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FOCUS ON THPEagXe-R1A6Y SKYMARCH/APRIL 2012  $5 Scaling the Universe Celebrating the centennial of a celestial yardstickT H E U N I V E R S I T Y O F T E XA S AT A USTI N McD ONA LD OBSE R VAT ORY StarDate 1

STARDATE STAFF MARCH/APRIL 2012 • Vol. 40, No. 2 EXECUTIVE EDITOR Features Departments Damond Benningfield 4 Henrietta & the Cepheids Merlin 3 EDITOR Rebecca Johnson A hundred years ago, one woman’s Sky Calendar MARCH/APRIL 10 patience and tenacity in pouring ART DIRECTOR over photographic plates packed with The Stars in MARCH/APRIL 12 C.J. Duncan stars changed our view of the cosmos AstroMiscellany  15 TECHNICAL EDITOR  By Barbara Ryden Dr.Tom Barnes AstroNews 20 16 A New Focus on the X-Ray Sky CONTRIBUTING EDITOR Five Moons in Four Days Alan MacRobert NuSTAR will scan the heavens to Two Ways to Make a Star Go Boom better understand high-energy X-ray Ready, Aim, Fire! CIRCULATION MANAGER phenomena Don’t Miss the Big Show Paul Previte Milky Way Teeming with Billions of Planets  By Rebecca Johnson Bedding Down for a Long Winter’s Nap MARKETING MANAGER Vincent Perez, III 18 Join the Club! McDONALD OBSERVATORY Astronomy clubs provide opportu- ASSISTANT DIRECTOR, nities for learning, friendship, and volunteering EDUCATION AND OUTREACH Sandra Preston  By Linton G. Robertson STARDATE ADVISORY BOARD On The Cover Dr. David Lambert, Director Henrietta Swan Leavitt’s studies McDonald Observatory of variable stars in the Small Magellanic Cloud, seen here in Dr. George F. Benedict a recent composite image from Dr. Karl Gebhardt the Herschel and Spitzer infrared Dr. Daniel T. Jaffe space telescopes, changed how we measure the cosmos. To learn how,For information about StarDate or other see Page 4.programs of the McDonald Observatory ESA/NASA/JPL-CALTECH/STScIEducation and Outreach Office, contact NASAus at 512-471-5285. For subscriptionorders only, call 800-STARDATE.StarDate (ISSN 0889-3098) is publishedbimonthly by the McDonald ObservatoryEducation and Outreach Office, The Uni-versity of Texas at Austin, 1 UniversityStation A2100, Austin, TX 78712. © 2012The University of Texas at Austin. Annualsubscription rate is $24 in the UnitedStates, $29 in Canada and Mexico, $40for foreign addresses. Subscriptions maybe paid for using credit card or moneyorders. The University of Texas cannotaccept checks drawn on foreign banks.Direct all correspondence to StarDate, TheUniversity of Texas at Austin, 1 Univer-sity Station A2100, Austin, TX 78712, orcall 512-471-5285. POSTMASTER: Sendchange of address to StarDate, The Univer-sity of Texas at Austin, 1 University StationA2100, Austin, TX 78712. PeriodicalsPostage Paid at Austin, TX. StarDate is aregistered trademark of The University ofTexas McDonald Observatory. Visit StarDate Online at stardate.org StarDate This Page Coming Up StarDate Magazine Frank N. Bash Visitors Center Comet Lovejoy, which survived a plunge near The May/June issue will bring you detailed the surface of the Sun, rises above Earth’s information on the May 20 solar eclipse for 2 M A R C H / A P R I L 2 0 1 2 atmosphere in this December 22 view from the the western United States, as well as the International Space Station. Lovejoy passed scoop on the transit of Venus in early June . less than one million miles from the Sun on We’ll also bring you Merlin’s answers to your December 15. The encounter stripped away its tough astronomy questions and the latest original tail but left the comet itself intact. A new astronomy news. tail quickly sprouted as more ice at Lovejoy’s surface vaporized. StarDate 2

MerlinDear Merlin, LAYNE LUNDSTRÖM Actually, over the last My husband and I disagree few decades, the Sep- fast airplane. It shines almost with a large core made of iron tember equinox, whichabout the motion of the Interna- as brightly as Venus, the bril- and nickel. It’s reasonable to marks the beginning oftional Space Station across the liant morning or evening star. assume that it has smatter- autumn in the northernnight sky. I think it is not moving ings of other heavy metals, hemisphere, has mostbut fixed at a place in orbit and it Dear Merlin, including gold, silver, and often fallen on the 22nd.is the spinning Earth that makes I understand that the surface platinum. The planet has alsoit look like it is moving. My hus- had abundant volcanic activ- The difference is causedband thinks it is propelled. of Mercury has some of the most ity (and may have some on- by the difference between valuable real estate in the solar going activity today), which the calendar year (either Tina Lipman system, its surface covered with is involved in concentrating 365 or 366 days) and Port Angeles, Washington heavy metals like gold, silver, and such elements. the true year, which is platinum. Why are these metals 365 days, 5 hours, 48 The space station is in a low so abundant on Mercury yet rare Yet the amounts of these minutes, and 45 secondsorbit (about 230 miles/370 on Earth? And how do I stake a elements, their distribution, long.km), so it is, in fact, its own claim in “them thar hills?” and many other factors aremotion that you are seeing completely unknown. The On average, the time(more than 17,000 miles per Roy MESSENGER spacecraft is of the equinox advances byhour). For it to remain at a Reading, Pennsylvania studying Mercury’s composi- those extra few hours and“fixed” point in the sky, it tion from orbit, but it doesn’t minutes each year (the exactwould have to be in geosyn- Merlin suggests holding off have the ability to detect indi- timing varies somewhat be-chronous orbit, at an altitude on filing a claim just yet. First, vidual deposits of interesting cause of the gravitationalof 22,300 miles (35,700 km). such things are subject to in- metals or other materials. A pull of the Moon and theIf that were the case, though, ternational treaties, which more detailed understanding other planets in the solar sys-it would appear to remain at means lots of paperwork. will have to wait for orbiters tem). Leap Year essentiallya fixed point in the sky, al- And second, no one has yet with more sensitive instru- pushes the equinox back tothough it would be moving measured the composition of ments, or, better yet, landers its starting position everyin orbit around Earth at the Mercury in enough detail to that can actually dig into the four years. So today, for threesame rate as Earth’s rotation determine how much of these surface to see what’s there. consecutive years the equi-on its axis. precious metals it contains. nox occurs on the 22nd for Dear Merlin, the Lower 48 states, then it It’s not correct to say that Like Earth, Mercury is I have noticed over the years jumps to the 23rd the yearthe station is propelled, how- a dense, metal-rich world, before Leap Year, as it did inever; it is “falling” around that the first day of autumn was 2011.Earth, with its orbital speed Send questions to generally either September 21keeping it in space. Astro- Merlin or 22. In 2011, however, it was This arrangement doesn’tnauts do occasionally fire its StarDate September 23. What causes this completely balance the books,thrusters to tweak its orbit, University of Texas at Austin variation? however. If uncorrected, itwhich decays as the station 1 University Station, A2100 would cause the date of thepasses through thin wisps of Austin, TX 78712 Jerry Hequembourg equinox to move about onethe atmosphere. [email protected] Eastham, Massachusetts day earlier every 128 years. stardate.org/magazine (In the first half of the 20th For those who haven’t century, for example, theseen it, the station can ap- equinox occurred most fre-pear shortly before sunrise or quently on the 23rd, not theafter sunset, moving across 22nd.) The current calen-the sky fairly quickly, like a dar system drops Leap Year in “century” years (such as Merlin is unable to send per- 1800 or 1900), unless those sonal replies. Answers to many years are divisible by 400 astronomy questions are avail- (such as the year 2000). able through our web site: For the most part, these ad- stardate.org/astro-guide justments keep the September equinox on the 22nd or 23rd. StarDate 3

