FOCUS ON THE X-RAY SKY

Page 16

MARCH/APRIL 2012 $5

Scaling the Celebrating the centennial of a celestial yardstick

THE UNIVERSITY OF TEXAS AT AUSTIN Mc DONALD OBSERVATORY S t a r D a t e 1 STARDATE STAFF EXECUTIVE EDITOR Damond Benningfield EDITOR Rebecca Johnson ART DIRECTOR MARCH/APRIL 2012 • Vol. 40, No. 2 C.J. Duncan TECHNICAL EDITOR Dr. Tom Barnes CONTRIBUTING EDITOR Alan MacRobert CIRCULATION MANAGER Paul Previte Features Departments MARKETING MANAGER Vincent Perez, III McDONALD OBSERVATORY Merlin 3 ASSISTANT DIRECTOR, 4 Henrietta & the Cepheids EDUCATION AND OUTREACH Sandra Preston A hundred ago, one woman’s patience and tenacity in pouring Sky MARCH/APRIL 10 STARDATE ADVISORY BOARD over photographic plates packed with Dr. David Lambert, Director changed our view of the cosmos The Stars in MARCH/APRIL 12 McDonald Observatory By Barbara Ryden Dr. George F. Benedict Dr. Karl Gebhardt AstroMiscellany 15 Dr. Daniel T. Jaffe 16 A New Focus on the X-Ray Sky AstroNews 20 For information about StarDate or other NuSTAR will scan the heavens to programs of the McDonald Observatory Education and Outreach Office, contact better understand high-energy X-ray Five in Four Days us at 512-471-5285. For subscription phenomena orders only, call 800-STARDATE. Two Ways to Make a Go Boom

StarDate (ISSN 0889-3098) is published By Rebecca Johnson Ready, Aim, Fire! bimonthly by the McDonald Observatory Don’t Miss the Big Show Education and Outreach Office, The Uni- versity of Texas at Austin, 1 University Teeming with Billions of Station A2100, Austin, TX 78712. © 2012 18 Join the Club! The University of Texas at Austin. Annual Bedding Down for a Long Winter’s Nap subscription rate is $24 in the United clubs provide opportu- States, $29 in Canada and Mexico, $40 nities for learning, friendship, and for foreign addresses. Subscriptions may be paid for using credit card or money volunteering orders. The University of Texas cannot accept checks drawn on foreign banks. By Linton G. Robertson Direct all correspondence to StarDate, The University of Texas at Austin, 1 Univer- sity Station A2100, Austin, TX 78712, or call 512-471-5285. POSTMASTER: Send change of address to StarDate, The Univer- On The Cover sity of Texas at Austin, 1 University Station ’s studies A2100, Austin, TX 78712. Periodicals Postage Paid at Austin, TX. StarDate is a of variable stars in the Small registered trademark of The University of

I Magellanic Cloud, seen here in c Texas McDonald Observatory. a recent composite image from the Herschel and Spitzer infrared Visit StarDate Online at space telescopes, changed how we stardate.org measure the cosmos. To learn how, see Page 4. ESA/NASA/JPL-CALTECH/STS

This Page Coming Up Lovejoy, which survived a plunge near The May/June issue will bring you detailed the surface of the , rises above ’s information on the May 20 solar eclipse for 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 in early June .  StarDate less than one million miles from the Sun on We’ll also bring you Merlin’s answers to your  StarDate Magazine December 15. The encounter stripped away its tough astronomy questions and the latest  Frank N. Bash Visitors Center original tail but left the comet itself intact. A new astronomy news. NASA tail quickly sprouted as more ice at Lovejoy’s surface vaporized. 2 MARCH/APRIL 2012 S t a r D a t e 2 Merlin

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

S t a r D a t e 3 OBSERVATORY (2) COLLEGE OBSERVATORY HARVARD

Above: Henrietta Swan Leavitt, about 1910. Background image: This 1905 view of the (LMC) taken at Harvard’s Boyden Station in Arequipa, , is one of many Leavitt studied in her search for stars. Today we know the LMC is a satellite of the Milky Way.

4 MARCH/APRIL 2012 S t a r D a t e 4 century ago this month, a human computer announced a finding that eventually expanded the size of our universe as much as Galileo’s first telescopic look at the stars. A hundred years ago, It was on March 3, 1912, that one woman’s patience Henrietta Swan Leavitt’s finding about the and tenacity in pouring behavior of a specific kind of pulsing star was published in the Harvard College Observatory over photographic plates Circular. Her finding allowed packed with stars changed to discover that the Milky Way is not the whole of the universe, and today remains our view of the cosmos 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 inA 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 , the shift in a star’s apparent position when viewed from different points on Earth’s orbit.

