SkyAndTelescope the essensial magazines of astronomy

spectrum ® Amateurs’ New Era I t’s rare to be present at a defining moment — a time when things change, a time when a paradigm shifts I’ve been lucky, attending such events as the 1963 Texas symposium where gravitational physics was reborn and the 1980 Tucson conference where ideas for today’s giant telescopes crystallized This June I may have attended another, at the summer meeting of the American Astronomical Society (AAS) Its highlight was a full day of presentations by amateurs and by professionals who work with them — the first such happening in 190 meetings of the society On stage, as you might expect, were “overachievers” like Don Parker, who reinvented planetary imaging To me, Don’s legacy goes much farther His work signals an epiphany to amateurs — that technology allows them to produce professional-quality work Yet even more significant were presentations by folks without international reputations I cochaired the session with Larry Marschall of Gettysburg College, and we got a lot of instant feedback All the professionals buzzed that all the amateurs did first-class jobs And they meant it “Let’s this every year!” echoed again and again Reaffirmation? Reawakening? Reconnection? Technology has made amateur astronomers invaluable in many arenas of “small science” — a term I’ve understood only in the context of little or no money So it’s important to bring every serious enthusiast into contact with professionals, so he or she can be guided toward promising avenues and coached in the way science is done If the trend we see today is a guide, research-oriented amateurs will tend to flourish as individuals, or in small, project-specific groups, rather than as members of a collective with an omnibus program Given both the capability and freedom modern technology offers, why shouldn’t amateurs think and work independently? As Albert Van Helden and Thomas Hankins wrote: “Because instruments determine what can be done, they also determine what can be thought.” Thoughts from collectives usually bore me because they stress commonality rather than individuality Where to go from here? Further sessions at AAS meetings seem obvious I also think pro/am sessions at major amateur gatherings would be extremely popular Organizer Alert! September 1997 Sky & Telescope ©1997 Sky Publishing Corp All rights reserved The Essential Magazine of Astronomy focal point Golden Opportunities To his surprise and delight, David Lustick has discovered that NASA loves to share its successes with curious correspondents I was thirteen in the summer of 1976 and the proud owner of a hand-me-down telescope from my older brother, Ian It was not much more than a glorified spyglass On many summer nights I would try in desperation to use this device, with very little luck What kind of magic does it take, I wondered, to actually witness the marvels of the night sky? It seemed I would never get to participate firsthand in the great exploration of the cosmos As it turned out, my cousin, Rick, would soon solve my problem Rick was a year older than I — and at 13 a year is an eternity He always seemed to be one step ahead in everything As I arrived at his house one Thanksgiving, Rick said, “Dave, come up to my room I got something in the mail yesterday that I think you’ll like.” Once upstairs, he picked up a Golden Packet from his desk that had “JPL” printed in the upper-left corner He opened the envelope and carefully withdrew several 8-by-10-inch lithographs Holding them by the edge, he passed them to me for inspection I knew exactly what they were: images from the surface of Mars from the Viking landers The quality of the pictures I held was so amazing that I stared at them dumbfounded ”Where did you get these?” I asked Rick explained that he’d written to the Jet Propulsion Laboratory in Pasadena, California, and he received the envelope full of images in reply The idea that photographs and information like this could be gotten — free — just by writing a letter was unbelievable to me Upon returning home, I immediately sent a letter to the address Rick had given me Finally, 21⁄2 months later, I received the same Golden Packet from JPL, stuffed full with the same prints and literature about Mars I would study and restudy the images for hours, poring over the descriptions on their backs Vicariously I was there with the Viking landers as they tested the soil and atmosphere I saw dust storms and ancient riverbeds, sunrises and sunsets, frost forming in the morning, and fresh trenches dug in the afternoon 10 September 1997 Sky & Telescope I was hooked on astronomy, and my appetite for more data became voracious I wrote more letters asking for more pictures and information In time I moved on from the plains of Mars to the Voyager encounters with Jupiter Then came Saturn with its spectacular rings and, oh, the joy of discovery! Through NASA, I was actively exploring the solar system With every new flyby, I wrote more letters and received more Golden Packets by mail No matter if I was at college, my first job, graduate school, or on a South American adventure — I have stayed my course of exploration for 20 years, crisscrossing the solar system from Uranus to Venus and back to Jupiter Each letter has triggered a mountain of information and breathtaking images in response Today, we have more than robotic probes to inspire awe The Hubble Space Telescope allows us to explore the farthest reaches of the universe Thanks to the World Wide Web, I can log on to any one of a hundred different sites and download virtually any picture ever taken in space! Young people today have so much data available at their fingertips, it amazes me that anyone can deal with it in a relatively coherent fashion (Will Internet surfers ever have the same appreciation for their digital downloads that I had for my highly coveted envelopes? I wonder.) As any passionate explorer would do, I now share the joy of astronomy with everyone I know I am a teacher, and I can always find a reason to have all my students write to NASA From second graders to seniors, they have all received their Golden Packets And if just one student gets turned on to astronomy from this exercise, then all the letter-writing will have been worth it Who could have predicted that my cousin Rick’s lithographs of the Martian surface would have had such an impact on my life? With more dazzling missions under way and planned for the future, any one of us can be onboard, vicariously exploring, learning, and dreaming Come to think of it, with discoveries happening at such breakneck speed, I’d better get busy — I’ve got letters to write! Founder of the American Astronomy Club in São Paulo, Brazil, David Lustick often conducts public star parties to showcase the southern skies He can be reached by e-mail at dlustick@eagle.aegsp.br Readers wishing to follow Lustick’s lead should write to: Jet Propulsion Laboratory, Public Services Office, Mail Stop 186-113, 4800 Oak Grove Dr., Pasadena, CA 91109 (e-mail: newsdesk@jpl.nasa.gov) ©1997 Sky Publishing Corp All rights reserved letters ® A Fair Portrayal I am a Seventh-day Adventist whose church arose from the Millerite movement, so the account of the “Millerite Comet” of 1843 in the May issue (page 46) caught my immediate attention The author, Bradley E Schaefer, pleasantly surprised me, and I was glad he didn’t mention ascension robes, widespread insanity, or any of the other falsehoods sometimes associated with the Millerites An Adventist editor and writer, Francis D Nichol, handily refuted all these in his exhaustively researched 1944 book, The Midnight Cry Nichol did confirm Schaefer’s account of the other “signs in the sky” noted by the Millerites Schaefer’s sidebar about the fictitious “virgin sacrifice” in 1910 and the stories of later “comet panics” show that such yarns, tendencies, and charlatanry were hardly confined to the sensational atmosphere of mid-19th-century journalism Unfortunately, sensationalism sometimes wins, at least temporarily, over truth Richard Rimmer Box 6005 Madison, TN 37116 Antlia Dwarf Galaxy Not New The report about a “new” nearby galaxy in Antlia (June issue, page 15) is an example of researchers not doing their homework The announcement by Michael Irwin and his colleagues is actually the fourth time this object has been reported as a nearby galaxy The first three came between 10 and 20 years ago when astronomers scanned early southern-sky surveys for new objects The galaxy is first mentioned in a list published by Harold G Corwin and his collaborators in 1978, where it is described as being a resolved dwarf This paper was an initial preview of what became the more comprehensive Southern Galaxy Catalogue (SGC), published in 1985 Here the Antlia dwarf is also described as being visible on prints from the first Palomar Observatory Sky Survey (I checked, and it is) In the same year, J V Feitzinger and T Galinski included the object in a list of southern dwarf galaxies found on plates taken with the European Southern Observatory’s Schmidt 12 September 1997 Sky & Telescope camera Finally, in 1987 Halton C Arp and Barry F Madore published their Catalogue of Southern Peculiar Galaxies and Associations, which includes the galaxy in a collection of other dwarfs and mentions that it is resolved into stars And these catalogs have not gone unnoticed For instance, Pascal Fouque and his colleagues found radial velocities for many southern dwarfs in the SGC, and their value for the Antlia dwarf (about 360 kilometers per second) is a sure sign that the galaxy is nearby Its location can hardly be described as “where astronomers thought there was only blank sky.” The contribution of Irwin’s group is that they made a color-magnitude diagram for the brightest stars in the galaxy, providing a better estimate of its distance They did not discover it The same news note makes passing reference to the Tucana dwarf, which was also listed in the SGC as a resolved dwarf well before being rediscovered in 1990 And finally, a decimal point was misplaced when the Antlia galaxy’s coordinates were given Its correct right ascension is 10h 04.1m Brian Skiff Lowell Observatory 1400 West Mars Hill Rd Flagstaff, AZ 86001-4499 bas@lowell.edu How Important Is ForwardScatter Geometry? Joseph Marcus’s letter in the April issue (page 8) suggested that forward-scattering geometry might play a significant role in the apparent brightness of many great comets Laboratory experiments have repeatedly demonstrated the effect of forward scattering — at very small angles brightness gains of a thousand times or more have been recorded But in my experience, empirical