HARVARD COLLEGE OBSERVATORY (2) Above: Henrietta Swan Leavitt, about 1910. Background image: This StarDate 4 1905 view of the Large Magellanic Cloud (LMC) taken at Harvard’s Boyden Station in Arequipa, Peru, is one of many Leavitt studied in her search for Cepheid variable stars. Today we know the LMC is a satellite galaxy of the Milky Way.4 M A R C H / A P R I L 2 0 1 2

A hundred years ago, Acentury ago this month, a humanone woman’s patience computer announced a findingand tenacity in pouring that eventually expanded theover photographic plates size of our universe as much aspacked with stars changed Galileo’s first telescopic look at the stars.our view of the cosmos It was on March 3, 1912, that astronomer Henrietta Swan Leavitt’s finding about the behavior of a specific kind of pulsing star was published in the Harvard College Observatory Circular. Her finding allowed astronomers to discover that the Milky Way is not the whole of the universe, and today remains an important rung on the “extragalactic distance ladder” that allows astronomers to measure distances across the cosmos. Measuring the distances to stars had been a longstanding, and highly frustrating, problem in astronomy (and still poses problems today). In the 16th century, Nicolaus Copernicus, who devised a new model of the universe in which Earth orbited the Sun, knew that the distances to stars must be much greater than the distance from Earth to the Sun. If the stars were close, Copernicus reasoned, then observers would be able to easily detect stellar parallax, the shift in a star’s apparent position when viewed from different points on Earth’s orbit.By Barbara Ryden StarDate 5

In 1838 Friedrich Bessel, after of Charles Darwin. “certificates” from the Harvardpainstaking efforts, measured the first The Leavitt family dedication to Annex), Leavitt did additionalstellar parallax, to 61 Cygni. From the graduate work in astronomy andtiny parallax he measured, he deduced learning extended — unusually for the worked as a volunteer research assistantthat the distance from the Sun to 61 time — to supporting higher education at Harvard College Observatory.Cygni was 657,700 times the average for women. Henrietta Swan LeavittEarth-Sun distance, equivalent to 10.3 was the oldest of five surviving siblings, The observatory director at the timelight-years. all of whom attended college. Leavitt’s was Edward Pickering, a pioneer in advanced education began after her the use of large photographic surveys Although parallax is the gold father became pastor of a church in in astronomy. Pickering realized thatstandard for determining stellar Cleveland in 1885, enabling her to the vast amounts of data contained ondistances, the minuscule angles are enter nearby Oberlin College. (She photographic plates of the stars woulddifficult to measure, even for the enrolled simultaneously in Oberlin’s require equally vast amounts of datanearest stars. As late as 1910, more conservatory of music, indicating that processing. Thus, Pickering was in needthan seven decades after Bessel’s the deafness that afflicted her later in of a small army of human “computers.”breakthrough, the Encyclopedia life was not yet troublesome.) He decided to hire women for the job,Britannica lamented the inability to in part, because they were thoughtmeasure stellar parallax for stars more After her sophomore year, Leavitt to have longer attention spans whenthan 70 light-years away. Compared transferred to the Society for the doing repetitive tasks, like sewing orto the size of our galaxy, a sphere Collegiate Instruction of Women in number crunching. Mainly, though,70 light-years in radius is ludicrously Cambridge, Massachusetts. At the Pickering hired women because hesmall; it contains about 4,500 of the time, the Society was better known had a limited budget, and women werehundreds of billions of stars in the by its nickname, the Harvard Annex. customarily paid less than a man doingMilky Way. To posterity, it is known by the name the same job. under which it was later chartered: Henrietta Swan Leavitt was to make Radcliffe College. The Harvard Annexa great stride beyond this limited was founded to give young women theneighborhood. She entered this world benefit of the same instruction thatwithout fanfare, unless you count the was received by young men at HarvardIndependence Day celebrations on College, taught by the same professors.July 4, 1868, the day of her birth.She was named after her mother, The sole astronomy course that shethe former Henrietta Swan Kendrick, took there, “Descriptive Astronomy,”who in turn was named after her was during her senior year. In thatmother, born Henrietta Swan. The course, Leavitt and the seven otherinfant Henrietta’s family tree bloomed students were, according to thewith doctors and ministers. Her father, course catalog, “given opportunitiesGeorge Roswell Leavitt, had a master’s for practical studies of the stars …degree from Andover Theological occasionally with the large telescopeSeminary. Her father’s father, Erasmus of the Harvard Observatory.” LeavittDarwin Leavitt, was named as a earned an A-minus for the course,tribute to a then-famous English and was left with a permanent lovenatural philosopher, the grandfather of astronomy. After her graduation in 1892 (one of 10 women receivingHARVARD COLLEGE OBSERVATORY; HARVARD UNIVERSITY ARCHIVES, HUV 1210 (9-4) Leavitt’s annotations on specific stars are preserved on this photographic plate. Right: An 1891 group of Harvard ‘computers;’ some pore over photographic plates with magnifying glasses. Observatory director Edward Pickering stands at left. A Mrs. Fleming stands at center; the identities of the remaining figures are unknown.6 M A R C H / A P R I L 2 0 1 2

Any skepticism about the ability of away from astronomy permanently. The sheer number of variable starswomen to handle the task of scientific In May 1902, she wrote to Pickering that Leavitt found was impressive;computing was soon dispelled by asking to resume an unfinished she roughly doubled the numberresults. According to an admiring project: “I am more sorry than I can of variables known to astronomers.article in the May 12, 1893, issue tell you that the work I undertook “What a variable-star ‘fiend’ Missof The Boston Globe, “These young with such delight … should be left Leavitt is,” wrote Charles Young ofwomen deal with difficult problems uncompleted.” She wanted a paid Princeton. “One can’t keep up withquite as successfully as do men in position in astronomy, but her doctor the roll of new discoveries.”other observatories. They not only had forbidden her to observe on winteraccomplish in a very satisfactory nights, fearing that the cold would Her most important result, though,manner the regular routine work of worsen her deteriorating hearing. is barely mentioned in the 1908computers at the same fixed rate per “Do you think it is likely,” Leavitt paper. The last of six tables in thehour as men, but are encouraged also wrote to Pickering, “that I could find paper contains a list of 16 variablesto undertake scientific investigation.” employment either in an observatory in the Small Magellanic Cloud for or in a school where there is a mild which the period of variation wasHenrietta Leavitt made her first winter climate?” well determined; the periods range appearance in the Harvard from 1.3 days to 4 months. In theCollege Observatory’s annual report Pickering wrote back immediately, text, Leavitt mentions, “It is worthyin 1896. “An interesting investigation offering Leavitt a position at Harvard of notice that in Table VI the brighterhas been made,” Pickering College Observatory. Although variables have the longer periods.”reported, “by Miss H. S. Leavitt Massachusetts is not known for itson the photographic brightness of mild winter climate, the job Pickering This preliminary result intriguedcircumpolar stars.” However, that year offered was an indoor position as a Leavitt. Unfortunately, she was computer. “I should be willing to pay delayed in following up her results,marked a temporary break in Leavitt’s thirty cents an hour in view of the first by illness, and then by herastronomical career. She spent two quality of your work,” Pickering wrote, father’s death. The much-postponedyears traveling in Europe, and on her “although our usual price, in such culmination of Leavitt’s work didn’treturn to the United States she went cases, is twenty five cents an hour.” come until March 3, 1912, withto Beloit, Wisconsin, where her father Leavitt, in accepting the position, the publication of Harvard Collegehad taken up a new ministry. referred to Pickering’s offer as “very Observatory Circular 173. Although liberal,” but that may have been sheer the three-page circular went out Leavitt, however, could not be kept politeness. Although the average over the signature of Pickering, its American wage in 1902 was just 22 first sentence reads, “The following cents an hour, this was at a time when statement regarding the period of 25 just 6 percent of Americans were variable stars in the Small Magellanic high school graduates. For a college Cloud has been prepared by Miss graduate — even if she suffered the Leavitt.” economic disadvantage of being female — a wage of 30 cents an hour The new, larger sample enabled was not large. Leavitt to find what she called “a remarkable relation between the After Leavitt returned to Harvard brightness of these variables and in August 1902, her new project the length of their periods.” Leavitt involved looking at photographic pointed out that since all the stars plates to find variable stars (stars that in the Small Magellanic Cloud are change brightness) in the Small and at nearly the same distance from Large Magellanic Clouds, which are Earth, the differences in the apparent small companion galaxies to the Milky brightness of the stars in the galaxy Way. Since the galaxies are too far are a result of differences in their south to be seen from Massachusetts, true brightness (or luminosity). Thus, Leavitt looked at plates that had Leavitt could conclude, for example, been snapped through a telescope that a star with a pulsation period of near Arequipa, Peru. The fragile glass 15 days is twice as luminous as a star plates were sent by railway to the with a period of 6.6 days. Peruvian coast, where they started their long sea voyage to Boston. The What Leavitt had discovered was a fruit of Leavitt’s long hours examining universal period-luminosity relation these plates is summarized in the title for a particular class of variable star. of her 1908 scientific paper “1777 Although she didn’t explicitly use the Variables in the Magellanic Clouds.” name, the stars Leavitt was looking at were Cepheid variable stars, named after their prototype, Delta Cephei. StarDate 7

