LOST IN THE GLARE: DIY: `OUMUAMUA: 24 Lesser-Known Targets Light Barriers The “Comet” from Another PAGE 58 PAGE 72 PAGE 20

THE ESSENTIAL GUIDE TO

On the Edge of the Abyss: Our Local Cosmic

PAGE 12

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October 2018 VOL. 136, NO. 4 THE ESSENTIAL GUIDE TO ASTRONOMY

FEATURES Cover Story: 12 The Void Next Door An enormous region of near- emptiness starts on our doorstep, giving astronomers their best chance to probe one of these gigantic cosmic structures. By Ken Croswell 58

20 `Oumuamua’s Dramatic Visit The space rock from beyond the OBSERVING S&T TEST REPORT solar system has left us amazed and 41 October’s Sky at a Glance 66 Meade’s 70-mm Astrograph perplexed. By Greg Laughlin Alan Dyer 42 Lunar Almanac & Sky Chart COLUMNS / DEPARTMENTS 28 A Tourist’s Guide to the 43 Binocular Highlight Autumn Highlights By Mathew Wedel 4 Spectrum Ramble through the skies of fall and By Peter Tyson check in on some favorite targets. 44 Planetary Almanac 6 From Our Readers By Jerry Oltion 45 Under the Stars By Fred Schaaf 7 75, 50 & 25 Years Ago 34 New Life for the Great By Roger W. Sinnott Melbourne Telescope 46 , & Planets Australian groups are restoring what By Fred Schaaf 8 News Notes was once the world’s largest 48 Celestial Calendar 57 Book Review equatorially mounted telescope. By S. N. Johnson-Roehr By Monica Young By Trudy E. Bell 52 Exploring the Moon 70 New Product Showcase 58 Lost in the Glare By Charles A. Wood 72 Astronomer’s Workbench Some interesting objects await 54 Deep-Sky Wonders By Jerry Oltion imagers who can tear their cameras By Sue French away from the showpieces of the 74 Gallery night skies. By Ron Brecher 84 Focal Point

Find us on Facebook & Twitter By Roger Sargent BRECHER RON

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SKY AT A GLANCE ASTROPHOTO GALLERY ONLINE MARKETPLACE Our popular column highlights celes- Enjoy readers’ best images and Browse personal used equipment tial delights for the upcoming week. upload your own to share with your and dark-sky lodgings and sell your Also available as an app — with sky fellow enthusiasts. Be sure to check own without paying a fee. charts included! out the Editor’s Choice picks. skyandtelescope.com/ skyandtelescope.com/ataglance skyandtelescope.com/gallery marketplace

Matter’s l ow outlines SKY & TELESCOPE (ISSN 0037-6604) is published monthly by Sky & Telescope, a division of F+W Media, Inc., 90 Sherman St., Cambridge, MA 02140-3264, USA. Phone: 800-253- several voids in our 0245 (customer service/subscriptions), 888-253-0230 (product orders), 617-864-7360 (all other calls). Fax: 617-864-6117. Website: skyandtelescope.com. ©2018 F+W Media, Inc. cosmic neighborhood. All rights reserved. Periodicals postage paid at Boston, Massachusetts, and at additional mailing offi ces. Canada Post Publications Mail sales agreement #40029823. Canadian return JOHAN HIDDING / UNIV. OF address: 2744 Edna St., Windsor, ON, Canada N8Y 1V2. Canadian GST Reg. #R128921855. POSTMASTER: Send address changes to Sky & Telescope, PO Box 420235, Palm Coast, FL GRONINGEN / KAPTEYN INST. 32142-0235. Printed in the USA.

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Find more Omegon products at www.omegon.com! SPECTRUM by Peter Tyson The Big Empty The Essential Guide to Astronomy

Founded in 1941 by Charles A. Federer, Jr. YOU MIGHT ASK WHY we would do a cover story on cosmic voids — and Helen Spence Federer thosestupendouslyvast,largelygalaxy-freeSaharasofspace.After EDITORIAL all, astronomy is all about observing things, not nothings, right? Editor in Chief Peter Tyson Even if you wanted to look there, as a zealous coterie of professional Senior Editors J. Kelly Beatty, Alan M. MacRobert astronomers does, it’s not a walk in the park. As one of these folks Science Editor Camille M. Carlisle wrylynotesinourarticleonpage12,“Observingemptyspaceisveryhard.” News Editor Monica Young Associate Editors S. N. Johnson-Roehr, Sean Walker Well, it turns out that cosmic voids play a key role in shaping the large-scale Observing Editor Diana Hannikainen structureoftheuniverse.Asgravitydrawsgalaxiestogether,soitluresthem Project Coordinator Bud Sadler away from voids. Take the example of our Local Void, as it’s prosaically known. Digital Content Strategist Janine Myszka

This fantastically empty zone steepens the gravitational “hill” that our Milky Senior Contributing Editors WayGalaxyslidesdownatadizzying630km/s(1.4millionmph). Robert Naeye, Roger W. Sinnott Voidsarecaptivatingtoresearchers,becausetheymighthelpusbetterprobe Contributing Editors those invisible presences, dark energy and dark matter. They may also aid us in Howard Banich, Jim Bell, Trudy Bell, John E. Bortle, testinggeneralrelativity:Anytinyeffectsthatmight Greg Bryant, Thomas A. Dobbins, Alan Dyer, sit uncomfortably with Einstein’s theory may be easier Tom Field, Tony Flanders, Ted Forte, Sue French, to detect in those desolate hollows than amid the hus- Steve Gottlieb, David Grinspoon, Ken Hewitt-White, Johnny Horne, Bob King, Emily Lakdawalla, tle and bustle of galaxies. In the end, to gain a robust Rod Mollise, James Mullaney, Donald W. Olson, understanding of our place in the universe, we can’t Jerry Oltion, Joe Rao, Dean Regas, Fred Schaaf, ignore voids. It’d be like learning all we can about Govert Schilling, William Sheehan, Mike Simmons, islandchainswhilepayingnomindtotheboundless Mathew Wedel, Alan Whitman, Charles A. Wood oceans around them. Contributing Photographers Barnard’s , a lonely And there are thingstoseeinvoids,justnotmany P. K. Chen, Akira Fujii, Robert Gendler, outpost between the Milky of them. Astronomers have identified a few lone Babak Tafreshi Way and the Local Void galaxies in our Local Void, for example. Each of them ART & DESIGN is beating a hasty retreat towards clumps of galaxies, like a lost hiker gravitat- Art Director Terri Dubé ing toward far-off sounds of people. The center of the Local Void happens to Illustration Director Gregg Dinderman Illustrator Leah Tiscione lie on the opposite side of our galactic core, which makes it a beast to observe. Butradiotelescopescanpenetratetheinterveningdust,gas,andstarlight.And ADVERTISING VP, Advertising Sales Kevin D. Smith because the Local Void juts above and below the core, amateur astronomers Advertising Sales Director Tim Allen mightbeabletohelpdiscoverfaintgalaxieswithinthevoidusingCCDcameras Advertising Coordinator Connie Kostrzewa underink-darkskies. F+W MEDIA Even armchair astronomers can get something out of voids, which offer Chief Executive Offi cer Gregory J. Osberg much to work the brain. The Local Void might be 250 million light-years across. Chief Financial Offi cer Kenneth Kharbanda Whoa.Onelight-yearequals63,240astronomicalunits,with1a.u.beingthe SVP / GM — F+W Fine Art, Writing, Outdoors & distance from Earth to the Sun. Multiply that 63,240 by 250,000,000. I’m out Small Business Group Ray Chelstowski Managing Director — F+W International of breath just thinking about it. Or try this on for size: Space expands faster in James Woollam voids than in galaxies. Who knew? Nothingness grows bigger faster than some- VP, Consumer Marketing John Phelan thingness does! VP, General Counsel Robert Sporn Perhaps now — if you didn’t already — you can see why VP, Human Resources, Customer Service & Trade Gigi Healy we devoted the cover to something unseeable. VP, Manufacturing & Logistics Phil Graham VP, Product Management Pat Fitzgerald

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4 OCTOBER 2018 • SKY & TELESCOPE Image courtesy of Tom O Donoghue. to use ourequipmentvisit:www.atik-cameras.com a fulllistofourstockistsandinformation onhow app availableonAndroidandApple mobiles. Go toourwebsiteandAtikCCDField Calculator of telescopes,wehaveacamerato suit yoursetup. With alargerangeofcamerastosuit alargerrange you’ve captured. showing friendsandfamilytheincredibleimages you getthebestoutofyourset-up.You’llsoonbe

`OUMUAMUA: © WILLIAM K. HARTMANN; MILLENNIUM FALCON: MANFRED SCHMID / GETTY IMAGES 1860s found that it appeared forked — thus power exceeding 1 megawatt) might be tinue the amazing articles explaining the feature is sometimes referred to as an infrequent or short-lived aspect of Earth’s events when the light that we Dawes’ Forked Bay. Later mappers, includ- technologically advanced civilizations. now see departed the celestial objects ing Richard A. Proctor (and Flammarion Note that much of the UHF band, a he names (S&T: June 2018, “Fifteen and Schiaparelli) continued to follow Beer frequency space once dedicated to TV Steps to Forever,” p. 64; December 2016, and Mädler’s convention in using this as the transmissions, has been switched to use “Twelve Steps to Infi nity,” p. 24). These Martian prime meridian. Since then, the IAU by mobile phones. space-and-time journeys with light has designated Airy, a 43-km-wide crater, as Third, there hasn’t been any irrefut- underscore the fascinating, incompre- the location of the “Martian Greenwich.” able evidence of extraterrestrial life, hensible size of the universe. though Mars provides some tantalizing Frederick J. Summers Funding SETI hints. We also might be on the verge Ferndale, California David Grinspoon attributes the 1990s of detecting the signature of life in the cut in funding for the search for extra- atmospheres of planets outside our solar FOR THE RECORD terrestrial intelligence to “anti-intellec- system. Finding that life of any kind • “Hunting Phobos and Deimos” (S&T: July tual budget cutters” (S&T: July 2018, exists elsewhere would be a huge boost 2018, p. 53) should note that Phobos can p. 12). But there are other, more legiti- in the incentives for SETI funding. appear as much as 22 arcseconds (not 16) mate reasons why SETI funding was not Erik Magnuson from the limb of Mars. a high priority in the 1990s. Cardiff, California • The Gallery caption for NGC 1514 (S&T: First, radio-based SETI is a huge July 2018, p. 75) should have stated that signal-processing problem, and it would A Wish for Wedel new i ndings show the companion star’s have been reasonable to expect that We wish upon a star that somehow orbital period to be 3,306 days, or a little hardware costs would decrease dramati- Mathew Wedel can fi nd a way to con- over 9 years. cally in the future (as they in fact have). Second, high-power radio-frequency SUBMISSIONS: Write to Sky & Telescope,90ShermanSt.,Cambridge,MA02140-3264,U.S.A.oremail:letters@ transmissions (with effective radiated skyandtelescope.com. Please limit your comments to 250 words; letters may be edited for brevity and clarity.

75, 50 & 25 YEARS AGO by Roger W. Sinnott comesfromsmallchangesnotedin theHubbleSpaceTelescopehave themotionofLunarOrbiter5,when become accustomed to inding 1943 º October 1943 very precise radio Doppler tracking curiousstructuresatthecentersof Mira’s Maximum “A recent publi- was continued for 80 consecutive active galaxies or galaxies under- cation from Stockholm reports on circuits of the moon. . . . going collisions. But now they’ve thediscoveryofoldrecordbooks “Five conspicuous mascons, found something odd in the core kept by the 18th-century Swedish each about 50 to 200 kilometers in of a seemingly normal, quiet spiral. astronomer, Peter Wargentin. They extent and perhaps 50 kilometers NewHubbleimagesshowthat contain valuable observations of below the surface, were detected neighboring M31 in MiraCetiintheyears1751–1782.... under...MareImbrium,Mare has a double nucleus. Happily they cover the brightest Serenitatis, Mare Crisium, Mare “Tod R. Lauer (National Optical 1968 maximumeverobservedforthat Nectaris,andMareHumorum.... Astronomy Observatories), Sandra much-examined variable star. “The JPL investigators comment M. Faber (University of California, “Mirahasaperiodofover in Science forAugust16,1968:... SantaCruz),andtheircolleagues 330 days. Individual cycles differ ‘Does each of these mascons made the announcement at the considerablyinamplitude....The represent an asteroidal-sized body Space Telescope Science Institute newlydiscoveredoldobservations whichcauseditsassociatedmare on July 20th. Their observations show that Mira attained magnitude by impact?’” with Hubble’s Planetary Camera 1.2onNovember11–12,1799— NASA’s 2012 GRAIL mission reveal that the bright spot identiied abouttwicethebrightnessofits gave new insight into mascons. A as the nucleus in ground-based Purdue University study concluded images is actually offset from 1993 more recent maxima.” that large asteroid impacts carved the true dynamical center of the º October 1968 huge craters, liquified the interiors, galaxy, marked by a fainter spot 5 Mascons “Mass concentrations anddrewinsurroundingmaterial light-years(½arcsecond)tothe of dense material lie beneath the that melted and congealed there. southwest.” surface of the moon, report Paul M. Furtherstudy,usingHST’scor- Muller and William L. Sjogren of the º October 1993 rected optics, showed the nucleus Jet Propulsion Laboratory. Their M31’sDoubleNucleus“Over the tobealopsideddiskofstarsorbit- evidence for . . . these ‘mascons’ last three years astronomers using ing M31’s central black hole.

skyandtelescope.com • OCTOBER 2018 7 NEWS NOTES

known Jovian moon,” Sheppard notes. SOLAR SYSTEM Designated S/2016 J2, it’s far enough from to be in the midst of the 10 New for Jupiter retrograde swarm. But this new find, provisionally named Valetudo, has a prograde orbit. With the exception of Valetudo, allofthenewfindsweresweptupin early 2017, when Sheppard was on solo Valetudo observing runs in Chile using the 6.5-

Galilean meter Magellan-Baade reflector at Las moons Prograde Campanas and the 4.0-meter Blanco group reflector on Cerro Tololo. “Jupiter just happened to be in the RetrogradeR groups sky near the search fields where we werelookingforextremelydistantsolar system objects,” he says. Sheppard leads Not to scale one of the teams searching for a puta- tive massive planet thought to lie far ON JULY 17TH, theIAU’sMinorPlanet p In this plot showing the orbits of Jupiter’s 79 beyond (S&T: Oct. 2017, p. 16). Center announced that a search team satellites, brighter colors indicate the 10 new Follow-up observations earlier this led by Scott Sheppard (Carnegie Institu- inds and two others from last year (S&T: Sept. year allowed Sheppard to establish firm 2017, p. 13). The prograde moons (purple, tion for Science) has identified 10 new blue) orbit relatively close to Jupiter, while its orbits for each object. Valetudo, in moons of Jupiter, bringing the known retrograde moons (red) are farther out. Valetudo particular, becomes eligible for naming totalto79—themostofanyplanetin (green) is the exception: a far-out prograde body. because it has now been observed during oursolarsystem.Ofthattotal,Shep- three oppositions of Jupiter. Valetudo pardhasledthesearchesthatdiscov- larger precursors that were shattered by is the Roman goddess of health and ered 51 of them. collisions early in Jupiter’s history. hygiene; she’s a descendant of Jupiter and Dozens of Jupiter’s moons circle the Ofthe10newfinds,sevenofthem known as Hygieia in Greek mythology. planet in a retrograde direction, that is, areamongtheseretrogradeobjects. Sheppard’s searches also swept up oppositethatoftheplanet’sspin,ina TwomoreofthemorbitJupiterin many of the 11 “lost” satellites of Jupi- swarm of distant orbits. They cluster prograde directions (in the same sense ter, bodies whose orbits are so poorly in three groups of 15 to 20 objects, as Jupiter’s rotation) and appear to be knownthattheyessentiallyhavetobe named for members Ananke (discovered members of a smaller group anchored discovered all over again. in 1951), Carme (1938), and Pasiphae by Himalia (discovered in 1904). ■ J. KELLY BEATTY (1908). Most likely each of these moon- “Our other discovery is a real • For more on this discovery, visit let “families” represents fragments of oddball and has an orbit like no other https://is.gd/10newmoons.

SOLAR SYSTEM Organics Inside Enceladus: Complex Enough for Life?

NASA’S CASSINI made Enceladus, one of (CH4) has an atomic mass of 16 amu. ’s icy moons, famous for its plumes But in this new study, published in of salty, organics-laced water-ice crys- the June 28th Nature, data from the tals. Now, a closer analysis of data from spacecraft’s Cosmic Dust Analyzer twospectrometersaboardthespacecraft (CDA) revealed that Enceladus’s organic reveals that the carbon-based brew inside complexity extends up to thousands of Enceladus must be more massive and atomic mass units. complex than previously realized. Moreover, the CDA researchers, led Scientists had used Cassini’s Ion and by Frank Postberg (Heidelberg University, Neutral Mass Spectrometer, which can Germany) detected high-mass assem- only measure up to 100 atomic mass blages containing a likely ratio of one An artist’s impression shows Cassini l ying units, to detect relatively simple organic hydrogen atom for every two carbons. through the plumes of Enceladus. compounds. For example, methane This implies the structures are “under-

8 OCTOBER 2018 • SKY & TELESCOPE ORBITS OF JUPITER MOONS: CARNEGIE INSTITUTION FOR SCIENCE / ROBERTO MOLAR CANDANOSA; ENCELADUS: NASA / JPL; EINSTEIN RING: ESO / ESA / HUBBLE/NASA;PULSAR:ESO/L.CALÇADA General Relativity General Best Long-range Test of COSMOLOGY of Enceladus and has overwritten any any overwritten has and of Enceladus remain. molecules resilient most the only so inventory, primordial the altered moon’s drastically the in interior cesses pro- hydrothermal that is explanation possible One atEnceladus. what’s seen than compounds ofprebiotic dance abun- and diversity agreater exhibit bodies small Antonio) those San says Institute, Research (Southwest Glein Christopher coauthor butstudy makeup, Enceladus’s to contributed likely and rial ornitrogen. oxygen as such atoms, other in rich and hydrogen with saturated” the mass the intervening galaxy would would galaxy intervening the mass the measured they Then it. within of stars movements the measuring by galaxy intervening ofthe mass the culated modifi on limits putstrong has none ofthem scales, on galactic tests some conducted have astronomers While system. solar our in itdoes than differently behaves of modifi light-years. On larger scales, theories of ormillions ofthousands on scales exist tests Butfewer system. solar our confi the within tests extensive passed —has on spacetime induces mass that curvature the as gravity matter. ofdark existence the to alternative main the provide theories ofmodifi theories all) not (but outsome itrules and yet, tivity rela- ofgeneral test galaxy-scale best the ASTRONOMERS HAVEASTRONOMERS CONDUCTED into a blue circle around itself. around ablue circle into galaxy star-forming adistant from light bent has gravity galaxy’s anearby where observations of a so-called ofaso-called observations Telescope Large Very and Telescope Hubble Space investigated team The test. June 22nd 22nd June the UK) in ofPortsmouth, (University Or perhaps life arose in the ocean ocean the in arose life perhaps Or mate- oforganic lots contain Comets General relativity — which describes describes —which relativity General Collett and colleagues fi colleagues and Collett Now, a study led by Thomas Collett Collett Thomas by led Now, astudy ed gravity. ed gravity predict that gravity gravity that predict gravity ed Science has provided such a such provided has ed gravity. These These gravity. ed rst cal- Einstein ring nes nes of

, o oeinformation. more for after subtractingthelensinggalaxy’s light. set). Theso-called distort thelightfrom amore distantgalaxy(in- galaxy inforeground) actsasacosmiclensto p • ■ biology. own its harbors Enceladus fi to decades wait might scientists planetary system, Saturn’s to fi no gone and Cassini With oflife. kind any lacks Enceladus that is hypothesis ditions by feasting on methane. con- Enceladus-like in survive can that recently identifi Austria) ofVienna, Taubner (University Ruth-Sophie by led Agroup heritage. cometary ofits signatures organic ■ test modifi to needed be will tests Additional years. 6,500 light- than less on scales expected described by relativity, behaves as scales tolength date.” onthese and type ofthis ofgravity test robust most “the measurements the Hecalls study. the in involved not was ofGeneva), who (University Lombriser Lucas says studies, previous plagued have that uncertainties of systematic is free relatively test So this ing galaxy. interven- ofthe nature the about tions on assump- less relied team Collett’s ity, predicts. relativity general as —exactly motions stars’ the by measured as mass the matches ture curva- spacetime by inferred mass The aring. into light galaxy’s background the bend to order in have to have rm plans to send another spacecraft spacecraft another send to plans rm

The nearbyESO325-G004(large elliptical Visit ELIZABETH HOWELL MONICA YOUNG Still, Glein cautions that the default default the that cautions Glein Still, This study shows that gravity, as as gravity, that shows study This ofrelativ- tests lensing other Unlike https://is.gd/enceladusorganics ed gravity more generally. more gravity ed ed a strain of bacteria ofbacteria astrain ed Einstein ring nd out whether nd outwhether becomes visible becomesvisible skyandtelescope.com 15th 15th June the in appear results The forces. known four ofthe weakest the already is gravity —and strength 1% ofgravity’s than less have itmust exist, does force afi if that conclude researchers the system, ofthis observations of radio orbit. mutual their altering slightly ways, different in dwarf white the and star neutron on the pull would center, galactic the in peaks density whose halo, Way’s matter dark Milky the exist, afi If compact. so nearly isn’t dwarf white The matter. dark with interactions possible any enhance could fi gravitational extreme its that dense so is neutrons, into compacted been have atoms whose pulsar, The center. galactic ofthe direction the in Earth from light-years 3,800 lie orbit, 68-day wide arelatively in are which panion, J1713+0747. PSR system binary the using effect for this tested colleagues and Germany) Astronomy, for Radio Institute Planck (Max Shao Lijing pull. tional matter’s gravita- dark or diminish strengthen could matter dark and with both normal interact to ability Butafi matter. dark toward freely fall should matter matter. work on dark a fi could one that ofnature, force fth of existence the about speculated have results experimental anomalous explain to attempting scientists Some forces. nuclear weak and strong the and tism, electromagne- gravity, forces: mental ofnature. force mental fi ofahypothetical existence the constrain to system binary pulsar of “Fifth Force” of “Fifth TestPulsar Existence Limits COSMOLOGY ■ SCIENTISTS RECENTLYSCIENTISTS STUDIED

ELIZABETH HOWELL Drawing from more than 20 years 20years than more from Drawing com- dwarf white its and pulsar This normal that predicts Relativity funda- four about know We already Physical Review Letters Review Physical fth force that has the the has that force fth pulsar–white dwarfpair Artist’s conceptof • fth force did did force fth OCTOBER 2018 . fth funda- fth a eld

9 NEWS NOTES

July 2005 BLACK HOLES Destroyed Star Feeds Black Hole Jet

FOR THE FIRST TIME astronomers have The mere existence of the jet witnessed the birth and growth of a doesn’t mean the fl are-up comes from black hole’s jet, fueled by a star shred- a disrupted star, cautions Suvi Gezari ded in the black hole’s gravitational (University of Maryland), as active fi eld. Such tidal disruption events are black holes often fl are unexpectedly. June 2011 May 2012 thought to fuel jets some 10% of the But this event, called Arp 299-B AT1, time, but until now the events have has a big point in its favor: It created a been too far away to see the resulting jet that’s angled away from the axis of beams of plasma. the supermassive black hole. We see the In January 2005 Seppo Mattila big dusty donut surrounding the black (University of Turku, Finland) and col- hole edge-on, which means that a jet leagues spotted an infrared fl are near fueled by an accretion disk ought to be Oct. 2013 Nov. 2013 the active black hole of the western oriented vertically. Instead, the newly galaxy in the galactic pileup Arp 299. By created jet points about 25° to 35° from July, a compact radio source had joined our line of sight. That’s easily done with it. Over the next decade, this radio a disrupted star, as its debris may fl y out source grew and stretched into a clumpy at any angle. streak. Material in the jet at fi rst moved Mattila and colleagues calculated at almost the speed of light, then slowed June 14th in Science that, based on their June 2015 June 2015 downtoamere22%oflightspeedasit estimates of the event’s radiative power, ran into surrounding gas and dust. thedestroyedstarcontainedbetween 2and7solarmassesandunleasheda t Over a decade, astronomers watched the radio-emitting region in Arp 299’s western core thousand times more radiation than a stretch out into a jet, using frequencies of 5.0 standard core-collapse supernova. GHz (orange) and 8.4 GHz (green). ■ CAMILLE M. CARLISLE

PULSARS Although astronomers have seen is right. Moreover, it amplifies the emis- A Magnifying Glass for plasma lensing before, it wasn’t obvious sionfromthepulsar’stwopolesdiffer- that it should happen in this system. ently,sothelensisactuallyresolving a Pulsar But when Robert Main (University of theemissionfromthetopandbottom ASTRONOMERS HAVE DISCOVERED a Toronto) and colleagues observed the oftheneutronstar—that’stheequiva- pulsar that comes with its own magnify- system for a full orbit using the 305- lent of resolving a flea on the surface of ing glass — courtesy of its brown dwarf meter dish at Arecibo Observatory, they Pluto using Earth-based telescopes. (For companion that’s being torn to shreds. sawtheradiopulsesbrightenjustbefore reference, New Horizons flew right by The pulsar PSR B1957+20 and the and just after every pulsar eclipse. The Pluto and still only resolved features 80 brown dwarf are dancing a cosmic magnification differed by frequency, meters, or 260 feet, wide.) The results dervish in an eclipsing binary system just as expected for a lensing event. appear in the May 24th Nature. 6,500 light-years away. During every In the same way that water bends ■ MONICA YOUNG 9.2-hour orbit, the brown dwarf eclipses sunlight, plasma the pulsar for about 50 minutes. around the brown Their dance won’t last — in addi- dwarf can bend and tion to its lighthouse-like beam of radio concentrate the waves, the so-called “black widow” pulsar’s radio beam pulsar releases a fi erce wind of energetic when the alignment particles that’s slowly blasting away its companion (S&T: Nov. 2013, p. 16). But u In this artist’s before the brown dwarf fully disinte- concept, the pulsar grates, its cocoon of plasma acts like a PSR B1957+20 is seen in the background through magnifying glass that resolves two areas the cloud of gas envel- of emission on the pulsar only 20 km oping its brown dwarf

(12 miles) apart. companion. RADIO S. MATTILA JET: AND M. PEREZ-TORRES ET AL. / BILL SAXTON (NRAO / AUI / NSF); PULSAR: MARK A. GARLICK / DUNLAP INSTITUTE FOR ASTRONOMY & ASTROPHYSICS, UNIV. OF TORONTO