S t a r D a t e 5 By Barbara Ryden In 1838 , after of Charles Darwin. “certificates” from the Harvard painstaking efforts, measured the first The Leavitt family dedication to Annex), Leavitt did additional , to . From the learning extended — unusually for the graduate work in astronomy and tiny parallax he measured, he deduced time — to supporting higher education worked as a volunteer research assistant that the distance from the Sun to 61 for women. Henrietta Swan Leavitt at Harvard College Observatory. Cygni was 657,700 times the average was the oldest of five surviving siblings, The observatory director at the time Earth-Sun distance, equivalent to 10.3 all of whom attended college. Leavitt’s was Edward Pickering, a pioneer in light-years. 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 that standard for determining stellar Cleveland in 1885, enabling her to the vast amounts of data contained on distances, the minuscule angles are enter nearby . (She photographic plates of the stars would difficult to measure, even for the enrolled simultaneously in Oberlin’s require equally vast amounts of data nearest stars. As late as 1910, more conservatory of music, indicating that processing. Thus, Pickering was in need than 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 After her sophomore year, Leavitt in part, because they were thought measure stellar parallax for stars more transferred to the Society for the to have longer attention spans when than 70 light-years away. Compared Collegiate Instruction of Women in doing repetitive tasks, like sewing or to the size of our galaxy, a sphere Cambridge, Massachusetts. At the number crunching. Mainly, though, 70 light-years in radius is ludicrously time, the Society was better known Pickering hired women because he small; it contains about 4,500 of the by its nickname, the Harvard Annex. had a limited budget, and women were hundreds of billions of stars in the To posterity, it is known by the name customarily paid less than a man doing Milky Way. under which it was later chartered: the same job. Henrietta Swan Leavitt was to make . The Harvard Annex a great stride beyond this limited was founded to give young women the neighborhood. She entered this world benefit of the same instruction that without fanfare, unless you count the was received by young men at Harvard Independence Day celebrations on College, taught by the same professors. July 4, 1868, the day of her birth. The sole astronomy course that she She was named after her mother, took there, “Descriptive Astronomy,” the former Henrietta Swan Kendrick, was during her senior year. In that who in turn was named after her course, Leavitt and the seven other mother, born Henrietta Swan. The students were, according to the infant Henrietta’s family tree bloomed course catalog, “given opportunities with doctors and ministers. Her father, for practical studies of the stars … George Roswell Leavitt, had a master’s occasionally with the large telescope degree from Andover Theological of the Harvard Observatory.” Leavitt Seminary. Her father’s father, Erasmus earned an A-minus for the course, Darwin Leavitt, was named as a and was left with a permanent love tribute to a then-famous English of astronomy. After her graduation natural philosopher, the grandfather in 1892 (one of 10 women receiving ARCHIVES, HUV 1210 (9-4) ARCHIVES, UNIVERSITY HARVARD

Leavitt’s annotations on specific stars are preserved on this . 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. HARVARD COLLEGE OBSERVATORY; HARVARD