The possible usefulness of the that the Sun’s motion through space falls short of the currently measured relation she discovered was obvious. relative to its nearest neighboring stars distance of 200,000 light-years. If you could measure the luminosity is about 12 miles (20 km) per second. Still, as the first attempt to stretch a of just one Cepheid, you could use He then asked, “If the Sun is moving yardstick to a galaxy beyond our own, Leavitt’s law to compute the luminosity at 20 kilometers per second, how the efforts of Hertzsprung and Shapley of any Cepheid whose pulsation period far away must the Cepheids be, on were impressive. was measured. Once you know the average, to produce their observed In fact, Shapley’s accomplishments, luminosity of that Cepheid, you could proper motions?” Hertzsprung’s answer of which measuring the distance to the compare that to its apparent brightness was that the 13 Cepheids were at an Small Magellanic Cloud was just one, to compute its distance. Thus, the average distance of 93 light-years, and led to his becoming the new director discovery of a period-luminosity relation for Cepheids provided a way ‘Miss Leavitt’s work on the variable stars of computing the distance to any in the Magellanic Clouds has afforded us galaxy in which these special stars a very powerful tool in measuring great could be observed. Leavitt pointed the way to making ste llar di sta nce s.’ – Harlow Shapley the Cepheid period-luminosity relation a useful distance indicator. “It is to be hoped,” she wrote, “that the parallaxes of some variables of that a Cepheid with a period of 6.6 of Harvard College Observatory in this type may be measured.” Knowing days had a visual absolute magnitude 1921. Shapley had little opportunity the parallax and apparent brightness of –2.3. In the Small Magellanic to interact with Leavitt, however. “I of a nearby Cepheid would allow Cloud, a Cepheid with the same period met her first when I went to Harvard astronomers to compute its distance had a visual apparent magnitude of as director,” Shapley recalled much and luminosity. 13, according to Leavitt’s law. (In later. “She was dying of cancer, but we Unfortunately, though, Cepheid the stellar magnitude scale, smaller didn’t mention it.” Leavitt’s death from stars are scarce. The nearest Cepheid numbers represent greater brightness.) stomach cancer came on the cold, rainy (which happens to be Polaris, the Given these numbers, Hertzsprung evening of December 12, 1921. The North Star) is 430 light-years away, calculated that the distance to appraised value of her estate, which outside the little sphere in which the Small Magellanic Cloud is she left to her mother, was merely stellar parallax can be accurately approximately 30,000 light-years. $314.91. Although she left behind measured by ground-based telescopes. (Unfortunately, a typographical error little of monetary value, Leavitt left After reading Leavitt’s 1912 paper, in his paper reduced this number to behind an enviable reputation among Danish astronomer Ejnar Hertzsprung 3,000 light-years. A careless typesetter her fellow astronomers. (Outside found a way to bypass the need to can really shrink your universe.) astronomy, though, she was less well measure parallax. He knew the proper In 1918, an improved calibration by known. Science magazine, for instance, motions (the distance a star moves American astronomer Harlow Shapley in its December 23 issue, noted the across the sky, measured in arcseconds led to an increase in the estimated passing of “Henrietta Swan Jewett,” per year) for 13 relatively nearby distance to the Small Magellanic along with the wrong date of death.) Cepheids. His sample included Polaris Cloud, to 63,000 light-years. Even A haunting coda to Leavitt’s and Delta Cephei. He also knew with Shapley’s correction, this still untimely death came in March 1925, when a letter addressed to Henrietta Leavitt arrived at Harvard College Observatory. It proved to be from Swedish mathematician Magnus Gustaf Mittag-Leffler, telling “Honoured Miss Leavitt” that “I feel seriously inclined to nominate you to the Nobel prize in physics for 1926, although I must confessNASA/ESA/HUBBLE HERITAGE TEAM (STScI/AURA) that my knowledge of the matter is as yet rather incomplete.” It fell to Shapley to write the regretful reply that Leavitt had died more than three Hubble Space Telescope image of the years earlier (making her ineligible for Andromeda galaxy highlighting V1, the Cepheid a Nobel Prize). “Miss Leavitt’s work variable Edwin Hubble used in 1923 to prove on the variable stars in the Magellanic Andromeda lies far outside the Milky Way. Clouds,” Shapley wrote, “which led to 8 M A R C H / A P R I L 2 0 1 2

TIM JONES/DAMOND BENNINGFIELD the discovery of the relation between out have led astronomers to realize Scaling the universe: The most accurate tool period and apparent magnitude, has that the pulsation period for a star of a for measuring cosmic distances, parallax, afforded us a very powerful tool in given luminosity depends on the star’s reaches nearby stars. Understanding measuring great stellar distances.” density. Thus, the period-luminosity Cepheid variables extended astronomers’ relation for Cepheids is actually a reach to nearby galaxies. By observing how The great power of Leavitt’s relation among period, luminosity, a certain type of supernovae brighten and discovery has been amply and density. dim, astronomers can gauge distances of illustrated in the decades since her several billion light-years. To reach even death. As early as February 1925, for For early observers such as Hubble, further, they study redshift, the effect of instance, Shapley received a letter one difficulty of observing Cepheids in the universe’s expansion on light traveling from Edwin Hubble, starting “Dear distant galaxies was that the light from toward us from the most distant galaxies. Shapley: You will be interested to hear the Cepheid star was blurred together that I have found a Cepheid variable with the light from numerous ordinary Resources in the Andromeda Nebula.” This was stars around it. This blurring makes it interesting news indeed; using Leavitt’s difficult to detect the variability of the Books law, Hubble was able to estimate the Cepheid and to measure its brightness Miss Leavitt’s Stars, by George Johnson, 2005 distance to the Andromeda Nebula with the desired accuracy. To reduce The Day We Found the Universe, by Marcia Bartusiak, 2009 as one million light-years (the current the blur, the best solution is to hoist Inte rne t measurement is roughly 2.4 million). a telescope above the atmosphere. Cosmic Distance Ladder At this great distance, it was clear that Thus, one of the main motivations for aavso.org/cosmic-distance-ladder the Andromeda Nebula was actually building and launching Hubble Space Carnegie Cosmology Timeline the Andromeda Galaxy, comparable in Telescope was an ambitious project cosmology.carnegiescience.edu/timeline/1912 size to our own galaxy. Before Leavitt’s to observe Cepheids in galaxies as StarDate: Beyond the Solar System discovery, it was uncertain whether far as 70 million light-years away. By stardate.org/astro-guide/btss the universe ended at the edge of the developing a more accurate distance Cosmic Rulers Milky Way, or was populated with scale in this region, the project has telescopes.stardate.org/research/cosmic_rulers other galaxies of stars far outside our given us a reliable measuring stick own. After Hubble’s findings, it was to use for intergalactic distances. clear that we live in an immense Before Henrietta Leavitt’s discovery universe full of galaxies. of the period-luminosity relation, Leavitt’s period-luminosity astronomers were unable to measure relation is not a dusty, outmoded accurately distances greater than 70 tool, but is used to the present day. light-years; by making use of Leavitt’s The underestimated distances of law, we are now able to find the Hertzsprung, Shapley, and Hubble distances to galaxies a million times were later corrected upward when the farther. dimming effects of interstellar dust Barbara Ryden is a professor of as- were better understood. Studies of tronomy at Ohio State University and a how Cepheids actually pulsate in and frequent contributor to StarDate. StarDate 9