10 OCTOBER 2018 • SKY & TELESCOPE The soft rock deposits of Medusae IN BRIEF Fossae Formation are easily eroded Webb Telescope To into a variety of shapes, as seen here on an isolated, windswept hill. Launch in 2021 The launch of NASA’s James Webb Space Telescope has been delayed to March 30, 2021. The new date is almost a year later than what NASA tentatively announced earlier this year (S&T: Jan. 2018, p. 12) and comes from a report released by an independent review board. The report puts a new price tag on the mission’s develop- SOLAR SYSTEM ment: $8.8 billion. This exceeds the $8 Long-ago Supervolcano Created Mars Rock Formation billion cap placed by Congress in 2011, which means that the mission will face SCIENTISTS HAVE ESTABLISHED that When a volcano explodes, explains Congressional reauthorization. While the 3 billion years ago, a supervolcano cre- lead author Lujendra Ojha (Johns Hop- astronomical instruments for Webb are ated one of the largest rock deposits on kins University), it spews gas, ash, and ready to go, the spacecraft bus and the Mars, the Medusae Fossae Formation lava into the atmosphere. The pressure i ve-layer sunshield designed to protect the infrared instruments from the Sun’s heat (MFF), which spans an area equivalent from the explosion causes lava to frag- are still undergoing integration and testing. to one-fourth of the contiguous U.S. ment. The highly fragmented lava then (To read more about specii c problems, Scientists have been probing the descends and starts to cool, trapping gas visit https://is.gd/JWSTtesting.) NASA nature of the massive formation since particles inside it to form porous rock. has fully endorsed the review board’s more the 1960s. Using orbiter radar, they This ancient supervolcano created than 30 suggestions, designed to address recently narrowed its composition down the largest known volcanic formation human errors as well as other factors to two main possibilities: porous rock or in the solar system. Its eruptions would impacting Webb’s development schedule, including what board chair Thomas Young kilometers-thick ice covered by ash. have had incredible effects on the Mar- termed “excessive optimism.” NASA Now, scientists have used grav- tian climate, spewing massive amounts and the independent review board both ity data from Mars orbiters to resolve of climate-altering gases into the atmo- conclude that Webb’s incredible science the confl ict, using the formation’s sphere and ejecting enough water to potential makes mission success criti- gravitational pull on the satellites to cover Mars in a global ocean more than cal: “Webb will be worth the wait,” says infer its mass and density. Combining 9 cm (4 inches) thick. Ojha and JHU Thomas Zurbuchen (NASA Science Mis- this information with the radar data collaborator Kevin Lewis report this sion Directorate). ■ enabled researchers to rule out ice as result in the June Journal of Geophysical MONICA YOUNG MFF’s main ingredient, leaving porous Research: Planets. Dawn Reaches Final Orbit rock as the viable candidate. ■ JULIE FREYDLIN Around Ceres NASA’s Dawn spacecraft has entered a new and i nal orbit that will take it less than 35 km (22 miles) above the surface of Hayabusa 2 Arrives asteroid Ceres. Since the two i rst rendez- voused on March 6, 2015, the probe has at Asteroid Ryugu come no closer than 385 kilometers to the On June 27th, after a 3½-year jour- dwarf planet’s surface (S&T: Dec. 2016, p. ney, Japan’s Hayabusa 2 (S&T: June 16). Attaining a lower orbit was no mean 2018, p. 22) arrived at its home for the feat: NASA engineers examined more than next 18 months: the kilometer-wide, die- 45,000 possible trajectories before settling shaped asteroid Ryugu (named after a on a solution. The i nal 27-hour, 13-minute dragon’s palace in a Japanese folktale). orbit puts Dawn in a 3:1 resonant orbit with the asteroid, which rotates once every 9 The view shows a bifurcated pole, an p Hayabusa 2’s view of Ryugu on June as-yet unnamed large crater crossing its hours, 4 minutes. In its last months, Dawn 26, 2018, one day before its offi cial will map Ceres in unprecedented detail equatorial bulge, and plenty of boulders rendezvous. strewn about its surface. Hayabusa 2 is while continuing to collect neutron and keeping pace 20 km (12 mi) from the as- gravitational fi eld before the spacecraft gamma-ray spectra, which probe the sur- teroid in its orbit around the Sun and was comes in for a series of sampling opera- face’s composition. Among other things, due to approach to within 5 km by the tions set to begin this fall. The sample engineers are targeting the crater Occator end of July. The mission team will map will return to Earth by December 2020. before the mission’s end later this year. the surface and analyze Ryugu’s weak ■ DAVID DICKINSON To see images from Dawn’s new vantage point, visit https://is.gd/DawnsFinalOrbit. ■ MEDUSAE FOSSAE: HIGH RESOLUTION STEREO CAMERA / ESA; HAYABUSA: JAXA / UNIV. OF TOKYO / KOCHI UNIV. / RIKKYO UNIV. / CHIBA UNIV. / NAGOYA INSTITUTE OF TECHNOLOGY / MEIJI UNIV. / UNIV. OF AIZU / AIST DAVID DICKINSON

skyandtelescope.com • OCTOBER 2018 11 OUR LOCAL VOID by Ken Croswell

AN EMPTY EXPANSE Just beyond the Milky Way begins a vast near-emp- tiness of space some 250 million light-years wide. Graduate student Johan Hidding visualized this void using computational geometry, starting with galaxies cataloged in the 2MASS Survey and then recreating the filamentary cosmic web of dark matter The

12 OCTOBER 2018 • SKY & TELESCOPE O O I ID Next Door Next probe oneofthesegigantic cosmicstructures. doorstep, givingastronomers theirbestchanceto An enormous region ofnear-emptiness D syntlsoecm• skyandtelescope.com starts onour OCTOBER 2018 13 VISUALIZATION: JOHAN HIDDING / UNIVERSITY OF GRONINGEN / KAPTEYN INSTITUTE; BACKGROUND: KRIANTI / GETTY IMAGES Sagittarius Dwarf Irregular Galaxy Our Local Void

alaxies are gregarious, most living near others. For HOME example, our galaxy and its great spiral neighbor 2.5 This view shows the Gmillion light-years away, Andromeda, rule the Local Milky Way, as well as Group, which boasts more than 100 galaxies. several of the dwarf But on the far side of our galaxy, starting less than 4 mil- galaxies around it, rela- lionlight-yearsfromEarth,lurksadarkdomainthatbears tive to the supergalactic almost no galaxies at all. Moreover, this void is gargantuan, plane (circular white spanning a quarter billion light-years. Its center hides behind lines). This plane con- thegalacticplaneinAquilaorSagittarius. Atfirstglance,voidsmightseemasuninvitingtoastrono- tains the of mers as treeless meadows are to arborists. After all, you’re not galaxies as well as the likely to dazzle your friends by showing them a void through Virgo Cluster. your telescope. But voids are important, because most of the space of the universe is in one void or another. Voids help sculpt the large-

The Local Void stretches out ahead of you for another 250 million light-years. It’s the intergalactic equivalent of driving through western Kansas.

scale structure of the universe, as galaxies flow out of them and into the glowing sheets and filaments that crisscross the cosmos. In addition, the few galaxies that still inhabit voids may evolve differently from galaxies elsewhere. Because of its proximity to us, the Local Void provides ourbestchancetostudyalloftheseeffectsinaction.Here, astronomers can search for galaxies so feeble they would be undetectable in more distant voids. And because the few galaxiesintheLocalVoidarenearby,wecanscrutinizethem to see whether they differ from galaxies that grew up in more urban locations.

Discovering the Local Void AXY: AXY: TwodecadesbeforeR.BrentTully(UniversityofHawai‘i) and J. Richard Fisher (National Radio Astronomy Observa- tory)discoveredtheLocalVoid,thepairhadmetingraduate school. “I was the data guy,” Fisher says, “and Brent was the interpreter.”FollowingthecompletionoftheirPhDtheses, Fisher set out to observe more than 1,000 galaxies and mea- suretheirredshifts,asignoftheirdistancesfromtheMilky Way. Tully then plotted the three-dimensional positions of theseandothergalaxies. “Therewasawholesectorofskythatwasreally,really emptyofgalaxies,”Tullysays.Unfortunately,thedusty galacticplanecutsrightthroughthisemptysector,obscuring any galaxies it might possess. “But it pokes out on each side, well above and below the plane of the galaxy,” he adds. In M33 their 1987 Nearby Galaxies Atlas, which contains information on2,367nearbygalaxies,TullyandFishercalledthisbarren

DIAGRAM: DANIEL POMARÈDE (CEA UNIVERSITÉ PARIS-SACLAY); BARNARD’S GAL ESO; SAGITTARIUS DWARF IRREGULAR: NASA / ESA / HUBBLE HERITAGE TEAM (STSCI / AURA), ACKNOWLEDGMENT: MOMANY Y. (UNIV. OF PADUA) region the Local Void.

14 OCTOBER 2018 • SKY & TELESCOPE u BARNARD’S GALAXY This dwarf irregular galaxy, also known as NGC 6822, lies 1.6 million light-years from Earth.

uu SAGITTARIUS DWARF IRREGULAR GALAXY Not to be con- fused with the Sagittarius Dwarf Spheroidal near the Milky Way, this galaxy l oats 3.4 million light- years away at the edge of the Local Void.

Barnard’s Galaxy

SUPERGALACTIC EQUATOR

Sagittarius Dwarf Spheroidal

Andromeda Milky Way

Large Magellanic Cloud

Small Magellanic Cloud

skyandtelescope.com • OCTOBER 2018 15 Our Local Void

By then, astronomers had realized that most galaxies link THE EIGHT GREAT up via dark matter to form a fi lamentary network across the GALAXIES NEXT DOOR universe. Between the bright nodes and fi laments are dark voids, the sparsely populated countryside of the cosmos (S&T: The Milky Way is such a colossus that only eight Feb. 2015, p. 20). According to standard cosmology, voids are other galaxies within 20 million light-years rival regions that started off with a bit less matter than average its size, mass, and luminosity. Remarkably, all and then expanded. of the great galaxies nearby occupy the same The overall universe is also expanding, of course, but plane, one that is proportionately even thinner different parts do so at different speeds. Some regions, than an American dime: the Milky Way and such as the , don’t expand at all, thanks to the Andromeda Galaxies, the two superpowers of gravitational pull of the member galaxies. In contrast, voids the Local Group; the giant spiral galaxy M81 contain so little matter that their gravity barely brakes the in ; the giant elliptical galaxy Maf- expansion, so they expand faster than the average. Over time, fei 1 and its giant spiral neighbors and galaxy groups and clusters use their gravitational pull to lure additional galaxies into their lairs, tugging galaxies out of the IC 342, which all hide behind interstellar dust centers of voids and toward their glowing edges. in Cassiopeia and Camelopardalis; the giant “The rich get richer and the poor get poorer,” Tully says. edge-on spiral galaxy NGC 253 in Sculptor; and Just as gravity causes water to fl ow from mountaintops to the giant elliptical galaxy A and the valleys, so gravity makes galaxies stream from voids to groups giant barred spiral galaxy M83 in Hydra. and clusters. Voids therefore assist groups and clusters in This plane nearly coincides with the so-called shaping the universe’s large-scale structure. supergalactic plane, which includes the Virgo Recent searches behind the Milky Way’s dusty veil con- Cluster. In supergalactic coordinates, the SGX fi rm the Local Void’s existence. “With a radio telescope, we and SGY coordinates describe the superga- can actually peer straight through the stars and the dust that lactic plane, and SGZ is perpendicular to it. The obliterate the optical and even the infrared view,” says Lister Great Attractor and Shapley Concentration Staveley-Smith (University of Western Australia). lie at negative SGX and the newfound distant His team used the Parkes Observatory to seek unseen gal- axies by the 21-centimeter radiation that their neutral hydro- void lies at positive SGX; the Virgo Cluster lies gen gas emits. “Astonishingly, we fi nd at positive SGY; and very few external galaxies behind the the Local Void lies at 700 ALFAZOA J1952+1428 central bulge of the Milky Way within positive SGZ, above quite a large radius,” he says. the supergalactic plane. These clusters Voyage to the Void and voids move us Visiting this dark realm is easy. Just toward negative aim your starship into the Milky Way’s KK 246

SGZ (km/s) disk, keeping on your left and SGX, positive SGY, The Local Void and negative SGZ, Sagittarius on your right. After 27,000 light-years you speed past the Milky

explaining the Local S Maffei 2 Way’s center in Sagittarius, then reach Group’s high speed M83 Milky Way M81 the far side of the galaxy. As you zoom through space. 0 past the disk’s edge, you look beneath u LOCAL SHEET the to see the Sagittarius Nine galaxies, including Dwarf Spheroidal, 85,000 light-years the Milky Way, dominate Centaurus A Andromeda from Earth. This galaxy is a satellite of IC 342 the Local Sheet, which NGC 253 the Milky Way that our galaxy’s tidal sits below the Local forces are tearing apart. , SOURCE: DANIEL POMARÈDE (CEA S&T

Void from the perspec- SGZ (km/s) tive of the supergalactic The Milky Way is mighty, far larger plane. Circles on this and brighter than most of its peers, but –450 plane mark 6.5 million, you soon leave our galaxy and its many 13 million, and 20 mil- 0 satellites behind. You hurtle past two lion light-years. Two more Local Group galaxies in Sagit-

galaxies, KK 246 and SGY (km/s) ALFAZOA J1952+1428, –450 tarius. The fi rst, 1.6 million light-years are l ying out of the void –450 0 450 from Earth, is Barnard’s Galaxy, also SGX (km/s) UNIVERSITÉ PARIS-SACLAY; SIDEBAR BACKGROUND: KRIANTI / GETTY IMAGE and toward the plane. known as NGC 6822. Farther out, at GALAXIES DIAGRAM: LEAH TISCIONE /

16 OCTOBER 2018 • SKY & TELESCOPE “I love to talk about nothing. It’s the 280 Sagittarius only thing I know anything about.” Void

— Oscar Wilde 190 Microscopium Void 3.4 million light-years, you spy the dim Sagittarius Dwarf

Irregular Galaxy patrolling the Local Group’s lonely frontier. 93 Local Then you plunge into darkness. The vast emptiness of the Void Local Void stretches out ahead of you for another 250 million light-years. That’s right: 100 times the distance between the 0 Milky Way MilkyWayandtheAndromedaGalaxy,withalmostnothing to see, left or right, up or down. It’s the intergalactic equiva-

Light-years (millions) Void lent of driving through western Kansas. –93

Nothing Really Matters The Local Void is essential for understanding our motion –190 Canis Major through the universe. Astronomers measure our movement Void relative to the cosmic microwave background, the Big Bang’s z –280 afterglow,whichcosmologistsdefinetobeatrestrelativeto yx theuniverse.Thisradiationisblueshiftedinthedirection –280 –190 –93 0 93 190 280 we’re approaching and redshifted in the direction we’re rac- Light-years (millions) ingawayfrom. p VOIDS IN THE NEIGHBORHOOD Using computational geometry, ThesemeasurementsrevealthattheMilkyWayandits Johan Hidding and others visualized the low of matter near the Milky neighbors are zipping through the universe at 630 kilome- Way, which serves to outline the Local Void and several other nearby terspersecond,or1.4millionmph.That’sfast:Earthcircles cosmic voids. The walls and ilaments shown here represent dark matter the Sun at only 30 km/s, the Milky Way moves toward the structures, based on the distribution of galaxies cataloged in the 2MASS AndromedaGalaxyatonly110km/s,andtheSunrevolves Redshift Survey. around the galactic center at approximately 250 km/s. Astronomers have long known of two strong gravitational through space. The Local Void supplies the third. tugs that explain most of our motion through the universe. In 2008, Tully’s team found that we stream away from the OnecomesfromVirgo,thenearestgalaxyclusterat54mil- gravitational hill the Local Void creates at about 260 km/s. lion light-years away, whose gravitational force tries to pull That’s greater than the Virgo-induced velocity, which the us toward it. The other tug comes from a grander gathering astronomers put at 185 km/s, but less than the speed toward of more distant galaxies in a direction nearly perpendiculartoVirgo—theGreatAttractor and, beyond it, the Shapley Concentration. Dipole Repeller Plus,anewfoundvoiddubbedtheDipole Void Repeller, much farther than the Local Void - and on the opposite side of us from these clus- ters,helpstheminthiseffort,makingusflow Arch down a steeper gravitational slope toward the Cluster clusters (S&T: May 2017, p. 8). Butthesemightystructuresexplainonly twoofthethreedimensionsofourmotion Local Void Loca r u ALL AROUND US Several cosmic structures deter- reat Attractor mine the motion of our galaxy, and indeed of the whole -Pisces Shapley Concentration Supercluster Local Group of galaxies, through space. We can un- Coma derstand this motion in three dimensions relative to the Cluster supergalactic plane: Our galaxy is moving back along the x axis, sliding down the gravitational hill created by the dense collections of galaxies in the Great Attractor and the Shapley Concentration on one end, and the SGZ Dipole Repeller void on the other end. The Virgo galaxy Lepus cluster pulls us along the y axis; meanwhile, the Local Cluster SGX Void steepens the gravitational hill that our galaxy SGY

STRUCTURE: DANIEL POMARÈDE (CEA UNIVERSITÉ PARIS-SACLAY, ACKNOWLEDG YEHUDAMENT: HOFFMAN (HEBREW UNIV. OF JERUSALEM), HÉLÈNE COURTOIS (UNIV. FRANCE), OF LYON, R. BRENT TULLY (UNIV. OF HAWAI‘I); LOCAL VOID IN CONTEXT: JOHAN HIDDING / UNIVERSITY OF GRONINGEN / KAPTEYN INSTITUTE slides down on the z axis.

skyandtelescope.com • OCTOBER 2018 17 Our Local Void

Patient observers could then a graduate student at the Univer- help cosmologists sity of New Mexico, was searching for 21-centimeter radiation from neutral reconcile reality with hydrogen gas in galaxies hiding behind theory by turning up new the galactic plane. He found lots of new galaxies, but the one in Aquila stood galaxies in the void. out by virtue of its small redshift. “It wasspecialbecauseitwassocloseto theGreatAttractorandtheShapleyCon- our own galaxy,” McIntyre says. Only centration, which amounts to 455 km/s. later did he and his colleagues spot the Furthermore, the Local Void’s “push” galaxy’s stars. is nearly perpendicular to the pulls from Becausethesetwovoidgalaxiesare both Virgo and the Great Attractor. To nearby, the can picture the situation, you must know detect their red giants, aging stars whose anamazingfactabouttheeightgreat apparent magnitudes reveal precise galaxies nearest our own: Every galactic distances to their galactic homes. That’s goliathwithin20millionlight-yearsof important, because by comparing the us resides in nearly the same plane (see galaxies’ distances with their velocities boxonpage16). derived via , astronomers can see These great galaxies constitute part whether the void is actually expanding. of what Tully calls the Local Sheet, It’s not easy, though. “Observing which is a wall of the Local Void. The empty space is very hard,” says Luca LocalVoidisabovetheLocalSheetand Rizzi (W. M. Keck Observatory). causes it to move down. As evidence Fortunately, the two void galaxies for this movement, he points to the nearby are like glowing flotsam tracing p KK 246 The gaseous disk of this void galaxy Leo Spur, a filament some 35 mil- in Sagittarius, marked here as contours, ex- thecurrentsofadarksea.“Theyarein lion light-years below the Local Sheet. tends ive times farther out than its stars do, as thevoid,buttheyareclosertousthan Because of the Local Sheet’s downward seen in the background black-and-white image. to the center” of the void, Rizzi says. movement, the Leo Spur’s galaxies In a study published last year, his team have smaller redshifts than they would otherwise. reportedthatbothvoidgalaxiesareracingawayfromthe LocalVoid’scenterandtowarditswallathundredsofkm/s,a Void Where Prohibited signthatthevoidisindeedexpandingandgrowingeveremp- Despite its name, the Local Void is not completely free of gal- tier.“Voidsliketogetridofgalaxiesasfastastheycan,”he axies. “The void is partitioned by these wispy filaments that says, as galaxies outside the voids tug the void galaxies away. tracethroughit,”Tullysays.Thefilamentscontainchainsof Both void galaxies are extremely isolated. Whereas lots of galaxies that glow like dimly lit towns on a rural road. Nor is galaxiesdwellclosetoourown,KK246doesn’thaveasingle theLocalVoidperfectlyround.Instead,it’slumpy. knownneighborwithin10millionlight-years. The two nearest-known inhabitants of the Local Void are KK Andyet,despitetheirextremeisolation,thevoidgalax- 246 and ALFAZOA J1952+1428; the two galaxies lie about 25 ies seem normal. They have gas, just like most of the Local million light-years away, in Sagittarius and Aquila, respectively. Group’s outlying members, and probably for the same reason: Both galaxies are dwarf irregulars, miniature versions of the becausethere’snogiantgalaxynearbytostealit.Infact,KK twobrightestsatellitesoftheMilkyWay,theLargeandSmall 246’s gas disk extends five times farther out than its stars

MagellanicClouds.Thevoidgalaxiesemitonlyafewpercentas do. Even that isn’t unique, however, as a few dwarf galaxies 2011; JUNE , muchlightastheLargeMagellanicCloud,butliketheMagel- elsewhere have equally impressive gaseous envelopes. lanicCloudstheybothpossessgasthatisspawningnewstars. Thus,aslongasadwarfgalaxysteersclearofgas-grabbing Infact,itwasthegas,notthestars,thatfirstsignaled giants,itcanleadanormallife,whetherornotit’sinavoid. thepresenceofthevoidgalaxyinAquila.TravisMcIntyre, Internal processes govern the galaxy’s evolution. THE ASTRONOMICAL JOURNAL ASTRONOMICAL THE THE LEO SPUR The Leo Spur is a \ lament of galaxies beneath the supergalactic plane and thus on the other side of us from the Local Void. Members include the irregular galaxy NGC 2337, which is 37 million light-years away in Lynx, and the edge-on spiral NGC 2683, which is 31 million light-years from Earth, also in Lynx. DIAGRAM: KRECKEL ET AL., SIDEBAR BACKGROUND: KRIANTI / GETTY IMAGES

18 OCTOBER 2018 • SKY & TELESCOPE u HIDING IN PLAIN Perseus- 75°N Local SIGHT In this all- Pisces Void Supercluster sky view of nearby 60°N galaxies, the plane of 45°N the Milky Way (gray) is almost directly 30°N perpendicular to the supergalactic plane, 15°N which extends from left to right. The Local 360° 340° 320° 300° 280° 260° 240° 220° 200° 180° 160° 140° 120° 100° 80° 60° 40° 20° 0° Void (black oval) sits directly behind the 15°S galactic plane, which makes i nding galaxies 30°S in this vast expanse a challenge. 45°S Distance (light-years) 60°S 0 185 million 370 million Coma 75°S Cluster 0 2,000 4,000 6,000 8,000 Eridanus Fornax Virgo Distance (km/s) Cluster Cluster Cluster

Nothing Ventured, Nothing Gained force to evacuate the mass out of the void, because gravity Still, the Local Void poses a possible problem for standard cos- itself can’t do it.” mology. “The Local Void is fascinating,” says P. James Peebles Peebles wonders whether amateur astronomers making (Princeton University). “From the point of view of a cos- long exposures with CCDs at dark sites might discern new mologist, the enigma is how few stars there are in this void.” dwarf galaxies in the Local Void. Numerical simulations of cosmic evolution predict that voids “Wouldn’t it be lovely?” he asks. “Amateurs pointing at the should have a mass density that is about 10% of the mean Local Void and just painfully stitching across it could pick up density of the universe. much fainter galaxies.” He cites the work of amateur R. Jay “That density — 10% of mean — is far greater than the GaBany, whose superb images have revealed dim structures number density of galaxies in the Local Void,” says Peebles. around other galaxies (S&T: Jan. 2009, p. 92). He estimates the actual number density of Local Void galaxies The ideal hunting ground would probably lie away from the is only about 1% of the cosmic mean. Milky Way’s dusty plane. Because the Local Void is so large, So where are all the galaxies? Giants like our own don’t it juts out well above the galactic plane in , north- form in such a sparse environment, but Peebles says dwarfs ernmost , and southernmost Libra. It can also be seen should still arise, albeit in smaller numbers than elsewhere. well below the galactic plane in and southeast- Because they are dim, dwarfs are ern Sagittarius. As a result, patient harder to fi nd than giants. How- observers of these constellations could ever, the Local Void is so close that help cosmologists reconcile reality astronomers should have found more with theory by turning up new void dwarf inhabitants than they have. galaxies in the vast expanse of dark- Not everyone thinks this “void ness next door. phenomenon” spells trouble, though. Meanwhile, voids themselves Jeremy Tinker (New York University) will keep expanding, evicting their THE ASTRO- THE says the apparent lack of dwarf galax- remaining residents and thereby THE ASTRONOMI- THE ies agrees with numerical simulations helping to build the glittering galactic of cosmic evolution. The matter that architecture that spans the cosmos. exists in voids consists primarily of Sometimes you really do get some- dark matter plus a smattering of gas. thing from nothing. In voids, this material may have gath- ered into dark galaxies that produced ¢ KEN CROSWELL earned his PhD few if any stars. at Harvard University for studying the p ALFAZOA J1952+1428 , 20 JANUARY 2017 “If there was literally no matter The second nearest gal- Milky Way Galaxy and is the author of inside of the voids, that would com- axy known in the Local Void also abounds with gas. The Alchemy of the Heavens: Search- , SEPTEMBER ALFAZOA: 2013; RIZZI ET AL. 2017, It’s 20 million light-years from KK 246 and 27 million pletely blow the doors off” standard light-years from Earth. Searchers found the galaxy ing for Meaning in the Milky Way, cosmology, Tinker says. “You would not by its stars but by the radio glow from its neutral which was a Los Angeles Times Book PHYSICAL JOURNAL LOCAL VOID BEHIND GALACTIC PLANE: COURTOIS ET AL., CAL JOURNAL have to come up with some extra hydrogen gas. Prize i nalist.

skyandtelescope.com • OCTOBER 2018 19 INTERSTELLAR INTERLOPER by Greg Laughlin

`Oumuamua’s Visit

SOLAR SYSTEM VISITOR This artist’s im- pression shows the fi rst discovered inter- stellar body, called `Oumuamua. Although estimates for the true shape vary wildly, its discoverers are sticking with this strange, highly elongated profi le. In this model, it’s about 400 meters (1,300 feet) long. ESO / M. KORNMESSER

20 OCTOBER 2018 • SKY & TELESCOPE The space rock from beyond the solar system was already well on its way out of the solar system. It had has left us amazed and perplexed. reached perihelion on September 9th, with a searing close approach that brought it four times nearer to the Sun than Earth comes. Outward bound, it passed below Earth’s orbit he Minor Planet Center announces dozens of new solar on October 10th and shortly thereafter cruised by our planet system discoveries every week. Most notices are mun- at a distance only 63 times that of the Moon. By the time T dane, describing the orbits, appearances, and sky loca- the MPC announcement went out, it was nearly as far from tions of unremarkable, newly detected comets and asteroids. the Sun as Mars. But last October 25th, the MPC’s Electronic Circular 2017- The Pan-STARRS astronomers turned to Karen Meech U181 reported the discovery of a singular outsider: a faint (University of Hawai‘i, Ma¯noa) to take the lead in organizing object rushing through the inner solar system that, based on their follow-up efforts. While no roadmap existed for what to its trajectory, was making a one-time visit from the stars. do when confronted with an object arriving from the inter- Postdoc Robert Weryk (University of Hawai‘i, Ma¯noa) had stellar depths, Meech had successfully coordinated worldwide made the discovery a week earlier on October 19th, while ground-based observing programs in support of several NASA looking for near-Earth objects with the aid of the 1.8-meter Pan-STARRS 1 scope. This robotically controlled telescope of WHIRLWIND TOUR The the Panoramic Survey Telescope and Rapid Response System track of the irst-known A (Pan-STARRS) program sits near the summit of the Haleak- interstellar object through ala¯ volcano on Maui. Its primary charge is to locate thou- the solar system. The round sandsofnewasteroidsandidentifythosethatmightthreaten inset shows its location Earth (S&T: June 2018, p. 12). when it was discovered on October 19th. Observations Weryksayshenoticedtheobject“intheprocessof when the object had passed doing my daily job.” (His official title is Planetary Defense the orbit of Jupiter indicate Researcher.)Thebodywasmovingveryfastacrossthe that it had traveled farther sky, which suggested it was close to Earth. Checking the than expected, perhaps pro- archive, Weryk also found it in images from the previous pelled by jets of sublimating ice (see page 25). night.“WhenIputthedatatogethertocomputeanorbit, theorbitdidn’tmakesense.Itwasn’t moving as you’d expect a near-Earth asteroid to move.”