6 MARCH/APRIL 2012 Any skepticism about the ability of away from astronomy permanently. The sheer number of variable stars women 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 number results. 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’ Miss of The Globe, “These young with such delight … should be left Leavitt is,” wrote Charles Young of women deal with difficult problems uncompleted.” She wanted a paid Princeton. “One can’t keep up with quite 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 winter Her most important result, though, accomplish in a very satisfactory nights, fearing that the cold would is barely mentioned in the 1908 manner the regular routine work of worsen her deteriorating hearing. paper. The last of six tables in the computers at the same fixed rate per “Do you think it is likely,” Leavitt paper contains a list of 16 variables hour as men, but are encouraged also wrote to Pickering, “that I could find in the for to undertake scientific investigation.” employment either in an observatory which the period of variation was or in a school where there is a mild well determined; the periods range enrietta Leavitt made her first winter climate?” from 1.3 days to 4 months. In the Happearance in the Harvard Pickering wrote back immediately, text, Leavitt mentions, “It is worthy College Observatory’s annual report offering Leavitt a position at Harvard of notice that in Table VI the brighter in 1896. “An interesting investigation College Observatory. Although variables have the longer periods.” has been made,” Pickering Massachusetts is not known for its This preliminary result intrigued reported, “by Miss H. S. Leavitt mild winter climate, the job Pickering Leavitt. Unfortunately, she was on the photographic brightness of offered was an indoor position as a delayed in following up her results, circumpolar stars.” However, that year computer. “I should be willing to pay first by illness, and then by her thirty cents an hour in view of the father’s death. The much-postponed quality of your work,” Pickering wrote, culmination of Leavitt’s work didn’t “although our usual price, in such come until March 3, 1912, with cases, is twenty five cents an hour.” the publication of Harvard College Leavitt, in accepting the position, Observatory Circular 173. Although referred to Pickering’s offer as “very the three-page circular went out liberal,” but that may have been sheer over the signature of Pickering, its politeness. Although the average first sentence reads, “The following American wage in 1902 was just 22 statement regarding the period of 25 cents an hour, this was at a time when variable stars in the Small Magellanic just 6 percent of Americans were Cloud has been prepared by Miss high school graduates. For a college Leavitt.” graduate — even if she suffered the The new, larger sample enabled economic disadvantage of being Leavitt to find what she called “a female — a wage of 30 cents an hour remarkable relation between the was not large. brightness of these variables and After Leavitt returned to Harvard the length of their periods.” Leavitt in August 1902, her new project pointed out that since all the stars involved looking at photographic in the Small Magellanic Cloud are plates to find variable stars (stars that at nearly the same distance from change brightness) in the Small and Earth, the differences in the apparent Large , which are brightness of the stars in the galaxy small companion to the Milky are a result of differences in their Way. Since the galaxies are too far true brightness (or ). Thus, south to be seen from Massachusetts, Leavitt could conclude, for example, Leavitt looked at plates that had that a star with a pulsation period of been snapped through a telescope 15 days is twice as luminous as a star near Arequipa, Peru. The fragile glass with a period of 6.6 days. marked a temporary break in Leavitt’s plates were sent by railway to the What Leavitt had discovered was a astronomical career. She spent two Peruvian coast, where they started universal period-luminosity relation years traveling in Europe, and on her their long sea voyage to Boston. The for a particular class of . return to the United States she went fruit of Leavitt’s long hours examining Although she didn’t explicitly use the to Beloit, Wisconsin, where her father these plates is summarized in the title name, the stars Leavitt was looking at had taken up a new ministry. of her 1908 scientific paper “1777 were Cepheid variable stars, named Leavitt, however, could not be kept Variables in the Magellanic Clouds.” after their prototype, .

S t a r D a t e 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 of computing the distance to any ‘Miss Leavitt’s work on the variable stars galaxy in which these special stars in the Magellanic Clouds has afforded us could be observed. Leavitt pointed the way to making a very powerful tool in measuring great the Cepheid period-luminosity stellar distances.’ relation a useful distance indicator. – “It is to be hoped,” she wrote, “that the 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 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 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 , 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. 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 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 confess I/AURA) c that my knowledge of the matter is as yet rather incomplete.” It fell to Shapley to write the regretful reply image of the that Leavitt had died more than three highlighting V1, the Cepheid years earlier (making her ineligible for variable used in 1923 to prove a Nobel Prize). “Miss Leavitt’s work Andromeda lies far outside the Milky Way. on the variable stars in the Magellanic

NASA/ESA/HUBBLE HERITAGE TEAM (STS NASA/ESA/HUBBLE HERITAGE Clouds,” Shapley wrote, “which led to

8 MARCH/APRIL 2012 TIM JONES/DAMOND BENNINGFIELD TIM JONES/DAMOND

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

S t a r D a t e 9 by Alan MacRobert

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

10 MARCH/APRIL 2012 little imagination (and a good dipper-length, and you will Nath (), which just constellation guide) you can Meteor Watch find yourself at bright Arc- missed fame and recognition spot the dog’s dim triangu- turus, the “spring star.” Its by not quite qualifying as The Shower lar head to the upper left of ascent in the eastern evening a first-magnitude star (it is Lyrids Sirius. Adhara is the dog’s sky parallels the rising of tem- magnitude 1.6). It is moving Named for the constellation , the harp, hind leg, Wezen is his rump, which is notable for its brightest star, , 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. Mars and Regulus are at North America. The dipper’s curving han- their highest in the south now dle also can guide you to a at dusk. For a while they were APRIL 1 - 15 Peak Changes are afoot in the lesser-known sight. If you making the moves on each Night of April 21 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 . 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 . providing perfect conditions for viewing the bright star — a have now separated to five de- shower. On the 2nd and 3rd it’s prac- gorgeous yellow-and-violet grees again and will be going tically inside the group, then 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- Arcturus now rules high in above them. star belt is becoming horizon- stellation Canes Venatici, the the eastern sky. But a chal- Or rather, Venus is stand- tal. Orion’s Belt points to the hunting dogs. lenger to its warm-season ing still with respect to your right, roughly to , preeminence is beginning to twilight landscape and the the Pleiades, and Venus. It APRIL 16 - 30 make itself known. Low in the Pleiades are sliding down to points leftward toward ever- And still Venus holds its twi- northeast now, Vega rises by the lower right behind it. And brilliant Sirius. 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- Meanwhile, Capella is night it’s almost upside down, though it is less high every nith as the “summer star.” moving downward, high to high in the north. week. The waxing Moon Venus’ upper right. Follow the curve of the dip- poses near Venus on April 24. Alan MacRobert is a senior With spring under way, per’s handle down and to the And look much closer editor of Sky & Telescope in Orion is tipping down into right, by a bit more than a above Venus for the star El Cambridge, Massachusetts.

ars marches boldly into March (which, like the planet, is Mnamed 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. SIDEBARIt looks HERE like 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. NASA A view of Mars from

Hubble Space Telescope 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.