by Alan MacRobertMarch and April bring astronomy-rich evenings markings, and perhaps some Brighter Venus stands almost even if you live in the heart of a light-polluted signs of white clouds around still from week to week, ascity. Most of the brightest stars and planets are up and the planet’s rim. high in the evening twilightwaiting to show off. as we ever see it. To the upper right of Mars by a fist-width or a bit more The waxing crescent Moon passes Jupiter and Venus lateMARCH 1 - 15 shines dimmer Regulus, in in the month. It hangs with shines Procyon. These are the Leo. The evening Moon glares Jupiter on the evening of the 25th and with Venus on theStart your tour of the big and little dog stars, re- to the right of Regulus on 26th.March sky with brilliant spectively. With Betelgeuse in March 6, then to the right The rest of March’s pan- orama of brightness remainsVenus and Jupiter, shining Orion’s shoulder, they form or lower right of Mars on the much the same as it was in the first half of the month,high in the west during twi- the bright, equilateral Winter 7th. except that Mercury is gone and everything has shiftedlight. Venus is the brighter Triangle. By late evening, two more westward with the advancing season. On the eastern side ofof the two. They begin the Turn farther left now to points are up in the east- the sky, celestial “westward” means up, so Mars and Regu-month 11 degrees apart, face east, where you will see southeast: Saturn, and to its lus shine higher in the east after dusk.which is about a fist-width the planet Mars shining fiery right, Spica. Far off to their And the Saturn-Spica pairat arm’s length. Watch them rises in the east earlier now, at roughly 10 p.m. Saturnmarch toward each other is the one on the left, shin- ing with a steadier glow thanday by day. They pass just twinkly Spica. The two are lined up nearly horizontally,three degrees apart (about three or four fingers apart.two finger-widths at arm’s Brilliant Sirius is now due south at nightfall. It’s thelength) on March 12, 13, ‘The bright dog tag on the chestand 14. Venus and Jupiter Sickle’ of Canis Major, the big dog. If you live under typical cityare the brightest objects in light poSllWution, only five stars of Canis Major show through,the heavens after the Sun and LEO forming more of a meat cleav-Moon. Mark your calendar to er than a dog. Sirius is a brightbe sure to catch this beautiful Regulus April 2 glint on the top corner of thetwilight conjunction. Mars cleaver. A fainter star to Siri- us’ lower right, Mirzim, marks And in the first week of Denebola the front corner of the cuttingMarch, while twilight is still edge. Three stars farther to the lower left form the nar-bright, look far below Venus April 3 rower back of the cleaver andand Jupiter and a bit to their its stubby handle. These last three stars are, from right toright to spot little Mercury, left, Adhara, Wezen, and Alu- dra. They are about as highthe innermost planet, low in right now as they ever get.the fading glow of sunset. In a dark sky more stars come out, and with only aThere’s nothing else there to C.J. DUNCANconfuse it with. SE About 10 p.m. Bright Capella, the goatstar, shines near the zenith atthat hour. yellow-orange, almost as left in the east shines brighterAs darkness falls, Orion bright as white Sirius. Mars Arcturus, the “spring star,” astands high in the south to is at opposition (opposite the match for Capella — which,southwest. It is, of course, Sun in our sky) on March 3 as the evening grows late,the brightest and most rec- and closest to Earth on March is moving down the sky’sognizable constellation of the 5. Don’t expect too much of northwestern wall.season. it in a telescope, though; thisSirius, the brightest star is a distant opposition, and MARCH 16 - 31in the night sky, shines to Mars appears only 13.9 arc Venus and Jupiter spendthe lower left of Orion. It is seconds wide — a tiny ball. the second half of Marchthe closest object beyond the With a good telescope on a pulling apart from each othersolar system that is visible night of steady atmospheric in the western evening sky.to the unaided eye from our seeing, however, you should Jupiter is heading downward,mid-northern latitudes. be able to make out Mars’ toward the Sun (and willTo the upper left of Sirius north polar ice, subtle dark pass behind the Sun in May).10 M A R C H / A P R I L 2 0 1 2

little imagination (and a good Meteor Watch dipper-length, and you will Nath (Beta Tauri), which just constellation guide) you can find yourself at bright Arc- missed fame and recognition spot the dog’s dim triangu- The Shower turus, the “spring star.” Its by not quite qualifying as lar head to the upper left of Lyrids ascent in the eastern evening a first-magnitude star (it is Sirius. Adhara is the dog’s Named for the constellation Lyra, the harp, sky parallels the rising of tem- magnitude 1.6). It is moving hind leg, Wezen is his rump, which is notable for its brightest star, Vega, peratures, leaves, and flowers closer to Venus every day. and Aludra is his tail. the third-brightest star visible from most of in March, April, and May. North America. Mars and Regulus are at APRIL 1 - 15 The dipper’s curving han- their highest in the south now Peak dle also can guide you to a at dusk. For a while they were Changes are afoot in the Night of April 21 lesser-known sight. If you making the moves on each western twilight. Jupiter is picture the handle and the other, but seem to have decid- dropping farther away from Notes side of the dipper’s bowl, it’s ed against it. They were five Venus, while Venus has an The Lyrids are a modest shower, with attached to a segment of a degrees apart at the start of encounter with the Pleiades. perhaps a dozen or two meteors per hour (rough) circle, then at the April, closed to within four de- On April 1, Venus shines just at best. The Moon is new on April 21, circle’s center is the modestly grees around mid-month, and below the little star cluster. providing perfect conditions for viewing the bright star Cor Caroli — a have now separated to five de- On the 2nd and 3rd it’s prac- shower. gorgeous yellow-and-violet grees again and will be going tically inside the group, then double star for viewing in any their own ways henceforth. on subsequent days it moves the southwest and his three- telescope. It’s in the dim con- above them. star belt is becoming horizon- stellation Canes Venatici, the Arcturus now rules high in tal. Orion’s Belt points to the hunting dogs. the eastern sky. But a chal- Or rather, Venus is stand- right, roughly to Aldebaran, lenger to its warm-season ing still with respect to your the Pleiades, and Venus. It APRIL 16 - 30 preeminence is beginning to twilight landscape and the points leftward toward ever- make itself known. Low in the Pleiades are sliding down to brilliant Sirius. And still Venus holds its twi- northeast now, Vega rises by the lower right behind it. And light position, flaming whitely late evening. Like Arcturus, so is the entire western starry It can’t be spring without high in the west as the “eve- it is magnitude zero, which backdrop. Aldebaran, for in- the Big Dipper. Look for it ning star.” Aldebaran and the is one step brighter than stance, is the orange point standing on its handle high Pleiades are moving farther first-magnitude on the stellar roughly a fist to Venus’ upper in the northeast as the stars below it. And Jupiter is much brightness scale. (This actual- left early in April, then to its come out. It moves even high- lower still, riding away into ly makes sense once you know left, and then to its lower left er and tips leftward as the the sunset. Capella remains the history.) Vega is beginning as the month proceeds. evening advances. By mid- higher to Venus’ upper right, a long ascent to claim the ze- night it’s almost upside down, though it is less high every nith as the “summer star.” Meanwhile, Capella is high in the north. week. The waxing Moon moving downward, high to poses near Venus on April 24. Alan MacRobert is a senior Venus’ upper right. Follow the curve of the dip- editor of Sky & Telescope in per’s handle down and to the And look much closer Cambridge, Massachusetts. With spring under way, right, by a bit more than a above Venus for the star El Orion is tipping down intoNASA A view of Mars from Mars marches boldly into March (which, like the planet, is Hubble Space Telescope named for the ancient god of war), shining as the fifth- brightest object in the night sky.The planet is at opposition on March 3, when it lines up opposite the Sun. For several nights around opposition, Mars rises at sunset, climbs high across the sky during the night, and sets at sunrise. It passes closest to Earth around opposition as well, so it’s brightest for the year. SIDEBItAlRooHkEs RlikEe a brilliant orange star, not far from Regulus, the brightest star of Leo, the lion. This is not a great opposition for Mars, however. Earth passes more than 60 million miles from the planet, versus just 35 million miles a few years ago. Mars follows a much more elongated orbit than Earth does, so its distance from the Sun varies by tens of millions of miles.When we pass Mars at this time of year it’s close to its farthest point from the Sun. In the years when we pass it during summer, though, and especially in August, Mars is much closer, so it shines much brighter. S t a r D a t e 11