evidence for this phenomenon among comets is lacking for visual observations If truly significant, the forward-scatter effect should reveal itself often, appearing as a dramatic but brief increase in brightness not necessarily corresponding to either the comet’s anticipated date of maximum brightness or time of perihelion passage ©1997 Sky Publishing Corp All rights reserved The Essential Magazine of Astronomy SEPTEMBER 1947 “A C B Lovell, director of radar research, [announces] the discovery of a new meteor shower occurring in daylight For the Eta Aquarid shower it became obvious that ‘the meteor stream visible to astronomers was merely the beginning of an extremely active belt stretching towards the Sun.’” These observations were conducted at Jodrell Bank, England, where meteor observing at radio wavelengths was a mainstay immediately after World War II Only later did Jodrell Bank become famous for galactic and extragalactic research, particularly because of its 250-foot, fully steerable telescope 50&25 Y E A R S A G In my 40 years of comet observing I know of only one incontrovertible case of this type — that involving the Sungrazing comet C/1979 Q1 (1979 XI) On the other hand, numerous instances can be cited where forward scattering might have been expected to show itself but did not Of the examples Marcus cited, I can find no compelling evidence in the comets’ light curves that they behaved other than expected Perhaps the most damning evidence against forward scattering is that its effect does not appear in dozens of lessspectacular comets that share the same favorable geometry as great ones If detectable by visual means, wouldn’t anomalous brightness enhancements have been noted and fully verified long ago? John E Bortle W R Brooks Observatory 39 Gold Rd Stormville, NY 12582 O Exaggerated Elevations SEPTEMBER 1972 “The title Physical Cosmology seems to promise a new look at the structure and evolution of the physical universe on the grandest scale yet revealed by our observations Indeed, this offering is rather a new look Although by comparison with other texts the theoretical development of relativistic cosmologies is played down, the author applies many sophisticated topics in microscopic physics to problems that may bear on cosmology.” The publication of this volume by P J E Peebles was arguably a watershed event, for it served a generation of students concerned with the “Grand Scheme.” A revised and much expanded work (including more than 200 pages devoted to relativistic cosmology) appeared in 1993 under the title Principles of Physical Cosmology “R F Griffin [gives his] visual impression of the great globular star cluster Messier 13 in Hercules, as viewed with the 200-inch reflector “ ‘The dense central part is several field diameters wide, and you can see the colours of the stars down to about the fifteenth magnitude In addition to the densely packed mass of individually resolved stars, in good seeing the whole cluster shows a granular background — it’s rather like looking into a bowl of sugar! There must be perhaps 200 [red giant stars] and you can pick them out at sight, even in the very middle of the cluster.’” 14 September 1997 Sky & Telescope In the April issue (page 63) John Mosley reviews the CD-ROM Mars Rover He notes that the vertical scale is “exaggerated considerably for drama” and he wishes he could reduce it I’ve noticed that many images of Venus and Mars have this distortion purposefully introduced When I view them I have to use a mental filter to imagine what the planet “really” looks like I would think the whole purpose of creating these images would have been to show just that Instead it seems that the decision makers think we would be bored with realistic images, and so they make the mountains and canyons impossibly steep to introduce an artificial “gee whiz” factor I’d strongly prefer to see the planets as they really are Mark Lancaster 22 Havenfield Dr Baltimore, MD 21234 mark-l@vm.vips.com Amateur Participation at Pic du Midi The plan to secure Pic du Midi Observatory’s future as a research institution by opening it to tourists includes the construction of a visitors’ center (S&T: October 1996, page 13) But the daily functioning of this facility will depend on the participation of amateur astronomers Members of the Pic 2000 project, ©1997 Sky Publishing Corp All rights reserved as it is called, would like to hear from amateur astronomy clubs worldwide that might be interested For more information please send a fax to +33-5-61-3328-88, or contact me at the address below Marc Montagne Observatoire Midi-Pyrénées 14, Ave Edouard Belin F-31400 Toulouse France montagne@obs-mip.fr 1999 Eclipse Bulletin On August 11, 1999, a total eclipse of the Sun will be visible from a narrow corridor traversing the Eastern Hemisphere (S&T: August 1996, page 51) A new NASA solar-eclipse bulletin covering the event is now available This 128page publication, prepared in conjunction with the International Astronomical Union’s Working Group on Eclipses, includes geographic coordinates and maps of the eclipse path, physical ephemeris of the umbra, local circumstances for some 1,400 cities, and much more Single copies of the bulletin are available at no cost by sending to one of the addresses below a 9-by-12-inch self-addressed envelope stamped with sufficient postage for 12 ounces (340 grams) and with “August 1999” printed in the lowerleft corner Cash or checks cannot be accepted Readers from outside the United States and Canada may send nine international postal coupons The bulletin is also available via the World Wide Web at http://umbra.nascom.nasa.gov/eclipse/ Fred Espenak Planetary Systems Branch, Code 693 NASA/Goddard Space Flight Center Greenbelt, MD 20771 espenak@lepvax.gsfc.nasa.gov Jay Anderson Environment Canada 123 Main St., Suite 150 Winnipeg, MB R3C 4W2 Canada jander@cc.umanitoba.ca When Writing Write to: Letters to the Editor, Sky & Telescope, P.O Box 9111, Belmont, MA 021789111 Please limit your comments to no more than 250 words Letters selected for publication may be edited for clarity and brevity Due to the volume of mail, not all letters can receive personal responses S&TNEWSWIRE LATE-BREAKING ASTRONOMICAL NEWS Pathfinder Reaches Mars (ARES VALLIS, MARS) In the predawn darkness of July 4th, the red planet gained two new inhabitants: NASA’s Mars Pathfinder and its six-wheeled companion, Sojourner (seen here before deployment) A week after bouncing onto this ancient, boulder-strewn floodplain, the lander and rover had surveyed the surroundings with stereo cameras, radioed weather conditions, and sampled rock and soil chemistry Pathfinder’s first results will appear in next month’s issue Courtesy NASA/JPL First Images from Orbiting Radio Dish (KANAGAWA, JAPAN) An orbiting radio telescope has success- fully linked up with Earthbound instruments to produce its first high-resolution images Astronomers have long combined the signals from separate radio telescopes to better resolve structure in cosmic radio sources With individual antennas spanning the globe, very long baseline interferometry (VLBI) routinely provides the resolution, if not the sensitivity, of a radio telescope almost as large as the Earth However, even that has failed to resolve a number of enigmatic objects such as quasars and active galaxies So an international consortium led by Japan’s Institute of VLBA alone VLBA + HALCA Beam size ISAS Beam size 16 September 1997 Sky & Telescope Space and Astronautical Science built the Highly Advanced Laboratory for Communications and Astronomy (HALCA), a spacecraft with an 8-meter-wide radio telescope (July issue, page 25) HALCA’s eccentric, six-hour orbit reaches as far as 21,000 kilometers from Earth, roughly tripling the width, and therefore the resolution, of ground-based VLBI networks The technique has been exploited before A member of the Tracking and Data Relay Satellite System (TDRSS) was used as a radio telescope in sync with several ground-based instruments in the 1980s But HALCA is the first operating satellite designed expressly for radio astronomy (A Russian predecessor remains to be completed) Astronomers hope to use HALCA to dissect the jets and lobes of sources like the quasar Q1156+295 (shown at left), whose core and jet were scanned by the spacecraft on June 5th in tandem with the Very Long Baseline Array (VLBA) The ovals in the lower-left corners show how the resolution improves with the satellite’s addition A July 4th newsletter from the VLBI Space Observatory Program reports that two of HALCA’s three receivers are working better than anticipated, although the third — designed in part for water-vapor emissions from masers circling black holes — has somehow 0.01 arcsecond lost 90 percent of its sensitivity ©1997 Sky Publishing Corp All rights reserved Amateur Finds Aten Asteroid Pele’s Plume (TUCSON, AZ) Roy Tucker has made the first amateur discovery of an asteroid in the rare class of Earth-approachers known as Atens The discovery netted Tucker the first $500 Benson Prize, announced only weeks earlier at the American Astronomical Society meeting in North Carolina In a deliberate search for unusual asteroids begun last May, Tucker images the sky with a homemade CCD camera and 14-inch Celestron Schmidt-Cassegrain telescope at his backyard Goodricke-Pigott Observatory near Tucson, Arizona “To filter out the distraction of most mainbelt asteroids, I concentrate on areas away from the ecliptic,” he told Sky & Telescope Tucker compares pairs of images in order to reveal moving objects He had searched only 28 hours (and accumulated 83 image pairs) when he found an 18th-magnitude asteroid moving rapidly against the stars near the border of Serpens and Scutum on the evening of June 28th (June 29th Universal Time) After securing confirming observations the next night, Tucker reported precise positions of his object to the Minor Planet Center in Cambridge, Massachusetts, where Gareth Williams solicited additional positions with a posting on the World Wide Web By July 2nd, observations from Australia, the Czech Republic, Italy, Japan, and the United States confirmed that the unusual object was an Aten-type asteroid, only the 25th known It was designated 1997 MW1 Like Apollo asteroids, Atens have orbits that cross Earth’s orbit Atens also have distances from the Sun that, on average, are less than Earth’s, and thus orbital periods less than one year 1997 MW1 circles the Sun every 332 days at a distance ranging from 91 to 189 million kilometers (0.61 to 1.26 astronomical units) The Benson Prize was established to spur amateur interest in nearEarth asteroids Space Development Corporation