Werykquicklycontactedacol- Path of league in Italy, Marco Micheli (Euro- `Oumuamua peanSpaceAgency),whohadseren- (1I/2017 U1) dipitouslygathereddatawithanESA telescope that also showed the object. Orbit of a “When the three nights were put typical comet together,” Weryk says, “it strongly within solar system

suggestedthatwehadsome- B A thing with an origin outside Saturn our solar system.” Jupiter Sun To the Telescopes! ThereasonWerykandhiscolleagues suspected they had an interstellar visitor on their hands was the object’s B orbit. It was notably hyperbolic,shapedlikeaflattenedU Difference in trajectory on May 3, 2018, instead of the elongated loops or parabolic paths that comets when `Oumuamua was at the same usuallyfollow.Occasionallyaplanetwilltorqueacomet distance as Jupiter from the Sun. intoaslightlyhyperbolictrajectory,butplanetaryscientists 100,000 kilometers

, TRAJECTORY CHANGE SOURCE: ESA hadneverseenonesoextreme.Itmeantthat,unlikeour S&T solarsystem’splanets,asteroids,andcomets,thebodywasn’t gravitationally bound to the Sun. Gravity only Time was very short. When first spotted by Pan-STARRS, Observed trajectory theinterstellarvisitor—whichwasinitiallyestimatedfrom

GREGG DINDERMAN / itsbrightnesstobemorethan100meters(300ft)across—

skyandtelescope.com • OCTOBER 2018 21

PEGASUS

18 Nov 1

h Dec 1

Interstellar Interloper h 0

20 Jan 1, h 22

h 2018 u SKY PATH `Oumuamua came tumbling out of Lyra in 2017 (not

that anyone saw it), looped through 16 h

July 1, h the sky, and was discovered cruis- PISCES Oct 19 2 ing near the Pisces- border 2016 on October 19th. It quickly receded HERCULES in the direction of . The tra- jectory spans 2012 through 2020, July 1, and the loops at its ends are a 2017 parallax effect due to Earth’s yearly BOOTES circuit around the Sun.

60° missions and had a good idea Aug 1

14

h of how to tackle the challenge. h 4 VIRGO “It meant dropping URSA ERIDANUS MAJOR 30° everythingandreallywork- ingaroundtheclock,”Meech says. Her team immediately 0° submitted emergency requests I C a Sept 1 I P T u for observing time to facilities E C L m ua um including the Very Large Tele- 12 O h h f ` 6 –30° h o scope,theGeminiSouthTele- Pat scope, and the Hubble Space CANIS MAJOR Telescope and were approved. Oct 1 HYDRA –60° Overthecomingnights,the world’s most capable instru- 10 h 8h ments turned to the mysteri- ous object. VELA They weren’t alone. Within minutes of the Minor Planet Center’s October 25th Early returns also came from a group headed by David

announcement that a comet of possible interstellar origin Jewitt (University of California, Los Angeles) and Jane Luu GREGG

had been located, other telescopes also began chasing the (MITLincolnLaboratory),whoin1992werethediscoverers object. Joseph Masiero (Jet Propulsion Laboratory) happened of15760Albion,thefirstKuiperBeltobject(besidesPluto). to be observing with the venerable 5.1-meter Hale Telescope TheteamincludingMeechandWerykalsoelicitedcritical LIGHT CURVE: LIGHT 2018 856:L21 2018

at Palomar Observatory. Under less-than-perfect conditions, results by piecing together several successive nights of obser- S&T; he obtained spectra indicating a dull red overall color. Early vations from different telescopes. Most importantly, all this observations also revealed the object looked point-like, with effortrevealedthatthebodyisnotacometinthetraditional no hint of cometary activity. sense.Eveninthedeepestexposures,itappearedasacom- , SOURCE: MICHAEL J. S. ET BELTON AL. / S&T

q `OUMUAMUA’S LIGHT CURVE Compiled by 13 telescopes, this composite light curve shows how `Oumuamua’s brightness changed as it tumbled through space. Although there is a clear periodicity, it doesn’t always follow the exact same pattern. Note that although the data have been converted SKYCHART: GREGG DINDERMAN / ASTROPHYSICAL JOURNAL LETTERS to visual magnitudes, many observations were taken in infrared. / DINDERMAN

Very Large Telescope (Chile) Nordic Optical Telescope (Canaries) Gemini South Telescope (Chile) WIYN Telescope (Arizona) Keck Telescope (Hawai‘i) Canada-France-Hawai‘i Telescope (Hawai‘i) United Kindom Infrared Telescope (Hawai‘i) Gemini North (Hawai‘i)

Oct. 25, 2017 Oct. 26, 2017 Oct. 27, 2017 Oct. 28, 2017 21 22

23

24

Visual magnitude 25

0 2:24 0 2:24 4:48 2:24 4:48 7:12 9:36 12 2:24 4:48 7:12 9:36 12 Time (Universal Time)

22 OCTOBER 2018 • SKY & TELESCOPE pletely star-like point; scientists arrival from beyond the solar sys- estimated that it could be spewing `Oumuamua at a Glance tem, the International Astronomi- out no more than a spoonful of cal Union announced an offi cial Size ~100 meters powdery dust per second. naming scheme, with code letter Perihelion 0.26 a.u. “I” for interstellar. In place of the A Class of Its Own (September 9, 2017) discoverer’s name — in this case, With measurements obtained over Orbital eccentricity 1.2 (hyperbolic) Pan-STARRS — the IAU accepted the a series of nights, observers con- team’s proposed name of `Oumua- structed a light curve of how the Distance from Earth 0.23 a.u. mua, a Hawaiian word for scout (see object’s brightness changed with when it crossed (October 10, 2017) sidebar, page 26). 90 lunar distances time. That plot was illuminating. below Earth’s orbit, With its remarkable name and First, the body is clearly rotating, outbound its remarkable properties, `Oumua- executing a full spin roughly every Closest approach 0.16 a.u. mua was ready for stardom. On 8 hours. Second, the light curve to Earth (October 14, 2017) November 20th, the European shows a startling degree of varia- 63 lunar distances Southern Observatory circulated tion during the course of a single a news release describing the ~20 rotation, as well as from one rota- Meech team’s results. The docu- when discovered tion to the next. The most likely ment linked the undeniably weird interpretation is that the object properties of a fi rst-ever object with has a highly elongated shape, like a weaver’s shuttle, with a name that brings to mind the hand of some far-distant estimates of its aspect ratio (length vs. width) ranging up to extraterrestrial agency and a stunning artist’s impression of 10:1. This measurement strongly suggests that it’s a mono- a menacing starship-like shard silhouetted against a glow- lithic object with some material strength: Were it a loose pile ing fi eld of stars. The story, which had gained international of rubble, as many asteroids are, it wouldn’t be able to prevent attention after being reported fi rst by Sky & Telescope nearly a itself from fl ying apart as it rotates. month prior, vaulted to massive prominence. The eerie paral- Moreover, the irregular brightness changes suggest that lels to Arthur C. Clarke’s novel Rendezvous with Rama were it is tumbling chaotically as it falls through space. Although given wide remark, and in a story for NBC News, astronomer some speculated that at least part of the oddness could arise Seth Shostak (SETI Institute) memorably wondered “if it’s a from patchy refl ectivity on the surface, spectra from all of rock or a rocket.” the telescopes that observed the body consistently indicate To rule out the latter, the Breakthrough Listen project a uniformly reddish surface that would be perfectly in place marshaled an effort in which the 100-m Green Bank Tele- among the icy, carbon-rich bodies (such as the Centaurs) that scope listened for radio broadcasts from `Oumuamua as it inhabit our own outer solar system. rushed away from the Sun. Results of the radio surveillance The newcomer presented a problem of nomenclature. showed no sign of technological activity. As much as it looked Based on its wildly noncircular orbit, the MPC’s fi rst like a spaceship, `Oumuamua was just a rock. announcement classifi ed it as a comet, giving it the designa- tion C/2017 U1. Shortly thereafter, as it became clear that the Slingshot Victim body showed no hint of a coma, it was reclassifi ed as asteroid `Oumuamua leaves both insights and unanswered questions A/2017 U1. As a storm of updated trajectory determinations in its wake. It is small and faint enough that an automated proved beyond doubt that the community was witnessing an survey telescope such as Pan-STARRS 1 was lucky to spot

Gemini North (Hawai‘i) Nordic Optical Telescope (Canaries) Telescope (Canaries) Canada-France-Hawai‘i Telescope (Hawai‘i) Apache Point Observatory (New Mexico) Discovery Channel Telescope (Arizona) Magellan-Baade Telescope (Chile) Hubble Space Telescope

Oct. 29, 2017Oct. 29, 2017 Oct. 30, 2017 Nov. 21, 2017 Nov. 22, 2017 Nov. 23, 2017

4:48 7:12 19:12 21:36 0 2:24 4:48 0 2:24 4:48 4:48 7:12 9:36 12 4:48 7:12 9:36 Time (Universal Time)

skyandtelescope.com • OCTOBER 2018 23 Interstellar Interloper

p JUST A SPECK This deep composite image shows `Oumuamua (circled), surrounded by the trails of faint stars that were smeared out as the tele- scopes tracked the moving object. The image combines multiple images from the Very Large Telescope and the Gemini South Telescope.

it. Had it arrived a few weeks earlier or later, the difference concluded that none is a particularly compelling candidate in Earth’s orbital vantage point would likely have let it slip for `Oumuamua’s parent. They did fi nd that, about 800,000 through undetected. years ago, `Oumuamua traversed within roughly 7 light-years Theveryfactthat`Oumuamuawasfoundhintsthatitis of the planet-bearing red dwarf Gliese 876. But the miss part of a very large population of similar objects pervading distance, while intriguing, was too large to be anything but the galaxy — it’s supremely unlikely that we would have been a chance close encounter; almost certainly, it was just one of luckyenoughtoseetheloneexample.Granted,extrapola- tions that point to a vast multitude on the basis of a single q ALTERNATIVE IDEAS Astronomers have suggested several different example do not generally inspire a great degree of confi dence. shapes for `Oumuamua. The squatter cigar gained popularity, but the Nonetheless, by taking careful account of the total volume body’s strange wobbling spin also leaves open the possibility that it’s a

of space that Pan-STARRS searches, Aaron Do (University of pancake (S&T: July 2018, p. 8). TRAILS:STAR ESO / K. MEECH ET AL; ALTERNATIVE SHAPES: PANCAKE: WILLIAM© 2018 K. HARTMANN, CIGAR: SQUAT ESO / M. KORNMESSER Hawai‘i, Ma¯noa) and colleagues estimated the interstellar density of `Oumuamua-like objects. They concluded that, if we were to slice up our galaxy into regions equal in size to the sphere circumscribed by Earth’s orbit around the Sun, there should be about one interstellar voyager per region. Their calculation suggests that one or more of these bodies is nearly always in the act of rushing through the inner solar system. Equally impressively, it suggests that more than a trillion qua- drillion (1027) of them are orbiting in the galactic disk. Projecting `Oumuamua’s path back in time indicates that it came from the direction of the constellation Lyra. Using its exact point of origin and the speed with which it approached the solar system, astronomers further backtracked its trajec- tory to check whether it may have been ejected from a known nearby star system. Piotr Dybczyn´ski (Adam Mickiewicz Uni- versity, Poland) and Małgorzata Królikowska (Polish Academy of Sciences) assessed more than 200,000 nearby stars but

24 OCTOBER 2018 • SKY & TELESCOPE star thousands of similarly wide stellar passes big planet that`Oumuamuahasexperiencedduring billions of years of galactic wandering. t GRAVITY ASSIST Such forlorn travelers were likely set on Giant planets orbiting far their journeys by massive planets in their asteroids / comets from their stars can kick home systems. We think the same hap- small bodies out of their pened here. In the so-called Nice Model, planetary systems. When a body encounters the thegiantplanetsthatorbitourownSunmigratedinwardand planet planet, the planet’s gravity outward as they were forming, launching many planetesi- orbit boosts the object’s veloc- mals into interstellar space. This haphazard rearrangement ity such that it whizzes explainsseveralfeaturesofoursolarsystem,suchasthe away at high speed. The existence of Trojan asteroids around Jupiter and Neptune and new trajectory could take any of a variety of angles thestructureoftheKuiperBelt(S&T: June 2016, p. 16). emanating forward from As the giant planets moved around, they also would have the planet’s direction of wrested at least several Earth masses’ worth of icy, comet- not to scale motion. like planetesimals — comprising quadrillions of individual objects—fromtheSun’sgripandspewedthemintointerstel- lar space. These losses occurred via the same gravitational Dust Problem slingshot mechanism that enabled Jupiter and the other giant If passing interstellar objects have a lot of ice, we’d expect planetstosendtheVoyager,Pioneer,andNewHorizons them to behave like comets when they are warmed by the probes barreling out of the solar system. When replicated Sun. `Oumuamua, however, showed no sign whatsoever of a acrosstheformationofallthestarsinourgalaxy,theprocess volatile-powered coma, indicating that it had no dust-infused couldproduceavastpopulationof`Oumuamua-massbodies. ice that was heated to vaporization — despite passing perihe- Yetconundrumsremain.Inorderforaparticularplanet lionjust0.26astronomicalunitfromtheSun,aregionwhere toejectasmallbodyfromitsparentsystem,thatplanetmust the solar radiation is 16 times stronger than at Earth. At first simultaneously be relatively massive and relatively far from its glance, this absence of activity would suggest `Oumuamua parent star. Put more precisely, the escape velocity from the didn’t have any near-surface ice. planetarysurfacemustcomfortablyexceedtheplanet’sown But Jewitt and his collaborators soon pointed out that it’s orbital velocity. Earth cannot produce solar system escapees possible the ice is there but couldn’t vaporize. `Oumuamua using its gravity alone, and interestingly, neither can the vast spent a very long time in the , and over S&T majority of known . Hot and short-period the eons it would have been both continually bombarded super-Earths are simply too close to their parent stars to be withtherelativisticparticlescalledcosmicraysandepi- effective, and in general, planets orbiting in “warm” regions sodically bathed in extreme-ultraviolet light from massive, near the star where rocky and metallic bodies form can’t eject young stars. Under such conditions, laboratory experiments them. A flurry of `Oumuamuas might shoot from binary-star (carried out by scientists such as Scott Sandford at NASA systemsor,alternately,theymightowetheirindependent Ames Research Center) show that simple carbon-containing orbits to countless Neptune analogs orbiting Sun-like stars at molecules gradually refashion themselves into complicated

GRAVITY EJECTION: LEAH TISCIONE / Neptune-like distances. tar-like complexes that evolve to have `Oumuamua’s char- acteristically ruddy hue. They also serve as remarkably good thermal insulators. A beverage cooler made from comet crust would keep bottles cold for much longer than one made from Styrofoam. Thermal modeling simulations by a number of groups show that if `Oumuamua is indeed covered by a modest insulating layer, then the Sun’s intense but brief heat likely would not have been suffi cient to warm any underlying ice to the sublimation point. Moreover, `Oumuamua’s odd shape and its tumbling motion may have provided further protec- tion. At many orientations, a cigar-like fi gure exposes only a small fraction of its surface area to direct irradiation, and the chaotic tumbling would have kept any one section from being regularly heated, helping to prevent isolated hot spots from blistering out. As `Oumuamua zipped away from the Sun, it rapidly grew dimmer, and by the end of 2017 it was about 27th magnitude.

skyandtelescope.com • OCTOBER 2018 25 26 Interstellar Interloper determine what lies beneath. lies what determine to of crust a patch excavating by or even view, up-close an by only answered be will that mystery origins an with left be will we ices, ofevaporating evidence shows bodies incoming noneofthe example, If, for population. ofthe emblematic be outto —turn ofcoma lack its and shape, its color, spin, —its its mua’s properties of`Oumua- which see to arrivals next months. several one every new a report to likely itis aconsequence, As separation. Earth-Sun the to equal roughly `Oumuamua atdistances like objects spot to enough sensitive be will Telescope Survey Synoptic Large upcoming the and or so, years several once every objects similar detect probably will Pan-STARRS as such for, look to facilities what know astronomers Nowthat visitors. such many herald may appearance Yet its itself. mua of`Oumua- observations direct more any won’t we get results, bring still will modeling detailed While One theNext for Preparing OCTOBER 2018 tion but registered `Oumuamua’s in Telescope Space direc- Spitzer the trained University) Arizona (Northern Trilling David by led A team computationally intensive. butvery feasible is that —aproject sheexplains manner, aconsistent in shape the and state rotation the modeling defi more (see possible 24). page also is shape pancake A alternative, an though curves, light the in dips 2½-magnitude observed the to best corresponds shape spindle The says. Meech too, light. atscattering ineffective hence and expected than larger were entrained particles dust any Perhaps gas. expelled the upwith caught dust by scattered light the to ible thanks vis- been have should jet `Oumuamua. Athruster-like from gas any observed noone ever that fact the with that square to awkward butit’s somewhat for acomet, unexpected not aspecifi in acceleration provides sion that kick. extra an body departing the gave something Rather, ofGravity. Law Newton’s from expect one would that arc hyperbolic the to adhere to failed system solar the one fi imparted fl ofits observations ofit. make to what knows really Noone surface. of atarry hints the given strange, is — which refl more much also and wavelengths believed atvisible ective initially than smaller both itis that suggests non-detection Astronomers are eagerly awaiting the the awaiting eagerly are Astronomers They’re still going with the bizarre 10:1 aspect ratio, ratio, 10:1 aspect bizarre the with going still They’re emis- gas Rocket-like outgassing. is guess team’s best The HST and ofground-based aseries made Meech’s team nitive analysis could be obtained by completely completely by obtained be could analysis nitive nal surprise: `Oumuamua’s trajectory outof `Oumuamua’s trajectory surprise: nal • SKY &TELESCOPE SKY no eeting departure, and these last looks looks last these and departure, eeting infrared heat signature from it. Their Their it. from signature heat infrared

c direction is is c direction alien spaceship. something that lookslike an enemy’s position. or ascout sent to survey an can refer to aleaderinbattle military connotations and to us.Buttheterm alsohas the distant pastreaching out the objectasamessenger from language experts to highlight consultation with Hawaiian discoverers chosethenamein repeated foremphasis).The mua from to aleaderorscout. Itcomes The term What’s inaName? An interesting choice for (“ rst, inadvance of,” `ou (“reach outfor”)and —Camille M.Carlisle `Oumuamua sampling Osiris-REX and Hayabusa 2( Hayabusa and Osiris-REX sampling a hyperbolic trajectory and then returning to Earth requires requires Earth to returning then and trajectory a hyperbolic on abody alongside Pulling feasible. be to it’s unlikely nately scientifi the be `Oumuamua would like object an to mission A sample-return Sun untilearlyAugust.) `Oumuamua crossed Earth’s orbitinlateJuly, itwasnot1a.u.from the 26, toofaintforPan-STARRS todetect.(Althoughwhenseenfrom above `Oumuamua’s averagebrightnessinJune2017atavisualmagnitudeof time tointercept theobjectinlateOctober. However, estimatesput enough, amissionlaunchedinlateJuly2017wouldhavehadenough p chasing Rosetta ( Rosetta chasing comet- the recently most out, carried successfully been have to fl IN HINDSIGHT A number of spacecraft missions that match velocities velocities match that missions ofspacecraft A number y alongside small bodies such as asteroids and comets comets and asteroids as such bodies small y alongside uy2,2017 25, July `Oumuamua refers Earth c equivalent of a grand slam, butunfortu- slam, ofagrand c equivalent If astronomers haddiscovered `Oumuamuaearly S&T: there will be similarly fortuitous chances! fortuitous similarly be will there years, coming in Hopefully, system. solar alien an from ashard with rendezvous for ahigh-speed adequate been have would second per kilometers ofafew boost space deep- amodest launch, to ready been had arocket if and approach, solar closest its to way on its August early in orbit Earth’s of sphere the itcrossed before weeks few a detected Had`Oumuamua been Earth. fl acompanion both from observed was that plume adebris ing Tempel 1, creat- Comet into smashed tor impac- akinetic which in mission, Impact NASA’s Deep with 2005-era precedent has Afl doable. be would job. dothe to rockets propelled forchemically energy much too planets at fessor atYale University. Heblogsabout ¢

May2017, p. 14) asteroid- the and GREG LAUGHLIN A one-way interceptor mission, however, however, mission, interceptor A one-way `Oumuamua oklo.org a.u. 1 . yby probe and from from and probe yby S&T: ight plan of this type type ofthis plan ight isanastronomy pro- coe 6 2017 26, October June 2018, June p. 22). uy2,2017 25, July Impact Launch Rocket

LEAH TISCIONE / S&T, SOURCE: D. SELIGMAN AND G. LAUGHLIN / ASTRONOMICAL JOURNAL 2018 (155:217) skyandtelescope.com • OCTOBER 2018 27 28 NASA / ESA BEAUTIFUL BRIGHT, BOLD, BIG, G Tourist’s G A hc no oefvrt targets. favorite some on and in fall check of skies the through Ramble OCTOBER 2018 tnigojcsi h k,adbsds tsoeo h first the of one it’s besides, and sky, the in objects stunning etei o neeigo qal odru bet scattered objects wonderful equally of allacrossthecelestialvaultofautumn. evening an it, for admire in look, a settle have So twilight. teaseouttheCassiniDivision,checkoutthemoons...then evening the in appear to CASSIOPEIA LACERTA ` PEGASUS 0 h f ¡ M52 oaheadandlookatSaturnfirst.Wealldo.When- everIgooutwithatelescopeandSaturnisup, that’sthefirstthingIlookat.It’soneofthemost EQUULEUS / _ M15 g _ 23 b ` • h SKY &TELESCOPE SKY VULPECULA c m o M39 a 22 61 CYGNUS h ` i _ _ ¡ 6940 ¡ _ 21 M29 h M27 a

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BIG, BOLD, BRIGHT, AND BEAUTIFUL The globular cluster M15 in Pegasus bedazzles with more than 100,000 stars. Big, Bold, Bright, Beautiful

This article is for the tourist. Whether you’re new to the N hobby or a hoary veteran, we all have nights when we just want a light show. When we grow tired of looking for faint fuzzies, autumn offers a veritable smorgasbord of eye candy for the spectacle-hungry. Here are some of my favorites, working more or less from north to south for a couple of hours after sunset in October. Let’s start with NGC 6543, the Cat’s Eye Nebula. This bright (8th-magnitude) in the neck of NGC 6826 16 Cygni Draco, the Dragon, is one of the most popular planetar- ies in the northern sky. It’s small but bright enough to see in almost any telescope, and it takes magnifi cation well, so crank it up and admire this twist of stellar atmosphere that has blown off a dying star. It’s decidedly oblong and does indeed look like the elongated pupil of a cat’s eye. With some aperture and steady sky you can see the central star, and maybe even detect the nebula’s greenish color. When you’re looking at the Cat’s Eye, you’re looking toward the north ecliptic pole, which means you’re looking straight up out of the plane of the solar system. N As long as we’re in Draco, we can’t skip Nu (ν) and Mu (μ)Draconis. They’re two double stars in Draco’s head, and they provide two completely different viewing experiences. Nu Draconis, also known as Kuma, is a wide, even double of two 4.9-magni- tude stars separated by an easy 63″. You can split it in binoculars if you hold them steady enough. The two components are so evenly matched that in a telescope they look like the headlights of an approaching car. Mu Draconis is another perfectly matched pair, with both components glowing at 5.7 magni- tude, but at a much closer 2.3″ separation. This is a medium-tough split, but well worth the effort, espe- cially after looking at Nu’s easy divide. It looks like the same pair of headlights, only much farther away. Fun fact: Mu Draconis’s common name is Arrakis, which Frank Herbert thought was cool enough to name his desert planet in his groundbreaking science fi ction novel, Dune. N From Arrakis, a quick hyperspace jump through pp NGC 6826 The Blinking Draco’s head takes you into Planetary Nebula is one of the upper wing of Cygnus, the the night sky’s few interactive Swan. About where the pinion objects. FOV = 50′ feathers would attach you’ll fi nd NGC 6826, the Blinking p DENSE SWARM M15 is one of the tightest globular clusters TYC 3168-590-1 Planetary Nebula. The Blink- 2030 in the galaxy. FOV = 20′ 2020 ing Planetary is even smaller 2010 than the Cat’s Eye, so you’ll u SPEEDY STAR 61 Cygni need some magnifi cation moves so quickly relative to here, but I include it because background stars that you can watch its position change it’s one of the best interactive from year to year. Component objects in the night sky. How A is upper right, B lower left. can something 5,200 light- FOV = 20′ years away interact with you?