How to use these charts: February 20 11 p.m. 1. Determine the direction you are facing. March 5 10 p.m. 2. Turn the chart until that direction is at the bottom. March 20 10 p.m.* NORTH * Daylight Saving Time begins March 11. M92 DRACO URSA MINOR CASSIOPEIA Etamin L A C E R TA Alderamin M13 BOCROERAOLINSA CEPHEUS M31 Kochab Polaris ClDuostuebrle AlmaakPEGASUS Mirach Alphekka Alkaid Mizar M81 LYNX Mirphak PERSEUS Algol TRIANGULUM Hamal M33 Thuban M101 M82 C A M E L O PA R D A L I S Alio URSMAerMakAJOR M51 Dubhe t hMV63ECNAANTEISCMI 106 Phad Capella ARIES M3 M64 M97 Arcturus AURIGA Pleiades M36 M38EAST COMA zenith Menkar CETUS WEST BERENICES Castor LEO M95 LEO M35 Alnath TAURUS M96 MINO M37 M1 Aldebaran Denebola R VIRGO ThSeickle CANCER M44 Pollux GEMINI Alhena Bellatrix M Regulus P r oCcAMyNoOInSN OMCI NEORRO S Betelgeuse ORION ERIDANUS M47 ECLIPTIC Spica M104 M67 SEXTANS HYDRA M42 Alphard Rigel CRATER WTirniatenrgle s LEPUS CORVUS Sir COLUMBA i u M68 M41 CMA NA IJSO R PUPPIS V SOUTH M Mars S 12 M A R C H / A P R I L 2 0 1 2 Charts produced with Voyager II software. S t a r D a t e 12

How to use these charts: March 20 11 p.m.1. Determine the direction you are facing. April 5 10 p.m.2. Turn the chart until that direction is at the bottom. April 20 9 p.m. NORTH CEPHEUS Alderamin Etamin DRACO ClDuostuebrle CASSIOPEIA M92 URSA MINOR M13 Polaris Mirphak ol Kochab CAMELOPARDALIS Alg HERCBUCOLORERESOANLIAS M101 Phad M82 Capella PERSEUS Alioth Mizar M81 Thuban Pleiades M51 Dubhe Alphekka Alkaid SERPENS Merak VENCAATNICEIS MAJOR AURIGA V M63 M97 M106 URSA LY N XEAST M5 M3 zenith Castor M35 M37 WEST Arcturus M1 LEO LEO MINOR Aldebaran Denebola TAURUS BECROEMMNIA6C4ES Pollux GEMINI Betelgeuse ORION STihcekle CANCER M44 MINOR Bellatrix VIRGO M96 M TriaWinntgleer S M95 Regulus M67 NIS M42 Rigel CORVUS CA M68 MONOCEROS ECLIPTIC Procyon M104 SEXTANS M47 Spica M41 Sirius C R AT E R Alphard VV LEPUS MM Mars SS SaturnMACJAONRIS V Venus HYDRA SOUTH M S Charts produced with Voyager II software. S t a r D a t e 13

by Damond Benningfield 8 MARCH Su M T W Th F Sa 1 23 3:39 am 3 Mars is at opposition, which means it lines up opposite the Sun in our sky. It puts in its 4 5 6 7 8 9 10 14 best showing of the year. It rises at sunset and 11 12 13 14 15 16 17 remains in view all night. The planet looks like 18 19 20 21 22 23 24 8:25 pm a bright orange star, and is passing through the 25 26 27 28 29 30 31 constellation Leo, where it stands about half- 22 way between the lion’s brightest stars, Regulus next night Saturn is to the upper left of the (above Mars) and Denebola (to its lower left). Moon, with Spica about the same distance above 9:37 am the Moon. 5 Mercury is farthest from the Sun for 20 Spring begins in the northern hemi- 30 its current evening appearance. It looks like a sphere with the vernal equinox at 12:14 a.m. bright star low in the west as night begins to fall, CDT. The Sun crosses the celestial equator, which 4:41 pm and sets in early evening. It is well below brighter is the projection of Earth’s equator on the sky, atMoon phase times are for Jupiter and Venus. that moment, heading from south to north.the Central Time Zone. 24-26 The crescent Moon climbs past Venus 6/7 The Moon, Mars, and Regulus team up. and Jupiter, which are the brightest objects in the They are in the east in early evening and climb night sky after the Moon itself. The Moon is well high across the sky later on. On the 6th, Regulus below them on the 24th, just to the upper right is close to the left of the Moon, with brighter of Jupiter on the 25th, and just to the upper left Mars to their lower left. Mars is to the upper left of Venus on the 26th. of the full Moon on the 7th, with Regulus well above them. 9/10 The Moon slides past the planet Saturn and the star Spica. As they rise on the night of the 9th, Spica is to the lower left of the Moon, with Saturn farther along the same line. TheAPRIL 62/3 Brilliant Venus, the “evening star,” 15 Saturn, the second-largest planet in the 2:19 pmslides past the Pleiades. solar system, is at its best for the year. It rises3 Bright orange Mars lines up to the upper around sunset and shines all night in Virgo, with 13left of the Moon at nightfall, with the star Regu- the constellation’s brightest star, Spica, to thelus close to the upper right of Mars. right of Saturn. Saturn looks like a bright golden 5:50 am6 The Moon lines up with the star Spica star.and the planet Saturn. Spica is close to the left 21of the Moon at nightfall, with brighter Saturn 22 Brilliant Jupiter, which is about to disap-farther to the left of Spica. pear in the Sun’s glare, stands directly below the 2:18 am9 Venus and Aldebaran are in the west at Moon as evening twilight descends.sunset, with fainter Aldebaran about the width 29of a fist at arm’s length from brighter Venus. 23 The crescent Moon passes through Tau- rus. The bull’s brightest star, Aldebaran, is to the 4:57 am Su M T W Th F Sa upper left of the Moon, and its shoulder, the Ple- 1 234567 iades star cluster, about the same distance to the 8 9 10 11 12 13 14 lower right. 15 16 17 18 19 20 21 22 23 24 25 26 27 28 24 Evening-star Venus is to the upper right 29 30 of the Moon this evening. 30 Venus shines brightest for its current evening appearance. 30 Orange Mars stands to the upper left of the Moon at nightfall, with the star Regulus closer to the upper right of the Moon.14 M A R C H / A P R I L 2 0 1 2

AstroMiscellany Looking for Neighbors NASA/ARC/JPLGet StarDate Just about every issueon Your of this magazineSmart Phone! brings you tales of newly discovered planets,The free University including a few that follow of Texas iPhone app roughly Earth-like orbitsnow provides a plethora around Sun-like stars. Indeed,of frequently updated the count of known planets ininformation from other star systems is nearingStarDate and McDonald 700, and almost certainly willObservatory. With the top 1,000 by year’s end. Yetapp, you can listen to there is no hint of life fromdozens of StarDate radio these or any other of the billionspodcasts (excluding the of planets that may populatecurrent day’s show), see the galaxy.what’s in the latest issueof StarDate magazine, In the newly updated Theand get weekly skywatching information from StarDate Living Cosmos, Chris Impey,Online. You can check out a guide to the constellations, astronomy chairman at the University of Arizona and aread up on the latest research from McDonald skilled writer for non-academic audiences, explores notObservatory, see a photo gallery, and get information only the challenges of finding life in the universe, but theon visiting McDonald — with an interactive map and challenges of life itself: the conditions necessary for life,driving directions. The app also will connect you with the twisting branches of evolution, the threats from theStarDate and McDonald Observatory’s social media sites universe. He also explains our current knowledge of life’son Facebook, Twitter, and YouTube. hardiness and of the birth and evolution of planets, and he discusses humanity’s future in space and the chancesTo get the app, visit: www.utexas.edu/iphoneapp that we’re not the only intelligent life in the universe. The journal Astronomy Education Review recently The Living Cosmos: compiled a list of astronomy apps for smart phones: Our Search for Life in the Universe aer.aas.org/resource/1/aerscz/v10/i1/p010302_s1 By Chris Impey Cambridge University Press, $20The lives of planets, stars, and galaxies are presented in color- Stars burst into life in IC 410, a stellar HARVARD-SMITHSONIAN CfA ful detail in “The Evolving Universe,” a new exhibition at the nursery about 13,000 light-years fromSmithsonian’s National Museum of Natural History in Wash-ington, D.C. Developed with the Smithsonian Astrophysical Earth, in this photo from the exhibit.Observatory, it features dozens of large photographs, snappedthrough a variety of telescopes, that document the evolution S t a r D a t e 15of the universe over the 13.7 billion years since the Big Bang.Admission is free. Those who can’t make it to the museum canexperience the exhibit through a companion website.www.mnh.si.edu/exhibits/evolving-universe