CEPHEUS TA

CER Alderamin

LA

Etamin

M92 DRA

CO

CASSIOPEIA

M31

M13 URSA

BOREALIS

K

is olar P COR ochab

le

Cluster

PEGASUS

ONA

Doub Mirach

Thuban

M101

Almaak

Alkaid

M33

Alphekka

phak

ALIS M82 Mir

ARD

M51

Algol

Dubhe Alioth

M81

CAMELOP

TRIANGULUM

M63

Merak VENA

Phad CANES

URSA MAJOR URSA

TICI

PERSEUS

ARIES

M97

M3

M106

Capella

Arctur

YNX Pleiades

L

us M38

EAST URIGA

BERENICES COMA

A M36 CETUS M64 zenith

MINOR

LEO

US WEST Denebola M37

Castor UR M1

Alnath

TA Menkar

M35

VIRGO The Aldebaran LEO ollux Sic P GEMINI CANCER ix kle M44 M96 Alhena

Bellatr

M M95 ANUS ECLIPTIC Regulus

Spica ERID M104 M67 ORION on Betelgeuse Procy OS M42 COR SEXT HYDRA CRA ANS MONOCER VUS TER Winter iangle Tr ius Sir M68 M47 LEPUS M41

CANIS MAJOR

COLUMBA V

M Mars

SOUTH S

Charts produced with Voyager II software.

12 MARCH/APRIL 2012 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

Alderamin

CEPHEUS

PEIA Etamin

DRA SIO

S

CO CA

r

le

Cluste

M92

Doub

is

olar P

M13 URSA MINOR URSA

K

ochab

Algol

ALIS

HERCULES phak

ARD

Mir

Thuban

BOREALIS

COR M101

M82

CAMELOP

Mizar ONA

PERSEUS

h Aliot M81

Capella Alkaid Dubhe

M5

Pleiades

Alphekka 1

Merak

SERPENS

Phad

VENA M63

M97

CANES V

M106

URSA MAJOR URSA TICI

URIGA

A

YNX L EAST

M3

M37

US M1

Arctur

M5 zenith

UR TA

BERENICES M35

LEO MINOR Aldebaran WEST COMA

us

e ix

M64

MINI

E

G Denebola Bellatr elgeus ollux t

P N

Be The

Sic R kle CANCER M44 ORIO O LEO N l M96 I M 2 ige S R M I M4 S M95 Regulus N A M67 C

Winter iangle on OS ECLIPTIC Tr M104 SEXT Procy S A pica NS MONOCER

CO rd LEPUS Alph a Sirius R CR 7 VU AT M4 S ER S M41 CANI MAJOR M68 HY DRA V V M M Mars S Saturn S V Venus SOUTH M S

Charts produced with Voyager II software.

S t a r D a t e 13 by Damond Benningfield

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

14 MARCH/APRIL 2012 AstroMiscellany Get StarDate Looking for Neighbors on Your ust about every issue Jof this magazine Smart Phone! brings you tales of newly discovered planets, he free University including a few that follow Tof Texas iPhone app roughly Earth-like now provides a plethora around Sun-like stars. Indeed, of frequently updated the count of known planets in information from other star systems is nearing StarDate and McDonald 700, and almost certainly will Observatory. With the top 1,000 by year’s end. Yet app, you can listen to there is no hint of life from dozens of StarDate radio

these or any other of the billions NASA/ARC/JPL podcasts (excluding the of planets that may populate current day’s show), see the galaxy. what’s in the latest issue In the newly updated The of StarDate magazine, Living Cosmos, , and get weekly skywatching information from StarDate astronomy chairman at the University of Arizona and a Online. You can check out a guide to the , skilled writer for non-academic audiences, explores not read up on the latest research from McDonald only the challenges of finding life in the universe, but the Observatory, see a photo gallery, and get information challenges of life itself: the conditions necessary for life, on visiting McDonald — with an interactive map and the twisting branches of , the threats from the driving directions. The app also will connect you with universe. He also explains our current knowledge of life’s StarDate and McDonald Observatory’s social media sites hardiness and of the birth and evolution of planets, and on Facebook, Twitter, and YouTube. he discusses humanity’s future in space and the chances To get the app, visit: www.utexas.edu/iphoneapp that we’re not the only intelligent life in the universe.