chairman James W Benson created the $500 prizes for the first 10 amateur discoveries of asteroids that cross Earth’s orbit Details are available on the World Wide Web at http://www.skypub.com/benson/prize.html (FLAGSTAFF, AZ) A newly JOHN SPENCER AND NASA released image from the Hubble Space Telescope shows the Jovian moon Io spouting off as never before On July 24, 1996, HST captured an eruption of the giant volcano Pele, the first such outburst to be imaged from Earth’s vicinity A towering plume, seen in silhouette on the lowerleft limb, extended more than 400 kilometers into space — topping the height seen during Voyager 1’s flyby in 1979 The false-color view shown here combines an ultraviolet-filtered image (in which the eruption is obvious) and a violet one (in which it’s absent) Based on this color dependency, John R Spencer (Lowell Observatory) believes the plume consists of very fine dust particles, sulfur dioxide gas, or some combination of both To attain this height the material had to be ejected at 1.1 km per second, roughly half of the escape velocity on Io Pele’s spoutings are so large in part due to Io’s low gravity and lack of a dense atmosphere, and in part because the eruptions are simply more energetic than those here on Earth “Ironically,” Spencer notes, “the presence of Jupiter in the background, which rendered the plume visible, was not intended and due to an HST scheduling error.” Details will appear in a forthcoming issue of Geophysical Research Letters NEAR Spacecraft Spies Mathilde (LAUREL, MD) Images of the main-belt asteroid 253 Mathilde acquired by the Near Earth Asteroid Rendezvous (NEAR) spacecraft have left mission scientists both gratified and amazed The probe flew a mere 1,200 kilometers from the minor planet on June 27th, taking more than 500 snapshots at visible and nearinfrared wavelengths According to mission director Robert W Farquhar (Johns Hopkins University), the resulting views proved “far better than we thought possible” for a close-range flyby at 9.9 kilometers per second The encounter was made even more difficult because the spacecraft approached from the asteroid’s unlit side The largest asteroid yet visited by any spacecraft, Mathilde measures 57 by 53 by 50 km — a bit smaller than anticipated Ground-based spectra had suggested that the asteroid is a dark, carbon-rich (type C) body, and NEAR’s findings bear this out Mathilde uniformly reflects only percent of the sunlight falling on it But no one expected this little world to be so severely battered “At first glance,” notes investigator Joseph Veverka (Cornell University), “there are more huge craters than there is asteroid.” Another puzzle is why Mathilde is much less massive than anticipated, cratered hollows notwithstanding Also not yet understood is why Mathilde rotates so slowly, once every 17.4 hours With a price tag of $108 million, NEAR represents the first of NASA’s lowcost Discovery missions (S&T: September 1995, page 6) The spacecraft’s primary objective is a long-term study of the Earth-approaching asteroid 433 Eros, which it will reach in January 1999 The asteroid 253 Mathilde bears at least five craters more than 20 kilometers across The NEAR spacecraft captured this view just prior to its June 27th flyby from a distance of 2,400 km Courtesy NASA and JHU/APL ©1997 Sky Publishing Corp All rights reserved Sky & Telescope September 1997 17 HANS H HEYER, EUROPEAN SOUTHERN OBSERVATORY NEWSNOTES Awaiting the Giant Telescopes Last year’s dedications of the second 10-meter Keck Telescope (S&T: July 1996, page 13) and the 11meter Hobby-Eberly Telescope (February issue, page 11) are only the beginning of a wave of large telescopes coming online Around the turn of the 21st century, the first of a dozen more 61⁄2-meter or larger instruments will be serving astronomers around the world Here’s an update of where construction stands: Subaru Telescope, Mauna Kea, Hawaii The dome and telescope structures are complete Its 8.3-meter mirror, now undergoing final polishing, will be transported to the mountain at the end of this year First light is expected before August 1998 Multiple-Mirror Telescope, Mount Hopkins, Arizona This telescope will soon no longer be “multiple.” Observations are to cease toward the year’s end so that the telescope’s six 1.8-meter mirrors can be replaced by a single 6.5-meter primary (The old “MMT” acronym will be preserved, but its new meaning has yet to be announced.) With modifications to the telescope structure nearly complete, first light for the new MMT is expected sometime in 1998 Very Large Telescope, Cerro Paranal, Chile The VLT consists of four identical 8-meter telescopes, currently in varying states of construction As of June, the initial telescope’s enclosure was undergoing final testing, while on the inside, the base of the altitude pedestal has been laid The first polished primary mirror should be shipped to Chile later this year, where it will be coated on site First light is expected in early 1998, with the other three reflectors to follow in 1999 and 2000 Large Binocular Telescope, Mount Graham, Arizona The first of two 8.4-meter mirrors was “topped off ” at the end of April at Steward Observatory’s Mirror Laboratory in Tucson, Arizona Inspection of the largest single glass mirror yet made revealed that several square Above: The four enclosures for the Very Large Telescope atop Cerro Paranal in Chile When completed in the year 2000, the quartet will be linked to create a powerful optical interferometer Left: Workers at the Steward Observatory Mirror Laboratory distribute borosilicate glass over an 8.4-meter mirror blank destined for the Large Binocular Telescope After placement, the mirror was reheated and spun in a rotating oven, allowing the glass to spread and adding several millimeters to the blank’s front surface Mirror photo by Lori Stiles, University of Arizona 18 September 1997 Sky & Telescope ©1997 Sky Publishing Corp All rights reserved Each of the two telescopes for the dual-hemisphere Gemini Project has an 8.1meter aperture Courtesy NFM Technologies meters of the surface were thinner than the 28 millimeters required to polish it safely So two more tons of glass were placed onto the 17-ton blank on April 25th, and the mirror’s crest was remelted over the following weeks (August issue, page 22) Meanwhile, atop nearby Mount Graham, the telescope’s foundation and the ring wall that will support the movable structure are in place With the telescope’s design now finalized, project managers are reviewing construction bids Magellan Project, Las Campanas, Chile The first of the planned twin 6.5-meter telescopes is to be shipped to its completed mountaintop enclosure in August The mirror, now undergoing final polishing, should be installed in mid-1999, with first light expected shortly thereafter Construction of the second telescope is also scheduled to begin by August Gemini Project, Mauna Kea, Hawaii, and Cerro Pachon, Chile This project calls for twin 8.1-meter instruments in the Northern and Southern Hemispheres The structure on Mauna Kea is ready, and the finished telescope frame should get there in August Both mirror blanks have been fabricated and are currently being ground and polished First light on Mauna Kea is planned for the end of 1998 Construction of the Chilean facility is expected to begin in September Our Galaxy’s Oldest Open Cluster Open star clusters like the Hyades are generally younger than the much more massive conglomerations called globular clusters But Berkeley 17, a diffuse stellar swarm in Auriga, appears to be 10 to 13 billion years old — raising the possibility that some of the stars in the Milky Way’s disk were born shortly after the Big Bang Randy L Phelps (Carnegie Observatories) used the 2.1-meter reflector atop Arizona’s Kitt Peak to measure the brightnesses and colors of Berkeley 17’s stars, confirming his suspicions of its extreme age Phelps’s deductions are detailed in the Astrophysical Journal for July 10th NGC 5084: A Cannibalistic Heavyweight You probably wouldn’t suspect NGC 5084 of throwing its weight around After all, the 12th-magnitude Virgo inhabitant doesn’t look too unusual when viewed with a backyard telescope But recent measurements suggest that the lenticular spiral is the most massive galaxy of its type and it has swallowed up numerous neighbors during its lifetime For several years now, astronomers have used small satellite galaxies — our Milky Way’s Magellanic Clouds being a prime example — to “weigh” the much larger spirals they orbit Such censuses have typically relied on only a couple of satellites for each spiral Now Claude Carignan (University of Montreal) and his collaborators have measured the line-of-sight velocities of eight dwarf galaxies that appear to orbit NGC 5084 They did so with a multiobject spectrograph on the Anglo-Australian Telescope at Siding Spring, Australia In the Astronomical Journal for May, the astronomers use the dwarf galaxies’ motions to ascribe a total mass of to 10 trillion Suns to NGC 5084 — making it the “heaviest” disk galaxy known In addition they noted whether each satellite was moving away from Earth at a faster or slower speed than NGC 5084 itself This showed an intriguing trend — nearly all the dwarfs follow retrograde orbits (That is, they appear to circle NGC 5084’s center in the opposite way than the galaxy’s own stars and gas.) Computer models have shown that dwarf galaxies in pro- grade orbits are much more likely than retrograde orbiters to be consumed by tidal interactions with the parent spiral Thus, NGC 5084 presumably once had a larger population of satellite galaxies but has absorbed many of them A subtle, 5° tilt in NGC 5084’s outer disk may attest to such cannibalistic accretion events in the galaxy’s past Our Milky Way is in the act of consuming a satellite galaxy of its own, the so-called Sagittarius dwarf (S&T: August 1994, page 14) ©1997 Sky Publishing Corp All rights reserved AURA / STSCI This degree-wide portion of the Palomar Observatory Sky Survey shows NGC 5084 (center) along with eight objects (circled) that appear to be dwarf galaxies in orbit around it The dwarfs’ motions imply a record-setting mass for NGC 5084 of to 10 trillion Suns North is up Sky & Telescope September 1997 19 NEWSNOTES The Great Wall: A Cosmological Mirage? places by the excess gravity of superclusters As a result, says Praton, “galaxies in the neighborhood of a [super]cluster are squashed together” in redshift maps This amplifies the prominence of those filaments that happen to lie at right angles to any sight line from Earth (The effect is illustrated at right below.) The bull’s-eye effect is