TA HNEE WX-RF OACYU SS KOYN NuSTAR will scan the heavens to better understand high-energy X-ray phenomena like exploding stars, black holes, and jets from distant massive galaxiesby Rebecca Johnson ORBITAL SCIENCES CORPORATION Astronomers will gain new insights into the scopes like Chandra X-Ray Observatory and Europe’s chaotic center of our Milky Way galaxy and XMM-Newton have studied the low-energy X-ray uni- uncover previously hidden supermassive black verse in depth. Both are still flying — but powerful as holes in remote dusty galaxies as early as this spring they are, they can’t see into all the dusty, hidden regions thanks to a satellite that’s scheduled for launch in that NuSTAR will probe. March. NuSTAR (Nuclear Spectroscopic Telescope Array) is an X-ray telescope that will study the high- “The particularly interesting thing about observing energy X-ray sky with much greater sensitivity than any high-energy X-rays is that they’re very penetrating,” previous instrument. Harrison said. “Baggage scanners at the airport, dental X-rays — these are all high-energy X-rays.” NuSTAR is a Small Explorer mission, which means it was designed and built much more quickly and inex- High-energy X-ray telescopes of the past have been pensively than billion-dollar projects like Hubble Space fairly crude. They operated much like sophisticated Telescope and its fellow Great Observatories. pinhole cameras rather than telescopes. That’s because focusing X-rays is notoriously difficult. “Not only will it be a factor of 500 times more sensi- tive than anything [like it] that’s been launched be- “X-rays only bend very slightly,” Harrison said. “You fore, it’s a factor of more than 10 times cheaper,” said can reflect X-rays, but the key, the challenge is that it Caltech’s Fiona Harrison, the mission’s principal inves- only works at very glancing angles — much less than tigator, in a recent public talk at NASA’s Jet Propulsion a degree.” The only part of a parabolic mirror that has Laboratory, which manages the mission. such a shallow angle is the edge, which makes for a tiny collecting area for an X-ray mirror. NuSTAR will probe the universe at wavelengths that have received scant attention before. Large X-ray tele- To increase the collecting area, which increases the instrument’s ability to see fine detail, engineers take 16 M A R C H / A P R I L 2 0 1 2

multiple mirrors and stack them in how chemical elements forged in Resources concentric shells inside an X-ray tele- supernova explosions are incorporated scope. NuSTAR has two telescopes, into the next generation of stars. Inte rne t each using 130 concentric mirror NuSTAR Mission Homepage shells. (Chandra has four such shells.) NuSTAR will look outside our www.nustar.caltech.edu Special atom-thick coatings on the galaxy for supermassive black holes at mirrors allow them to reflect higher- the hearts of distant galaxies. These Launch Information energy X-rays. monster black holes, weighing in at www.nasa.gov/mission_pages/nustar/launch millions or billions of times the Sun’s The two telescopes will focus the mass, also are surrounded by hot, Slide Show incoming X-rays to two identical swirling disks that give off X-rays. www.scientificamerican.com/article.cfm?id=nustar- detectors. The images from the two Though some have been studied, telescope-photos telescopes will be added together once NuSTAR will add many more to the the data are transmitted to Earth. census because it can see the ones Article s currently hidden inside dusty galaxies. “X-ray Vision: NASA’s NuSTAR Telescope,” by Fiona These complicated optics will be Harrison and Charles J. Hailey, Scientific American, used to tackle a diverse list of In digging into the secrets of February 2011 science goals. One is to take a census supermassive black holes, NuSTAR of black holes, both inside and outside will attack one of the toughest “How to Make Telescopes Lenses to Spot Black Holes our galaxy. problems astrophysicists currently (for Cheap),” by Cassie Rodenberg, Popular Mechanics, face, Harrison said: They don’t really May 4, 2010 Inside the Milky Way, NuSTAR will understand the relationship between look for stellar-mass black holes that a supermassive black hole and the “Urban Jungle,” by Damond Benningfield, StarDate, can form when a heavy star burns all of galaxy that surrounds it. Astronomers September/October 2011 its nuclear fuel and either explodes as know there is a tight correlation a supernova or implodes before it can between the black hole’s mass and all measure, so that we can say, ‘What explode. Of course, no telescope can the mass of the galaxy’s central bulge. kind of galaxies are these black holes see a black hole directly — they don’t They also know there’s a relationship growing in? How much of this dust emit light. But a black hole’s powerful between the black hole’s mass and the that they’re hidden behind are they gravity pulls matter into a swirling disk galaxy’s rate of star formation. What actually swallowing?’” around it. This matter gets so hot that they don’t know is how the black hole it emits X-rays. is influencing the surrounding galaxy, APegasus XL rocket will propel and vice versa. NuSTAR into space. In mid- NuSTAR also will study the March, the rocket will be dropped chemistry of material spewed into Until now, it’s been a difficult at 40,000 feet from an L-1011 space by supernova explosions by mystery to probe because the best aircraft flying from the Ronald probing the expanding clouds of pictures of high-energy X-rays coming Reagan Ballistic Missile Defense Test gas and dust known as supernova from near supermassive black holes Site on the Kwajalein Atoll in the remnants. The composition of this look like shapeless blobs. Marshall Islands. After free falling for detritus will provide clues about the five seconds, it will ignite and carry explosions themselves, and in turn “This is what we want to do with NuSTAR into low-Earth orbit for its the physics of what goes on inside NuSTAR,” Harrison said. “We two-year primary mission. massive stars. These studies also will want to turn [the blobs] into point help astronomers better understand sources, whose brightness, energy Once it enters orbit, the spacecraft output, positions, distances we can will deploy a boom that will push its optics out to 10 meters (33 feet)NASA/CXC/CfA/R.KRAFT A Chandra X-ray view of a jet shooting out of from the detectors. Focusing X-rays Centaurus A, a galaxy with a supermassive requires such a long focal length, and black hole at its core. NuSTAR will offer a the extendable boom made it possible sharper view of this and other X-ray sources. for NuSTAR to fold and fit into the Pegasus rocket. Once the boom is extended and the systems check out, astronomical observations will begin. By bringing both the nearby and distant high-energy universe into focus for the first time, NuSTAR will foster a new understanding of many diverse realms of the cosmos. Rebecca Johnson is editor of StarDate magazine. S t a r D a t e 17

JOIN THE CLUB!ASTRONOMY CLUBS PROVIDE OPPORTUNITIESFOR LEARNING, FRIENDSHIP, AND VOLUNTEERINGAs a StarDate reader, you know that you don’t have to be an expert astronomer to enjoy the Not every club belongs to the Astronomical League, but wonders of the cosmos. But in addition to most do, and its website is a good place to start looking for books, magazines, and websites, there is anoth- a club near you.er great resource that can help you gain a deeper delightand appreciation for the night sky. I’m talking about an Additionally, you could contact the physics or astron-astronomy club. omy department of your local university or community There are at least 250 clubs in the United States, com- college, or check with local camera shops or astronomyprising almost 20,000 members. The largest is the Texas supply vendors.Astronomical Society of Dallas, with about 700 members. Astronomy clubs offer lots of benefits for their mem- bers. First, there’s the sense of camaraderie you getNo matter where you live, though, there’s a good chance from being with people who share a passion for the nightthere’s one close to you. sky. This fellowship can be a blessing if your friends and The Astronomical League, which has been around since family members don’t share your enthusiasm for staying up TWAN/BABAK TAFRESHI late at night outdoors in the cold to look skyward!1947, is the national umbrella organization for most clubs. BY LINTON G. ROBERTSON18 M A R C H / A P R I L 2 0 1 2 S t a r D a t e 18