The Living Cosmos: The journal Astronomy Education Review recently Our Search for Life in the Universe compiled a list of astronomy apps for smart phones: By Chris Impey aer.aas.org/resource/1/aerscz/v10/i1/p010302_s1 Cambridge University Press, $20

he lives of planets, stars, and galaxies are presented in color- Tful detail in “The Evolving Universe,” a new exhibition at the Smithsonian’s National Museum of Natural History in Wash- ington, D.C. Developed with the Smithsonian Astrophysical Observatory, it features dozens of large photographs, snapped A through a variety of telescopes, that document the evolution f of the universe over the 13.7 since the . Admission is free. Those who can’t make it to the museum can experience the exhibit through a companion website. Stars burst into life in IC 410, a stellar nursery about 13,000 light-years from www.mnh.si.edu/exhibits/evolving-universe

Earth, in this photo from the exhibit. C HARVARD-SMITHSONIAN

S t a r D a t e 15 A NEW FOCUS ON THE X-RAY SKY NuSTAR will scan the heavens to better understand high-energy X-ray phenomena like exploding stars, black holes, and jets from distant massive galaxies ORBITAL CORPORATION

stronomers 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 by Rebecca Johnson by Rebecca A 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 “The particularly interesting thing about observing Array) is an X-ray telescope that will study the high- high-energy X-rays is that they’re very penetrating,” energy X-ray sky with much greater sensitivity than any Harrison said. “Baggage scanners at the airport, dental previous instrument. X-rays — these are all high-energy X-rays.” NuSTAR is a Small Explorer mission, which means High-energy X-ray telescopes of the past have been it was designed and built much more quickly and inex- fairly crude. They operated much like sophisticated pensively than billion-dollar projects like Hubble Space pinhole cameras rather than telescopes. That’s because Telescope and its fellow Great Observatories. focusing X-rays is notoriously difficult. “Not only will it be a factor of 500 times more sensi- “X-rays only bend very slightly,” Harrison said. “You tive than anything [like it] that’s been launched be- can reflect X-rays, but the key, the challenge is that it fore, it’s a factor of more than 10 times cheaper,” said only works at very glancing angles — much less than Caltech’s Fiona Harrison, the mission’s principal inves- a degree.” The only part of a parabolic mirror that has tigator, in a recent public talk at NASA’s Jet Propulsion such a shallow angle is the edge, which makes for a tiny Laboratory, which manages the mission. collecting area for an X-ray mirror. NuSTAR will probe the universe at wavelengths that To increase the collecting area, which increases the have received scant attention before. Large X-ray tele- instrument’s ability to see fine detail, engineers take

16 MARCH/APRIL 2012 multiple mirrors and stack them in how chemical elements forged in concentric shells inside an X-ray tele- explosions are incorporated Resources scope. NuSTAR has two telescopes, into the next generation of stars. Interne t each using 130 concentric mirror NuSTAR will look outside our NuSTAR Mission Homepage shells. (Chandra has four such shells.) galaxy for supermassive black holes at www.nustar.caltech.edu Special atom-thick coatings on the the hearts of distant galaxies. These mirrors allow them to reflect higher- monster black holes, weighing in at Launch Information www..gov/mission_pages/nustar/launch energy X-rays. 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 Articles the data are transmitted to Earth. census because it can see the ones currently hidden inside dusty galaxies. “X-ray Vision: NASA’s NuSTAR Telescope,” by Fiona Harrison and Charles J. Hailey, Scientific American, hese complicated optics will be In digging into the secrets of February 2011 Tused to tackle a diverse list of supermassive black holes, NuSTAR science goals. One is to take a census will attack one of the toughest “How to Make Telescopes Lenses to Spot Black Holes of black holes, both inside and outside problems astrophysicists currently (for Cheap),” by Cassie Rodenberg, Popular Mechanics, our galaxy. face, Harrison said: They don’t really May 4, 2010 Inside the Milky Way, NuSTAR will understand the relationship between “Urban Jungle,” by Damond Benningfield, StarDate, look for stellar-mass black holes that a supermassive and the September/October 2011 can form when a heavy star burns all of galaxy that surrounds it. Astronomers 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 pulls matter into a swirling disk galaxy’s rate of . 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, XL rocket will propel NuSTAR also will study the and vice versa. ANuSTAR into space. In mid- chemistry of material spewed into Until now, it’s been a difficult March, the rocket will be dropped space by supernova explosions by mystery to probe because the best at 40,000 feet from an L-1011 probing the expanding clouds of pictures of high-energy X-rays coming aircraft flying from the Ronald gas and dust known as supernova from near supermassive black holes Reagan Ballistic Missile Defense Test remnants. The composition of this look like shapeless blobs. Site on the Kwajalein Atoll in the detritus will provide clues about the “This is what we want to do with Marshall Islands. After free falling for explosions themselves, and in turn NuSTAR,” Harrison said. “We five seconds, it will ignite and carry the physics of what goes on inside want to turn [the blobs] into point NuSTAR into low-Earth orbit for its massive stars. These studies also will sources, whose brightness, energy two-year primary mission. help astronomers better understand output, positions, distances we can Once it enters orbit, the spacecraft will deploy a boom that will push its optics out to 10 meters (33 feet) from the detectors. Focusing X-rays requires such a long focal length, and the extendable boom made it possible 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 A Chandra X-ray view of a jet shooting out of realms of the cosmos. , a galaxy with a supermassive black hole at its core. NuSTAR will offer a sharper view of this and other X-ray sources. Rebecca Johnson is editor of StarDate magazine. NASA/CXC/CfA/R.KRAFT