further enhanced, Praton suggests, by random galaxy motions in the densest regions Only the line-of-sight component of any galaxy’s motion is reflected in a redshift map; this reinforces the illusion that our vantage point is somehow special Praton and her colleagues demonstrate these effects in the Astrophysical Journal Letters for April 10th John P Huchra (Harvard-Smithsonian Center for Astrophysics), who helped discover the Great Wall, admits that such effects may enhance the prominence of the Great Wall and the Perseus-Pisces chain But he nevertheless notes that numerous measurements have demonstrated the reality of these structures This suggests they are no mere artifacts Furthermore, Huchra says, there is nothing unusual about our lying in a cosmic bubble, since the universe at large seems to be pervaded by such structures (S &T: July 1996, page 15) Finally, he notes that in the Great Wall, peculiar velocities of galaxies — motions that are caused by the supercluster’s gravity — The map at left shows the actual positions of 52,000 galaxies in a computer simulation of a uni- are small As a result, says Huchra, “it’s verse like our own The map at right is what astronomers at the center “see” when they measure not clear to me that the peculiar velociredshifts, not distances, and when they limit themselves to the 20,000 galaxies brighter than ties can actually cause the [appearance of] overdensity in the redshift maps.” 17th magnitude Each panel spans billion light-years Courtesy Elizabeth Praton Surveys have revealed that thousands of galaxies eerily surround our own Milky Way in several arclike filaments, each hundreds of millions of light-years long (S &T: June 1994, page 11) Many astronomers have wondered why we appear to be encircled by these large-scale structures, which go by names like the Great Wall and the Perseus-Pisces Supercluster A Copernican answer to this quandary has now been offered by Elizabeth Praton and Margaret McKee (Grinnell College) and Adrian Melott (University of Kansas) The so-called Hubble law allows the redshifts, or recession speeds, of galaxies to be taken as proxies for those objects’ distances (which are much harder to measure) But the universe’s expansion is retarded in A Lopsided Universe? A remarkable claim made headlines in April: the universe as a whole has a preferred direction Borge Nodland (University of Rochester) and John P Ralston (University of Kansas) announced this finding in the April 21st Physical Review Letters Their universities’ press offices promoted the story to news media as a stunning cosmological breakthrough But some astronomers find the analysis flawed Nodland and Ralston’s case for an asymmetric universe came from distant galaxies that emit radio waves Often those waves are slightly polarized (This means the electric-field component of an incoming radio wave has a slight tendency to be oriented a particular way.) Nodland and Ralston compared radio-wave polarization in 160 galaxies with those galaxies’ own orientations on the sky, working on the assumption that the two are somehow related The data had already been corrected for Faraday rotation, the twisting that happens when radio signals pass through cosmic magnetic fields But Nodland and Ralston discerned an additional rotation from galaxies along an axis from Cancer to Aquila This would imply that electromagnetic radiation travels differently in different directions, upsetting the cherished cos20 September 1997 Sky & Telescope mological notion of an isotropic universe (one that looks the same in all directions) Within weeks, however, other astronomers contested the evidence for cosmic asymmetry Sean M Carroll (University of California, Santa Barbara) and George B Field (Harvard-Smithsonian Center for Astrophysics) reexamined Nodland and Ralston’s data and found the result statistically insignificant And a third group scrutinized the polarization properties of 26 quasars but found no evidence for the controversial effect Both counterclaims are being reviewed for publication Of course, the universe does have a preferred direction — that of the solar system’s motion toward southern Leo at one one-thousandth the speed of light The motion was first revealed by hot and cold spots 180° apart in the microwave radiation from the Big Bang (April issue, page 15), and it lies within 30° of the radio-galaxy vector Ronald N Bracewell and Von R Eshleman (Stanford University) see a natural connection According to Einstein’s special theory of relativity, the Sun’s motion should gently rotate the electromagnetic waves through which it travels If this interpretation holds, Nodland and Ralston have simply found an independent means to track our motion with respect to distant galaxies The Stanford study has been submitted to Physical ReviewLetet rs ©1997 Sky Publishing Corp All rights reserved NEWSNOTES King of the Kuiper Belt A sizable body recently found beyond Neptune has a unique orbit with links to the distant Oort Cloud of comets When first spotted last October 9th by Jane Luu (Harvard University) and three colleagues, 1996 TL66 was 51⁄4 billion kilometers (35.2 astronomical units) from the Sun That put it squarely in the realm of more than 40 other trans-Neptunian objects collectively known as the Kuiper Belt And its red-light magnitude of 20.9 made 1996 TL66 the brightest of the entire lot — save for Pluto and its moon Charon Assuming it has a relatively dull surface, the new find could be up to 500 km across 20 a.u But after a few months’ tracking by New Mexico amateur Warren Offutt and others, it became evident that this distant denizen has an orbit unlike any other in the Kuiper Belt “It was clear,” Luu and 1996 TL66 six collaborators write in Nature for June 3rd, “that (~1600 A.D.) the object had to be close to the perihelion of a much more eccentric orbit.” The looping track proved to have a semimajor axis of 84 a.u and a period of nearly 800 years Only one other object, designated 1996 RQ20, is believed to venture much beyond the tangle of known Kuiper Belt orbits A trio led by Eleanor F Helin (Jet Propulsion Laboratory) discovered it last September 6th with the 5-meter Hale reflector on Palomar Mountain Ranging 33 to 61 a.u from the Sun, 1996 RQ20 takes some 327 years to complete its steeply inclined orbit These two finds appear to represent a new class of solar-system bodies Recent computer simulations confirm that a great many such objects should populate the region a few hundred astronomical units away Whether initially members of the Kuiper Belt or left over from the formation of Neptune, they were flung by that planet’s gravity toward the Oort Cloud — but somehow never reached that very distant cometary reservoir As Martin J Duncan (Queens University) and Harold F Levison (Southwest Research Institute) note in Science for June 13th, this “scattered disk” could harbor up to 600 million objects Oct 15, 1996 Whatever its origin, Vesta-size 1996 7:14 UT TL66 undoubtedly represents the first of many such discoveries Luu and others have outfitted the 2.2-meter reflector atop Mauna Kea with a wide-field CCD to hunt down as many bright Kuiper Belt objects as possible (A second object netted last October, 1996 TO66, looks to be 600 km across.) Because 1996 TL66 was spotted after examining only 25 square degrees of sky, Luu estimates that thousands more bodies of comparable Oct 15, 1996 size and distance await discovery within 12:41 UT 30° of the ecliptic plane Above: The breakaway object 1996 TL 66 has an orbit much larger than those of other known Kuiper Belt members (gray band), and those of the outer planets (blue) Left: It might not look like much here, but 21st-magnitude 1996 TL 66 (box) is an estimated 500 km across These red-light images are 1.6' wide; south is up and east is to the left Diagram and images courtesy Jane Luu 22 September 1997 Sky & Telescope ©1997 Sky Publishing Corp All rights reserved 1996 TL66 (now) S J U N Solar Twin Sited in Scorpius A dead ringer for our Sun has been identifi ed by two Brazilian astronomers Gustavo F Porto De Mello (Federal University, Rio de Janeiro) and Licio da Silva (National Observatory) scrutinized light from 18 Scorpii, a 5th-magnitude star some 46 light-years away According to their June 10th Astrophysical Journal Letters report, 18 Scorpii is percent more luminous than the Sun, implying a slightly greater age But other properties, from color to iron abundance, are nearly identical in the two stars A Binary Precursor for SN 1987A? Although it’s now widely accepted that the star that blew up as Supernova 1987A was a blue supergiant, astronomers remain puzzled by the supernova’s axisymmetric rings At the United Kingdom’s National Astronomy Meeting last April, Phillipp Podsiadlowski (University of Oxford) suggested a solution A binary star, he says, merged to form a blue supergiant shortly before the blast Such a supergiant would have anomalously high angular momentum, as suggested by the ringlike remnants Saturn’s Satellites Sept EAST WEST Titan 10 11 12 13 14 Dione Enceladus 15 16 17 18 19 Advertisement 20 21 22 23 Rhea 24 25 26 27 Tethys 28 29 30 Oct The curving lines represent Saturn's brightest moons The planet's disk and rings are indicated by vertical bands Titan is the easiest to see, followed by wide-ranging Iapetus (which is plotted only when near the planet) A 4-inch telescope often shows Rhea and Dione and sometimes Tethys Enceladus may need a 12inch The wavy-line chart gives only east-west displacements Since the orbits are not edge on to our view, refer to the bottom diagram to estimate each moon's location south (above) or north (below) of the ring extension ©1997 Sky Publishing Corp All rights reserved Sky & Telescope September 1997 95 ILLUSTRATION BY JAY RYAN, HTTP://WWW.CYBERDRIVE.NET/~STARMAN pearance should be more dramatic (if sky conditions are still good) because Saturn will be easier to watch when it’s a little removed from the glary lunar landscape The reappearance will also take the better part of a minute, so you’ll have time to locate Saturn emerging The table, provided by David W Dunham, gives the times of Saturn’s disappearance and reappearance for various cities in Universal Time (which is explained at right) Also given are the altitudes of the Moon and Sun above the horizon at these times Astronomical twilight begins when the Sun is 18° below the horizon (altitude –18°) When the Sun is less than 6° down it’s nearly daylight Much more extensive predictions are on the World Wide Web at http://www.sky.net/~robinson/0918sat.htm Beautiful as a Saturn occultation may be, it’s tough to capture on a photograph The best exposures for the Moon