This support can take many forms. where the dark-sky site is in the desert HALFBLUE your own star party at the club’sFor example, regular meetings are the or mountains. site. This may cost extra, usually paidbackbone of any club. They tend to yearly, and you may have to pledge tobe light, informative, and extreme- Some clubs even offer telescopes use it or lose it; policies vary from clubly friendly. Programs usually consist that you can control from your home to club.of a short introduction, a welcome computer. This removes the need tofor newcomers, some information on trek miles into the outback to get a Many clubs sponsor on-line chats,what the club is doing that month, good look at the sky targets of your texting, and group message boards forand the main event: a talk on a topic desire. members to ask questions, keep up toin astronomy. date on happenings, and notify mem- Many clubs offer small specialty bers of unusual skywatching events. Big names in astronomy often give groups, and finding your niche For the really adventurous, clubs fre-these talks. You might hear a lecture can be rewarding. Some people enjoy quently sponsor telescope-makingfrom a famous comet discoverer, a astrophotography, some like observing classes taught by a master. If you haveNASA bigwig, an astronomer who and learning about comets and planets the time, you can build an instrumenthas just discovered an extrasolar plan- in our own solar system, some prefer of superior optical quality for the sameet, or an astronaut. You never know the deep-sky wonders of galaxies and or less money than purchasing one.who is going to turn up, but it might nebulae. Some people like to observebe someone you otherwise would see variable stars, and others concentrate If you’re more interested in buying aonly on TV. strictly on meteor showers. And there telescope, club members can steer you are some who are as fascinated with toward good manufacturers, makes, Once you’ve attended a meeting or the observing equipment as in what and models, and save you a lot oftwo and decided to join the club, the they’re using it to observe. grief. Ask questions, and don’t be shypossibilities can be truly remarkable. about asking to look through another The better-developed clubs lease person’s telescope. (Always ask first, Many clubs schedule field trips to private telescope pads where you can though! It’s good astro-etiquette.)NASA centers and science muse- come and go as you please, miss the This is a wonderful way to learn aboutums. They can also be your gateway crowds, bring a few friends, and host binoculars, telescopes, filters, vendors,into your local state or community and the like before taking the plunge.college’s observatory, where you can Resources Many a greenhorn has thrown awayget a look through some pretty big a lot of money on bad equipment be-telescopes. Inte rne t cause he or she doesn’t wish to appear The Astronomical League ignorant by asking questions. Some clubs also have their own astroleague.org“dark-sky sites.” A dark sky site can World Astronomy Clubs Club membership also gives yourange from a farmer’s field in the astronomyclubs.com plenty of chances to give back. Formiddle of nowhere (with the farmer’s Beginner’s Guide to Stargazing example, you can help out at publicpermission, of course!), to more so- stardate.org/nightsky/bguide star parties. Clubs stage skywatchingphisticated club-owned sites. The lat- International Dark-Sky Association events to educate and amaze schoolter could offer bathrooms, showers, www.darksky.org groups and the public. You also couldconcrete pads with electrical outlets volunteer your time to the club it-where members and guests can set up self: sites have to be maintained, andtheir telescopes, barbecue pits, visitor events are always in need of docentsparking, and a club-owned telescope. and organizers. Some clubs have monster telescopes There’s work to be done, too, inthat they open to the public twice a the field of preserving our night skymonth or more, and they are happy from the continuing and acceleratingto train you, as a club member, to use problem of light pollution; many clubsit yourself. This is a truly marvelous work directly with the Internationalplus to those who have no telescope Dark Sky Association and provideof their own, but, for a small mem- clout when cities decide to put up badbership fee, will have full use of a street lighting or adopt lighting ordi-17-inch, 22-inch, or perhaps even a nances that threaten the night sky.36-inch giant. In short, membership in a club can “Warming rooms” for winter and enhance your love of the night sky in“cooling rooms” for the heat of sum- ways you never envisioned.mer can be a real blessing, and manyclubs even feature meal preparation fa- Linton Robertson has been a lover of thecilities at their observing sites. These night sky since 1956, when his late motheramenities can extend your yearly cal- took him as a five-year old to Griffith Obser-endar of visits to the club site quite vatory in Los Angeles.a bit, especially if you live in an area S t a r D a t e 19

by Rebecca Johnson and Damond Benningfield NASA/JPL/SSI (3) From left: Smog-enshrouded Titan against Saturn’s rings and the planet itself; icy Enceladus; the best look at Janus to dateFive Moons in Four DaysSaturn orbiter to probe cold skies and warm geysers, and look for hidden moonsThe Cassini spacecraft faces a busy few days in late Saturn’s rings. March. The Saturn orbiter will scan five of the giant The star of the week, though, is Enceladus. Geysers ofplanet’s moons, taking a look at everything from clouds togeysers. water and ice shoot into space from “hot spots” near the moon’s south pole. Cassini has taken several close looks at During the March 26-29 encounters, Cassini will take that region, and at the geysers.regular looks at Saturn’s largest moon, Titan, which isenveloped by a thick, cold atmosphere, with clouds of frozen On March 27, Cassini will swoop to an altitude of 46methane floating through its skies. Cassini will watch the miles (74 km) above Enceladus. The craft will approachmotions of the clouds to plot the big moon’s weather. from the nightside, so it will see the spray of ice backlit by the Sun. It then will pass around to the dayside, providing a The craft will also look for tiny moons orbiting at 3D view of the geysers, plus one of the best looks yet at thegravitational balance points near Titan and another moon, hot spots that give them birth.Rhea. And it will make its closest approach yet to thesmall moon Janus, which shares an orbit with yet another Cassini will stage equally close encounters with Enceladusmoon. The two of them work together to clear out a gap in on April 14 and May 2, providing the most detailed look to date at the ice-covered moon and its explosive geysers. DBAstronomers Find Two Ways to Make a Star Go BoomLast year’s Nobel Prize for Physics honored the star or from a collision with a second white dwarf. discovery of dark energy — a mysterious force Hubble view of a supernova remnant that NASA/ESA/HUBBLE HERITAGE TEAM LSU astronomers Ashley Pagnotta and Bradleythat is causing the universe to accelerate faster as might have been triggered by the mergerit expands. Astronomers discovered the expansion of two white dwarf stars. Schaefer examined Hubble Space Telescope imagesby measuring the speeds of exploding stars known of four supernova remnants in the Large Magel-as Type Ia supernovae in galaxies at different lanic Cloud, a companion galaxy to the Milky Way.distances from Earth. These stars all appear to In three of these expanding clouds of gas andbrighten and fade in the same way, making them dust, they found stars near the explosion site thatgood “standard candles” for measuring intergalac- could have supplied the gas needed to trigger antic distances. explosion. In the fourth, however, they found no possible companion at all, suggesting that the blast Yet the stars themselves don’t seem to meet a was triggered by the collision of two white dwarfs,single standard. Instead, recent research suggests which left no surviving stars.there are two ways to create a Type Ia supernova. The possibility that the explosions can form in All of these explosions occur when extra matter different ways doesn’t lessen their value for mea-piles atop a dense stellar corpse known as a white suring the expansion of the universe, Pagnotta saiddwarf, triggering an explosion that blasts the star during a recent presentation. “They’re still goodto bits. It is unclear, however, whether the extra standard candles even if they come from differentmatter comes from a flow of gas from a companion [types of] systems,” she said.20 M A R C H / A P R I L 2 0 1 2