S t a r D a t e 17 JOIN THE CLUB! ASTRONOMY CLUBS PROVIDE OPPORTUNITIES FOR LEARNING, FRIENDSHIP, AND VOLUNTEERING s a StarDate reader, you know that you don’t Not every club belongs to the Astronomical League, but have to be an expert astronomer to enjoy the most do, and its website is a good place to start looking for wonders of the cosmos. But in addition to a club near you. Abooks, magazines, and websites, there is anoth- Additionally, you could contact the physics or astron- er great resource that can help you gain a deeper delight omy department of your local university or community and appreciation for the night sky. I’m talking about an college, or check with local camera shops or astronomy astronomy club. supply vendors. There are at least 250 clubs in the United States, com- prising almost 20,000 members. The largest is the Texas stronomy clubs offer lots of benefits for their mem- Astronomical Society of Dallas, with about 700 members. Abers. First, there’s the sense of camaraderie you get No matter where you live, though, there’s a good chance from being with people who share a passion for the night there’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 1947, is the national umbrella organization for most clubs. late at night outdoors in the cold to look skyward!

BY LINTON G. ROBERTSON TAFRESHI TWAN/BABAK

18 MARCH/APRIL 2012 S t a r D a t e 18 This support can take many forms. where the dark-sky site is in the desert your own star party at the club’s For example, regular meetings are the or mountains. site. This may cost extra, usually paid backbone of any club. They tend to Some clubs even offer telescopes yearly, and you may have to pledge to be light, informative, and extreme- that you can control from your home use it or lose it; policies vary from club ly friendly. Programs usually consist computer. This removes the need to to club. of a short introduction, a welcome trek miles into the outback to get a Many clubs sponsor on-line chats, for newcomers, some information on good look at the sky targets of your texting, and group message boards for what the club is doing that month, desire. members to ask questions, keep up to and the main event: a talk on a topic date on happenings, and notify mem- in astronomy. any clubs offer small specialty bers of unusual skywatching events. Big names in astronomy often give Mgroups, 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-making from a famous comet discoverer, a astrophotography, some like observing classes taught by a master. If you have NASA bigwig, an astronomer who and learning about and planets the time, you can build an instrument has just discovered an extrasolar plan- in our own solar system, some prefer of superior optical quality for the same et, 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 observe If you’re more interested in buying a be someone you otherwise would see variable stars, and others concentrate telescope, club members can steer you only on TV. strictly on meteor showers. And there toward good manufacturers, makes, Once you’ve attended a meeting or are some who are as fascinated with and models, and save you a lot of two and decided to join the club, the the observing equipment as in what grief. Ask questions, and don’t be shy possibilities can be truly remarkable. they’re using it to observe. about asking to look through another Many clubs schedule field trips to The better-developed clubs lease person’s telescope. (Always ask first, NASA centers and science muse- private telescope pads where you can though! It’s good astro-etiquette.) ums. They can also be your gateway come and go as you please, miss the This is a wonderful way to learn about into your local state or community crowds, bring a few friends, and host binoculars, telescopes, filters, vendors, college’s observatory, where you can and the like before taking the plunge. get a look through some pretty big Many a greenhorn has thrown away telescopes. HALFBLUE a lot of money on bad equipment be- Some clubs also have their own cause he or she doesn’t wish to appear “dark-sky sites.” A dark sky site can ignorant by asking questions. range from a farmer’s field in the Club membership also gives you middle of nowhere (with the farmer’s plenty of chances to give back. For permission, of course!), to more so- example, you can help out at public phisticated club-owned sites. The lat- star parties. Clubs stage skywatching ter could offer bathrooms, showers, events to educate and amaze school concrete pads with electrical outlets groups and the public. You also could where members and guests can set up volunteer your time to the club it- their telescopes, barbecue pits, visitor self: sites have to be maintained, and parking, and a club-owned telescope. events are always in need of docents Some clubs have monster telescopes and organizers. that they open to the public twice a There’s work to be done, too, in month or more, and they are happy the field of preserving our night sky to train you, as a club member, to use from the continuing and accelerating it yourself. This is a truly marvelous problem of light pollution; many clubs plus to those who have no telescope work directly with the International of their own, but, for a small mem- esources Dark Sky Association and provide bership fee, will have full use of a R clout when cities decide to put up bad 17-inch, 22-inch, or perhaps even a Interne t street lighting or adopt lighting ordi- 36-inch giant. The Astronomical League nances that threaten the night sky. “Warming rooms” for winter and astroleague.org In short, membership in a club can “cooling rooms” for the heat of sum- enhance your love of the night sky in World Astronomy Clubs mer can be a real blessing, and many astronomyclubs.com ways you never envisioned. clubs even feature meal preparation fa- cilities at their observing sites. These Beginner’s Guide to Stargazing Linton Robertson has been a lover of the amenities can extend your yearly cal- stardate.org/nightsky/bguide night sky since 1956, when his late mother endar of visits to the club site quite International Dark-Sky Association took him as a five-year old to Griffith Obser- a bit, especially if you live in an area www.darksky.org vatory in Los Angeles.