and Saturn differ by about eight f/stops And the high magnification required to show Saturn’s rings makes the whole setup very sensitive to vibrations and poor atmospheric seeing As always, if you succeed Sky & Telescope would love to see your results A.M 96 September 1997 Sky & Telescope calendar notes Asteroid occults a bright star Late on the night of September 15th the faint asteroid 906 Repsolda will occult a 5.6-magnitude star between the Pleiades and Hyades as shown at right The occultation should take place along a narrow track running from the vicinity of Texas through Lake Superior Anyone near the middle of North America with a small telescope or firmly mounted binoculars is encouraged to try to time this event The star should vanish for up to seconds within a few minutes of 6:04 Universal Time September 16th in Texas and 6:09 UT in Wisconsin See the map and table in the February issue, pages 73 and 74 For late updates call 301-4744945 a day or so before the event The International Occultation Timing Association maintains an asteroid occultation Web page at http://www anomalies.com/iota/splash.htm Eurasian lunar eclipse A total eclipse of the Moon will be visible from Europe, Asia, Africa, and Australia on September 16th The partial phase of the eclipse begins at 17:08 Universal Time, when the edge of the Moon first enters the dark umbra of the Earth’s shadow Total eclipse lasts from 18:15 to 19:18 UT, and the final partial phase ends at 20:25 UT The eclipse is total during dusk and moonrise in westernmost Europe and Africa, when the Moon is high in the middle of the night in the longitudes of central Asia, and around dawn and moonset in Australia and New Zealand Universal Time (UT) To convert a UT time and date to a standard time and date in North America, subtract the following hours: to get Eastern TA U R U S Pleiades SAO 76505 Re ps ol da 37 ω ε Aldebaran Hyades Standard Time, 5; CST, 6; MST, 7; PST, 8; Alaska, 9; or Hawaii, 10 To obtain daylight saving time (“summer time”), subtract one hour less than these values If you get a negative number of hours, add 24; in this case the result is on the date before the UT date given For example, 6:45 UT September 9th is 2:45 a.m on the 9th EDT and 11:45 p.m on the 8th PDT You may find it easier just to remember when 0:00 UT happens in your time zone This is on the previous date at p.m EST, p.m CST, p.m MST, or p.m PST When daylight saving time is in effect: p.m EDT, p.m CDT, p.m MDT, or p.m PDT A note on sky positions In Sky & Telescope, descriptions of where things appear with respect to the horizon or zenith are written for the world’s midnorthern latitudes observer’s log Mars Watch ’97 Summary: Cloudy but Quiet Professional and amateur astronomers worldwide conduct an intensive study of Martian weather By Stephen James O’Meara s a pair of spacecraft headed toward Mars last winter, professional and amateur astronomers were focused on Martian weather conditions — specifically dust-cloud activity One of the most exciting challenges facing Mars observers is identifying where dust storms originate This information is critical to researchers working on present and future space missions to the red planet For instance, A “Dust opacity,” explains James F Bell (Cornell University), “will affect the entry and operations of Pathfinder and the aerobraking maneuver of Mars Global Surveyor.” These missions were scheduled to arrive in July and September, respectively (S&T: December 1996, page 24) Dust storms usually begin every Martian year around the time of summer solstice in the planet’s southern hemisphere For its most recent apparition, the dust- storm season was expected to start by September 1996, with Mars visible in the morning sky Spotting a storm then would have been difficult at best because the telescopic disk of Mars was only about 41⁄2 arcseconds in diameter — about the average apparent size of Uranus An emerging dust storm might appear only 1⁄10 that size Amateur coverage of Mars was not expected to begin until late November or early December, when Mars attained an apparent size of arcseconds But on September 18th Donald C Parker (Coral Gables, Florida) proved his imaging prowess by capturing a possible dust Last March 10th the Hubble Space Telescope’s Wide Field and Planetary Camera snapped these views of Mars prior to opposition, when the planet’s north-polar “hood” of carbon dioxide ice was rapidly sublimating The dark ring surrounding the remnant cap is a “sea” of sand dunes In the view at left, note the orographic (mountain-hugging) clouds attending the great volcanoes of Mars’s Tharsis region at the right side of the image A white cloud can be seen topping Elysium in the center of the middle image And dark Syrtis Major and Sabaeus Sinus-Meridiani dominate the southern half of the right image, with hazes brightening the Hellas basin further to the south North is up in all the images DAVID CRISP AND WFPC2 SCIENCE TEAM Central longitude=210˚ Central longitude=305˚ Central longitude=160˚ 5" ©1997 Sky Publishing Corp All rights reserved Sky & Telescope September 1997 99 ND NA SA PHILIP J AME S, TO D DC LAN CY , ST EV EN LE E, A observer’s log storm with his 16-inch f/6 Newtonian reflector and CCD camera The planet, whose northern hemisphere was tilted toward Earth, was then only 4.6 arcseconds across; the storm measured some 1⁄2 arcsecond in diameter Assisting Parker was Carlos E Hernandez, one of the Association of Lunar and Planetary Observers’ (ALPO) Mars Section coordinators Hernandez first noted the dust cloud on one of Parker’s red-light images, which depicted a “bright, wedge- As Mars’s polar cap recedes, cloud formation increases across the planet This effect is evident during aphelic apparitions, when Mars is close to Earth but is farthest from the Sun The cold temperatures stimulate cloud production This HST blue-light image made on March 20th is centered at longitude 94° shaped feature” (about 80° west longitude, 40° north latitude) in the Tempe desert region south of the north polar cap That same day the Hubble Space Telescope (HST) took its first 1996 Mars images Although HST and Parker imaged opposite sides of the planet, the orbiting observatory also found evidence for an atmospheric dust storm near the north polar region The HST storm covered the area at approximately 160° to 200° west longitude and 55° to 70° north latitude Apparently the Martian winds were stirring up several storms simultaneously When HST resumed its Mars observa100 September 1997 Sky & Telescope tions between October 8th and 15th, the planet’s northern cap extended down to 60° latitude (nearly its maximum winter extent) A crescent-shaped, salmon-colored veil of dust could be seen arching over the polar ices Interestingly, the dust cloud’s shape and its longitude and latitude are comparable to that of Rima Borealis, a “fissure” in the northern cap first noted by E M Antoniadi in 1903 Could veils of dust silhouetted against the polar caps be the explanation for all dark, riftlike features such as Rima Borealis and Rima Tenuis? Or was the position of the HST dust cloud merely a coincidence? I believe the association is worth investigating, though, as Audouin Dollfus (Paris Observatory) points out in The Book of Mars by Samuel Glasstone, “Each Martian year the same details [in the polar caps] are seen in the same locations during the same part of the Martian season although some delays or variations may occur, as is characteristic of natural phenomena.” This may be so for Rima Borealis, for instance, but the aberrant sightings of Rima Tenuis over the years make a good case for polar dust-cloud activity (see the box on the facing page) False Alarm? Hernandez was among the first to submit visual Mars observations in early December 1996 On the 9th he saw very bright clouds over the Chryse desert and Hellas basin But no dust activity was noted in red light; albedo features appeared normal The Martian weather remained like this until January, when cloud activity increased On the 6th Hernandez found the Chryse-Xanthe desert regions “partially obscured by a thin, bright veil north of a dark Mare Erythraeum and Aurorae Sinus.” This region includes Ares Vallis, the landing site for Mars Pathfinder and the rover Sojourner By January 29th Hernandez was certain dust was once again infiltrating the Martian atmosphere over Thaumasia, just south of the famous dark albedo feature Solis Lacus (the so-called Eye of Mars) Regions surrounding Solis Lacus have ©1997 Sky Publishing Corp All rights reserved long been regarded as notorious hotbeds for dust storms Indeed, two nights later Hernandez recorded further dust activity northwest of the Eye, the “cloud” appearing as three distinct patches This region, he reported, “appeared brightest while using a Kodak Wratten 23A (light red) filter, which may indicate Martian surface activity, such as a dust storm.” Confirmation appeared to come from Johann Warell, coordinator for the Nordic Mars Observers Warell says he “paid special attention” to the Solis Lacus region on the evening of January 31st under an unusually stable atmosphere At first the planet looked normal through all color filters — with a moderately bright evening cloud over Chryse and a moderately bright morning limb haze near the north polar cap Within an hour, however, using a light red filter, he noticed the morning haze contained “three areas slightly lighter than the bright haze along the limb.” These were situated approximately over the deserts Arcadia, Amazonis, and Tharsis “The region near Solis Lacus,” he continues, “was also marginally brighter in [a red filter] than the moderately light haze, while the two other regions were not.” Despite the long-held belief that dust storms stand out best when seen through yellow filters, research by ALPO Mars recorders have proved that dust storms actually appear strongest in red light Thus, the observations by Hernandez and Warell would lead one to believe that dust was indeed kicking up again on Mars And perhaps it was — if briefly Then again, perhaps the excitement of finding possible dust-cloud activity near the proposed landing site for the Mars Pathfinder mission caused some unnecessary heart pounding After discussing the Hernandez and Warell reports, members of the Terrestrial Planets section of the British Astronomical Association (BAA) concluded that there really was no dust storm over Thaumasia on January 29th “Four visual observations and two CCD runs in late January were negative,” reports Richard McKim, director of the Mars section, “although brightening, very likely due to morning and evening clouds, was noted.” As the Cap