h UT The stars above the 2 18 map’s horizon now Asteroid Ceres is stationary, The Moon is at perigee

R match what’s 13h UT (361,896 kilometers from Earth),

HO in the sky. 17h00m UT Neptune is at opposition, 17h UT

The Moon passes 3° south of ERIDANUS The Moon passes 6° north of Uranus, 17h UT Mercury, 17h UT 21 Mercury is stationary, 10h UT The Moon passes 0.4° north of Jupiter, 22h UT The Moon passes 0.2° north of

Aldebaran, 23h UT FORNAX 3 The Moon passes 1.1° north of Venus, 11h UT 22 September equinox occurs at 14h21m UT

6 OE The Moon is at apogee

23 PH (405,055 kilometers from Earth), Last Quarter Moon occurs at 18h45m UT 9h56m UT 8 The Moon passes 4° north of 26 Pluto is stationary, 3h UT SGP Saturn, 21h UT Jupiter is in conjunction with 9 First Quarter Moon occurs at the Sun, 7h UT

NGC 253 NGC 11h49m UT Mira E 28 Mercury is at greatest western The Moon passes 8° north of elongation (18°), 20h UT CETUS Mars, 14h UT 29 The Moon passes 0.7° south of 13 Mercury is in inferior conjunction, Mercury, 11h UT 0h UT Asteroid Parthenope is at 15 The Moon passes 1.2° north of opposition, 13h UT Pat Neptune, 20h UT h of the S un (eclipt ic) Uranus 16 Full Moon occurs at 19h05m UT; penumbral lunar eclipse

PISCES

STAR COLORS: Stars’ true colors PEGASUS 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. ANDROMEDA 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. REGISTERED USERS GET EXCLUSIVE ACCESS! Enjoy MORE from Astronomy when you register online! • Get a weekly email newsletter featuring astronomy news, reader gallery, and sky events. • Submit your photos and be inspired by readers’ images. • Watch exclusive videos on observing, new discoveries, cutting-edge science, and more. • Comment on articles and share your thoughts.

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with you ASTRONOMY’S DIGITAL EDITION lets you: ✱ Link to website content, blogs, advertisers’ websites, audio, and video. ✱ Zoom in and magnify to see all the details of Astronomy’s stunning images. ✱ Take your issues with you wherever you go — and save on storage space! ASTRONOMY.COM/DIGITALSUB

Powered by ZinioTM, digital editions are available on PC; Macintosh; AndroidTM; iPad®; iPhone®; and Windows 8. Zinio is a registered trademark of Zinio, LLC. Android is a trademark of Google Inc. Macintosh, iPad, and iPhone are trademarks of Apple Inc., registered in the United States and other countries. Windows is a registered trademark of Microsoft Corporation in the United States and other countries.. P27545 SOUTHERN MARTIN GEORGE describes the solar system’s changing landscape SKY as it appears in Earth’s southern sky. September 2016: A twilight trio