30 OCTOBER 2018 • SKY & TELESCOPE By disappearing when you look directly at it! The central behind looking for all the world like a glittering diamond star that produced the nebula is bright enough (magnitude swinging back and forth at the end of a string attached to the 10.6) to overwhelm the soft glow of the nebula when you primary. For this reason, Enif is called the Pendulum Star. look straight at it, but averting your eyes brings the nebula What’s happening here? It’s a latency effect: Your eye takes a right back to surprising prominence. The moment longer to register a dim star than nebula isn’t doing the blinking; you are it does a bright one, so when the stars are by moving your eyes away and back. It’s in motion the dim one lags behind. a great effect, probably best in an 8-inch While you’re in Enif’s neighborhood, telescope, but you can play with magni- you might as well move 4° to the north- fi cation or an aperture mask to get it the west and have a look at M15, a tight, right brightness in just about any scope. bright globular cluster that’s spectacular If you’re having trouble fi nding the in any scope. This is one of the most Blinking Planetary, look for 16 Cygni, a tightly packed globulars in the sky, with double star about ½° due west. 16 Cygni half its mass concentrated in the cen- is naked-eye visible (its components are tral 10 light-years of its 175 light-year magnitudes 6.0 and 6.2, for a combined expanse. You can really see that when brightness of 5.3) and easy to split (39″), you crank up the magnifi cation and try and it makes for a good signpost that to split the core into individual stars. you’re close to the Blinking Planetary. Since the planetary lies There are just too many to do it! directly east of it, just center 16 Cygni, wait three minutes, Let’s move back up toward the zenith again to pick up a and the Blinking Planetary will be centered. couple more neat objects we passed over on our way to Enif. As long as we’re playing with interactive objects, there’s We’ve probably all heard of, and seen, Epsilon (İ) Lyrae, the another great one to the south a ways: Epsilon (İ) Pegasi, famous double-double star in Lyra. With two tight (2.1″ and or Enif, the nose of Pegasus. This one is a wide double star 2.4″) pairs separated by a generous 210″, this is a favorite test with enough difference in brightness between its components of telescope optics. But Lyra holds a second double-double (magnitudes 2.5 and 8.7) to play a neat trick on your eye. If that I think is even prettier: Struve 2470 and Struve 2474. you wiggle the telescope in a direction perpendicular to the These pairs are separated by an even more generous 10′, and binary split, you’ll see the bright component move back and the individual pairs are separated by 16″ and 14″. Both of forth just as you would expect, but the dim component lags them split east-west, and both have the brighter component to the east. They look like a double and its refl ection in still water. This is a great object for star parties; they’re much easier to split than Epsilon, and more beautiful. N

N

NGC 6802

p EPHEMERAL CLUSTER u DO YOU SEE IT? The Coathanger looks Soft and delicate NGC 6940 is just like its namesake. In Newtonian scopes, one of the most beautiful open it’s right-side up. Look for diminutive NGC

JERRY OLTION (5) OLTION JERRY clusters in the sky. FOV = 1° 20′ 6802 just to the east of it. FOV = 3°

skyandtelescope.com • OCTOBER 2018 31 Big, Bold, Bright, Beautiful

While you’re in the neighborhood, of course you should from A as A is from B. With a little patience, you can watch check out M57, the Ring Nebula. This is probably the most a star move! This is a double to look at several times a year, accessible planetary nebula anywhere. It has all four B’s and you should make an effort to sketch it at least once a — Big, Bold, Bright, and Beautiful — and I never pass by year for the rest of your life. If you keep watching, you’ll be without a look. If you’ve got serious aperture (18 inches or amazed at how far it moves. better) and steady seeing, try for the central star. It’s a tough We haven’t looked at any open clusters yet. How about fi nd, but the feeling of accomplishment when you spot it is NGC 6940, often overlooked but Big, Bold, Bright, and well worth the trouble. Beautiful nonetheless. It’s in Vulpecula, right under the body At the risk of overdoing it with double stars, I have to of Cygnus, below the Great Rift in the Milky Way. There are point out at least one more in the autumn sky: 61 Cygni, or dozens of open clusters in the area, but this one stands out Piazzi’s Flying Star. This is another easy split (31″) between for me because of its size (nearly as big as the Moon) and the bright (magnitudes 5.3 and 6.1) stars, both with a distinctly relative uniformity of its stars. There are a few bright stars, reddish hue to them. But the cool thing about this system including a nice red giant near the cluster’s center, but most isn’t the pair itself; it’s the split with tiny little 11th-mag- of the 50–100 stars that you can see easily are about 11th to nitude TYC 3168-590-1 next door. 61 Cygni is only 11.4 12th magnitude. That makes for a soft, delicate, yet very defi - light-years away and moving fast, so it really scoots across nite concentration amid the general glow of the Milky Way. If the sky. It moves 5″ per year, which is 1/6 of its separation. most clusters look like salt on velvet, this looks like powdered TYC whatever is way off in the background, so it doesn’t sugar sifted over chocolate ice cream. move much, which makes it a great marker for watching You’ll want low power for NGC 6940. Give yourself at least 61 Cygni’s position from year to year. In 2012, 61 Cygni A a degree of fi eld, more if you can, so you can see it in context. crossed right over it, and this year it’s the same distance It looks great in binoculars, too.

Celestial Ramble

Object Alternative Name Type Mag(v) Size/Sep RA Dec. NGC 6543 Cat’s Eye Nebula Planetary nebula 8.1 20″ 17h 58.6m +66° 38′ Nu Draconis Kuma Double star 4.9, 4.9 63″ 17h 32.2m +55° 11′ Mu Draconis Arrakis Double star 5.7, 5.7 2.3″ 17h 05.3m +54° 28′ NGC 6826 Blinking Planetary Planetary nebula 8.8 36″ 19h 44.8m +50° 32′ 16 Cygni Double star 6.0, 6.2 39″ 19h 41.8m +50° 32′ Epsilon Pegasi Pendulum Star Double star 2.5, 8.7 144″ 21h 44.2m +09° 53′ M15 Globular cluster 6.3 18′ 21h 30.0m +12° 10′ Epsilon Lyrae Double Double Double star 5.0, 5.3 210″ 18h 44.3m +39° 40′ Epsilon1 (ε1) Lyrae Double star 5.0, 6.1 2.1″ 18h 44.3m +39° 40′ Epsilon2 (ε2) Lyrae Double star 5.3, 5.4 2.4″ 18h 44.3m +39° 40′ Struve 2470 Double star 7.0, 8.4 14″ 19h 08.8m +34° 46′ Struve 2474 Double star 6.8, 7.9 16″ 19h 09.1m +34° 36′ M57 Ring Nebula Planetary nebula 8.8 76″ 18h 53.6m +33° 02′ 61 Cygni Piazzi’s Flying Star Double star 5.3, 6.1 31″ 21h 06.9m +38° 45′ NGC 6940 Open cluster 6.3 25′ 20h 34.5m +28° 17′ Collinder 399 The Coathanger Asterism 3.6 90″ 19h 25.4m +20° 11′ NGC 6802 Open cluster 8.8 5′ 19h 30.6m +20° 16′ NGC 6633 Open cluster 4.6 20′ 18h 27.2m +06° 30′ IC 4756 Open cluster 4.6 40′ 18h 38.9m +05° 26′ NGC 6572 Emerald Nebula Planetary nebula 8.1 11″ 18h 12.1m +06° 51′ Angular sizes and separations are from recent catalogs. Visually, an object’s size is often smaller than the cataloged value and varies according to the aperture and magnii cation of the viewing instrument. Right ascension and declination are for equinox 2000.0.

32 OCTOBER 2018 • SKY & TELESCOPE N Another excellent binocular target is Collinder 399, also known as Brocchi’s Cluster and The Coathanger. It’s an aster- ism, a chance alignment of stars that in this case looks like a coathanger. It’s upside-down in binoculars but upright in a Newtonian telescope. You’ll want your widest fi eld possible for this one since it spans 1½°. Just a little to the east of The Coathanger, straight in line with the bar, you’ll fi nd the small open cluster NGC 6802, whose stars are arranged in an oblong oval that looks a little like a fi gure 8 or a helix. Plus there’s a bonus to the cluster’s north: yet another double-double. Heading back into the southwest toward Saturn, we fi nd two more nice open clusters. The fi rst, NGC 6633, is all four B’s. At 4th magnitude it’s easily visible by naked eye, and in binoculars or a telescope it’s beautiful. The cluster is elongated northeast-southwest with a scattering of bright (7th–9th-magnitude) stars, with many more faint ones mixed in. On the western edge is a mini asterism that looks like a tiny Cassiopeia. N IC 4756 is another open cluster nearby that’s also visible by naked eye under dark sky, and even bigger (although a little sparser) than NGC 6633 next door. It spans more than ½° and looks great in binoculars or at low power in a telescope. For our grand fi nale let’s look at NGC 6572, the Emerald Nebula. This is a small planetary nebula, but it’s bright enough (magnitude 8.1) to see in any telescope, and if you have even a little bit of aperture (say 4 inches or better) it’ll be bright enough to trigger color vision. And when that happens, it’s amazing! This is one of the most brilliant green objects in the sky. You only have color vision when you’re looking directly at an object, so it’s green when you look straight at it, and it turns to gray (but it gets brighter) when you look away. pp LIGHT DUSTING NGC 6633 is a i ne mix of bright NGC 6572’s surface bright- and faint stars between ness is 100 times greater than N Aquila and Ophiuchus. the Ring Nebula’s, so it will FOV = 1° 30′ handle magnifi cation well, but I’ve found that it looks bright- p SPRINKLING OF STARS In the same neighborhood est and greenest with just as NGC 6633, IC 4756 enough magnifi cation to make is larger but somewhat it bigger than a point source. sparser. Both clusters are Somewhere around 80–90× visible by naked eye under seems to be ideal. dark sky. FOV = 5° By now, Saturn has prob- t SHIMMER IN THE SKY ably set. If not, have another The Emerald Nebula is one look. Hey, cool, the moons of the most vivid green have moved! objects in the night sky. Use just enough magnii cation ¢ JERRY to make it stand out but not Contributing Editor so much that you dim it. OLTION loves interactive tourist FOV = 30′ attractions. Contact Jerry at

JERRY OLTION (3) OLTION JERRY [email protected].

skyandtelescope.com • OCTOBER 2018 33 RESTORATION DOWN UNDER by Trudy E. Bell

ext year is the 150th anniversary of fi rst light for Nthe 48-inch Great Melbourne Telescope (GMT) of the state of Victoria, Australia. For more than two decades after the English-mounted refl ector was completed in 1869, the GMT was the largest equatorial telescope in the world, and it remained the largest telescope in the Southern Hemisphere until 1922. Its users’ early achievements include the fi rst visual observation of the spectrum of an extragalac- tic nebula (1870), the world’s fi nest photographs of the Moon (1872), the fi rst photographs of southern nebulae (1883), and the discovery of more than 50 nebulae and galaxies. However, the GMT eventually fell on hard times. Chal- p THE MOON REVEALED Joseph Turner, a local photographer and lenges in printing delicate nebulae sketches plus a worldwide amateur astronomer, was appointed lead astronomer at the GMT after Albert Le Sueur’s resignation in May 1870. Though Turner completed fi nancial crisis in the 1890s that also took its toll on Austra- many i ne drawings and spectroscopic studies, he also mastered the lia prevented the publication of two decades of observations, telescope’s photographic equipment. Turner captured this view of the making it seem that the telescope had been unproductive. In Moon through the GMT in 1875. part as a result, telescope optician George W. Ritchey (who later helped fi gure Mount Wilson Observatory’s 100-inch ments to reveal thousands of faint nebulae amidst the stars mirror) famously passed off the GMT as a “failure” in 1904. inthenorthernheavens;inthe1830s,William’sson,John In 1945, the GMT was sold to Mount Stromlo Observa- Herschel, discovered countless more in the southern heavens. tory near Canberra. There, it was reconstructed three times Were these nebulous clouds of gases relatively nearby, lying (1950–55, 1960–61, and 1989–91), including being fitted with within our own “sidereal system”? Or were they indepen- two different 50-inch borosilicate glass mirrors. During each dent “island universes” at such vast distances that their stars rebuild, more of the GMT’s original parts were removed. For- could not be resolved? tunately, Museums Vic- toria retrieved them for safekeeping in off-site collection storage in the 1980s. The telescope’s last incarnation, as an automated instrument for the that discovered a form New Life of dark matter in 1993, incorporated just fi ve assemblies of the GMT’s original mount. In Janu- Great Melbourne ary 2003, the telescope was engulfed in raging wildfi res that swept Mount Stromlo. The upshot of this story: Many today are left thinking that Those fundamental questions might be answered by sta- the GMT was originally fl awed and then was taken out of tioning a capable observer at the eyepiece of a gigantic tele- commission. However, neither of these “facts” is true. For the scope in the Southern Hemisphere, to compare later observa- past decade, several organizations in Melbourne have been tions with John Herschel’s meticulous drawings of decades documenting, cleaning, and reassembling the GMT from its earlier to see whether any nebulae had changed appearance. original parts — 70% of which survive at Museums Victoria. In 1852, the British Association for the Advancement of Their goal is to reconstruct the instrument with as much Science and the Royal Society of London jointly appointed historical authenticity as possible, but with modern optics a Southern Telescope Committee of the British Empire’s top so the public may look through it and amateurs can use it astronomers, to determine what kind of instrument should for research. In so doing, they also seek to restore the GMT’s be built, who should build it, and where it should be located. reputation and its rightful place in history. By 1853, the committee had settled on a design and appointed a subcommittee to oversee a proposed contract Chronology of the GMT with Dublin telescope engineer Thomas Grubb — but then Beginning with William Herschel’s large reflecting telescopes the Crimean War (1853–1856) halted everything. It seemed

in the 1780s, astronomers used a half dozen major instru- the project was dead. MOON: MUSEUMS VICTORIA / CC BY 4.0; PATTERN: HUI-YING TING-BORNFREUND / GETTY IMAGES

34 OCTOBER 2018 • SKY & TELESCOPE COLOSSAL INSTRUMENT The London Illustrated News dedicated a full-page review to the Great Melbourne Telescope in Novem- ber 1868. The writer enthusiastically described the mechanics of the Cassegrain focus, which gave the telescope “some important advantages, foremost among which is the fact the observer is never more than about 4 ft. off the ground.” The benefi ts of the lattice-work optical tube were listed as “great stiffness and freedom from tremor, combined with lightness and freedom from currents of air . . .” The scope was also praised for its “improved” equatorial mounting and “effi cient photographic apparatus.”

Australian groups are restoring what was once the world’s largest equatorially mounted telescope. Telescope HULTON ARCHIVE / STRINGER / GETTY IMAGES

skyandtelescope.com • OCTOBER 2018 35 Restoration Down Under

and silvering such a large glass mirror was as yet untried; the long-term stability of glass as a material and silver as a coat- ing were unknown; and silver, although more refl ective than speculum metal, tarnished more quickly. Moreover, the use of speculum metal would minimize differences in refl ectance as a factor in comparing observations made decades apart. The telescope was to have a Cassegrain focus rather than Herschelian or Newtonian, a pioneering choice that let the astronomer observe more safely from the ground or low steps instead of perched two or three stories up in the air in the dark. Nebulae were to be drawn by hand by a visual observer using a precision bifi lar micrometer (photographing them was impossible with the very slow emulsions of the 1860s), but the secondary mirror cell could be swapped out for a cam- era to allow photography of bright objects at prime focus. The mounting would be an equatorial made of cast iron, rather than an alt-azimuth built largely of wood (like John Herschel’s) or masonry (like Lord Rosse’s). Despite the tele- scope’s moving mass topping 18,000 pounds, Grubb devised a pioneering system of counterweights to relieve frictional loads on bearings. Thus, one person could slew the telescope with ease, and a gravity-powered clock drive acting on the polar axis could compensate for Earth’s rotation. The tele- scope would be sited at low elevation near a thickly settled area (a practical cost-saving choice, then the norm). The order was signed with Thomas Grubb in early 1866, and the entire 48-inch telescope was completed by Febru- ary 1868. Construction was supervised primarily by Grubb’s 21-year-old engineering student son Howard, who was in the process of launching his own illustrious telescope-making career. The Grubbs cast and fi gured two speculum primary mirrors, so that (following the method used by John Her- schel in South Africa) one could always be used for observing p SOUTHERN SUCCESS Following improvements of developing and while the other was being repolished to remove tarnish. They printing processes, astronomers at Melbourne Observatory began photo- deliberately designed the English cross-axis equatorial mount graphing nebulae with the GMT in 1882. Taken on February 26, 1883, to be strong and stiff enough to carry the mass of a 60-inch Turner’s image of the Great Nebula was one of the earliest photos of nebulae taken in the Southern Hemisphere. refl ector, should a larger telescope someday be desired. And to support the 2,200-pound 48-inch mirror without noticeable A decade passed. In 1863, the British colony of Victoria — distortion at all viewing angles, Howard refi ned his father’s wealthyfromagoldrushsince1851andhankeringtoestab- 48-point fl oating suspension system of counterbalanced tri- lishitselfasaculturalcenteroflearning—authorized£5,000 angular levers — a design still often used today. for a large telescope for Victoria’s capital city of Melbourne. After meticulously inspecting the assembled GMT in the TheSouthernTelescopeCommitteedustedoffitsplans. Grubb factory yard and testing the mirrors and photographic After extensive discussion about technical advances over the system on various celestial objects, including the Moon, intervening decade, it reaffirmed the major concepts of the double stars, and nebulae, the Southern Telescope Committee original plan. The telescope’s final specs were thus a combina- was delighted with both its optics and mechanics. The GMT tion of conservative and innovative design choices. was disassembled, crated, and shipped to Australia, arriving at Melbourne in November 1868. It was reassembled on blue- Something Old, Something New stone (basalt) foundations and piers. A rectangular telescope Theproposedmirrorwouldbe48inchesindiameter,made house with a novel roll-off roof — likely the world’s largest at of polished speculum metal — a white bronze alloy of copper the time (although not the world’s fi rst) and now the oldest andtinwhosecasting,figuring,andmaintenancewerewell surviving — was built around it so observing could be done understood.Despitetheadaptationofaprocessfordepositing in the open air (a choice both conservative and prophetic). At athincoatofsilveronglasstotelescopemirrorsbyphysicists last, in mid-1869, the GMT turned its giant eye up toward the

LéonFoucaultandCarlAugustvonSteinheilin1857,casting spectacular southern heavens. : MUSEUMS VICTORIA / PUBLIC DOMAIN; PHOTO OF TELESCOPE: PUBLIC / VICTORIA MUSEUMS OBSERVATORY: MELBOURNE VICTORIA; MUSEUMS DOMAIN; PATTERN: HUI-YING TING-BORNFREUND / GETTY IMAGES

36 OCTOBER 2018 • SKY & TELESCOPE Disentangling Controversies Almost immediately, complaints arose about poor imaging. Finger-pointing letters sailed between the Northern and Southern Hemispheres, some printed in British newspapers. The Southern Telescope Committee and the Grubbs had made what in retrospect was a problematic call. Instead of sending Howard south with the telescope to supervise its installation, the intended primary observer — a Cambridge mathematician named Albert Le Sueur — was hired by the Melbourne Obser- vatory. Le Sueur was sent to the Grubb factory to witness the casting of the mirrors and other key milestones, and to learn how to reassemble and operate the telescope, as well as the mirror grinding and polishing machine. But once en route to Australia, Le Sueur was on his own and had to make judg- ment calls. Grubb had specifi ed that the mirrors’ protective coating of shellac be removed with pure ethyl or methyl alco- hol. But pure alcohol was in short supply in Victoria. Instead, Le Sueur started the job using methylated spirits and fi nished with pure alcohol. Although the smaller mirrors retained their high polish, either the shellac applied to one of the p OBSERVATORY OVERVIEW This image offers a view of the Mel- primary mirrors in Dublin or parts of its surface may have bourne Observatory as it appeared in the 1880s. The main observatory been contaminated. A cloudy residue yielded diffuse refl ec- building is at center. The GMT, workshop, and engine for the mirror- tions, and accusations fl ew. Making matters worse, an irate grinding apparatus are at the far right. Melbourne amateur astronomer wrote angry letters both to British and Australian scientifi c societies, claiming (inaccu- In the meantime, no one in the Southern Hemisphere had rately) that “[t]he instrument has cost us colonials £14,000” experience in working with a telescope of such a large aper- and asserting, “It is a grievous failure.” ture, so on nights of ordinary seeing, a person accustomed to Over the next year, Le Sueur hand-polished both primaries observing with smaller apertures could fi nd the GMT’s per- with washed chalk to near perfection, but in August 1870 he formance on a planet or double star actually “disappointing,” resigned in frustration and returned to England. Although noted Ellery. But “on really good nights it is quite different . . . he and Melbourne Observatory director Robert Ellery were indicating an optical perfection which under other condi- staunchly backed by the observatory’s capable Board of Visi- tions was not apparent.” tors, the bad-PR mud stuck. Moreover, the Southern Telescope Committee’s intended observing program — visual observations of nebulae to detect changes — was highly subjective, depending on individual observers’ visual acuity and artistic skill. Indeed, for those nebulae that were distant galaxies, detecting any change (short of an extragalactic supernova) over mere decades was downright impossible — although, of course, absence of change was a crucial test. Finally, after the fi nancial crash of the 1890s nearly halved the observatory’s budget at a time when it had committed heavy resources to the international Astrographic Catalogue, the GMT was not adequately maintained and most of the astronomers’ meticulous drawings were never published. Against this background of woes, in 1904 Ritchey paren- thetically commented in a treatise on making and testing

t PHOTO ASSIST Since no original drawings for the GMT survive, photographs such as this one, which shows the telescope as it was in 1875, have been crucial in helping the restoration team reverse-engineer the telescope’s assembly. The weight hanging next to the man (who is believed to be Joseph Turner) and the chain going over the top of the larger pier were part of Thomas Grubb’s design to relieve frictional load on the main bearing of both axes so the telescope could be clock-driven. The clock drive is next to the weight.

skyandtelescope.com • OCTOBER 2018 37 Restoration Down Under

telescope mirrors, “I consider the failure of the Melbourne sum the groups hoped to raise via grants and donations. In refl ector to have been one of the greatest calamities in the 2013, the Bureau of Meteorology also joined as Melbourne history of instrumental astronomy; for by destroying confi - Observatory had operated the Victorian Weather Offi ce from dence in the usefulness of great refl ecting telescopes, it has 1863 to 1907. hindered the development of this type of instrument . . .” Since 2009, a dozen or so ASV volunteers — mostly retired Ritchey never looked through the GMT, much less tested it. engineers and optical specialists — have spent Wednesdays Nonetheless, his offhand remark was the last straw for the working under the leadership of museum curators and con- GMT’s reputation. servation staff in Museums Victoria’s cavernous warehouse, complete with 10-ton overhead crane. Because the telescope Phoenix from the Ashes is part of Victoria’s State Heritage Collections, decisions are Fast forward a century to the year after the devastating guided by the Australia International Council on Monuments Mount Stromlo bushfi re. Members of the Astronomical Soci- and Sites (ICOMOS) Burra Charter for the conservation of ety of Victoria (now 1,000+ members strong) began brain- historic structures. storming with managers at Museums Victoria. If the major Volunteers began by photographing, weighing, and mea- castings of the equatorial mount were retrieved from Mount suring every component as it existed (including any Mount Stromlo, could the GMT be reconstructed from surviving Stromlo modifi cations) and ascertaining their positions and functions in the GMT. Then came the writing of a proposal for the work needed to restore the telescope. Every part and fastener was numbered and tracked; by the end of 2017, the inventory identifi ed some 1,200 components and included some 700 drawings. Because no original engineering records survived the 2003 Mount Stromlo bushfi re (or an earlier one in 1952), CAD drawings had to be reconstructed for the entire GMT — including the shapes and dimensions of missing components (40 to 50 major parts plus several hundred knobs, gears, and other small items). Although schematic drawings for some larger assemblies were published in 1868, for other parts all that remained were several 19th-century photographs. Finally, a gigantic fl ow chart was drawn up to identify critical paths: which jobs needed to be done in what order, including contracting for custom-made missing pieces. Then came the heavy physical labor: unbolting and disas- sembling every subassembly and cleaning every part and fastenerbyhanddowntobaremetal.Tosupporttheproject, p AFTER THE FIRE In 1945, the GMT was moved to Mount Stromlo both individuals and philanthropic organizations donated Observatory, where it was modii ed three times. The only original parts half a million dollars plus crucial in-kind design and engi- engulfed by a wildi re in 2003 were the cube (center), the polar axis south neering work. or upper cone (above the cube), the declination axis with its bell-shaped housing (left of the cube), and the north bearing quadrant (unseen below In late 2014 came a trial reassembly of the cleaned parts. the wall). Fortunately, they survived. This photo was taken in 2008 before The cube and southern cone of the polar axis were bolted those pieces were retrieved for restoration. together, the upper and lower bearings placed on a giant frame, and the tube suspended from the overhead crane for a original parts using modern optics? In November 2008, the stagedphotoshootgivingafeelfortheGMT’smass,size,and GMT’s cube, polar axis and bearing mounts, declination axis eventual appearance. and bell-shaped housing, north bearing quadrant, modern mirror cell, and fragmented 50-inch mirror were retrieved Optics and Observatory Plans from the incinerated building and trucked to Melbourne. Onlyoneofthetwooriginal48-inchspeculummirrorsis Extensive talks led to a formal memorandum of under- extant; the other broke at Mount Stromlo c. 1948. The GMT standing among Museums Victoria (owner of the GMT parts restoration team intends to put the remaining mirror on and eventually of the completed GMT), the Royal Botanic static display with its 48-point flotation system. For actual Gardens Victoria (manager of the Melbourne Observatory use,theteamfirstsoughtdonationofasecondhandmirror site where the original GMT house still stands), and the (including, through this author in 2012, the 48-inch mirror Astronomical Society of Victoria (ASV, source of volunteer fromtheformerTableMountainObservatory).Allattempts labor with optical and engineering skills). The projected cost ran afoul of either legalities over an international transfer or

of the restoration project was estimated at A$3,000,000, a lackofacentralholeforaCassegrainfocus.SoinOctober FIRE AFTERMATH: STEVE ROBERTS; GRINDER: STEVE ROBERTS; CENTRAL CUBE: TRUDY E. BELL; DAD’S ARMY: TRUDY E. BELL; PATTERN: HUI-YING TING-BORNFREUND / GETTY IMAGES

38 OCTOBER 2018 • SKY & TELESCOPE p THE GREAT GRINDER While most ASV volun- teers focused on the telescope itself, the oldest ASV team member, David Linke, devoted his attention exclusively to Thomas Grubb’s two-ton p EXEMPLARY EFFORT Some 8 to 15 members of the Astronomical Society of Victoria — mirror-grinding and polishing machine. The appa- most of them retired engineers, machinists, and other technical professionals — meet ratus was used several times in the 19th century at the Museums Victoria warehouse every Wednesday to work on the GMT restoration. to remove tarnish that gradually accumulated on Much of the work has been done by hand or using original techniques. Here Graeme the GMT’s speculum mirrors. Bannister was photographed in 2011 removing rust from the central cube.

p DAD’S ARMY ASV volunteers at the Museums Victoria warehouse stand in front of a wall-sized photograph of the GMT as it appeared in 1875 — an image essential to the task of recreating detailed engineering designs. Nicknaming itself “Dad’s Army” after a 1970s BBC TV sitcom about the work of a detachment of Home Guard older than those sent into combat during World War II, some two dozen ASV members have dedicated well over 20,000 hours of volunteer labor over 400+ weekly sessions since 2009.