Shrinks, the Clouds Grow Following the dust “scare,” BAA observers reported that the north polar cap, while retaining its dark collar, had been shrinking appreciably during the first two weeks in February, with indications that it was asymmetric about the rotation pole — an aspect confirmed by Warell and ALPO member Richard Schmude Furthermore, the bright feature Olympia (a detached segment of the northern cap) was observed by a member of the Oriental Astronomical Association as early as January 31st (Interestingly, the rift that separates Olympia from the main cap is Rima Borealis.) These observations all hinted at an early retreat of the polar cap Former ALPO Mars Section recorder Jeffrey D Beish comments that with high magnifications and apertures of 10 inches or more, detached features usually become apparent soon after the Martian summer solstice, which, during this apparition would not occur until mid-March Paradoxically, the dust observed by HST, Parker, and Hernandez should have prevented some solar radiation from reaching parts of the cap and thus prolonged its retreat Regardless, HST im- Carlos E Hernandez suspected Martian dust activity on January 29, 1997, when he made this drawing using an 8-inch f/7.5 Newtonian reflector at 305× and a Wratten 23A (light red) filter Solis Lacus (the so-called Eye of Mars) is the star-shaped albedo feature surrounded by a bright border of possible dust ages from December 30th to January 4th confirmed that sublimation of polar ices had been under way during midspring in the Martian northern hemisphere As the polar cap thaws, cloud formation in Mars’s atmosphere increases This effect is magnified during aphelic apparitions because the faint sunlight results in cold atmospheric temperatures, which stimulate cloud production The clouds further reduce atmospheric temperatures by reflecting sunlight back to space, resulting in more clouds Again, after analyzing the 1984 apparition, Beish found an interesting correlation: the appearance of orographic (mountain-hugging) clouds forming over the Tharsis volcanoes was delayed nearly one Martian Rima Tenuis hile using a -inch refractor in 1888, the Italian astronomer Giovanni Schiaparelli observed a dark rift or fissure dividing the north polar cap of Mars into two parts The feature was observed irregularly from 1901 through 1918, and in 1929 E M Antoniadi named it Rima Tenuis (meaning “narBy Jeffrey D Beish row fissure”) Records from the British Astronomical Association indicate that Rima Tenuis had also been observed in 1933 and again in 1950 Charles F Capen (Lowell Observatory) searched for Rima Tenuis during the 1960s But even though he used telescopes of 16 -, 30-, and 82-inch apertures at various observatories, his attempts were unsuccessful Not until late 1979 did the fissure appear again ALPO Mars Section coordinator Daniel M Troiani first noted the feature’s return, saying it appeared as a dark notch at the south edge of the north polar cap near 335° longitude Later, I and several other observers around the world observed Rima Tenuis within days of Troiani’s first sighting On February 22, 1980, Patrick Moore and Capen observed the complete Rima Tenuis using Lowell Observatory’s 24-inch refractor It became a regular feature during the 1980 apparition and again in 1982 ALPO astronomers have photographed Rima Tenuis and W month, corresponding to an observed delay in the north polar cap’s recession “Our Martian Meteorological Survey,” he explains, “had revealed that the time of appearance of the northern summer orographic clouds is highly predictable, so their tardiness in 1984 is significant We feel that these observations have, for the first time, demonstrated a direct link between the north polar cap’s recession and orographic cloud formation.” captured it with CCD imagers, but due to the extremely low contrast and small size of the feature, it does not appear on reproductions It would seem that a Mars-orbiting spacecraft would have recorded the phenomenon, and surely the Hubble Space Telescope images should reveal this feature if it appeared during periods of observations Yet to date, no feature resembling a rift or fissure has been seen in the north polar cap in the observed position of Rima Tenuis This is not to say we should rule out the existence of riftlike features; however, with the recent revelations from HST images that show several dust streaks crossing the cap, we may have to begin rethinking our theories for Rima Tenuis But all the evidence is not yet in I prefer to reserve judgment on this until a dust streak is seen crossing the polar cap at the longitudes corresponding to Rima Tenuis An expert on Martian meteorology, Jeffrey Beish can be reached at 14522 Bisbee Court, Dale City, VA 22193 Using Hubble Space Telescope images of Mars taken between October and 15, 1996, NASA scientists constructed this pole-centered mosaic At that time, Mars’s northern hemisphere was experiencing springtime conditions and the polar ices were near their maximum southern extent Note the ocher-colored dust cloud at the lower-left edge of the cap This dust cloud is a remnant from a storm discovered by HST on September 18th last year Courtesy Philip James, Todd Clancy, Steven Lee, and NASA ©1997 Sky Publishing Corp All rights reserved Sky & Telescope September 1997 101 observer’s log If this is true, then the formation of orographic clouds during the 1997 apparition should have appeared earlier than the expected time of mid-March And it did Using an 8-inch f/7.5 Newtonian reflector at 305×, Hernandez first sighted hints of wispy cloud activity forming over the Tharsis volcanic region as early as January 6th Two weeks later he saw an “extremely bright oval-shaped cloud” appear over Elysium — another volcanic region — which connected to a “rare equatorial cloud band” that was best detected using ultraviolet and violet filters These clouds, he deduced, “reside at chilly high altitudes and are probably composed of carbon-dioxide crystals.” By January 29th Hernandez noted a bright strip of clouds extending over Tharsis with an extremely bright central condensation that he believed might have been an orographic cloud adjacent to the volcano Ascraeus Mons While surveying Mars with a 10-inch f/9 Newtonian reflector in the Florida Keys on February 8th, ALPO Mars Section coordinator Daniel M Troiani confirmed the formation of the Tharsis orographic clouds The cloud activity continued to intensify throughout February Brazilian International Mars Patrol member Nelson Falsarella saw orographic clouds forming on all the days he observed that month, especially over Olympus Mons, Tharsis Ridge, and Alba Patera “They were very bright too,” he exclaims, “and easily seen without color filters!” Beish suspects that the increase in the number of blue and white clouds throughout the last decade points to the fact that Mars may be experiencing a period of arctic warming “One may conjecture that the mechanism responsible for the apparent warming on Mars,” he says, “was a contributing factor in producing the high number of dust storms during the 1983–85 apparitions.” But dust production on Mars remained negligible throughout February 1997, as verified by images taken at NASA’s Infrared Telescope Facility on Mauna Kea, Hawaii (see the example at right) And the planet remained dust free as it approached Earth in mid-March HST images of Mars before and after the red planet’s closest approach to Earth on March 20th (about 100 million kilometers) tell a story of cloudy conditions on Mars — with cold fronts moving off the north pole, intricate patterns of clouds hugging the Tharsis volcanoes, and a diffuse haze covering much of the Martian tropics And these conditions held as the planet’s apparent size waned from its maximum diameter of 14.2 arcseconds on March 20th to a mere arcseconds in early June Winding Down If these weather patterns continued to hold throughout the summer, Mars Pathfinder may have been in for a dustfree ride to the Martian surface Meanwhile, an intensive analysis of Martian weather is now in progress by the ALPO Mars Section using visual data and images from professionals and amateurs around the world (See the ALPO Web site at http://www.lpl.arizona.edu/~rhill/ alpo/mars.html.) Usually aphelic apparitions of Mars are touted as being the worst for visual observing Perhaps the size of the planet discourages amateurs from dusting off their telescopes and pointing them toward the red planet — the fear being that little surface detail can be seen But, as Beish points out, “Today we know much about long-term weather and surface conditions on Mars thanks to amateurs armed with little more than a set of color filters and a telescope inches or larger.” Indeed, this apparition was the best for Richard W Wilhelm of Manorville, New York, who used a modest 41⁄2-inch Newtonian reflector to keep a watchful eye on Mars “I did not have high expectations Experienced astro imager Gregory Terrance from Lima, New York, made this red-light CCD image of Mars on March 22, 1997 Note the dust-free atmosphere Terrance used a 16inch f/5 Newtonian reflector coupled with a Celestron PixCel 255 CCD camera 102 September 1997 Sky & Telescope ©1997 Sky Publishing Corp All rights reserved This 2.3-micron image of Mars, obtained on February 17, 1997, from the NASA Infrared Telescope Facility on Mauna Kea, may be the best ground-based near-infrared image of Mars ever made The resolution is about 40 to 50 kilometers per pixel “For a few sweet but brief hours that night, it was as if the skies parted and there was no atmosphere above us at all!” exclaims James Bell, who was teamed with Jeff Moersch (Cornell University) and William Golisch (IRTF) when I began observing Mars at the beginning of the recent apparition,” he writes “The most I had hoped to see was a polar cap and perhaps a dark smudge or two Instead, I was pleasantly surprised with what has proven to be the most rewarding of observing experiences.” In a series of observations spanning several days around the planet’s closest approach to Earth, Wilhelm easily saw dark surface features — such as Syrtis Major, Sabaeus Sinus, and Mare Acidalium — and enough detail at the threshold of visibility to keep him at the eyepiece for hours He also saw cloud covers over Chryse and Hellas, a morning haze over the Tharsis region, and some obscure features, such as Utopia and Nilokeras “Obviously there is no substitute for a larger aperture telescope when it comes to resolution of fine planetary detail,” he offers, “but given the right set of conditions, proper accessories, and patient observation, one can make a smaller instrument go a long way The observational skills learned and visual acuity gained while using such instruments are valuable training for the day when amateur astronomers make the transition to their ‘dream telescopes.’ Users of small instruments should take heart in this knowledge.” Contributing editor O’Meara is one of the foremost visual planetary observers today observer’s notebook By Dennis di Cicco The Missing Mushroom f you’re among the fraternity of observers that enjoys sweeping the sky with binoculars and small telescopes, then there’s a good chance you have your own personal stash of asterisms While some star patterns, such as the Sagittarius Teapot or the Hercules Keystone, are better known than their parent constellations, most asDelphinus is home to the toadterisms reside only in the stool asterism mentioned by minds of those who creSusan French in the June issue ated them A few years ago I was Although it is barely visible on the wide-field view of the concaptivated as a colleague stellation, it shows well on the 1⁄4°-wide inset from the Digital who frequently scanned Sky Survey (the little “fuzzy” is NGC 7025, a galaxy that will the Milky Way with bin- challenge small telescopes) The mushroom appears upside oculars in search of novae down on these views with north up began pointing out his “drunken sailor,” “barking dog,” and How could this be? I had seen the pat“crooked walking stick” on one of my tern on photographs while reviewing ilwide-field photographs Just hearing these lustrations for French’s article about names made me want to hunt down his deep-sky observing in Delphinus A clue asterisms to the mystery of the missing mushroom Apparently I’m not alone Judging by came in an e-mail message from Brian the letters and e-mail we received con- Cuthbertson “The position isn’t even in cerning the little stellar “toadstool” casu- Delphinus,” he wrote Sure enough, a ally mentioned by Susan French in the quick check revealed that a digit was inJune issue, page 107, many readers are advertently dropped from the asterism’s fascinated by asterisms The messages, published declination, placing the fickle however, had a common theme that was fungus in Equuleus 10° south of its true summarized best by the anonymous ob- location server who simply lamented, “There’s Those wishing to check out the celestinothing there.” al toadstool should aim their scopes at right ascension 21h 7m, declination +16° 18' (epoch 2000.0 coordinates) This Monthly Sunspot Numbers is close to the Delphinus60 Pegasus border, some 61⁄2° 50 east-northeast of the cen40 ter of the diamond pat30 tern forming the Dol20 phin’s head The 10'-wide 10 asterism shines with 9th0 and 10th-magnitude stars Oct ’96 Dec Feb ’97 Apr Jun Aug After viewing it with the 5Pierre Cugnon of the Sunspot Index Data Center supplied inch 17× apogee scope that these provisional sunspot numbers The range of minimum and belonged to the late deepmaximum daily numbers (vertical lines) and monthly means (connected points) are shown for the nine most recent months sky pundit Walter Scott There are also three months of predictions Daily numbers are Houston, I’d rate the toadavailable at http://www.oma.be/KSB-ORB/SIDC/index.html stool “two thumbs up!” P K CHEN I Advertisement 104 September 1997 Sky & Telescope ©1997 Sky Publishing Corp All rights reserved telescope techniques Mastering Polar Alignment When you set up your telescope’s equatorial mount, you need to align it an illusion — it’s the Earth that turns Picture the Earth as a rotating globe at only well enough to the job you want By Alan MacRobert the center of the celestial sphere, as in the diagram on the facing page Because the ost amateurs use a port- telescope along every few seconds And world feels motionless as it smoothly carable telescope, whether in most cases, a well-aligned mount is es- ries us along, we perceive the sky turning they carry it to remote, sential for astronomical photography instead, in the opposite direction dark-sky hideaways or to The axis on which the sky seems to roAs performed by many amateurs, a familiar spot in the backyard But if polar aligning is too much work You can tate is simply the axis of the Earth exyour telescope has an equatorial mount- waste a lot of time getting it more pre- tended to infinity Imagine the Earth’s ing, this means you need to realign it on cise than you need for what you intend latitude and longitude lines ballooning the celestial pole every time you set up to Mastering polar alignment isn’t outward and printing themselves onto Doing so can seem like a lot of work just a matter of knowing the techniques the sky sphere They become lines of An equatorial mount has many bene- It’s also knowing when not to bother declination and right ascension, respecfits It can easily compensate for the tively These serve to locate stars on a cemovement of celestial objects as the The Basics lestial atlas just like cities on a map Earth turns Its motions show you which The first step in understanding a teleA telescope mounting is called “equaways are celestial north-south and east- scope mounting is to understand the mo- torial” if one of its two axles can be made west in your eyepiece view, making it tion of the sky This motion, of course, is parallel to the Earth’s axis When this is easier to navigate with a sky map done, the sky’s motion can be canWith a motor drive, an equatorial Above: The sky is always turning, so a telescope needs to celed out simply by turning the mount can make objects stand still turn the opposite way to keep a star in view Stefan Bin- axle at the same rate as the Earth in the eyepiece even at high power, newies took this 8-hour exposure of stars circling the ce- but in the opposite direction, eiso you don’t have to nudge the lestial pole from below the equator in Namibia ther by hand or by a motor drive M 106 September 1997 Sky & Telescope ©1997 Sky Publishing Corp All rights reserved 22h Polar axis To P olar is +60 C°e les tia lE qu at or 18 h move it and repeat step 6h Leave it out for all +30° subsequent steps Equa tor Don’t use a diagonal 8h on the finderscope at all It mirror-images the 10h view, making it nearly imCele stial possible to compare the star Equato r 0° –6 patterns you see with those 0° on a map .3 The declination setting circle, which is graduated in degrees, proba–30° bly needs adjustment to make it read correctly the setting of the mount Turn the telescope to 90° declination as indi- no declination setting completely elimicated by the circle The tube should now nates image drift as you turn the telebe parallel to the polar axis Clamp the scope in right ascension This means that declination axle tight, then rotate the either the optical or the right-ascension telescope in right ascension while looking axis is not exactly at a right angle to the through either the main eyepiece or the declination axis finder Any object, whether a star or a First recheck that the optics are collidistant treetop, should stay centered in mated correctly Then try adding thin the view If it doesn’t, move the telescope shims of metal or cardboard to change the in declination slightly and repeat When angle the tube makes with its cradle, or the scope stays aimed at the same object try otherwise tinkering with the mount as it spins in right ascension (at least as If your telescope does not allow for best you can do), loosen the declination dial, turn it to read exactly 90°, and tighten permanently Note: If you’re sighting through a fork-mounted telescope, you can aim at an object nearby If you are using the finder, the object ought to be at least 600 feet away For a telescope on a German-type mount (standard for equatorial reflectors), sight on something more than 1,000 feet away This may require loosening the latitude adjustment — the pivot that sets the angle the polar axis makes with the ground — and tilting the One way to set an equatorial mount to your latitude By movpolar axis so it’s nearly ing the latitude adjustment, level the tube while the telehorizontal scope is locked at a declination of 90° minus your latitude (as In carrying out step shown by the setting circle) and pointed due north If a level is 3, you may discover that not available, eyeball judgment will 16h 12h CHUCK BAKER 0° Preliminaries The following adjustments need to be done only once, and they can be carried out during the day For rough alignment only step is required, but many telescope owners will want to work through the whole series to get everything shipshape (In these instructions we’ll assume that collimation, or optical alignment, of the telescope’s lenses and/or mirrors has already been done.) Aim the finderscope to point in the same direction as the main telescope Center an object at least a quarter mile away in the telescope’s high-power view A treetop works fine Then use the thumbscrews on the finderscope mount to center the object in the finder’s cross hairs .2 If you use a right-angle star diagonal (eyepiece prism) on the main telescope, check that it does not shift the direction of view Take out the diagonal and center an object while viewing “straight through.” Then insert the diagonal and look again The object should still be centered If it’s not, turn the little adjustment screws in the diagonal’s back until it is If the diagonal fails this test and is unadjustable, re- On the celestial sphere, declination and right ascension are similar to latitude and longitude on Earth If a telescope’s polar axis is made parallel to the Earth’s axis, as 0h shown, the Earth’s rotation can be canceled out by turning the telescope in 4h the opposite direction –3 The axle of the mounting that points at the celestial pole is called the polar axis Sight along it (as in the diagram at right), and you should see Polaris, the North Star It’s also called the right-ascension axis, because turning the telescope on it sweeps the view in right ascension (celestial east-west) The mount’s other motion, perpendicular to the first, swings the telescope north-south around the declination axis To make an equatorial mount work as intended, you aim its polar axis at the pole This needs to be done only roughly for casual observing Better alignment helps in tracking objects carefully at high power Still greater precision is needed if you want to use conventional setting circles to point the telescope at hard-to-find objects Astrophotography usually demands the highest precision of all A commercially made telescope on an equatorial mount will come with instructions Some telescopes have built-in alignment aids, such as a Polaris sighter Computerized mountings are a whole different category; they can eliminate the need to