Ready, Aim, Fire!Ablack hole near the center of the gal- NRAO/NASA/GSFC axy is firing bullets. Once every eight DARLENE MCELROY/LANA Artist’s concept of a neutronmonths or so, it shoots a blob of super- star’s surface cracking duringheated gas into space at a quarter of the An artist’s concept shows,speed of light. from top: the black a powerful ‘starquake’ The black hole, known as H1743-322, hole steals gas from its fNoArSXA-RTauyrnTselOesffctohpeeLightsis about 28,000 light-years away, in the companion star; some ofconstellation Scorpius. It’s probably about the gas forms a ‘knot’ in An orbiting X-ray telescope that studied some of the5 to 10 times the mass of the Sun, with a the disk around the black most bizarre objects in the universe was shut downcompanion star that probably resembles on January 4, ending a 16-year mission. The telescope,the Sun. The two are so close together that hole; the knot moves Rossi X-ray Timing Explorer (RXTE), was showing signsthe black hole pulls gas off the surface of close to the black hole of age, and a review panel recommended ending itsthe companion, forming a spinning disk itself; magnetic fields eject operations to save money for higher-priority projects.around the black hole. The gas gets so the knot as twin ‘bullets’hot that it produces X-rays, although their Among its many accomplishments:intensity varies. • Confirmed the existence of magnetars, which are Three years ago, a team of astronomers highly magnetic versions of the crushed stellarmonitored the system with a network of corpses known as neutron stars.radio telescopes on the ground and anX-ray telescope in space. They found that • Provided the first observational evidence thatshortly after the intensity of the X-rays black holes drag spacetime around them like apeaked, the black hole fired two bullets cosmic whirlpool, confirming a prediction frominto space. The bullets followed jets of Albert Einstein’s theory of gravity.charged particles that shoot into space fromthe poles of the black hole. • Provided the strongest confirmation to date of the existence of an event horizon, which is the point The bullets probably formed as gas piled of no return for matter falling into a black hole.up in the disk around the black hole, form-ing a dense knot. Just before it reached the • Studied the process by which black holes andblack hole itself, the knot was blasted into neutron stars steal gas from companion stars, andspace along the lines of its magnetic field, how the gas behaves as it nears the dense objects.which funnel the jets into space. • Measured a powerful starquake on the surface of a There are several ideas for how that neutron star, providing new insights into its innerhappens, but all of them have problems. structure.Watching the whole process of such aneruption is helping astronomers narrowthe list.Don’t Miss the Big Show Coming to the Galactic Center!The black hole at the center of the Milky Way galaxy is usually pretty quiet. But it Simulation of the cloud’s orbit lurks, waiting for tasty morsels to get pulled in by its immense gravity. Astronomers and break-up as it nears theexpect to see such a show pretty soon. galactic center (red) and theIn 2008, Reinhard Genzel of Germany’s Max Planck Institute for Extraterrestrial orbits of nearby stars (blue).Physics and his partners discovered a gas cloud three times the mass of Earth picking upspeed as it approaches the Milky Way’s black hole. The cloud of hydrogen and heliumcould fall into the spinning disk of material around the black hole within a year. By2013, it should give off X-rays and radio waves as it’s pulled apart.“This is an unprecedented opportunity to obtain unique observations and insight intothe processes that go on as gas falls into a black hole, heats up and emits light,” Genzel ESO/MPE/MARC SCHARTMANNsaid. “It’s a neat window onto a black hole that’s actually capturing gas as it spirals in.”Genzel’s group calculated that the region around the black hole could grow 100 to1,000 times brighter. Chandra X-Ray Observatory and other space- and ground-basedtelescopes will watch the fireworks throughout the year. RJ S t a r D a t e 21

Milky Way Teeming with Billions of Planets, Some Orbiting Binary Stars Scientists presented a hoard of re- more abundant than large gas giants. cent findings on planets around A vastly different study from other stars at a meeting of the Ameri- NASA’s Kepler mission agrees with can Astronomical Society in Austin Sahu’s conclusions on the abundance in January. of small planets. Caltech astronomer Philip Muirhead announced that A study by Kailash Sahu of the his team used Kepler to discover a Space Telescope Science Institute in- miniature solar system in which three dicates that our galaxy contains at planets smaller than Earth orbit a least 100 billion planets. Sahu heads red dwarf star. The smallest planet a large team that looks for planets is about the size of Mars; all are using a technique called gravitational presumably rocky. As red dwarfs are microlensing. When a star passes in the most common stars in our galaxy, front of a more distant one, the nearby the finding suggests there could be lots star’s gravity acts like a lens that bends of small, rocky planets in the Milky and magnifies the distant star’s light. If Way. a planet is orbiting the nearby star, its Kepler also has helped astronomers presence will magnify that light just a discover more examples of a new little bit more, in a characteristic way. class of planets. William Welsh of Knowing precisely how much more San Diego State University mined tells astronomers the planet’s mass. Kepler data to discover two examples of planets that orbit both stars in a Over several years, Sahu’s team binary star system. Such planets are predicted and observed about 40 of called circumbinary. Together with the these microlensing events. Their first case, announced in September, findings indicate that one in six Milky which astronomers thought might be Way stars hosts a Jupiter-like planet, an anomaly, Welsh’s announcement half host Neptune-mass planets, and two-thirds have Earth-mass planets. Overall, their findings indicate the Milky Way holds at least 100 billion planets, and small rocky planets areMARK A. GARLICK Artist’s concept of a indicates there may be millions of NASA/JPL/CORNELL/ARIZONA STATEcircumbinary planet.circumbinary planetary systems in the galaxy. RJBedding Down fora Long Winter’s NapThe Opportunity rover is hunkering down for the Mars winter on the inner rim of Endeavour crater (right). Opportunity’s solar panels are covered with so much dust that it must stand still during the winter and use most of its energy to stay warm. It is studying nearby rocks, however, and scientists are using its radio transmissions to help probe the Martian interior. Op- portunity arrived at Mars in early 2004, and has covered more than 21 miles (34 km). The next rover, Curiosity, which will arrive at Mars in August, is monitoring solar radiation and cosmic rays during its interplanetary cruise. The readings will help scientists determine the risk to Mars- bound astronauts.22 M A R C H / A P R I L 2 0 1 2

© BILL NOWLIN PHOTOGRAPHY pend your bring break with us under starry West Texas skies. We’ve expanded our schedule of tours and star parties March 10-17. Daytime tours include large research telescopes and 100-mile vistas in a beautiful mountain setting. After hours, enjoy one of our famous star parties under the darkest night skies of any professional observatory in the continental United States.To guarantee your spot, make your reservations online at mcdonaldobservatory.org/visitor. EXPANDED SCHEDULE OF GUIDED TOURS* March 10-17: 10:30 a.m., 11:15 a.m., 12 noon, 12:45 p.m., 1:30 p.m., 2:15 p.m., 3 p.m., 3:45 p.m. March 12-14, 16-17: All of the above, plus 4:30 p.m. TWILIGHT PROGRAM AND STAR PARTIES* March 10: Twilight program at 4:45 p.m. and 6:05 p.m. Star party starts at 7:30 p.m. March 12-14, 16-17: Twilight programs will be offered at 6:15 p.m. and 7:35 p.m. Star parties start at 9 p.m. For more information mcdonaldobservatory.org/visitor | toll-free 877-984-7827 *Daylight Saving Time begins March 11. Event times listed for March 10 are Central Standard Time. All other dates are Central Daylight Time. S t a r D a t e 23

Thousands of young stars are being born in Cygnus X, one of the NASA/JPL/CALTECH/HARVARD-SMITHSONIAN CfAlargest stellar nurseries in the galaxy, in this infrared image fromSpitzer Space Telescope. The image shows bubbles blown by hotyoung stars, which compress clouds of gas and dust around them,giving birth to more stars. The long finger-like structures arecolumns of gas and dust that are being eroded by radiation fromthe hot stars. Many contain starbirth activity at their tips. Thewhite regions, which are the hottest in this false-color depiction,are the most vigorous areas of starbirth. Green represents relativelywarm dust, while red is cooler dust and gas. The complex iscentered about 4,500 light-years away in the constellation Cygnus. S t a r D a t e 24