skyandtelescope.com • OCTOBER 2018 39 Restoration Down Under

u REFLECTED GLORY This image, taken in section of the telescope tube — is now 2014 during a photo shoot to assist with being fabricated in the workshop of fundraising, shows the polar axis of the Scienceworks, another Museums GMT’s mount — consisting of the cube and upper (south) cone — joined with Victoria institution. And the the bell-shaped housing of the dec- Australian Antiquarian Horo- lination axis. The entire assembly logical Society has generously is anchored to a custom stand offered to make replacement whose design was donated by an telescope clockwork. The engineering i rm. An overhead original clock drive was crane holds the surviving section of the original optical tube near gravity-powered by descend- its correct position. The scene is ing weights that could rel ected in the partially cleaned run for up to two hours front surface of the surviving before requiring winding; original 48-inch speculum-metal mirror. The scene was shot in the its speed (sidereal, diurnal, storehouse of Museums Victoria, or lunar) was regulated by a where the 150-year-old instrument is centrifugal governor and dif- being brought back to life. ferential gearbox. The current plan for most observing is to drive 2017, the restoration project issued a the polar axis with an unobtrusive formal Expression of Interest document electric motor. However, in accordance totheopticalindustryforacustommirror with the Burra Charter, which advocates a of low-expansion borosilicate glass, fused silica, or cautious approach to change but allows for the glassy ceramic. introduction of new material during reconstruction as long TheoriginalGMTprimarymirrorshadafocallengthof as it doesn’t damage a site’s historical signifi cance, a working 366 inches (f/7.625); at the f/41.5 Cassegrain focus, the effec- reproduction of the missing clock drive will be installed. tivefocallength(EFL)was1,994inches.Thatgaveanactual The current goal is to fi t the telescope with its new, full- field of view of just 13 arcminutes with the lowest-power length tube and put it on display at Scienceworks by June eyepiece,somewhatnarrowforpublicviewing.Althoughcur- 2019, the 150th anniversary of the GMT’s fi rst light from rent plans still call for reconstructing the GMT’s iconic open Australia. There, its magnifi cence will be seen by the public lattice tube to full length, actual optical focal lengths will as well as by the media, and by federal and state politicians. be somewhat shorter to allow a usable field of 17 arcminutes That, it’s hoped, will result in more funding to support the whilekeepingthesecondaryobstructionunder14inches.The original ambitious goal: reconstructing the GMT to full new perforated Cassegrain primary is to be f/7.0 (336 inches); working order inside its original observatory building to withanewsecondary,thefinalfocalratiowillbef/31.2(EFL make it the largest telescope in the Southern Hemisphere for 1,498 inches). astronomy public outreach. By June 2018, it was evident that the quoted prices for the new optical train were higher than the budget could afford, ¢ Contributing Editor TRUDY E. BELL, formerly an editor so the ASV is looking for more cost-effective alternatives. One for Scientifi c American and IEEE Spectrum magazines and possibility is for a team of ASV optical specialists to grind, senior writer for the University of California High-Performance polish, and figure the hyperboloidal secondary themselves, AstroComputing Center, is the author of a dozen books and usingasecondhand310-mmSchottZerodurblank. over 500 articles. Her journalism prizes include the 2006 David Meanwhile, in February 2018, the Melbourne Observa- N. Schramm Award of the American Astronomical Society. She tory was permanently added to Australia’s Federal Heritage can be reached at [email protected]. List, opening up both greater protection and a new source of funds for the GMT restoration. In May, the Australian She gratefully acknowledges information and images from federal government awarded a grant of A$250,000 (about the following sources: Roger Ceragioli, Matthew Churchward, U.S.$185,000)torestoretheroll-offroofoftheGMT’s Barry Clark, Philip Edwards, Richard Gillespie, Frederick Orth- telescope house to working order. The bluestone piers must lieb, Jim Pollock, Steve Roberts, John Robinson, and Matilda be rebuilt as well (the original stone blocks went to Mount Vaughan. Some information they and primary source docu- Stromlo but were discarded when the mount was modified). ments provided corrects errors in earlier secondary literature. In2013,aninspectionrevealedthatthepiers’remaining bluestone foundations were still in excellent condition. Resto- FURTHER READING: The 19th-century debates over the design ration of the brickwork is expected to be completed by 2019. and viability of the GMT are detailed in Richard Gillespie’s book, Theteamisalsofocusingonrebuildinglosttelescope The Great Melbourne Telescope (Melbourne: Museum Victoria

components. The biggest missing part — the upper lattice Publishing, 2011). JOHN ROBINSON / ASTRONOMICAL SOCIETY OF VICTORIA, AUSTRALIA

40 OCTOBER 2018 • SKY & TELESCOPE OBSERVING October 2018

4 EARLY MORNING: Watchasthe 20 EVENING: Algol shines at 26 ALL NIGHT: The cradle the thinwaningcrescentMoonandthe minimum brightness for roughly two waning gibbous Moon until sunrise. Beehive Cluster (M44) rise together hours centered at 10:39 p.m. EDT. in the east-northeast and climb ever 31 NIGHT: We have come full cycle, as higher before sunrise. 20–22 MORNING: The medium- the last quarter Moon rises in Cancer. strength Orionid is Watch as the Beehive Cluster and the 5 EARLY MORNING: Athinner expected to peak in the afternoon lunar crescent sweep across the sky, Moon has slipped down into Leo, the of the 21st. Best opportunities for some 4° apart. Lion,andleadsRegulusbyabout7° as spotting meteors are in the early The Milky Way arches overhead while the they soar into the pre-dawn sky. morning, but the nearly full Moon will zodiacal light spills along the ecliptic in this hamper viewing somewhat (see p. 49 all-sky view captured in northern Maine. 11 DUSK: Resplendent Jupiter for more on this shower). BABAK TAFRESHI gleamsinLibraasacrescentMoon, only a few days past new, stands guard 3° above.

13 DAWN: Look toward the east before morning twilight for the soft glowofthezodiacallight.Youmustbe at more northerly latitudes, but if you are you might see this phenomenon forthenexttwoweeks.Lookfora tallpyramidoflightstretchingupto Gemini, tilted toward the right.

14 DUSK: After sunset, the waxingcrescentMoonand Saturn will emerge from the gloaming, 2° or fewer apart. Look for the pair where Saturnhasbeenroosting the past few months, above theTeapotinSagittarius. Fading Jupiter and fiery Mars anchor at either end tocompleteagraceful celestial arc.

17 EVENING: Algol shines at minimum brightness for roughlytwohourscenteredat 10:50 p.m. PDT.

17 & 18 EVENING: Watch as thefatteninggibbousMoon hopscotches over Mars, first appearing some 5° right of the Red Planet and then 6° upper left, as it continues on its trek along the ecliptic.

skyandtelescope.com • OCTOBER 2018 41 OCTOBER 2018 OBSERVING Lunar Almanac Northern Hemisphere Sky Chart

Double starGalaxy Variable star Open cluster Diffuse nebula Globular cluster 26 Planetary nebula

October 1



Yellow dots indicate which part of the Moon’s limb is tipped the most toward Earth 14 by libration. NASA / LRO 12

MOON PHASES

SUN MON TUE WED THU FRI SAT 1 2 3456

7 8 9 10 11 12 13

14 15 16 17 18 19 20

21 22 23 24 25 26 27

28 29 30 31

LAST QUARTER NEW MOON October 2 October 9 09:45 UT 03:47 UT

FIRST QUARTER FULL MOON October 16 October 24 18:02 UT 16:45 UT

LAST QUARTER October 31 -1 16:40 UT 0 DISTANCES 1 Perigee October 5, 22h UT 2 366,392 km Diameter 32′ 37″ 3 Apogee October 17, 19h UT 4 404,227 km Diameter 29′ 34″

h Planet location Perigee October 31, 20 UT shown for mid-month 370,204 km Diameter 32′ 17″ USING THE NORTHERN HEMISPHERE MAP FAVORABLE LIBRATIONS Go out within an hour of a time listed to the • Bunsen A Crater October 1 right. Turn the map around so the yellow label for the direction you’re facing is at the 1 • Mare Australe October 12 bottom. That’s the horizon. The center of the • Gum Crater October 14 map is overhead. Ignore the parts of the map • Regnault Crater October 26 above horizons you’re not facing.

42 OCTOBER 2018 • SKY & TELESCOPE c M56

CYGNUS q

LYR

Albireo `

10 HD 184590

Stock 1 w ie _ v r la cu no 5° bi VULPECULA

M27

a SAGITTA

Binocular Highlight by Mathew Wedel Harvest the Stars he Milky Way offers so many open clusters that T I have to consciously resist their pull, lest this column turn into “all open clusters, all the time.” Still, there’s no denying that open clusters offer a larger variety of rewarding binocular targets than any other class of celestial object. This month we’ll visit one that’s easy to  nd, but which hasn’t reaped as much attention as its neighbors. Imagine an equilateral triangle, about 3.5° on a side, formed by Albireo, Alpha (α) Vulpeculae, and 10 Vulpeculae. About halfway between the latter two stars lies the open cluster Stock 1. Perched on the western edge of the dark Cygnus Rift, Stock 1 sprawls across almost a full degree of arc. At about 15 light-years in diameter, it’s not an unusually big cluster. Rather, it appears large because it is fairly close to us, only 1,000 light-years away. The cluster is noticeably asymmetric. Its stars are most concentrated toward the southeast, and they spread out to the northwest. In fact, instead of coming to a sharp cutoff, the northwest end of the cluster grades smoothly into several chains of stars that seem to radiate north-northwest toward Albireo. Especially in this season, I always see the cluster and its neighboring spray of stars as a sheaf of grain, bundled from the harvest. The illusion is enhanced by a number of K-type orange giants that lend the scene a golden hue. Most of these aging stars are as WHEN TO close or closer to us than Stock 1, but HD 184590, an USE THE MAP M-type orange-red giant, glares back at us across 2,000 light-years. At 7th magnitude, it’s bright enough Late Aug Midnight* to show up even in smaller binoculars. Look for it Early Sept 11 p.m.* perched right on — or rather, behind — the north- Late Sept 10 p.m.* western edge of Stock 1. EarlyOct 9p.m.* Late Oct Nightfall ¢ MATT WEDEL is out in the dark with his binos, *Daylight-saving time bringing in the harvest. You should give him a hand.

skyandtelescope.com • OCTOBER 2018 43 OCTOBER 2018 OBSERVING Planetary Almanac

PLANET VISIBILITY : hidden in the Sun’s glow all month • : visible at dusk through the 7th • Mars: visible at dusk, sets after midnight • Jupiter: visible at dusk, sets early evening • Mercury Saturn: visible at dusk, sets mid-evening

Oct 1 11 21 31 October Sun & Planets Venus Date Right Ascension Declination Elongation Magnitude Diameter Illumination Distance Sun 1 h 27.6m –2° 59′ —–26.831′ 57″ —1.001

31 14h 19.6m –13° 56′ —–26.832′ 13″ —0.993

Mercury 1 h 56.8m –5° 27′ 8° Ev –0.9 4.8″ 98% 1.406

11 13h 55.6m –12° 27′ 14° Ev –0.4 4.9″ 93% 1.365

21 14h 52.4m –18° 16′ 19° Ev –0.2 5.3″ 86% 1.276

h m ′ ″ 1316 131 15 46.9 –22° 32 22° Ev –0.2 5.9 75% 1.138 Mars Venus 1 h 21.8m –21° 19′ 33° Ev –4.8 46.2″ 17% 0.361

11 14h 20.5m –21° 52′ 24° Ev –4.6 53.9″ 8% 0.310

11631 21 14h 05.4m –20° 13′ 11° Ev –4.2 59.9″ 2% 0.278 Jupiter 31 13h 44.6m –16° 34′ 9° Mo –4.2 60.9″ 1% 0.274

Mars 1 h 36.3m –22° 37′ 118° Ev –1.3 15.8″ 88% 0.592

16 21h 03.0m –20° 02′ 110° Ev –1.0 13.7″ 87% 0.682

31 21h 34.1m –16° 56′ 103° Ev –0.6 12.0″ 86% 0.781 16 Jupiter 1 h 18.4m –17° 29′ 44° Ev –1.8 32.6″ 100% 6.046 Saturn 31 15h 43.2m –19° 01′ 21° Ev –1.7 31.4″ 100% 6.285

Saturn 1 h 12.0m –22° 46′ 85° Ev +0.5 16.5″ 100% 10.097

16 31 18h 20.0m –22° 47′ 57° Ev +0.6 15.7″ 100% 10.563

Uranus Uranus 16 1h 54.8m +11° 10′ 172° Mo +5.7 3.7″ 100% 18.884 Neptune 16 23h 02.1m –7° 16′ 142° Ev +7.8 2.3″ 100% 29.153 Neptune 10" The table above gives each object’s right ascension and declination (equinox 2000.0) at 0h Universal Time on selected dates, and its elongation from the Sun in the morning (Mo) or evening (Ev) sky. Next are the visual magnitude and equatorial diameter. (Saturn’s ring extent is 2.27 times its equatorial diameter.) Last are the percentage of a planet’s disk illuminated by the Sun and PLANET DISKS have south up, to match the the distance from Earth in astronomical units. (Based on the mean Earth–Sun distance, 1 a.u. is 149,597,871 kilometers, or view in many telescopes. Blue ticks indicate the 92,955,807 international miles.) For other dates, see skyandtelescope.com/almanac. pole currently tilted toward Earth.

+40° 12h 10h 8h 6h 4h 2h 0h 22h 20h 18h 16h 14h Castor GEMINI RIGHT ASCENSION Vega BOÖTES +30° Pollux CYGNUS +30° ARIES LEO 31 HERCULES +20° 5 PEGASUS +20° 28 E C L Oct I P T 2 I C Uranus DECLINATION +10° +10° Oct PISCES AQUILA VIRGO 0° Procyon 24 –25 0° ORION EQUATOR Neptune AQUARIUS OPHIUCHUS Rigel Mercury 20 LIBRA CORVUS CETUS 16 Jupiter ERIDANUS Saturn 13 –20° HYDRA Mars CANIS Venus MAJOR –30° CAPRICORNUS –30° SCORPIUS LOCALTIMEOFTRANSIT SAGITTARIUS –40° 10 am 8am 6am 4am 2am Midnight 10 pm 8pm 6pm 4pm 2pm –40°

TheSunandplanetsare positioned for mid-October; the colored arrows show the motion of each during the month. The Moon is plotted for evening dates in the Americas when it’swaxing(rightside illuminated)orfull,andformorningdateswhenit’swaning(leftside).“Localtimeoftransit”tellswhen(inLocalMeanTime)objectscross the meridian — that is, when they appear due south and at theirhighest—atmid-month.Transitsoccuranhourlateronthe1st,andanhourearlieratmonth’send.

44 OCTOBER 2018 • SKY & TELESCOPE Under the Stars by Fred Schaaf

The Sea Goat in the Skies The ancient constellation Capricornus bears an interesting history.

apricornusiscertainlynotaveery is rather compact makes C bright constellation, nor onew ith it easier to fi nd and study alotofnotabledeep-skyobjectswithin than the more sprawling and its bounds. Even so, I find it more faas- complicated forms of Aquarius cinating and more of a standout thaan and Pisces. many other constellations, even somme What should also be quite notice- the name is the others of the zodiac. able to those who follow the planets “horn” part: A cor- WhydoIfinditsocompelling?First is how large the gap — consisting of nucopia is a horn of plenty of all, no other constellation represents mostly faint and disorganized starry (“copia” as in copious) and a mythical somethingsopeculiar—acreature heavens — actually is between the Tea- one-horned creature is a unicorn. But half-goat and half-fish. Yet its strange pot of Sagittarius and the interesting the fi rst part of the name Capricor- goat-fish form is also the key to directly western end of Capricornus. Of course, nus means “goat” — baby goats (kids) identifying it as one of the most ancient in recent years the Teaspoon asterism hopping around playfully are capering, of all constellations. Other notable in Sagittarius has (rightfully) gained and we call their behavior capricious. attributes of Capricornus include its greater fame. But the naked-eye dull- One of several possibilites is that the compactness, its rich connections ness of eastern Sagittarius still may be age-old Italian resort, the Isle of Capri, with language, its remarkable double the largest such gap anywhere along the was named for being the “isle of goats.” stars, and its position with regard to zodiac — and western Capricornus is at At the very time of our October all-sky the zodiac, the , and the end of that gap. map, with Capricornus at its high- certain deep-sky objects. The goat or boat. Astronomy writer est, the brilliant star just rising in the Capricornus, the compact stand- Guy Ottewell has said that the pat- northeast is , which means “she- out. AtthetimeofourOctoberall-sky tern of Capricornus looks more like a goat” (the mother goat held by , map, the pattern of Capricornus is at boat than a goat — though I would say the Charioteer). its exact highest in the south. Capricor- a oddly formed little paper boat or an Capricornus to be continued. nus is fairly dim, though certainly no origami bird. However, we now know The head of the Sea Goat is marked by more so than the other two constella- that Capricornus was indeed imagined Alpha (α) and Beta (β) Capricorni, just tionsthatformtheautumnalzodiac, to be a boat — the boat of the god Enki a few degrees apart — with Alpha a wide Aquarius and Pisces. But according to — in Mesopotamia about 5,000 years naked-eye double star and Beta a wide themodernboundariesoftheconstel- ago (S&T: Mar. 2015, p. 36). Interest- binocular double star. Next month we’ll lations, the area of the heavens that ingly, only a few hundred years later examine them, plus several other choice belongs to Capricornus is actually the pattern became associated with one deep-sky objects in and near Capricor- smallerthanthatofanyotherzodiac of Enki’s various forms — front-half nus. We’ll also consider other fascinat- constellation, even a little smaller than goat and back-half fi sh. And up to our ing aspects of Capricornus’s positioning that of Aries. Aquarius and Pisces are present day, Capricornus is still pictured and objects to which its odd shape has both more than twice as big in area as that way. It is supposed to be a “Sea been compared. Capricornus (so is Capricornus’s west- Goat” or “Goat-Fish.” ernneighbor,Sagittarius—andVirgo Capricornus in name and lan- ¢ Contributing Editor FRED SCHAAF is more than three times larger). But guage. The name Capricornus is Latin welcomes your letters and comments at

LIBRARY OF CONGRESS / RESTORATION: ADAM CUERDEN the fact that the pattern of Capricornus for “horned goat.” The second half of [email protected].

skyandtelescope.com • OCTOBER 2018 45 OCTOBER 2018 OBSERVING Sun, Moon & Planets by Fred Schaaf To i nd out what’s visible in the sky from your location, go to skypub.com/ almanac. Enter the Ice Giants The brighter planets begin to give way as Uranus and Neptune jostle for our attention this month.

he glorious evening bridge of DUSK DUSK THROUGH EVENING T four bright planets we’ve enjoyed Venus starts October very low in the Saturn is already past the meridian as through summer comes to an end this west after the Sun sets for viewers night falls but doesn’t set until after 11 month. Venus falls and fades from sight around latitude 40° north. It gets even p.m. October 1st and after 9 p.m. late into the Sun’s afterglow, then leaves the lower and even more diffi cult to spot in the month. Serene Saturn dims from evening sky altogether later in October. with each passing day. It’s out of sight by magnitude +0.5 to +0.6 during October Jupiter is visible in the west-southwest the 7th. Venus reaches inferior conjunc- and its globe shrinks to less than 16″ at nightfall, lower and for less time, and tion on October 26th and is then 6° in equatorial diameter. But the rings, near month’s end is close to low and south of the Sun — after which it starts though now a year past their time of elusive Mercury. Saturn shines in the emerging before sunrise (see below). maximum tilt, are only slightly less south-southwest at dusk, much higher Jupiter shines at magnitude –1.7 by tilted and remain a stirring sight. Sat- than Jupiter, and remains visible into late October and the interval between urn is slowly trekking eastward above the second half of evening. Mars at sunset and Jupiter-set decreases to only the Teapot of Sagittarius. nightfall burns in the south-southeast about 1 hour by month’s end. Even Jupi- Mars loses half its brightness yet and, though it fades, still shines brighter ter is less than 32″ wide by the second again this month, dimming from mag- than any star until after the mid- half of October and presents a shaky nitude –1.3 to –0.6 — but even the latter night hour when it sets and Sirius rises. image so low in the sky. fi gure is impressive. The Red Planet cul- The only bright planet visible at dawn Mercury may be glimpsed very low in minates around 9 p.m. in early October, this month is Venus, very low and late in the west shortly after sunset toward the and about an hour earlier by the end morning twilight, at the end of October. end of the month; optical aid will help. of the month. That’s when it’s high-

u These scenes are drawn for near Dusk, Oct 5 Dusk, Oct 11–14 the middle of North 1 hour after sunset 30 minutes after sunset America (latitude 40° north, longitude 90° west); European observers should 10° move each Moon Moon symbol a quarter of Saturn Oct 14 Saturn the way toward the one for the previ- Moon ous date. In the Far Oct 13 East, move the Moon Moon Moon halfway. The blue 10° Oct 12 β Oct 11 scale bar is about Antares the width of your i st SAGITTARIUS SCORPIUS at arm’s length. For δ clarity, the Moon is Cat’s Jupiter shown three times its Eyes actual apparent size.

Looking South-Southwest Looking Southwest

46 OCTOBER 2018 • SKY & TELESCOPE est and most likely to provide a steady sharp image in telescopes. The apparent December diameter of Mars shrinks from 16″ to solstice 12″ in October — only half as wide as it was in late August. Nevertheless, this is Uranus Earth still large enough to get some fi ne views Venus Mars of Martian surface and atmospheric March features with a good telescope on a equinox Jupiter Sun good night. The northern hemisphere Neptune Mercury of Mars reaches its winter solstice on Saturn Sept. equinox October 16th. For information about observing the Martian north polar hood June clouds and north polar icecap, along solstice with other features at this apparition, see p. 22 in the July issue. ORBITS OF THE PLANETS Mars races eastward across most of The curved arrows show each planet’s movement during October. The outer planets don’t the compact pattern of Capricornus change position enough in a month to notice at this scale. this month. At the end of October the planet approaches the eastward end of Neptune,inAquarius,isonlymagni- MOON PASSAGES the Sea Goat, marked by the magni- tude 7.8 and 2.3″ wide but is already on The Moon is a thin waxing crescent tude-2.85 star Delta (δ) Capricorni, also themeridianbylateeveningormid- some 3° upper right of Jupiter at dusk known as Deneb Algedi (see p. 45 for evening. Finder charts for Uranus and onOctober11thandathickercrescent more on the stars of Capricornus). NeptuneappearintheSeptemberissue. 2°upperrightofSaturnonOctober 14th. The waxing gibbous Moon is ALL NIGHT DAWN about 6° either side of Mars on Octo- Uranus arrives at opposition on October Venus leaps back into view at the very ber 17th and 18th. The waning gibbous 23rd so is highest in the middle of the endofOctober,risinglessthan40min- Moon shines in the Hyades on October night this month. It shines at magnitude utes before the Sun on the 31st. Venus 27th at dawn. 5.7 in southwestern Aries and thus is is then about 61″ wideandlittlemore capable of being seen with the naked than1%lit.Viewersaroundlatitude40° ¢ Contributing Editor FRED SCHAAF eye at dark locations. Telescopes show north can see it that dawn about 4° high has been writing about the skies above its blue or blue-green globe 3.7″ wide. andupperrightoftheSunatsunrise. us for more than 40 years.

α Dusk, Oct 14 – 15 Dusk, Oct 17–18 Dawn, Oct 26– 28 45 minutes after sunset 1 hour after sunset β 1 hour before sunrise

Moon δ Mars Moon β Oct 15 Moon Oct 17 Oct 18 ζ Saturn Moon Oct 14 Moon Oct 28 CAPRICORNUS TAURUS SAGITTARIUS

Aldebaran Pleiades Cat’s Moon Oct 27 Eyes Hyades

Moon Looking West, Oct 26 Looking South-Southwest Looking South-Southeast high in the sky

skyandtelescope.com • OCTOBER 2018 47 OCTOBER 2018 OBSERVING Celestial Calendar by S. N. Johnson-Roehr

_ e M37 AURIGA +30° o g ` f p `

g 1 ¡ M35 Another TAURUS 2 16 + 3 b M1 13 GEMINI 4 c d 1 5 +20° 10 2 r c

Bright Star magnitudes Nov 1 r 6 7 0h UT i 2392 4 Comet? h 29 a j 26 Oct 2 23 h Comet 38P/Stephan-Oterma P 20 i 0 UT ath 17 Sept 17 of 14 0h UT is ideally placed in the Co 11 me 8 j t 38 5 P/ 23 20 northern skies this month. Ste 29 +10° pha 26 n-Ot erma ` + h his month sees the return of the a Betelgeuse THalley-type comet 38P/Stephan- _ CANIS _ MINOR ORION Oterma. It feels like ages since a Procyon binocular-bright comet graced the northern skies. As we put this issue to bed, we’re waiting to see if Comet 21P/ 0° MONOCEROS Giacobini-Zinner will hit its predicted M78 7th-magnitude peak and/or if Comet b PanSTARRS (C/2017 S3) will get even 7h 30m 7h 00m 6h 30m 6h 00m 5h 30m brighter after a series of outbursts in mid-July bumped it to magnitude 8. Comet 38P shouldn’t grow brighter Periodic comet 38P/Stephan-Oterma skates across the night sky this au- than 9th magnitude — comparable in tumn. Look for it north of Betelgeuse at the beginning of October. It will be brightness to what it reached during previous apparitions — but that still at its brightest in November, when it passes through southeastern Gemini. puts it within easy range of small bin- Stars are shown to magnitude 6.5 with 38P’s position marked at 0h UT oculars and telescopes. every three days. Comet 38P last arrived at perihelion in late 1980. French astronomer Jérôme Eugène Coggia discovered 38P from Marseilles Observatory on January 22, observing from Turku Observatory in The comet then passes south of Orion’s 1867, and added it to his list of uncata- November 1942. Subsequent observa- club, spending several mornings a bit loged nebulae. Credit for the discovery tions led to tighter orbital and period more than 1° from Xi (ξ) Ori. From was given to the observatory’s director, calculations; the apparition in 1980 there, it zips across Gemini on its way Édouard J. M. Stéphan, who confi rmed allowed even more refi nement, giv- to a November 10th perihelion. the comet’s (new) position on January ing us an orbital period of 37.96 years. Fortunately, the Twins climb higher 24th and subsequently authored the This means that what should have been each October night, so 38P will be well discovery bulletin. The comet was then 38P’s second apparition in 1904–05 placed in the late evening throughout lost, with return predictions ranging went unobserved. the month, about one-third of the way from 34 to 40 years based on the 1867 Comet 38P should come into visual up the eastern sky for observers at mid- observations. The second half of the range in September, when it will still be northern latitudes. November sees the comet’s familiar name rewards the re- an early-morning object in Orion. By icy dust ball at its brightest and possibly discoverer, Liisi Oterma. Oterma, the the fi rst week of October, it’s predicted most photogenic, but it should remain fi rst woman to receive a PhD in astron- to shine at magnitude 10.5 about 5° a 10th-magnitude object through the omy in Finland, picked up 38P while north of Alpha (α) Orionis (Betelgeuse). New Year.