As darkness settles in during even faster clip than Jupiter. It’s magnitude –0.3 and lies in Way’s hub. The galactic center early September, an attractive still worth the effort to view Scorpius just 6° southeast of lies in the direction of Sagit- trio of planets adorns the west- through a telescope, however. Saturn. That gap grows to 20° tarius the Archer, which holds a ern sky. The grouping of Mer- On the evening of the 1st, the at month’s end, by which time feast of wonderful star clusters cury, Venus, and Jupiter will be innermost planet shows a beau- magnitude 0.1 Mars has crossed and nebulae. sure to draw the attention of tiful crescent that spans 10". southern Ophiuchus and A small patch of the Milky even the most casual observers. Mercury disappears in the entered western Sagittarius. Way here played an outsized The most conspicuous of the twilight glow by September’s Observers who followed role in astronomical history. three is Venus, which shines second week. It then passes Mars through a telescope dur- Called Baade’s Window, this brightest (at magnitude –3.8) between the Sun and Earth on ing its great autumn and winter area spans about 1° and lies 0.6° and appears highest. As Sep- the 13th before re-emerging in show see that spectacle winding northwest of 3rd-magnitude tember progresses, the planet the eastern predawn sky at down in September. The plan- Gamma (γ) Sagittarii. Seventy draws farther from the Sun month’s end. Observers at mid- et’s disk drops below 10" in years ago, while working with and climbs into a darker sky. It southern latitudes will have a diameter on the 8th, so surface the 100-inch Hooker Telescope slides 3° north of 1st-magnitude hard time spotting the planet in features become harder to dis- at Mount Wilson Observatory, Spica on September 17. Despite bright twilight, but those closer cern. It’s still worth a look, how- astronomer Walter Baade noted being Virgo’s brightest star, it to the equator should be able to ever, particularly if you trained that this direction was remark- glows just 1 percent as bright as find its magnitude –0.6 glow. your eye to spot subtle detail ably clear of the interstellar Venus. The planet’s eastward Back in the evening sky, during the past several months. dust that obscures our view of motion carries it into Libra on Saturn continues to put on a The Moon passes directly in the Milky Way’s center. September’s final day. great show. The ringed planet front of the Sun on September 1, Although other such patches Although Venus looks lies high in the west once dark- bringing an annular solar exist, Baade’s Window is the pretty in the twilight sky, the ness falls. You can find it edging eclipse along a narrow corri- most significant. Writing in same can’t be said of its tele- eastward against the backdrop dor that cuts across central and the Publications of the Astro- scopic appearance. Even at the of Ophiuchus the Serpent- southeastern Africa as well as nomical Society of the Pacific end of September, the planet’s bearer. Glowing at magnitude Madagascar. Outside the path in 1946, he announced that his disk measures just 12" across 0.5, it easily outshines the stars of annularity, people in most of observations of the globular star and shows a fat gibbous phase. of its host constellation. Africa and all of Madagascar cluster NGC 6522 and numer- While Venus grows more Of all the planets visible can witness a partial eclipse. ous variable stars in this win- prominent during September, these September nights, Saturn From Cape Town, South Africa, dow yielded a distance to the Jupiter fades away. On the deserves the most scrutiny. the eclipse runs from 7h43m galactic center of about 9 kilo- 1st, the magnitude –1.7 planet The view through a telescope to 9h58m UT and the Moon parsecs (29,000 light-years). stands nearly 10° high 45 min- inspires awe whether you’re blocks 26 percent of the Sun’s NGC 6522 glows at 8th utes after sunset. By midmonth, seeing it for the first or the hun- diameter at maximum. magnitude and is worth view- however, it sets barely a half- dredth time. Even small scopes The month’s second eclipse ing if only because of its his- hour after sundown, and it reveal the planet’s 16"-diameter occurs September 16 when the torical importance. Find it by passes behind the Sun from disk surrounded by a beautiful Moon passes through Earth’s first centering Gamma Sgr in our viewpoint on the 26th. ring system that spans 37" and penumbral shadow. This lunar your field of view and then Needless to say, you’ll tilts 26° to our line of sight. eclipse reaches maximum at nudging the scope 0.6° north- want to get your last evening You’ll also see Saturn’s brightest 18h54m UT when 91 percent west. Even relatively small glimpses of Jupiter in early moon, 8th-magnitude Titan, as of Luna lies in our light outer apertures will reveal a fuzzy September. The giant planet’s it slowly changes position from shadow. Observers in Australia, patch a few arcminutes across, low altitude means you likely night to night. Asia, and Africa should notice but you’ll need a 30cm or larger won’t get crisp views of its You’ll find Mars even higher a slight shading across the instrument to begin resolving 31"-diameter disk, though you and shining brighter in the west northern part of the Moon. it. While you’re in the vicinity, should see its two dark equato- after night falls. The Red Planet check out the 10th-magnitude rial belts and four satellites. passed Saturn late last month The starry sky globular NGC 6528. It lies in Mercury also makes its way and continues to pull away. On September evenings provide the same low-power field, just back toward the Sun, but at an September 1, Mars shines at exquisite views of the Milky 16' to the east.