S t a r D a t e 19 by Rebecca Johnson and Damond Benningfield NASA/JPL/SSI (3) From left: Smog-enshrouded against Saturn’s rings and the planet itself; icy Enceladus; the best look at Janus to date Five Moons in Four Days Saturn orbiter to probe cold skies and warm geysers, and look for hidden moons he Cassini spacecraft faces a busy few days in late Saturn’s rings. TMarch. The Saturn orbiter will scan five of the giant The star of the week, though, is Enceladus. Geysers of planet’s moons, taking a look at everything from clouds to and ice shoot into space from “hot spots” near the geysers. 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 is On March 27, Cassini will swoop to an altitude of 46 enveloped by a thick, cold atmosphere, with clouds of frozen miles (74 km) above Enceladus. The craft will approach methane floating through its skies. Cassini will watch the from the nightside, so it will see the spray of ice backlit by motions of the clouds to plot the big moon’s weather. 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 the gravitational balance points near Titan and another moon, hot spots that give them birth. Rhea. And it will make its closest approach yet to the Cassini will stage equally close encounters with Enceladus small moon Janus, which shares an orbit with yet another on April 14 and May 2, providing the most detailed look to moon. The two of them work together to clear out a gap in date at the ice-covered moon and its explosive geysers. DB Astronomers Find Two Ways to Make a Star Go Boom ast year’s Nobel Prize for Physics honored the star or from a collision with a second . Ldiscovery of — a mysterious force LSU astronomers Ashley Pagnotta and Bradley that is causing the universe to accelerate faster as Schaefer examined Hubble Space Telescope images it expands. Astronomers discovered the expansion of four supernova remnants in the Large Magel- by measuring the speeds of exploding stars known lanic Cloud, a companion galaxy to the Milky Way. as Type Ia supernovae in galaxies at different In three of these expanding clouds of gas and distances from Earth. These stars all appear to dust, they found stars near the explosion site that brighten and fade in the same way, making them could have supplied the gas needed to trigger an good “standard candles” for measuring intergalac- explosion. In the fourth, however, they found no tic distances. 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 . 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 Hubble view of a that suring the expansion of the universe, Pagnotta said dwarf, triggering an explosion that blasts the star might have been triggered by the merger during a recent presentation. “They’re still good to bits. It is unclear, however, whether the extra of two white dwarf stars. standard candles even if they come from different

matter comes from a flow of gas from a companion TEAM NASA/ESA/HUBBLE HERITAGE [types of] systems,” she said.

20 MARCH/APRIL 2012 Ready, Aim, Fire! black hole near the center of the gal- Aaxy is firing bullets. Once every eight Artist’s concept of a neutron months or so, it shoots a blob of super- star’s surface cracking during heated gas into space at a quarter of the a powerful ‘starquake’ . MCELROY/LANA DARLENE The black hole, known as H1743-322, is about 28,000 light-years away, in the constellation Scorpius. It’s probably about NASA Turns Off the Lights 5 to 10 times the mass of the Sun, with a companion star that probably resembles for X-Ray Telescope the Sun. The two are so close together that n orbiting X-ray telescope that studied some of the the black hole pulls gas off the surface of the companion, forming a spinning disk Amost bizarre objects in the universe was shut down around the black hole. The gas gets so on January 4, ending a 16-year mission. The telescope, hot that it produces X-rays, although their Rossi X-ray Timing Explorer (RXTE), was showing signs intensity varies. of age, and a review panel recommended ending its Three years ago, a team of astronomers operations to save money for higher-priority projects. monitored the system with a network of Among its many accomplishments: radio telescopes on the ground and an X-ray telescope in space. They found that • Confirmed the existence of , which are shortly after the intensity of the X-rays highly magnetic versions of the crushed stellar peaked, the black hole fired two bullets corpses known as neutron stars. into space. The bullets followed jets of • Provided the first observational evidence that charged particles that shoot into space from black holes spacetime around them like a