48 OCTOBER 2018 • SKY & TELESCOPE October 21 11:30 pm Pleiades October TAURUS Orionids Capella AURIGA TWICE A YEAR, barring interference from weather and moonlight, we get to Aldebaran 10° see Halley’s Comet again — or at least the bits and pieces it’s left in our region of the solar system. In the spring, we experience Halley’s dusty detritus as the Eta Aquariid meteor shower, which occurs when Earth passes through a trail of dust that’s slowly moving out- ward from the comet’s orbit. In Octo- ORION ber, we see it as the Orionid meteor Orionid Betelgeuse shower, when Earth once more encoun- Radiant GEMINI ters a dust stream far from Halley’s Castor Rigel path. This year, the predicted peak for the Orionids falls on the afternoon of Pollux October 21st. Full Moon is on October 24th, so peak activity coincides with a wax- Looking East ing gibbous Moon. Even at their best, Orionid meteors are fast (66 km/s) but p The radiant for the Orionids is located northeast of Betelgeuse. Astronomers once suspected faint. The best viewing for any shower that the shower had several radiants, each tied to a separate ribbon of dust and each with a differ- comes when looking 45°–90° away ent peak date, but recent observations suggest that shower activity is quite stable. from the radiant, and this year some extra strategizing to avoid moonlight 10th, only about 5 Southern Taurids fi reballs, so it’s always worth keeping an is in order. Try facing north, with the per hour will spark through the sky. eye open for them on either side of the Moon at your back. The shower’s radi- However, the shower is known for its peak date. ant peaks over the horizon near 10 p.m. and is highest around 5 a.m. local time. The diagram at right shows the radi- ant’s location at 11:30 p.m. The Moon is already high in the south as the radiant Minima of Algol rises in the east. Sept. UT Oct. UT 29 You may see as many as 20 mete- 28:52 10:58 18 ors per hour under ideal conditions, 30 5 5:40 3 21:47 but expect a number closer to 10. It’s PERSEUS possible that the Orionids operate on a 82:29 618:35 38 12-year cycle, with the number of mete- 10 23:18 9 15:24 Algol 21 ors increasing after a point of lesser 13 20:06 12 12:13 activity. The low point was calculated 16 16:55 15 9:02 to fall between 2014 and 2016, so the 19 13:43 18 5:50 number of Orionids per hour may be on TRIANGULUM the (slow) rise, on its way to an out- 22 10:32 21 2:39 3 burst in or after 2026. 25 7:21 23 23:28 If you see a bright meteor but its path 28 4:09 26 20:17 p doesn’t seem to track back to a point 29 17:05 With autumn returning, Perseus is rising into of origin in Orion, check to see if it’s a the northeastern sky. Every 2.7 days, Algol These geocentric predictions are from the Southern Taurid. Birthed by Comet 2P/ (Beta Persei) dips from its usual magnitude 2.1 recent heliocentric elements Min. = JD to 3.4 and back. Use this chart to estimate its Encke, the Southern Taurids appear to 2445641.554+ 2.867324E, where E is any integer. For a comparison-star chart and brightness with respect to the comparison stars emanate from a point close to Mu (μ) more info, see skyandtelescope.com/algol. of magnitude 2.1 (Gamma Andromedae) and Ceti. At the shower’s peak on October 3.4 (Alpha Trianguli).

skyandtelescope.com • OCTOBER 2018 49 OCTOBER 2018 OBSERVING Celestial Calendar Action at Jupiter JUPITER SHINES LOW in the west at nightfall this month. It’s still in Libra for the fi rst half of October, shining at magnitude –1.8. On the 11th the gas giant pairs with the waxing crescent Moon before dropping below the hori- zon in the west-southwest. Bring bin- oculars to catch it at its highest. Jupiter passes into Scorpius on November 20th and is largely lost to view by the end of the month, when it stands only 5° above the horizon 30 minutes after sun- set. When it reappears as a dawn object Asteroid Occultation in December, it will have already moved on from Scorpius to Ophiuchus. Because Jupiter is low, viewing will p Roughly as long as Lake Michigan is wide, 216 Kleopatra looks like a giant dog bone tossed into the Main Belt. Kleopatra is composed mostly of iron and nickel (its “bone heads” may contain be tough this month, but here are the solid metal cores), so it relects radio waves well enough to permit astronomers to construct rela- times, in Universal Time, when the tively accurate 3D models. Great Red Spot should cross Jupiter’s central meridian. The dates, also in UT, NORTHERN NORTH AMERICA sees Alexhelios, has a diameter of approxi- are in bold. (Eastern Daylight Time is the asteroid 216 Kleopatra occult an mately 9 km, while the inner moon, UT minus 4 hours.) 11.1-magnitude star in northern Canis Cleoselene, is only 7 km wide. Sept. 1, 1:39, 11:34, 21:30; 2, 7:26, MinoronthemorningofSunday, The International Occultation Tim- 17:22; 3, 3:18, 13:13, 23:09; 4, 9:05, October28th.Astheasteroidpasses ing Organization (IOTA) notes that 19:01; 5, 4:57, 14:53; 6, 0:48, 10:44, betweenEarthandthestarTYC765- although radar data have helped build a 20:40; 7, 6:36, 16:32; 8, 2:28, 12:23, 506-1, observers will see the combined strong 3D model, amateur observations 22:19; 9, 8:15, 18:11; 10, 4:07, 14:03, lightofthetwoobjectsdropto11.4,the are still needed to resolve the asteroid’s 23:58; 11, 9:54, 19:50; 12, 5:46, 15:42; brightness of the asteroid, for as much true shape. The predicted region of vis- 13, 1:37, 11:33, 21:29; 14, 7:25, 17:21; as 10 seconds. ibility for an occultation can be uncer- 15, 3:17, 13:12, 23:08; 16, 9:04, 19:00; AmetallicMainBeltasteroid, tain by about ½ a path width (pw), but 17, 4:56, 14:52; 18, 0:47, 10:43, 20:39; Kleopatraboastsadiameterofabout the uncertainty with Kleopatra is only 19, 6:35, 16:31; 20, 2:27, 12:22, 22:18; 138 km. Don’t let that number mislead 0.13 pw. A line drawn on a map from 21, 8:14, 18:10; 22, 4:06, 14:02, 23:58; you, though; Kleopatra offers nothing central Alberta (north of Edmonton) 23, 9:53, 19:49; 24, 5:45, 15:41; 25, like the elegant sphere of Ceres or the through Syracuse, New York, to New 1:37, 11:33, 21:28; 26, 7:24, 17:20; 27, oblate spheroid of Vesta. Rather, it’s Haven, Connecticut, provides a good 3:16, 13:12, 23:08; 28, 9:03, 18:59; 29, unevenandelongated,resemblingthe estimation of the central occultation 4:55, 14:51; 30, 0:47, 10:43, 20:38. classic dog bone more than anything path. For observers in Alberta, the event Oct. 1, 6:31, 16:27; 2, 2:23, 12:19, else, as is shown in the above depictions should begin within a minute or two 22:14; 3, 8:10, 18:06; 4, 4:02, 13:58, of 3D models based on radar observa- of 8:31 UT (2:31 MDT). Observers near 23:54; 5, 9:49, 19:45; 6, 5:41, 15:37; 7, tions. This distorted shape is probably Peterborough, Ontario, can expect it 1:33, 11:29, 21:24; 8, 7:20, 17:16; 9, theresultofanancientimpactthathol- to begin near 8:33 UT (4:33 a.m. EDT), 3:12, 13:08, 23:04; 10, 9:00, 18:55; 11, lowed out the asteroid’s central region, while those closer to the East Coast will 4:51, 14:47; 12, 0:43, 10:39, 20:35; 13, leaving behind a body that’s roughly see it near 8:34 UT (4:34 a.m. EDT). 6:30, 16:26; 14, 2:22, 12:18, 22:14; 15, four times as long as it is wide. About a week before both events, 8:10, 18:06; 16, 4:01, 13:57, 23:53; 17, Thesamecollisionthatcreated more precise predictions and path maps 9:49, 19:45; 18, 5:41, 15:36; 19, 1:32, Kleopatra’s evocative form also may will be available from Steve Preston’s 11:28, 21:24; 20, 7:20, 17:16; 21, 3:11, havereleasedthematerialthatnow minor planet occultation website 13:07, 23:03; 22, 8:59, 18:55; 23, 4:51, comprises the asteroid’s two moons, (asteroidoccultation.com). For advice 14:47; 24, 0:42, 10:38, 20:34; 25, 6:30, Alexhelios and Cleoselene. Named for on timing occultations and report- 16:26; 26, 2:22, 12:17, 22:13; 27, 8:09, the children of Cleopatra, the last Ptol- ing observations, see the IOTA website 18:05; 28, 4:01, 13:57, 23:53; 29, 9:48,

emaicpharaohofEgypt,thesesatellites (occultations.org/observing) as well as 19:44; 30, 5:40, 15:36; 31, 1:32, 11:28, / JPL

are quite small in size. The outer moon, asteroidoccultation.com/observations. 21:23. NASA

50 OCTOBER 2018 • SKY & TELESCOPE Jupiter’s Moons These times assume that the Great Features on Jupiter appear closer to Red Spot will be centered at longitude the central meridian than to the limb 292° measured in System II. If the Great for 50 minutes before and after transit- Red Spot has moved elsewhere, it will ing. A light blue or green fi lter slightly Oct 1 transit 12/3 minutes earlier for each increases the contrast and visibility of 2 degreelessthan292°. It will transit Jupiter’s reddish and brownish mark- 3 EAST WEST approximately 12/3 minutes later for ings; an orange fi lter helps darken the each degree more than 292°. blue features. 4

5 Phenomena of Jupiter’s Moons, October 2018 6 Callisto Oct. 1 2:28 I.Oc.D 2:27 I.Sh.I 8:51 II.Tr.I 15:09 II.Sh.E 7 5:32 I.Ec.R 3:51 I.Tr.E 10:14 II.Sh.I Oct. 24 3:01 I.Oc.D 8 23:41 I.Tr.I 4:36 I.Sh.E 11:12 II.Tr.E 5:46 I.Ec.R 6:02 II.Tr.I Oct. 2 0:32 I.Sh.I 12:32 II.Sh.E Oct. 25 0:12 I.Tr.I 9 1:51 I.Tr.E 7:38 II.Sh.I Oct. 17 1:00 I.Oc.D 0:44 I.Sh.I 2:42 I.Sh.E 8:23 II.Tr.E 3:51 I.Ec.R 2:23 I.Tr.E 10 Europa 3:13 II.Tr.I 9:55 II.Sh.E 22:11 I.Tr.I 2:54 I.Sh.E 5:01 II.Sh.I 22:59 I.Oc.D 22:50 I.Sh.I 6:01 II.Oc.D 11 5:34 II.Tr.E Oct. 10 1:56 I.Ec.R Oct. 18 0:22 I.Tr.E 9:24 II.Ec.R 7:18 II.Sh.E 20:11 I.Tr.I 1:00 I.Sh.E 18:24 III.Tr.I 12 20:58 I.Oc.D 20:55 I.Sh.I 3:13 II.Oc.D 20:30 III.Tr.E 22:21 I.Tr.E Oct. 3 0:01 I.Ec.R 6:49 II.Ec.R 20:39 III.Sh.I 13 Io 18:11 I.Tr.I 23:05 I.Sh.E 13:58 III.Tr.I 21:32 I.Oc.D 19:01 I.Sh.I Oct. 11 0:26 II.Oc.D 16:04 III.Tr.E 22:30 III.Sh.E 14 20:21 I.Tr.E 4:14 II.Ec.R 16:40 III.Sh.I Oct. 26 0:14 I.Ec.R 21:10 I.Sh.E 9:34 III.Tr.I 18:30 III.Sh.E 18:42 I.Tr.I 15 21:40 II.Oc.D 11:40 III.Tr.E 19:30 I.Oc.D 19:13 I.Sh.I Oct. 4 1:39 II.Ec.R 12:42 III.Sh.I 22:20 I.Ec.R 20:53 I.Tr.E 16 5:12 III.Tr.I 14:32 III.Sh.E Oct. 19 16:41 I.Tr.I 21:23 I.Sh.E 17 7:17 III.Tr.E 17:29 I.Oc.D 17:18 I.Sh.I Oct. 27 1:06 II.Tr.I 8:44 III.Sh.I 20:25 I.Ec.R 18:52 I.Tr.E 2:09 II.Sh.I 18 10:33 III.Sh.E Oct. 12 14:41 I.Tr.I 19:28 I.Sh.E 3:27 II.Tr.E 15:28 I.Oc.D 15:24 I.Sh.I 22:16 II.Tr.I 4:27 II.Sh.E 19 18:30 I.Ec.R 16:51 I.Tr.E 23:32 II.Sh.I 16:02 I.Oc.D 17:34 I.Sh.E Oct. 5 12:41 I.Tr.I Oct. 20 0:37 II.Tr.E 18:43 I.Ec.R 20 13:30 I.Sh.I 19:26 II.Tr.I 1:50 II.Sh.E Oct. 28 13:12 I.Tr.I 14:51 I.Tr.E 20:56 II.Sh.I 14:01 I.Oc.D 13:41 I.Sh.I 21 15:39 I.Sh.E 21:47 II.Tr.E 16:48 I.Ec.R 15:23 I.Tr.E Ganymede 16:37 II.Tr.I 23:13 II.Sh.E Oct. 21 11:12 I.Tr.I 15:51 I.Sh.E 22 18:19 II.Sh.I Oct. 13 12:00 I.Oc.D 11:47 I.Sh.I 19:25 II.Oc.D 18:58 II.Tr.E 14:54 I.Ec.R 13:22 I.Tr.E 22:41 II.Ec.R 23 20:36 II.Sh.E Oct. 14 9:11 I.Tr.I 13:57 I.Sh.E Oct. 29 8:53 III.Oc.D Oct. 6 9:59 I.Oc.D 9:53 I.Sh.I 16:37 II.Oc.D 10:33 I.Oc.D 24 12:59 I.Ec.R 11:21 I.Tr.E 20:06 II.Ec.R 12:47 III.Ec.R Oct. 7 7:11 I.Tr.I 12:02 I.Sh.E Oct. 22 4:27 III.Oc.D 13:12 I.Ec.R 25 7:58 I.Sh.I 13:50 II.Oc.D 6:34 III.Oc.R Oct. 30 7:43 I.Tr.I 9:21 I.Tr.E 17:31 II.Ec.R 6:55 III.Ec.D 8:10 I.Sh.I 26 10:08 I.Sh.E Oct. 15 0:01 III.Oc.D 8:31 I.Oc.D 9:53 I.Tr.E 11:03 II.Oc.D 2:08 III.Oc.R 8:47 III.Ec.R 10:20 I.Sh.E 27 14:57 II.Ec.R 2:57 III.Ec.D 11:17 I.Ec.R 14:31 II.Tr.I 28 19:36 III.Oc.D 4:48 III.Ec.R Oct. 23 5:42 I.Tr.I 15:27 II.Sh.I 21:43 III.Oc.R 6:30 I.Oc.D 6:16 I.Sh.I 16:53 II.Tr.E 29 22:57 III.Ec.D 9:22 I.Ec.R 7:52 I.Tr.E 17:45 II.Sh.E Oct. 8 0:48 III.Ec.R Oct. 16 3:41 I.Tr.I 8:25 I.Sh.E Oct. 31 5:03 I.Oc.D 30 4:29 I.Oc.D 4:21 I.Sh.I 11:41 II.Tr.I 7:40 I.Ec.R 7:27 I.Ec.R 5:52 I.Tr.E 12:51 II.Sh.I 31 Oct. 9 1:41 I.Tr.I 6:31 I.Sh.E 14:02 II.Tr.E

Every day, interesting events happen between Jupiter’s satellites and the planet’s disk or shadow. The fi rst columns give the date and mid-time of the event, in Universal Time (which is 4 hours ahead of Eastern Daylight Time). Next is the satellite The wavy lines represent Jupiter’s four big satellites. The involved: I for Io, II Europa, III Ganymede, or IV Callisto. Next is the type of event: Oc for an occultation of the satellite behind centralverticalbandisJupiteritself.Eachgrayorblack Jupiter’s limb, Ec for an eclipse by Jupiter’s shadow, Tr for a transit across the planet’s face, or Sh for the satellite casting its h own shadow onto Jupiter. An occultation or eclipse begins when the satellite disappears (D) and ends when it reappears (R ). horizontalbandisoneday,from0 (upper edge of band) h A transit or shadow passage begins at ingress (I) and ends at egress (E ). Each event is gradual, taking up to several minutes. to 24 UT (GMT). UT dates are at left. Slide a paper’s edge Predictions courtesy IMCCE / Paris Observatory. down to your date and time, and read across to see the satellites’positionseastorwestofJupiter.

skyandtelescope.com • OCTOBER 2018 51 OCTOBER 2018 OBSERVING Exploring the Moon by Charles Wood

A Hole in the Moon’s Magnetic Field Astronomers propose a new origin for this mysterious magnetic void.

ach time you aim your telescopes researchers propose that they E toward the Moon, you concentrate were caused by ejecta from on what’s visible: the lunar surface. But an iron-rich asteroid that ever since the fi rst probes entered lunar obliquely hit the Moon to orbit, scientists have been continually form the giant South Pole- surprised by discoveries invisible to Aitken (SPA) impact basin on normal telescopes. For example, track- the lunar farside. Intriguingly, ing of NASA’s Lunar Orbiter spacecraft some magcons coincide with in the 1960s revealed that the Moon’s enigmatic swirls such as Reiner gravity fi eld is lumpy. Spacecraft pass- Gamma, suggesting that the SPA ing over some lunar maria were pulled event tossed out clumps of debris strongly toward the surface, illustrat- with enough magnetism to defl ect ing that there was a concentration mare-darkening solar radiation and thus of mass under these areas that didn’t preserve these odd, bright splotches. occur under highlands. Later studies But the largest and most surprising showed that these mascons only occur magnetic feature of the Moon is a vast 0.1 0.2 0.5 1 2 5 10 20 over maria within impact basins such as nearside area where the fi eld nearly dis- Magnetic fi eld strength (nanotesla) Imbrium, Humorum, and Crisium. This appears. Mark Wieczorek of the Obser- realization led to a new understanding vatoire de la Côte d’Azur in France and that the dense lunar mantle rose up his colleagues call this area — centered under impact basins. on Mare Imbrium and encompassing It was no surprise that the Moon has nearby parts of Oceanus Procel- a gravity fi eld because, after all, it has larum and Mare Frigoris — the mass. But early spacecraft found no evi- “Great Magnetic Low” (GML). The dence for a global lunar magnetic fi eld. surface fi eld there is less than a Later, samples returned from the Apollo tenth as strong as the average 15 mission showed evidence of an lunar fi eld. ancient magnetic fi eld roughly one tenth When fi rst discovered about the strength of that at Earth’s surface. 18 years ago, the GML’s asso- Today the fi eld is much weaker, more like a thousandth that on Earth. NASA’s puTop: The total magnetic i eld Lunar Prospector and JAXA’s Kaguya strength over the nearside of the spacecraft, which orbited close to the Moon compiled from Lunar Prospector lunar surface, both carried sensitive and Kaguya data reveals a large “hole” instruments that mapped the Moon’s in the northwestern quadrant. weak magnetic fi eld. It’s highly vari- Bottom: The majority of the “Great Mag- netic Low” in the lunar magnetic i eld corre- able, much stronger at some locations sponds to the Imbrium impact basin (shown as than elsewhere. The origin of these an oval) but also includes parts of Mare Frigoris “magcons” is poorly understood. Some and Oceanus Procellarum.

52 OCTOBER 2018 • SKY & TELESCOPE MAGNETIC FIELD: JGR PLANETS / HIDEO TSUNAKAWA ET AL; GREAT MAGNETIC LOW: NASA / LUNAR RECONNAISSANCE ORBITER; REINER GAMMA: SEAN WALKER / S&T perature, now known as the the as nowknown perature, tem- atacertain magnetization their lose they laboratory, his in materials magnetized heated heprogressively as that discovered ago long Curie Pierre plenty. be outto Itturns magnetism? boundaries. PKT the fl Moon’s lava nearside ofthe most why explain could released they heat extra The Serenitatis. Mare western and Nubium, Imbrium, larum, ofProcel- lavas the under quadrant, nearside’s northwest the in centrated con- are elements radioactive reason, phosphorus). P(for elements) and (rare-earth REE for potassium), K (the symbol atomic letters the from built acronym an is way, decay. the KREEP, by they as heat release that uranium and potassium, thorium, elements radioactive of the levels high by distinguished Moon the of aprovince is (PKT). This Terrane fi sions exten- spatial its and GML the that that resolves these confl interpretation alternative an propose fi magnetic weak similarly lack basins impact other and basin, Imbrium the beyond extends GML Butthe plausible explanation. very and elegant It’s an rocks. target the in fi magnetic any erased also Imbrium formed that event the theory, this to According fi magnetic external by organized previously atoms in alignments netic mag- the randomize can waves shock These basin. impact that formed that collision the by generated waves shock lowfi very its that suggested Imbrium with ciation direction. fi the in freeze solid, fi magnetic ambient the acquire 770°C, they below cool lavas as fi amagnetic don’tthus carry 1100°C atabout and erupt typically fl to similar (1418°F). lavas, basaltic Terrestrial at770°C occurs point Curie the lavas, in magnetism carries which iron, For But what does heat have to do with dowith to have heat does But what understood poorly still some For now colleagues and Wieczorek t within the Procellarum KREEP KREEP Procellarum the t within elds. present been had that eld ows found on the Moon, Moon, on the found ows eld strength was due to due to was strength eld eld’s intensity and and eld’s intensity ows are within within are ows eld and, once once and, eld icts. They note note They icts. Curie point Curie eld. But eld. elds. . ei field. mag- weak netic a retain only cooled would slowly lavas Such off. had turned dynamo nearly lunar the time which by delayedbyasmuchasabillionyears, cool- that ingtotheCuriepointcouldhavebeen show heating in radioactive decline PKT the of models researchers’ mathematical The years. the billion over 3½ 10 past of factor a by decreased magnetic fieldgeneratedbyanearlylunardynamo ambient the in locked sumably p a e rbes n sta the that is GMLcoversanareaconsiderably One problems. few a has vrg antcfil teghhas strength field the magnetic that average show ages various of samples lava lunar of measurements because where.Thatextratimeiscrucial,pointmuchlongerthanthoseelse- Curie the above crust PKT the lavas within the kept radioactivity excess GML? the So about this. special done was have what to seem GML the in astheycooled.Allmariaexceptthose solar radiation. perhaps hasshieldedthe lunarsurfaceattheselocationsfrom thedarkeningeffects ofprolonged mle hntePTs ehp since Perhaps PKT’s. the than smaller Bright swirlssuchasReiner Gammacoincidewithlocalizedareas ofhighmagnetism,which hsmdl hl luil,still plausible, while model, This h onsaudn aaflw pre- flows lava Moon’s abundant The icoe’ ru rpssthat proposes group Wieczorek’s skyandtelescope.com inside andout. CHUCK WOOD plains owe their existence to the PKT, the to existence their owe plains Nubium the Imbrium region of the GML. ofthe region Imbrium the fi ofamagnetic lack the to uted contrib- have also might turn in which Procellarum, Mare Imbrium, Imbrium, Mare Procellarum, enriched when Oceanus observing be will experience Butyour telescope. fi magnetic alone. heating PKT’s radioactive the from resulted have would GLM ofthe rest the by ited fi magnetic stronger slightly fi of magnetic lack complete nearly forthe accounting point, Curie the to cooled lavas and basin’s crust Imbrium the until time the extended have could heat extra of pulse This depth. great to crust the heated have must surely impact forming Imbrium- The happened. both plausible, both are models PKT and impact the ¢ ti s When observing,ContributingEditor by recognizing that these vast lava lava vast these that recognizing by Unfortunately, you can’t observe youcan’t observe Unfortunately, , and western western , and elds even with the best best the with even elds eld there. In this case, the the case, this In there. eld envisionstheMoonboth Mare Serenita- • OCTOBER 2018 eld exhib- Mare eld in in eld

53 54 Deep-Sky Wonders OCTOBER 2018OBSERVING I Visual Observations of Planetary Nebulae ofPlanetary Observations Visual book new Wallace’s Kent in impressive included are origins their and names These ofnicknames. acollection them who’ve bestowed observers, on other isn’t lost charm Their green. blue and of blends interesting commonly most color, boast visibly to prone wonders sky deep- rare the among rank and shapes Let mecount the ways. How doIlove wonders? these deep-sky Planetaries I OCTOBER 2018 Gem, fi the hence and three, ofthe lowest The fi magazine this when viewed best they’re so October, early in falls darkness when meridian writes, “Of all the planetaries in the the in planetaries the all “Of writes, and name for its credit claims Mallas

They come in a wealth of fascinating offascinating awealth in come They nebulae. planetary love observing Our fi Our nudge the planetaries few rst G 811. 2421 12.4 10.5 NGC 6891 G 07851. 55 16.2 8.5 NGC 7027 G 841. 4366 14.3 12.0 NGC 6804 betMgv eta ieR Dec. RA 46 Size 16.9 Central 9.3 Mag(v) NGC 6818 Object Love to Planetaries Right ascension and declination are for equinox 2000.0. equinox for are declination and ascension Right magni and aperture tothe according varies and value cataloged the ob an Visually, catalogs. recent from are separations and sizes Angular G 4 091. 4.1 11.9 10.9 NGC 246 G 01. 1574 11.5 12.3 NGC 40 ese 61. 593.1 15.9 10.1 Messier 76 G 711. 671.9 16.7 11.4 6781 NGC G 62831. 37 13.2 8.3 NGC 7662 rst to depart our sky, is the Little Little sky, the is our depart to rst NGC 6818 rst reaches your hands. hands. your reaches rst • by SueFrench in Sagittarius. John H. H. John Sagittarius. in SKY &TELESCOPE SKY

. at 164 10-inch refl 10-inch my In side. eastern brighter and center farther away to the east-northeast. the to away farther abit rests another and northwest, the south. At 299 At south. north- nearly aligned oval, slightly and haze. At 187 At haze. with softened hue ofablue sky the in dressed and fringe afainter in swathed blue-gray disk at102 disk blue-gray bright, fairly asmall, Itbecomes stars. the as sharp doesn’t as look that object 23 Astronomy: color.”the ( describe to paint artist’s an see to yet Ihave and beautiful, is color Its bluest. heavens × Through my 130-mm refractor at refractor my130-mm Through , NGC 6818 stands out as the only only the 6818 outas , NGC stands ″ ″ ″ ″ ″ ″ ′ ′ × ′ , displaying a somewhat darker darker asomewhat , displaying , ‘the Little Gem’ is probably the the probably is Gem’ Little , ‘the i cation of the viewing instrument. i instrument. viewing the of cation June/July 1963) June/July ector at43 ector ject’s size is often smaller than than smaller often is size ject’s The Review of Popular ofPopular Review The × the annulus is fairly wide wide fairly is annulus the × 23 19 20 19 21 19 a faint star sits close to to close sits star afaint 0 1 0 h h h h h h h h h 42.3 13.0 47.1 44.0 25.9 31.6 07.0 15.2 18.5 m × m m m m m m m m . It remains bluish bluish . Itremains × , NGC 6818, NGC is +06° 32 +42° 32 +09° 14 +42° 14 +51° 35 +72° 31 +72° +12° 42 +12° –14° 09 –14° –11° 52 ′ ′ ′ ′ ′ ′ ′ ′ ′ looks roundish, about 1¾ about roundish, looks 15-inch refl my with better much shows structure nebula’s The rim. the emphasizing fi band OIIIor narrow- an Adding south. the in mainly rim, the around brighter tad 130-mm scope, even at48 even scope, 130-mm the in sizable fairly is glow brightness low-surface- Its view. early foran us mm scope at48 scope mm s from afi from scope at216scope 15-inch the in planetary apretty is this page, facing on the mysketch in shown As better. outalittle stands nebula the fi OIIIor narrowband an using when vanishes star The edge. eastern north- on the superimposed star faint The petite disk is quite obvious at102 obvious quite is disk petite The etary nebula the Snowglobe Nebula. Snowglobe the nebula etary plan- little wonderful dub this to him led ring” outer smooth but otherwise complexity internal its “coupled with edge nebula’s the hard that He writes mm scope at63 scope mm 12th-magnitude star 1 star 12th-magnitude a by accompanied disk bluish small, 6781 a17.5-inch with at500 scope NGC observed Gramer Lew amateur fi fat fi band ofanarrow- use the with enhanced where we’ll visit visit we’ll where detail. outnebular for teasing used lled with fainter haze. Massachusetts Massachusetts haze. fainter with lled mall, moderately faint glow in the 130- the in glow faint moderately mall, NGC 6781 Also in Aquila, Aquila, in Also Let’s trek eastward to Delphinus Delphinus to eastward trek Let’s C open to the north-northwest and and north-northwest the to open lter gives a nice contrast boost, boost, contrast anice gives lter lter. The brightest part forms a forms part brightest The lter. lterless view, while fi while view, lterless ector at216ector × . The stars were drawn drawn were stars . The in Aquila also beckons beckons also Aquila in × × NGC 6891 shows a bright, very very abright, shows . At 102. At NGC 6804 ′ west-northwest. west-northwest. × and is further further is and × ′ across, and a and across, I see a very a very Isee × . My 130- . At 102. At lters were were lters is a fairly afairly is lter, lter, but × × . it × ,