STAR S

DOME VOLANS

THE ALLSKY MAP CRUX CARINA

SHOWS HOW THE b

a

_ SKY LOOKS AT: CHAMAELEON

10 P.M. September 1 2070 NGC

`

P.M. 4755 NGC

9 September 15 LMC

RETICULUM

8 P.M. September 30 5128 NGC MENSA

Planets are shown 5139 NGC

SCP

`

at midmonth AUSTRALE CENTAURUS

TRIANGULUM

OLOGIUM

HYDRUS

R

_

SMC

OCTANS CIRCINUS

NGC 104 NGC

Achernar

PAVO ARA

TUCANA

NORMA

NGC 6397 NGC

TELESCOPIUM LUPUS

INDUS

NIX

NGC 6231 NGC

OE

LIBRA

GRUS SCORPIUS

AUSTRALIS

Antares

CORONA

M4

M7 M6

SAGITTARIUS

SCULPTOR Mars

Saturn

M8

M20 Fomalhaut W MICROSCOPIUM

M22

M17

M5 PISCIS M16 AUSTRINUS SCUTUM

OPHIUCHUS CAPRICORNUS

SERPENS CAUDA M11 AQUILA

SERPENS CAPUT

AQUARIUS EQUULEUS

Altair Enif

SAGITTA M15 DELPHINUS VULPECULA

HERCULES

MAGNITUDES LYRA Sirius Open cluster LACERTA 0.0 Globular cluster Vega CYGNUS 1.0 Diffuse nebula 2.0 Deneb 3.0 Planetary nebula 4.0 5.0 Galaxy

N HOW TO USE THIS MAP: This map portrays the sky as seen near 30° south latitude. SEPTEMBER 2016 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 New Moon occurs at 9h03m UT; 17 Venus passes 3° north of Spica, direction you’re facing. annular solar eclipse 23h UT The stars above the 2 18 map’s horizon now Asteroid Ceres is stationary, The Moon is at perigee

R match what’s 13h UT (361,896 kilometers from Earth),

HO in the sky. 17h00m UT Neptune is at opposition, 17h UT

The Moon passes 3° south of ERIDANUS The Moon passes 6° north of Uranus, 17h UT Mercury, 17h UT 21 Mercury is stationary, 10h UT The Moon passes 0.4° north of Jupiter, 22h UT The Moon passes 0.2° north of

Aldebaran, 23h UT FORNAX 3 The Moon passes 1.1° north of Venus, 11h UT 22 September equinox occurs at 14h21m UT

6 OE The Moon is at apogee

23 PH (405,055 kilometers from Earth), Last Quarter Moon occurs at 18h45m UT 9h56m UT 8 The Moon passes 4° north of 26 Pluto is stationary, 3h UT SGP Saturn, 21h UT Jupiter is in conjunction with 9 First Quarter Moon occurs at the Sun, 7h UT

NGC 253 NGC 11h49m UT Mira E 28 Mercury is at greatest western The Moon passes 8° north of elongation (18°), 20h UT CETUS Mars, 14h UT 29 The Moon passes 0.7° south of 13 Mercury is in inferior conjunction, Mercury, 11h UT 0h UT Asteroid Parthenope is at 15 The Moon passes 1.2° north of opposition, 13h UT Pat Neptune, 20h UT h of the S un (eclipt ic) Uranus 16 Full Moon occurs at 19h05m UT; penumbral lunar eclipse

PISCES

STAR COLORS: Stars’ true colors PEGASUS 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. ANDROMEDA 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. REGISTERED USERS GET EXCLUSIVE ACCESS! Enjoy MORE from Astronomy when you register online! • Get a weekly email newsletter featuring astronomy news, reader gallery, and sky events. • Submit your photos and be inspired by readers’ images. • Watch exclusive videos on observing, new discoveries, cutting-edge science, and more. • Comment on articles and share your thoughts.

Register now and you’ll get a FREE collection of Astronomy articles Gift! to download instantly!

It’s FREE to sign up! Visit Astronomy.com/FreeGift with you ASTRONOMY’S DIGITAL EDITION lets you: ✱ Link to website content, blogs, advertisers’ websites, audio, and video. ✱ Zoom in and magnify to see all the details of Astronomy’s stunning images. ✱ Take your issues with you wherever you go — and save on storage space! ASTRONOMY.COM/DIGITALSUB

Powered by ZinioTM, digital editions are available on PC; Macintosh; AndroidTM; iPad®; iPhone®; and Windows 8. Zinio is a registered trademark of Zinio, LLC. Android is a trademark of Google Inc. Macintosh, iPad, and iPhone are trademarks of Apple Inc., registered in the United States and other countries. Windows is a registered trademark of Microsoft Corporation in the United States and other countries.. P27545