the poles of the black hole. NRAO/NASA/GSFC cosmic whirlpool, confirming a prediction from The bullets probably formed as gas piled An artist’s concept shows, Albert Einstein’s theory of gravity. up in the disk around the black hole, form- from top: the black • Provided the strongest confirmation to date of the ing a dense knot. Just before it reached the hole steals gas from its existence of an event horizon, which is the point black hole itself, the knot was blasted into companion star; some of of no return for matter falling into a black hole. the gas forms a ‘knot’ in space along the lines of its magnetic field, • Studied the process by which black holes and which funnel the jets into space. the disk around the black hole; the knot moves neutron stars steal gas from companion stars, and There are several ideas for how that how the gas behaves as it nears the dense objects. happens, but all of them have problems. close to the black hole Watching the whole process of such an itself; magnetic fields eject • Measured a powerful starquake on the surface of a eruption is helping astronomers narrow the knot as twin ‘bullets’ , providing new insights into its inner the list. structure. Don’t Miss the Big Show Coming to the ! he black hole at the center of the Milky Way galaxy is usually pretty quiet. But it Simulation of the cloud’s orbit Tlurks, waiting for tasty morsels to get pulled in by its immense gravity. Astronomers and break-up as it nears the expect to see such a show pretty soon. galactic center (red) and the In 2008, Reinhard Genzel of ’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 up speed as it approaches the Milky Way’s black hole. The cloud of and helium could fall into the spinning disk of material around the black hole within a year. By 2013, 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 into the processes that go on as gas falls into a black hole, heats up and emits light,” Genzel said. “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 to 1,000 times brighter. Chandra X-Ray Observatory and other space- and ground-based telescopes will watch the fireworks throughout the year. RJ ESO/MPE/MARC SCHARTMANN

S t a r D a t e 21 Milky Way Teeming with Billions of Planets, Some Orbiting Binary Stars cientists presented a hoard of re- more abundant than large gas giants. Scent 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 A study by Kailash Sahu of the Philip Muirhead announced that Space Telescope Science Institute in- his team used Kepler to discover a dicates that our galaxy contains at miniature solar system in which three least 100 billion planets. Sahu heads planets smaller than Earth orbit a a large team that looks for planets star. The smallest planet using a technique called gravitational is about the size of Mars; all are microlensing. When a star passes in presumably rocky. As red dwarfs are front of a more distant one, the nearby the most common stars in our galaxy, star’s gravity acts like a lens that bends the finding suggests there could be lots and magnifies the distant star’s light. If of small, rocky planets in the Milky a planet is orbiting the nearby star, its Way. presence will magnify that light just a Kepler also has helped astronomers little bit more, in a characteristic way. discover more examples of a new Knowing precisely how much more class of planets. William Welsh of tells astronomers the planet’s mass. San Diego State University mined Over several years, Sahu’s team Kepler data to discover two examples predicted and observed about 40 of of planets that orbit both stars in a these microlensing events. Their binary . Such planets are findings indicate that one in six Milky called circumbinary. Together with the Way stars hosts a Jupiter-like planet, first case, announced in September, half host Neptune-mass planets, and which astronomers thought might be two-thirds have Earth-mass planets. an anomaly, Welsh’s announcement Artist’s concept of a Overall, their findings indicate the indicates there may be millions of circumbinary planet. Milky Way holds at least 100 billion circumbinary planetary systems in the

MARK A. MARK A. GARLICK planets, and small rocky planets are galaxy. RJ Bedding Down for a Long Winter’s Nap he Opportunity rover is hunkering down Tfor 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. NASA/JPL/CORNELL/ARIZONA STATE

22 MARCH/APRIL 2012 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 © BILL NOWLIN PHOTOGRAPHY © BILL NOWLIN *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 X, one of the A largest stellar nurseries in the galaxy, in this infrared image from f Spitzer Space Telescope. The image shows bubbles blown by hot young stars, which compress clouds of gas and dust around them, giving birth to more stars. The long finger-like structures are columns of gas and dust that are being eroded by radiation from the hot stars. Many contain starbirth activity at their tips. The white regions, which are the hottest in this false-color depiction, are the most vigorous areas of starbirth. Green represents relatively warm dust, while red is cooler dust and gas. The complex is centered about 4,500 light-years away in the constellation Cygnus. NASA/JPL/CALTECH/HARVARD-SMITHSONIAN C NASA/JPL/CALTECH/HARVARD-SMITHSONIAN

S t a r D a t e 24