NGC 6818: MARTIN GERMANO; NGC 6818 HUBBLE IMAGE: ESA / HUBBLE SPACE TELE- SCOPE / NASA / JUDY SCHMIDT; HEART ICONS: ALEX C. / THE NOUN PROJECT NGC 6804 IMAGE: VOLKER WENDEL / STEFAN BINNEWIES / JOSEF PÖPSEL; NGC 6804 SKETCH: SUE FRENCH tp tor. TheHubbleSpaceTelescope image 75 minuteswitha14.5f/5Newtonianr of thenebula the bluetoasoftblue.MartinGermano’s image the more ghostlypartsoftheannulusandmute blue-gray color. More magnii cation willdrawout 6818 appearsnonstellarandboastsabright have elongatedthenebula’s shell. optical wavelengths,showshowstellarwinds which wasprocessed from datacaptured across oe n o ut sbih.Tecolor The bright. as quite not and rower 234 flauntsitscolorevenbetter,whileat 130-mmscopeat37spotwithahalowhenseenthroughthedescribedasahotcoalonacarpet. about reading aHubbleimageofthenebulabeing after name second the throughhis20-inchscope.Hecoined bognrhetsuhata 164 at northwest-southeast oblong lsosa 102 at blossoms an,rudrhalo. rounder faint, a ae r h ricide fKent of Wallace,thefirstforitsappearance brainchildren the nick- are These names Nebula. and Carpet Magic Rectangle the Green the as known also 5ic cp t345 at scope 15-inch ufc-rgtesnbl t234 at nebula surface-brightness a definiteappearanceagainstthehigh- makes star central 12.4-magnitude euai bu 10 about the is star, nebula 12th-magnitude the central and the star between fit 6891 could NGC disks many how by neighboring Judging the star. of north bit a points planetaryhasaslightelongationthat ihaheta em oi’-g blue robin’s-egg tome.Onlysuspectedat164 seems that hue a with G 07i rgt qa starlike aqua, bright, a is 7027 NGC ynsi h oeof home the is Cygnus × In theeyepieceatlowmagnii itssoutheasternendappearsnar- (left) represents atotalexposure of × .Theplanetaryappears ″ cos ihthe With across. × × ,andasmalldisk h euasports nebula the , G 7027 NGC cations, NGC NGC cations, × NW ,the el × ec- (right) .The × , and , on the next page was made at345 made was page next on the My sketch 15-inch scope. the through 7027 NGC intriguing is bright. prisingly sur- still sky-blue, adeep into morphs Tie or the Scarab nebula. The origin of origin The nebula. Scarab the or Tie the features to search for are labeled. for are search to features the NGC 7662 ( Copeland S. Leland by article an from springs name common Its Snowball. euiu ih t164 at sight a is blue and beautiful nicely remains nebula The interior. and fringe dimmer somewhat 23 at scope my130-mm in blue disk small, avery as visible It’ssnowball.” readily blue alight like “looking as nebula the etecnessta o Tie refers to Bow that consensus the to be butitseems hazy, is monikers these hog h 5ic cp at493 scope 15-inch nebula the stunning through this of view the page next shows the on sketch My the in northwest. subdued more and brightness in t234 at blue even and bright remarkably stays NGC 7662 edge. east-northeastern its off lies star 13th-magnitude a and northeast-southwest, oval slightly looks pu the eyepiece. guide yourobservations at secondary focus,canhelp with a60cm-Hypergraph in right, whichwascaptured such astheoneshownat details to pulloutthenebula’s author usedanOIIIi on outl effects ofthestellarwind distortion thankstothe NGC 6804showssome S&T: × Another brilliant planetary nebula is is nebula planetary brilliant Another G 40 NGC . At 102. At Like NGC6818, Feb. 1960, Feb. p. 216), describes who owing material. The (above) × . The annulus seems irregular irregular seems annulus The . in Andromeda, aka the Blue the aka Andromeda, in × in Cepheus is called the Bow Bow the called is Cepheus in . Images it appears annular with a with annular itappears lter × . The bright ring ring bright The . skyandtelescope.com × × . , and , and Nebula for its appearance in some some in appearance for its Nebula 24 shaped in the 130-mm refractor at48 refractor 130-mm the in shaped cork- and bar. faint M76 moderately is ofits shape the depicts last the while (M27) Nebula Vulpecula, in Dumbbell the to resemblance asupposed indicate fi The Cork. the and Barbell, and a power of102 apower and bar. Examining M76 at164 bar. Examining ofthe structure lumpy the accentuates OIIIfi an while sides, long cork’s the from ballooning extensions fi a narrowband Adding cork. ofthe ends atthe caps a cork length of1¾ length a cork view at345 view the shows page next on the my sketch and 15-inch scope, the through geous 12 star 6.7-magnitude orange, vividly the nicknames: the Little Dumbbell, the the Dumbbell, Little the nicknames: refractor at48 refractor 130-mm the in star central its by dotted blue-gr little anice is 40 NGC images. in seen shape beetle-like the from comes Scarab while arcs, brighter two its by given impression visual the the 15-inch scope. At 216 At 15-inch scope. the in greenish-blue alovely is nebula The ends. or the interior the than brighter abit seem sides long the and oval, ends fade away into the background sky. background the into away fade ends the while north, the in enhanced arc ern defi quite ′ 6 We’ll wind up our tour with with tour upour We’ll wind Messier 76 east-southeast of planetary. this in Cetus, nicknamed the Skull Skull the nicknamed Cetus, in nitely brighter, with the west- the with brighter, nitely × . While visiting, look for look visiting, . While × in Perseus bears a few afew bears Perseus in lter brings out faint outfaint brings lter . At 164. At × ′ . The nebula is gor- is nebula . The exposes brighter exposes

• × it’s vaguely it’s vaguely OCTOBER 2018 × lter nicely nicely lter its sides are are sides its × rst two two rst , I estimate , Iestimate ay disk ay disk NGC × ,

55 OCTOBER 2018 OBSERVING Deep-Sky Wonders

tq It’s easy to see the resemblance of NGC 7027 to the magic carpets of legends old. In the eyepiece, look for a bright aquamarine disk that elongates along a northwest-southwest axis under magniication.

q In a tour of planetary nebulae in the Febru- ary 1960 issue of Sky & Telescope, Leland S. Copeland described NGC 7662 as “looking like a light blue snowball.” Even at lower magnii- cations, the nebula is distinctly nonstellar and images and the Cetus Bubble, which that the dimmest star is in a dark cavity reveals a bright cyan color. This sketch by the author shows the view through her 15-inch Kent Wallace credits to Gregg D. denting into that side of the nebula. A relector at 493×. Thompson’s book, The Australian Guide 164× view hints at other weak bright- to Stargazing. Although this large bubble ness variations. Careful study with the has low , it’s eas- 15-inch scope at 216× teases out these ilyspottedasadimglowwiththree features. My sketch below is a com- faintstars,includingthecentralstar, posite of the views with and without a throughthe130-mmscopeatjust23×. narrowband filter. At 63× thetrioisjoinedbyadimmer I hope you’ll these planetaries, too. star in the east-southeastern edge. A narrowband filter improves the nebula ¢ Contributing Editor SUE FRENCH a skosh and preserves the stars. Upping welcomes your comments scfrench@ the power to 102×,itbecomesclear nycap.rr.com.

N W

p Left: French astronomer Pierre Méchain discovered M76 in 1780. The planetary nebula’s bipolar structure is evident in the eyepiece even under low power. Use an O III ilter to draw out more of the shell’s details. This sketch shows the view in the author’s 15-inch relector at 345×. Right: The faint glow of NGC 246 envelops three dim stars, including the central star, a 12th-magnitude white dwarf. This sketch is a composite of the iltered and

uniltered views through the author’s 15-inch relector. NGC IMAGE: 7027 ESA / HUBBLE SPACE TELESCOPE / NASA / JUDY SCHMIDT; SKETCHES: SUE FRENCH HEART (4); ICON: ALEX C. / THE NOUN PROJECT

56 OCTOBER 2018 • SKY & TELESCOPE BOOK REVIEW by Monica Young

A Conversational Guide to Gravitational Waves RIPPLES IN SPACETIME: Einstein, Gravitational Waves, and the Future of Astronomy

Govert Schilling delivered Sagan-style: Perhaps because of Belknap Press of Harvard University “If you wish to make an the book’s conversational Press, 2017 apple pie from scratch, style, Schilling takes 339 pages, ISBN 978-0674971660 you must fi rst invent the several opportunities $29.95, hardcover. universe.” Only in this to explain not only the case, it’s not apple pie science itself but also GRAVITATIONAL WAVES ARE A HEAVY but neutron stars that we his own role, and that topic that could easily take a college want to understand, and of other journalists, in semester to understand. If you can’t for that we delve into a reporting the science. A quite squeeze that into your life, there’s chapter-long overview of great deal of media hype an easier way to grasp the history and stellar evolution. surrounded the detec- science behind all the gravitational-wave Likewise, after tion of gravitational-wave hoopla: S&T Contributing Editor Govert recounting the long polarization in the CMB, Schilling’s Ripples in Spacetime provides a history of gravitational a detection that was later comprehensive and approachable guide waves and the various detectors made shown to be a hasty misinterpretation to a complex subject. to fi nd them, Schilling leaps back in of the data (S&T: May 2015, p. 12). This The book begins with a visualization time to the Big Bang. Even though it’s was a case in which words like “break- of the fi rst recorded gravitational wave a mind-bending change of topic, it’s through” and “Nobel Prize” weighed event, known as GW150914, as it passes necessary, as a signature of gravitational more heavily in the mainstream media’s through the universe, our solar system, waves could lie hidden in the Big Bang’s attention than did the scientists’ cau- and ultimately across the Laser Interfer- afterglow, the cosmic microwave back- tions, such as, “if confi rmed by other ometer Gravitational-wave Observatory ground (CMB). Schilling gently guides experiments.” Schilling chronicles the the reader through these switchbacks, disappointment that followed the ini- Have you ever wondered offering encouragement even as he tially exhilarating press conference. tackles common misconceptions about Media hype also surrounded the fi rst why, if the cosmic microwave the origin of the universe. actual detection of gravitational waves, background was emitted Schilling’s adept use of analogies is a though this time with the opposite 380,000 years after the Big great help to understanding these heady outcome: The detection of GW150914 subjects. For example, have you ever panned out and revolutionized astron- Bang, we still see its glow? wondered why, if the CMB was emitted omy. Schilling recounts the early leaks, 380,000 years after the Big Bang, we theLIGOscientists’effortstokeepalid (LIGO) detectors. Schilling returns to stillseeitsglow?Schillingoffersthesce- ontheresultsuntiltheywerecon- this history-making event several times nario of a crowded city square: If every- firmed, and the elation that followed throughout the book, each time from one shouts “Boo!” at exactly noon, and the official announcement. a different angle. That thread ties the soundtravels1meterpersecond,then Schilling’s personal experiences, various chapters together as Schilling you’d hear “Boo” from people one meter intuitive analogies, and broad back- tours the history of our understanding away after one second, from people two ground make this introductory take on of gravity and gravitational waves, cov- meters away after two seconds, and so the search for gravitational waves both ering topics such as cosmology, neutron on. Even an minute after noon, you’d approachable and insightful. stars, pulsar timing arrays, black holes, still hear “Boo!” from people 60 meters and multimessenger astronomy. away — even though no one is shouting ¢ News Editor MONICA YOUNG carries Along the way, Schilling takes plenty anymore. Similarly intuitive analogies a book with her at all times, so she pre- of conversational detours. The fi rst is abound throughout the book. fers light books on heavy topics.

skyandtelescope.com • OCTOBER 2018 57 LESSER-KNOWN IMAGING TARGETS by Ron Brecher

in Lostthe Glare

Some interesting objects await imagers who can tear their cameras away from the showpieces of the night skies.

ears ago, when comedian Rodney Dangerfield said, “I don’t get no respect,” he might as well have been Y empathizingwiththesubjectsofthisarticle.I’mtalk- ing about deep-sky objects (DSOs) that are often ignored or underappreciated by most astrophotographers. While trophy objectssuchasM31,theAndromedaGalaxy,orM42,the OrionNebula,aregreat,it’stimetogivesomeless-imaged (orless-noticed)astronomicalgemsamomenttobaskinthe spotlight in their own right. Not all of these overlooked targets are faint. Even bright DSOscanfailtogettherespecttheydeservewhentheyliein the shadow of something “bigger and better.” On the other hand,sometimestheyoccupyaregionofskythatamateurs ignoreduetoaperceivedlackofinterestingdeep-skyobjects; these are lost in the dark, rather than the glare. p STEALING THE SPOTLIGHT Many i ne deep-sky objects reside in Targets Near Bright Stars the shadow of more glorious targets. Take NGC 2023 above — this com- DSOs that are tucked up against a bright star can literally plex mixture of rel ection and resides about 5 arcminutes get lost in the star’s glare. In this situation, clean optics and from B33, the famous Horsehead Nebula, which draws more attention. The close-up image reveals a complex interplay of dust and emission adry,transparentskyareextraimportant,sinceanydirtor nebulosity that makes this and other similar targets worthy subjects for moisture amplifies light scatter around bright stars, over- astrophotographers to pursue. North is to the left in these images. Unless

whelmingtheviewofanythingnearby. otherwise noted, all images are courtesy of the author. NGC 2023: S. MAZLIN / M. HANSON KELLER / W. / R. PROULX TSEPARKER / P. (SSRO) / T.

58 OCTOBER 2018 • SKY & TELESCOPE Lying adjacent to the bright, 2nd-magnitude star (γ Cas) are two attractive nebulae, IC 59 and IC 63. Both contain a mix of red emission and blue refl ection components. But don’t let the brightness of γ Cas scare you away. The right hardware, such as an anti-blooming camera, a hydrogen-alpha fi lter (instead of or in addition to RGB fi lters), combined with careful processing, allows these pretty nebulae to be revealed basking in the rays of γ Cas. Another interesting target also lies beside a bright naked- eye star. The dwarf spheroidal galaxy Leo I hides within the glare of 1st-magnitude . Even though the galaxy has a respectable integrated brightness of magnitude 11.2, it’s low surface brightness renders it nearly invisible next to Regulus, which is more than 5,000 times brighter. Leo I displays little detail, but it’s an accomplishment just to be able to record it. As a galaxy, it emits light at all visible wavelengths, so narrowband fi lters won’t help to record it. However, careful processing of a combination of short and long exposures will reveal this subtle galaxy while still controlling light scatter around Regulus.

Overlooked Galaxies p NEIGHBORS Another target that gets little attention due to its Speaking of galaxies, the best places to hunt them down is proximity to a showpiece object, dwarf elliptical galaxy Messier usually far from the dense star fi elds of the Milky Way. This 110 orbits M31 and displays tantalizing dark dust near its core is because the myriad stars and vast clouds of galactic dust when imaged with larger apertures. seen within the plane of our home galaxy block distant gal- axies, making them much harder to detect. But galaxies actu- ally appear all over the sky — you simply need to know where q IN PLAIN SIGHT NGC 6888, the , is immersed in a dense nebulous i eld. The recently discovered Soap Bubble to look for them. In fact, you might have already imaged a planetary nebula (PN G75.5+1.7) is the thin sphere just visible on the few unknowingly. bottom left side. For example, M13, the Hercules Clus- ter, is arguably the fi nest globular clus- ter visible from mid-northern latitudes. Because of its brilliance, it’s easy to give short shrift to the many galaxies in or just outside its halo, including NGC 6207. If you’re processing your image to highlight the contrast between bold M13 and a dark background, the galaxy might be rendered too dark to see its structure. This approach would also render another galaxy invis- ible, namely IC 4617, which lies just off the line connecting M13 and NGC 6207. Brightening up the background or inverting the image (black stars on white) can make these tiny galaxies stand out better from the background. Even relatively bright galaxies can some- times get passed over, particularly when they are members of a crowded galaxy clus- ter. Markarian’s Chain in the Virgo Cluster is one of the most popular fi elds for galaxy hunters. But next time you’re thinking of exploring Virgo, why not go after NGC 4216 a bit to the chain’s west? It makes a

skyandtelescope.com • OCTOBER 2018 59 Lesser-Known Imaging Targets

photogenic trio with fainter NGC 4222 and NGC 4206 and One of my favorites in this category is Trumpler 5 (Tr is bright enough (10th magnitude) to record with relatively 5), which lies not far from the more famous Christmas Tree short exposure times. Cluster and Cone Nebula, together designated NGC 2264. In Another example of a galaxy gem hiding in plain sight is contrast to most open clusters, which tend to have white or M110, one of the ’s large satellite galax- bluish colors, Tr 5 is composed primarily of red, yellow, and ies. It looks like a spider’s nest — or perhaps a tightly wrapped orange stars. The cluster is much older than most, so its hot- meal in a spider’s web. Although M110 appears relatively large ter, more massive blue and white stars have long since faded, and bright, it is completely overshadowed by its proximity to imparting a golden hue to Tr 5. spectacular M31 and is rarely the main focus of imagers. But There are a few more “surprise” clusters that I now look high-resolution images of M110 show mottling and a distinct for through the eyepiece, having fi rst seen them as bonus dark feature, while long integration times reveal a faint bridge objects in my photos. Two favorites are NGC 436, which lies of stars that appears to tether the satellite galaxy to M31. beneath the “feet” of the famous E.T. Cluster (NGC 457) in Cassiopeia, and NGC 6802, next to Brocchi’s Cluster (the Buried Treasure Coathanger) in Vulpecula. In contrast to galaxies, the rich star clouds of the Milky Way are a great place to fi nd attractive open clusters. Yet they Lonely Outposts seem to be less popular with astrophotographers than other I have friends who think that if you’ve seen one globular classes of DSOs, such as galaxies and nebulae. I’ve heard cluster you’ve seen them all. I disagree. I think each has its many people say that open clusters look better through the own character, and I’ve shot many of them over the years. eyepiece than through a camera. However, some gorgeous One of my favorites is NGC 2419. It tends to be ignored examples are worth exploring with your camera, even though because there are so many bigger, brighter globular clusters they’re not easily accessible to most visual observers. available. I think the location of NGC 2419, in the relatively

60 OCTOBER 2018 • SKY & TELESCOPE t WASHING AWAY The comet-like shapes of nebulae IC 59 (left) and IC 63 (bottom) are due to the ionizing radiation from the luminous star Gamma Cassiopeiae at upper right, which is slowly dissipating the two objects. North is to the left. p FAINT TREASURE While the large, faint emission nebula Sharpless 2-129 has been known for more than a half century, the teal-colored object within called Ou 4 was only discovered in 2011. u GALACTIC CASCADE When imaging the Virgo Cluster of galaxies, most imagers focus on Markarian’s chain. But only about 2° west is a wonderful cascade of three moderately large spiral galaxies, including NGC 4222 (lower left), NGC 4216 (center), and NGC 4206 (upper right), collectively spanning about ½°. North is at left.

sparse constellation Lynx, also contributes to its obscurity. Its nickname, the “Intergalactic Wanderer,” just feels right. About 300,000 light-years away, it’s farther than galaxies like the Large and Small Magellanic Clouds and the Sagittarius Dwarf. There’s not much in the fi eld around it, except for two Nebula (NGC 7635), Pleiades (M45), and Dumbbell Nebula bright fi eld stars that enhance the perception that NGC 2419 (M27) are examples. But many other, less familiar examples is tiny, dim, and distant. In reality, it’s one of the Milky Way’s are worthy of your camera’s gaze. The is full most massive star clusters. of dim emission nebulae (and some of other types). One of The dwarf spiral galaxy NGC 6503 in Draco gives me the the most interesting yet least appreciated is Sh2-290 in Can- same feeling of isolation. Every star in the fi eld surrounding it cer. It’s a classic planetary nebula, showing distinct red- and lies in the Milky Way, so there’s mostly empty space between teal-colored regions corresponding to hydrogen-alpha and us and it. The galaxy actually does lie at the edge of a vast, oxygen-III emissions, respectively. nearly empty region of space called the Local Void (see page Planetary nebula Abell 39 in Hercules has to compete for 12). Only about 30,000 light-years across, the galaxy is puny attention with bright globular clusters M13 and M92. This compared to the Local Void, which might be as big as 250 ghostly green object is a near-perfect sphere about 2½ light- million light-years across! years in diameter, making it the largest such sphere currently known. Several background galaxies are seen through the Obscure Nebulae nebula that are thousands of times more distant. Like star clusters, nebulae abound in the Milky Way. This Another faint spherical structure, PN G75.5+1.7 known catchall term includes pinkish emission nebulae, blue (and as the Soap Bubble Nebula, is hidden in plain sight in Cygnus sometimes yellow) refl ection nebulae, and planetary nebu- just ½° southeast of NGC 6888, the Crescent Nebula. In fact, lae with a colorful mix of emission nebulosity. The Bubble (continued on page 64)

skyandtelescope.com • OCTOBER 2018 61 Lesser-Known Imaging Targets

u LOOK TO THE RIGHT Just 1° west of NGC 2264 is the beautiful old open cluster Trumpler 5, which is populated by old reddish stars and is a treat for observers and imagers alike.

p LONELY GLOBULAR Relatively dim, NGC 2419 is the most distant globular cluster associated with the Milky Way.

u CLUSTER COMPANIONS M13 is perhaps the showpiece globular cluster for northern observers and imagers. Long exposures of this target with 6-inch or larger instruments will reveal a wealth of detail in the bonus spiral galaxy NGC 6207 (top left) just ½° to its northeast. Between it and M13 lies an even more distant galaxy, IC 4617 (arrowed).

uu BANDED NEBULA About 1½° south of IC 5070, the Pelican Nebula in Cygnus, resides another large-but-faint nebula, IC 5068, which rewards imagers shooting through narrowband i lters with complex, over- lapping bands of nebulosity in a roughly rectangular shape.

62 OCTOBER 2018 • SKY & TELESCOPE skyandtelescope.com • OCTOBER 2018 63 Lesser-Known Imaging Targets

(continued from page 61) HH 170. This hourglass-shaped Herbig- due to its subtle, thin shape and the Haro object signals the recent birth of a nebulous fi eld it sits in, the Soap Bubble new star at its center. was only discovered about a decade ago One of the most photographed DSOs by amateur astronomer Dave Jurasevich is the Horsehead Nebula (B33) in Orion, using a 160-mm refractor and CCD often sharing the fi eld with the spectac- camera with narrowband fi lters. The ular (NGC 2024). NGC object was independently noted and 2023 usually appears in these portraits reported to the International Astronom- p NEARBY PLANETARY The large nebula too, since it lies more or less between ical Union by amateurs Keith B. Quat- Sh2-290 in Cancer, also known as Abell 31, the Horsehead and the Flame. But due to is among the closest and largest planetary trocchi and Mel Helm who imaged PN its location, NGC 2023 is rarely imaged nebulae in the sky, but it is exceedingly faint G75.5+1.7 in 2008. and requires long exposures to reveal all its at high resolution, when it can reveal colorful glory. tremendous color and detail. Surrounded by Bling Similarly, try photographing the Speaking of busy nebulous fi elds, one of my favorites is the regions in Cygnus around the (NGC region around the Bubble Nebula (NGC 7635), which is full 7000), particularly beneath the “Gulf of Mexico” and the of splashy star clusters like M52 and other emission nebulae. neighboring Pelican Nebula (IC 5070). IC 5068 is a boldly Amid all these sparkling jewels, it’s easy to overlook little textured, rhombus-shaped patch of emission nebula full of col- orful stars. Not far to its west is the blue refl ection nebula NGC 6914, within a Lost in the Glare Targets few degrees of Simeis 57, the Propel- ler Nebula, another underappreciated Object Type Size RA Dec. nebula often misidentifi ed as DWB 111. IC 59 Emission nebula 10′ × 5′ 0h 56.7m +61° 04′ IC 63 Emission nebula 10′ × 3′ 0h 59.5m +60° 49′ Resources Planetarium software is helpful for Leo I Dwarf spheroidal galaxy 10′ × 7′ 10h 08.5m +12° 18′ identifying potential subjects in loca- h m NGC 6207 Spiral galaxy 3.0′ × 1.3′ 16 43.1 +36° 50′ tions that are off the beaten track, or IC 4617 Spiral galaxy 1.2′ × 0.4′ 16h 42.1m +36° 41′ in the background that might be worth NGC 4216 Spiral galaxy 8.3′ × 2.2′ 12h 15.9m +13° 09′ our attention. My fi rst clue that there were hundreds of galaxies in the same NGC 4222 Spiral galaxy 3.1′ × 0.5′ 12h 16.4m +13° 18′ fi eld as the Pleiades was when I zoomed h m NGC 4206 Spiral galaxy 6.2′ × 1.0′ 12 15.3 +13° 01′ in on the fi eld in Software Bisque’s M110 Dwarf elliptical galaxy 17′ × 10′ 0h 40.4m +41° 41′ TheSkyX (bisque.com). While these Tr 5 Open cluster 20′ 6h 36.5m +9° 29′ galaxies appear small and featureless, just being able to resolve them in the NGC 436 Open cluster 5′ 1h 16m +58° 49′ distant background imparts a sense of NGC 6802 Open cluster 5′ 19h 30.5m +20° 16′ the vastness of the cosmos that M45 NGC 2419 Globular cluster 4.7′ 7h 38.1m +38° 53′ on its own can’t deliver. Most camera- NGC 6503 Dwarf spiral galaxy 7.1′ × 2.4′ 17h 49.5m +70° 09′ control and planetarium software can chart the location of celestial objects. A Sh2-290 Planetary nebula 17′ 8h 54.2m +8° 54′ great freeware option is Stellarium (stel- h m Abell 39 Planetary nebula 3′ 16 27.5 +27° 55′ larium.org), which can display Digi- PN G75.5+1.7 Planetary nebula 4.3′ 20h 15.5m +38° 03′ tized Sky Survey image overlays that HH 170 Herbig-Haro object 1′ 23h 17.5m +60° 51′ provide a more photo-realistic view. Get familiar with compilations of NGC 2023 Refl ection nebula 10′ 5h 41.6m -2° 16′ nebulae, like the Sharpless (Sh) and IC 5068 Emission nebula 40′ × 29′ 20h 50.8m +42° 31′ van den Bergh (vdB) catalogs, as well NGC 6914 Refl ection nebula 12′ × 12′ 20h 24.7m +42° 29′ as Lynd’s Bright Nebulae (LBN) and Simeis 57 Emission nebula 30′ × 20′ 20h 16.1m +43° 41′ Lynd’s Dark Nebulae (LDN). Many of their members aren’t visible through Sh2-129 Emission nebula 175′ × 113′ 21h 11.7m +59° 58′ the eyepiece and are only revealed in Ou 4 Emission nebula 68′ × 23′ 21h 11.8m +59° 59′ deep exposures. These catalogs are Angular sizes are from recent catalogs. Right ascension and declination are for equinox 2000.0. accessible via the planetarium soft- ware mentioned previously, with many

64 OCTOBER 2018 • SKY & TELESCOPE EXPANDING SPHERE Abel 39 in Hercules is a challenging target for imagers with larger scopes. This ancient planetary nebula appears as a nearly perfect teal-colored sphere. online resources providing photos or descriptions. While ing them when they are at their highest in your sky, say 2 or I don’t try to duplicate the aesthetic, I sometimes refer to 3 hours on either side of the meridian (the imaginary line others’ results — or more specifi cally, their technical informa- passing through both celestial poles and the zenith). That way tion — to help me decide what scope and camera combination you’ll be shooting through less atmosphere and will be able to might achieve a desired composition, and to estimate how reveal fainter structures and fi ner details. much exposure time might be needed. Narrowband fi lters — particularly hydrogen alpha — can be useful to better record fi ne structure in emission nebulae, Imaging Strategies planetary nebulae, and supernova remnants. What’s more, test Most of these DSOs are much fainter than their better- shots can be taken even when there’s a bright Moon up (S&T: known kin or are challenging to see due to their environ- Nov. 2017, p. 68). ment, such as the proximity to a bright star. Successfully imaging them requires a total integration time long enough Conclusion to reveal the dimmest features in the fi eld. In some cases, We all want to capture showpiece DSOs. Those big, bright, extremely long total exposure time is required, sometimes and beautiful objects impress astronomers and non-astron- along with specialized narrowband fi lters. For example, for omers alike. While you’re imaging their amazing fi elds, be my sky conditions and equipment, Sh 2-129, the Flying Bat, alert to hidden treasures you might be missing. Eventually, is known to be exceedingly faint. I didn’t stop data acquisi- you’ll have shot most of the popular Messier and NGC objects tion until I had 104 hours total exposure, including 30 hours accessible from your site. When that day comes, it’s time to through an oxygen III fi lter, which was needed to reveal the start looking further afi eld for new wonders to photograph. exceedingly faint Squid Nebula, Ou 4, discovered in 2011 by Use the examples described above to get started, and then French astro-imager Nicolas Outters. dive into the catalogs and online tools I’ve mentioned to fi nd While patience is a virtue when going after low-surface- even more candidates to explore. And when you’re preparing brightness DSOs, at some point you need to call it a day. to image your chosen subjects, have a good look around it to Increasing exposure time yields diminishing returns in see what you might be missing — maybe it’s worth a test shot terms of signal-to-noise ratio (SNR). For example, doubling or two or a little adjustment to the framing of your shot. a 10-hour exposure only nets you about a 40% improve- By the way: Don’t be surprised if you can’t fi nd much tech- ment; doubling the SNR would require a whopping 40 hours! nical information about some of your chosen targets. After “Going long” requires a shift in mindset: When I fi rst began all, they just don’t get no respect! imaging I went after three or four targets in a night. Now I spend several nights — sometimes months during the short ¢ RON BRECHER likes to image lesser-known deep-sky nights of summer — dedicated to a single patch of sky. objects from his home observatory in Guelph, Ontario. Visit his Your best results on faint objects will come from captur- website at astrodoc.ca.

skyandtelescope.com • OCTOBER 2018 65 S&T Test Report by Alan Dyer

The Meade 70-mm astrograph is dwarfed by the author’s large mount used for test- ing. Any small equatorial mount capable of smooth tracking and autoguiding will be a good match for the little Meade.

Meade’sMiniAstrograph The new Series 6000 70-mm apo astrograph delivers tack-sharp images across a wide field.

70mm Astrograph HERE’S A CLASS OF TELESCOPE largeMilkyWaystarfieldsandcolorful Quadruplet APO Refractor I think every deep-sky astrophotogra- regionsofnebulosity. pher should have in his or her toolkit. It’s called an astrograph, as this is an U.S. Price: $1,199 Indeed, for those starting out in deep- instrument designed specifically for pho- meade.com skyimaging,it’stheclassoftelescope tography. Unlike many other refractors I often recommend. But even veteran inthe70-to80-mmapertureleague, What We Like imagerswillfindaplaceforalittle the Meade can’t really be used to look Sharp, well-corrected field astrograph like this. through—thedistancefromthefocuser with minimal vignetting Meade’s new Series 6000 astrograph tothefocalplaneisoptimizedforattach- Excellent focuser and is a 70-mm apochromatic refractor with ingaDSLRcamerabody.Aneyepiecewill camera rotator a focal length of just 350 mm and an reach focus only if it is attached looking f/5 focal ratio. That’s fast, short, and straight through without a star diagonal, What We Don’t Like wide. With its generous field of 6° ×4° hardly convenient. In any case, Meade No provision for adding a filter onacamerawithfull-framesensor,the provides no adapters for even a straight-

No optional wide 48-mm T-ring Meade astrograph is perfect for framing through visual configuration. ALL PHOTOS BY THE AUTHOR

1. 2. 3.

66 OCTOBER 2018 • SKY & TELESCOPE Butasaphotographicinstrument, Mechanical Features fi guration would be to use the supplied the little Meade really excels. Much the same can be said of the dovetail base to attach an easily remov- scope’smechanicalperformance.Inany able 50-mm fi nderscope to serve as a Photographic Tests such instrument, the focuser is para- guidescope in conjunction with a small TheSeries600070-mmastrographisa mount,andthedual-speedfocuserper- CCD or CMOS autoguider camera, an four-element design incorporating one formed admirably. The 10:1 fine focus accessory sold by several manufacturers. elementofFPL53EDglassforcolorcor- was smooth and backlash-free. I did The Series 6000 astrograph focuser rection. According to Meade, the front need to tighten one setscrew to prevent is terminated with a 48-mm male objective is a doublet lens, matched to a some initial slippage of the fine focus thread. To this you can screw on a large- two-element field-flattener at the rear. knob, but after that the Meade focuser aperture, 48-mm T-ring, which mini- The flattener lens is built into the tube worked consistently well. The focuser mizes vignetting but is not a common assembly and is not an add-on acces- canbelockeddown,andIhadnoissues sory,whichmakesforasoliddesign. with it slipping under the weight of a 1. The astrograph’s lens elements are all thor- As an astrograph, the configura- heavy full-frame DSLR camera when oughly multi-coated and the tube very well tion worked superbly. Color correction aimedtowardthezenith. blackened and bafl ed along its entire length. was top class, with little sign of blue Whilethefocuserasawholecan- Images were free of l are and ghosting from ormagentahaloesaroundbrightstars. notrotatewithrespecttothetube,the bright stars off-center and off the frame edge.

Star images across a full-frame DSLR focuserdoeshaveacamerarotatorbuilt 2. The dewcap extends 2 inches. DSLR cam- sensorwerenearlyperfect—tightand in,andthis,too,wasextremelysolid. eras can be attached directly with a wide 48- sharp—righttothecorners.Therewas Looseningtherotator’slock,turning mm T-ring (here attached to the telescope), no evidence for astigmatism, field cur- thecameratoreframeatarget,thenre- or with a more commonly available 42-mm vature,orlateralchromaticaberration tightening the rotator produced no shift T-ring using the supplied M48-to-M42 step- down ring, shown in front. affectingoff-axisimages. in focus. Excellent! The Meade projects a measured The little tube rings that come with 3. The i eld l attener lens is integrated into 60-mmilluminatedcircle,muchlarger thescopeareeachdrilledwithametric the rear of the tube assembly. The focuser than the specifications promised, and M6-1.0 bolt hole on both the top and has a male M48 thread for accepting either more than enough to cover a full-frame bottom,withonesurface(whichcould the supplied step-down ring (left) or a user- supplied 48-mm T-ring (right). sensor.Asaresult,Isawlittlevignett- be at the top or bottom) also having a ingattheframecorners.Illumination pair of smaller bolt holes on either side 4. The focuser incorporates a rotator locked proved uniform in images taken of twi- ofunspecifiedthread.AVixen-style with the knob indicated [yellow arrow]. light skies, requiring little correction in dovetail bar is supplied, itself machined Rotating the camera did not shift focus. The processing, with no great need to apply withalongslotandseveralcountersunk tension of the helical rack-and-pinion focuser can be adjusted, and it can be locked by the flat-field frames unless the intention holes for a variety of mounting configu- knob indicated [blue arrow]. istostretchimagestotheextremeto rations. I show it here with the rings reveal the very faintest nebulosity. close together to allow the dew shield to 5. The tube rings are tapped with M6-1.0 bolt TryasImight,Icouldnotgetthe fully retract for storage, making the tube holes top and bottom for attaching guide- Meade to produce flaring or ghost assemblyjust12inches(30cm)long. scope rings. Or a small guidescope can be mounted in the standard i nderscope shoe, artifactsinmyimages.Ishottest The dew shield extends 2 inches. A which has two setscrews for a more solid at- frames with bright stars at the edges of slip-onmetaldustcapissuppliedfor tachment. No i nderscope is supplied. theframeandjustoutsidetheframe, thefrontanda48-mmscrew-onmetal andIneversawanyflaresorsignsof cap for the rear, but it fits on only when 6. The Meade astrograph comes with a internal reflections. The multi-coatings the adapter ring is removed. compact metal case which can store the telescope with tube rings attached provided and thorough internal tube baffling did It is possible to bolt a separate guide- they are spaced close together to allow the their jobs very well. Optically, I had no scope in rings to the Meade’s own tube dewcap to fully retract, as it is here. complaintswhatsoever. rings.Howeveramorepopularcon-owever,amorepopularcon

4. 5. 6.

skyandtelescope.com • OCTOBER 2018 67 S&T Test Report

accessory. Meade does not offer one, so of the focuser to the focal plane is As good as the focuser is, its pri- buyers will have to search for one from 66 mm, and the focuser has 32 mm mary drawback is that it provides no another source. For all my testing I used of travel. When using a DSLR with accommodation for dropping in a fi lter one I had on hand. conventional 55-mm back focus, the between the telescope and camera. Alternatively, you can use the sup- focuser is racked out 11 mm, leaving DSLR owners wanting to shoot fi ltered plied M48-to-M42 step-down ring to just 22 mm of further outward travel to images (particularly with modifi ed cam- attach the more standard 42-mm T-ring accommodate the shallower back-focus eras) would need to use clip-in fi lters (such as from Meade) for DSLRs, or for requirements of many dedicated CCD inserted into the camera’s mirror box. attaching other types of CCD cameras cameras. CCD cameras with sensors These require the mirror to be locked fi tted with standard M42 threads. close to the front will require a short up, preventing any use of the optical The distance from the back surface M42 extension tube to reach focus. viewfi nder to fi nd or frame objects.

A single 5-minute exposure with a modii ed Canon 5D MkII DSLR at ISO 1600 shows stars as pinpoints to the very corners of the full-frame sensor (insets). Focus was uniform across the i eld. The slight asymmetric purple halo around Deneb is an artifact from the camera’s internal IR i lter and is seen in images taken with all telescopes.

68 OCTOBER 2018 • SKY & TELESCOPE Recommendations 5-pound (2.3-kg) weight (including to exotic skies. Or, more to the point, The Meade 70-mm astrograph is the tube rings) make it easy to pack for air- the Meade astrograph and the required perfect instrument to shoot wide-fi eld line trips. While in a pinch it could be small mount simply allow for deep-sky deep-sky targets. With a focal ratio of mounted on a small tracker, the Meade shooting sessions close to home with a f/5, it’s not as fast as some of the com- performs best on a full-sized but small minimum of setup fuss and maximum petitor’s similar instruments, but it does equatorial mount capable of accept- results. I liked the Meade astrograph a provide an exceptionally large unvi- ing an autoguider. There are many fi ne lot and can recommend it highly. gnetted fi eld, not true of some faster choices these days, including Meade’s systems I’ve used. And f/5 is plenty fast new LX85 German equatorial mount. ■ Visit Contributing Editor ALAN DYER’s enough under most circumstances. All the required gear could go in website at amazingsky.com with links to The Meade’s compact size and checked or carry-on luggage for fl ights his social media connections.

skyandtelescope.com • OCTOBER 2018 69 NEW PRODUCT SHOWCASE

u SMARTPHONE ADAPTER Celestron announces the NexYZ 3-Axis with the X and Y knobs, and then mov- Universal Smartphone Adapter ($59.95). ing up or down with the Z knob over The unit allows you to use most any the eyepiece until you have the entire smartphone camera to capture the i eld of view in your shot. The NexYZ brighter solar system objects and even attaches securely to any eyepiece some deep-sky targets. Its spring-load- from 35- to 60-mm in diameter with a ed clamp and innovative 3-axis adjust- padded clamp and adjustable safety ments permit you to place your device’s lock. Two additional adapter rings are camera perfectly against virtually any included for connecting the device to eyepiece on a telescope, binocular, or smaller microscope eyepieces. microscope quickly and precisely. Celestron Simply place your phone on the plat- 2835 Columbia St., Torrance, CA 90503 form, centering it over the eyepiece 310-328-9560; celestron.com

t SOUTHERN PRIMER Author (and former S&T editor) Stephen James O’Meara rolls out his latest ebook Diamonds in the Sky: Discover the Stars Over Botswana ($5.98). This introductory i eld guide to explor- ing the night skies is geared towards, though not limited to, anyone considering a trip to the exceedingly dark southern skies of Botswana. Diamonds is sprinkled with the perspective and history of the indigenous peoples of the region, beginning with a naked-eye primer on what is visible without optical aid from the country’s national parks. O’Meara details specii c sights to look for each month throughout the year with insightful recounting of local lore. Ad- ditional sections on the Sun, Moon, and planets are included, as well as information about the country’s meteor craters. 188 pages. Diamonds in the Sky Available on the Amazon Kindle store.

u BIG TRUSS DOB Hubble Optics, known for manufactur- enhanced-rel ectivity coatings, and its ing high-quality Newtonian rel ector eyepiece stands just 77 inches from optics, now offers the UL24, a 24-inch the ground when pointed at the zenith. f/3.3 ultra-light Dobsonian ($9,500). The telescope uses eight precision- This fast Newtonian rel ector is built machined trusses and an optimized for travel, featuring a lightweight primary l otation system supporting the “sandwich” mirror that drastically primary mirror. The telescope includes reduces its weight and cool-down a dual-speed, 2-inch Crayford-style period compared to solid mirrors. The focuser with linear bearings engineered UL24 weighs only 154 lb (70 kg) when to support the heaviest eyepieces fully assembled, and breaks down into available today. See the manufacturer’s its constituent parts to i t into most website for additional details. compact vehicles. The scope’s primary Hubble Optics and secondary mirrors feature 96% hubbleoptics.com

New Product Showcase is a reader service featuring innovative equipment and software of interest to amateur astronomers. The descriptions are based largely on information supplied by the manufacturers or distributors. Sky & Telescope assumes no responsibility for the accuracy of vendors’ statements. For further information contact the manufacturer or distributor. Announcements should be sent to [email protected]. Not all announcements can be listed.

70 OCTOBER 2018 • SKY & TELESCOPE ONE HALF OF THIS THE OTHER WAS TAKEN IMAGE WAS TAKEN WITH A SCOPE THAT WITH A $2,499 ESPRIT COST TWICE AS MUCH

Imager: Jerry Gardner of Fort Worth, Texas Actually, the other telescope cost more than twice as much as (Three Rivers Foundation Volunteer) the Esprit, but that’s not really the point. The point is, do you Scopes: Sky-Watcher Esprit 100mm EDT f/5.5 World-class 4-inch astrograph see twice as much performance on one side of the page than Mount: Takahashi EM200 Temma2M the other? Take a close look. Are the stars twice as pinpoint? Camera: Canon 60Da @ 800 ISO Is the color doubly corrected? Exposure: 20 light frames and 20 dark frames @ 300 seconds. No flats, dark flats or bias frames were used. We don’t think so. 30 light frames and 15 dark frames @ 30 seconds were used for toning down the core of M31. The same processing was used for both scopes. If you don’t think so either, perhaps you should consider purchasing a Sky-Watcher Esprit triplet. At Sky-Watcher USA we pride ourselves on offering products with world-class performance at affordable prices. Because we know there are other things you could be spending that money on. Like a mount. Or a camera. Or even a really, really sweet monster flat-screen television, just for fun.

The Sky-Watcher line of Esprit ED Apo triplets. All of the performance, half the price. disappointed with you, though. very ngtostopyou.Wewillbe thout notice. 20-1016. ©2018 Sky-Watcher USA. Specifications and prices subject to change wi Ifyoureallywanttospendtwiceasmuchforthesameperformance,we’renotgoi

Starting at only $ 1,649, the Esprit line is offered in 80, 100, 120 and 150mm apertures and comes complete with a 9 x 50 right angle finderscope, 2-inch Star diagonal, 2-element field flattener, camera adapter, mounting rings, dovetail plate and foam-lined hard case.

For information on all of our products and services, or to find an authorized Sky-Watcher USA dealer near you, just visit www.skywatcherusa.com. Don’t forget to follow us on Facebook, Twitter and Instagram! ASTRONOMER’S WORKBENCH by Jerry Oltion

Ken Martin’s light-block- ing panels quickly turn Easy and his driveway into a fi ne Eff ective observatory. Light Barriers Block your neighbors’ lights with these simple panels.

IT SEEMS LIKE NEARLY EVERYONE Nights, I decided to make these PVC light gets through them. To really block with a telescope also has a neighbor or panels.” Their construction is simple, all the light, Ken found that Duvetyne, twelve with unshielded porch lights. straightforward, and relatively inexpen- a black cotton twill commonly used in Even if they’re good neighbors and sive, yet they’re lightweight, durable, the stage and movie industry, is ideal. It keep the lights off when they’re not and easy to use. comes in various widths, so Ken chose actually using them, interior lights Ken used ¾-inch class 200 PVC pipe 54-inch so he could make his panels 4 still leave brightly lit windows. Plus, if for the framework. Class 200 is the feet wide and have 6 inches of cloth left you observe from your driveway there lightweight, thin-walled stuff, which to overlap onto the next panel. He made are the headlights of passing cars, the is plenty strong for this application. A his panels 6 feet tall, which is high inevitable street lights, and the person handful of tees and elbows connect the enough to block neighbors’ lights but walking his dog with an aircraft land- pipe sections into rectangles, and wide- doesn’t cut off too much sky. Duvetyne ing light for a headlamp. head screws hold the fabric to the pipe. comes in 8-, 12-, or 16-ounce weights. Amateur astronomers need a reli- Using the proper fabric is the key to Ken used the 16-ounce for maximum able way to block all those lights so we success. Plastic tarps, canvas, denim, light blocking. can protect what dark adaptation we duck cloth, and similar materials may Assembly is simple: Just cut the pipe can achieve. I’ve tried tarps suspended look dense by day, but at night with to length, insert it in the fi ttings, and from poles, cut-open dark-adapted eyes it’s attach the fabric. Ken says “I chose not cardboard refrigera- surprising how much to glue the fi ttings, as I didn’t feel it tor boxes, strategically parked cars, and even, I confess, a slingshot. None of those worked as well as the solution that Oregon amateur Ken Martin came up with: multiple panels of light-blocking material that he can place in whatever arrangement is necessary. Ken looked for inspiration online and reports that “After

reviewing the many tp Above: The panels are made of PVC pipe and Duvetyne fabric. DIY dark sky panel Top left: Velcro straps hold the panels together. Bottom left: Wide-headed screws projects in the ‘Carol’s hold the cloth to the pipe. Ken painted the heads black. Picks’ thread on Cloudy

72 OCTOBER 2018 • SKY & TELESCOPE ALL PHOTOS BY THE AUTHOR gets along fi along gets he and observatory, adecent into way drive- suburban his turned have panels white. shiny pipe the leaving forthis, work great els tow- paper and Acetone it. you assemble before pipe the off printing the clean tion at all. direc- that from coming nolight There’s hole on one sideofyou. ablack having it’s like panels, ofthese a semicircle you’re inside When gaps. the through leak can nolight and pipe any can’t see you so junction pipe the across Velcroed is offabric 6inches extra the together, suffi is water fi jugs gallon to them tying simply though, often Most conditions. breezy in down panels the stake can he so to ropes tie hecan that bolts eye do.) will strap Velcro around #45-V11BKW, wrap- any about butjust part strips,” grip “cord organizer Bender Gardner (Ken used straps. Velcro with together them heholds and themselves, by stand they’ll so curve a in them Hearranges 20feet. span neighbors intoamateur astronomers. someofthose and haseventurned shielded mostofhisneighbors’ lights, ■ to ½-inch of fabric to the PVC.” the to offabric ½-inch to ¼- extra the secure to great worked glue “The that reporting screws, the above pipe the to ends loose the tack to glue Stitch Seamless heused bottom and top pipes.) the On bend itwill and tight (Too tight. drum-head butnot snug, Duvetyne the Hestretched screws. visible. is pipe nowhite and youobserve, you when sidefaces velvety the so pipe the against side rough the Put side. ultra-dark vety, seated completely.” tomallet make sure the fi arubber use Idid It won’t apart. come attached. fabric the with necessary was Contributing Editor Ken reports that these light-blocking light-blocking these that reports Ken fi anice For connected are panels the Once put Ken panels, end ofthe top On Ken made fi made Ken forthe pipe the in holes drilled Ken avel- side and arough has Duvetyne ne with his neighbors, too. neighbors, his ne with cient. nished look, you can youcan look, nished ve panels, which together together which ve panels, JERRY OLTION ttings were ttings lled with has skyandtelescope.com/2019eclipseflight and return to Santiago, Chile. Chile. Santiago, to return and from depart will coast). flight Our Chilean the from minutes (vs. 2½ lurk below, of totality 3¼might upto minutes seeing above that you’ll clouds above any Ocean, behigh Pacific the 37,000 flying A320 of point an feet aircraft vantage From the See all See all 2020 Eclipse Cruise: Chile, Argentina, Chile, 2020 Eclipse Cruise: n nacia• Antarctica and See all all See S&T 7 seconds of totality off the coast of Argentina of Argentina coast the off seconds of totality 7 and muchand more: glaciers, and fjords Chilean S&T the legendary Drake Passage, four days and Drake legendary the S&T ’s 2 offers 2020 cruise Chile 2019 Eclipse Flight: mdAtrtc’ aesadicebergs. and waters Antarctica’s amid or at tours tours at tours skyandtelescope.com/chile2020 skyandtelescope.com/astronomy-travel skyandtelescope.com

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July 2, 2019 2, July Nov. 27–Dec. 19,Nov. 27–Dec. 2020

minutes, • OCTOBER 2018

73 GALLERY

p CRATER SUNRISE q PLANET PARADE Brian Ford Ryan Imperio The massive, 93-kilometer-wide crater A cascade consisting of Saturn, Mars, Copernicus displays its complex ter- the Moon, and Jupiter (left to right) raced walls and central peaks in this rises over Jordan Lake in North Caro- detailed view captured several days lina in the early morning hours of after fi rst quarter. March 8th. DETAILS: Celestron EdgeHD 14 DETAILS: Nikon D90 DSLR camera with Schmidt-Cassegrain telescope with ZWO 18-to-105-mm zoom lens at 18 mm. ASI290MM monochrome video camera. Exposure: 70 seconds.

74 OCTOBER 2018 • SKY & TELESCOPE SHINE DOWN ON SHANGHAI David Xu A dramatic display of crepuscular rays fans across the sky in late-afternoon hours as seen from the 118th fl oor of Shanghai Tower in Shanghai, China. DETAILS: Nikon D3100 DSLR camera with 18-to-300-mm zoom lens at 52 mm. Exposure: 1/440000 second, ISO 400.

skyandtelescope.com • OCTOBER 2018 75 GALLERY

u KING OF RINGS Brian Ford Besides the wide Cassini Division and the thin Encke Gap at the outer edge, Saturn’s ring system displays sev- eral distinct bright and dark regions in this sharp image captured on July 1st. DETAILS: Celestron C14 EdgeHD Schmidt-Cassegrain telescope with ZWO ASI290MM video camera. Stack of 10 de-rotated video results recorded through RGB fi lters.

q DIAMONDS IN THE SKY Dan Crowson A smattering of reddish stars stands out among fainter yellow members of open cluster NGC 6819 in Cygnus. DETAILS: Astro-Tech AT90EDT apochromatic refractor with SBIG ST-8300M CCD camera. Total exposure: 4½ hours through LRGB fi lters.

Gallery showcases the fi nest astronomical images submitted to us by our readers. Send your best Visit skyandtelescope.com/gallery shots to [email protected]. See skyandtelescope.com/aboutsky/guidelines. for more of our readers’ astrophotos.

76 OCTOBER 2018 • SKY & TELESCOPE FEATHERS OF THE SWAN Douglas J. Struble Among the many nebulae that com- pete for attention in Cygnus, Sh2-115 (center), Sh2-112 (top), and Sh2-116 (lower left) all present interesting small- and large-scale details for imag- ers looking for lesser-known targets. DETAILS: Stellarvue SV70T apochromatic refractor with ZWO ASI1600MM Pro CMOS camera. Total exposure: 29 hours through Astrodon narrowband fi lters.

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skyandtelescope.com • OCTOBER 2018 83 84 FOCAL POINT OCTOBER 2018 How the hehadgalaxies author learned comingouthisears Outwitted ASIDE FROM THE ESSENTIALS ASIDE then focused back on my back focused then It’s fi again. ies polite. being just likely asked, in. Sue walked when charts star and myjournal with table room dining the over hunched Iwas off, cooling backyard the in stood Dobsonian my10-inch while night, That again. trying into lured I was when ago. years her upon encouraging gave I why is Which level. next the itto take to enough butnot curious, people: most like is hand, other on Sue, the My wife m inside been astronomy’s then since and step,” “small Armstrong’s Neil watched old, I 9years At high. been always cultures. ofall people unites that one passions, universal one of those be to happens Astronomy everybody. est inter- to worldseem this in things few out one’s ears.” come to big too they’re it’s that galaxies, about I’ve learned there’s one thing ears.” outyour coming galaxies have “You commented, sheplayfully ing, ofobserv- kind my favorite was fuzzies y head . . . in more ways than one. one. than ways more .in y head I looked at her and smiled. “Galax- smiled. and ather I looked she tonight?” youseeking are “What is, that evening, one recent Until has offascination level My own Without looking up I quipped, “If “If upIquipped, looking Without faint the hunting that Knowing she wantedme. Sue hadmerightwhere brilliant strategistsheis, myself, butbeingthe was feelinggoodabout stepping intoatrap. I I hadn’trealizedwas

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