polar-align altogether Here we’ll discuss several generic polar-alignment methods, from quick and rough to very exact But first you need to some preliminary adjustments to your telescope ©1997 Sky Publishing Corp All rights reserved Sky & Telescope September 1997 107 this, just carry out step as best you can The final task is to match the angle of your polar axis to the latitude where you live This adjustment determines how high the polar axis points above the horizon Set up the telescope on a level surface and turn it in declination so the setting circle reads 90° minus your latitude (If you don’t know your latitude, find it on a map.) For example, if you live at 40° latitude, turn the telescope to 50° declination Clamp the declination axle tight Now turn the telescope in right ascension to make the mount’s declination axis lie as nearly horizontal as you can judge (High precision is not required.) Clamp the right-ascension axle With both axles locked in place, put a carpenter’s bubble level on the telescope’s tube, loosen the latitude adjustment (carefully!), move it until the tube is exactly level, and tighten permanently See the photograph on the previous page The next steps are done outdoors at the beginning of each observing session Advertisement Rough Polar Alignment For ordinary visual observing, just plunk the mount down so the polar axis is aimed at Polaris as best you can judge by looking That’s it! You will probably be no more than 5° or 10° off This is good enough for using the mount’s motions to tell celestial north, south, east, and west in your field of view, and for following the sky’s motion easily with or without a motor drive If that’s all you want to do, why make life complicated? Better Alignment For a quick improvement, you can choose one of the following two methods: A Swing the telescope to 90° declination and clamp it there Then turn the entire mount until Polaris is as nearly centered in the finder as you can get it .B If you don’t have setting circles, use your star charts to find two stars 10° or more apart that have either the same declination or right ascension Turning the scope on only one axle, sweep from one star to the other while looking though the finder Both stars should go through the finder’s cross hairs If they don’t, move the whole mount around until they The telescope should now be aligned to within a degree or two A motor drive will follow an object much longer, and direction finding in the eyepiece becomes more precise You can now locate difficult objects by the offsetting method: moving 108 September 1997 Sky & Telescope ©1997 Sky Publishing Corp All rights reserved Fine Alignment This is the stage of accuracy most amateurs mean when they say a telescope is “aligned.” Corrections are made for Polaris not being quite at the pole and for the telescope not resting on perfectly level ground Use either of these two methods: A Set the telescope to 90° declination and clamp it there Using the chart below, note where the true celestial pole lies with respect to Polaris and its surrounding stars Turn the whole mount sideways until the finder’s cross hairs appear either directly above or below this point among the stars Now loosen and tilt the latitude adjustment (or move the tripod legs) to aim the cross hairs up or down exactly at this point B This method requires a movable “slip ring” right-ascension setting circle, provided on many telescopes Align roughly, then aim at a bright star of known right ascension fairly near the equator Turn the right-ascension circle (the slip ring) so it reads the correct value for this star Using the circles, swing the telescope to hours 30 minutes, which is nearly the right ascension of Polaris, and To Big er’s Dipp ers t Poin Polaris 2000 1950 1900 To Ca ssiop eia h h 12h North Pole δ UMi Litt le D a ipp To Veg er 1° 18h The north celestial pole moves slowly against the starry background from year to year due to the Earth’s precession The current position of the pole is where to aim when doing fine alignment of an equatorial mount A finderscope will take in most of this field to +89 1⁄4°, Polaris’s declination Now move the tripod and the latitude adjustment to center Polaris in the finder’s cross hairs If the mounting had to be moved a lot, repeat from the beginning The telescope is now aligned to a fraction of a degree You may be able to use the setting circles to find objects simply by dialing in their coordinates A motor drive will keep the telescope on an object indefinitely, allowing long-exposure photography Method B automatically places the right-ascension circle at the correct value to start an evening’s observing If the circle is driven by a motor drive, it doesn’t need to be touched again If it’s undriven, turn it to the right ascension of the object you’re currently viewing just before swinging the telescope to a new reading DENNIS DI CICCO the correct amount of right ascension and declination to get from an easy-tofind star to the desired object Best Possible Alignment The two methods above are limited by the accuracy of the setting circles and how well you were able to the preliminary steps through The following method is independent of these factors Since it takes some time, it’s most appropriate for permanently mounted telescopes or those that can be replaced in exactly the same position on future nights First aim the polar axis roughly at Polaris Now point the telescope at a star that’s somewhat above the celestial equator and nearly due south Put in a highpower eyepiece If the eyepiece has cross hairs, center the star on them Otherwise put the star on the north or south edge of the field and defocus it a little Turn on the clock drive, and ignore any eastwest drift If the star drifts south in the eyepiece with time, the polar axis is pointing too far east If the star drifts north, the polar axis is too far west Moving the whole mount, shift the polar axis left or right accordingly until there is no more north-south drift Now aim at a star that’s near the celestial equator low in the eastern sky If the star drifts south, the polar axis points too low If the star drifts north, the polar axis points too high Again, shift the polar axis accordingly Now go back and repeat from the beginning, because each adjustment throws the ©1997 Sky Publishing Corp All rights reserved The polar axis of a German equatorial mount properly aligned on the celestial pole previous one slightly off When all northsouth drift is eliminated the telescope is very accurately aligned, and you can take long exposures for deep-sky photography If your eastern sky is blocked, you can use a star low in the west and reverse the words “too high” and “too low” in the instructions If you’re in the Earth’s Southern Hemisphere, reverse the words “north” and “south.” All these procedures may seem complicated to the uninitiated Part of becoming initiated is knowing that most of them can be ignored most of the time So there’s no reason to be intimidated by an equatorial mount You can take full advantage of the benefits it offers for whatever level of observing you Further Reading “Understanding Celestial Coordinates.” Sky & Telescope, September 1995, 38; http:// www.skypub.com/backyard/celcoord.html “Setting Circles: Using Them Right.” Sky & Telescope, September 1990, 246; http://www.sky pub.com/backyard/ setcircs.html Sky & Telescope September 1997 109 gallery Lunar Eclipse Close-Up (right) By Gregory Terrance Although percent of the Moon’s disk remained outside Earth’s umbral shadow at mideclipse on March 23rd, the event reminded many observers of recent total eclipses where one limb of the Moon was bright during totality Lunar Eclipse Sequence (below) By Jerry Schad Veteran astrophotographer Jerry Schad chose the spectacular setting of Zion Canyon in Utah’s Zion National Park as the foreground for this lunar-eclipse series Schad made more than two dozen exposures by removing and replacing the lens cap to create this view Milky Way Vista (facing page) By Carl and Chris Weber The region around the red giant Antares is one of the most colorful in all the heavens Streams of obscuring dust crisscross the area, reflecting light from several of the brighter stars The pinkish glow of emission nebulae is apparent, especially around Zeta Ophiuchi at top 112 September 1997 Sky & Telescope ©1997 Sky Publishing Corp All rights reserved ©1997 Sky Publishing Corp All rights reserved Sky & Telescope September 1997 113 Copeland’s “Christmas Tree” (left) By Chuck Vaughn The scattered open cluster NGC 2264 became a favorite with observers after Leland S Copeland nicknamed it the Christmas Tree in the 1950s Seen upside down in this view, the tree has its base marked by the 5th-magnitude variable star S Monocerotis (at center of field), while the Cone Nebula is at the tree’s top The whole region is awash with bright and dark nebulosity IC 410 and IC 405 in Auriga (lower left) By Michael Stecker The area around the 6th-magnitude variable star AE Aurigae (upper right) is a popular target for astrophotographers because of several glowing clouds of hydrogen IC 405, the Flaming Star Nebula, surrounds AE, while IC 410 lies about 2° to the southeast The open cluster NGC 1893, which appears within the boundaries of IC 410, is almost lost in the rich background of the Milky Way The Crab Nebula (below) By Chuck Vaughn The brightest supernova remnant in the sky, the Crab Nebula, M1, in Taurus is the expanding shell of debris marking the site of an outburst recorded in A.D 1054 The nebula’s delicate filamentary structure is emphasized in this photograph that isolates red, hydrogen-alpha light Circumpolar Comet Hale-Bopp (facing page) By S Binnewies, P Riepe, H Tomsik, R Sparenberg, D Sporenberg, and B Schröter At an elevation of 3,130 meters (10,270 feet) in the Swiss Alps near Gornergrat, members of the German astrophotography group VdS-Fachgruppe Astrophotographie captured this 7-hour sequence of Comet Hale-Bopp sweeping along the northern horizon on April 2nd 114 September 1997 Sky & Telescope ©1997 Sky Publishing Corp All rights reserved HOW THEY DID IT Milky Way Vista Pentax 6×7 camera, 105-mm lens set to f/4 Two 25minute exposures on Kodak Pro 400 PPF color-negative film were stacked and printed on 4×5-inch Vericolor film to make a transparency.Two transparencies were stacked and copied onto 4×5-inch negative film to produce a “master” negative from which this print was made The stacking and copying process increases contrast and color saturation Field nearly 30° wide centered at approximately 16h 40m, –22°; north is at upper right Lunar Eclipse Close-Up 10-inch f/6 Newtonian reflector, Fujicolor Super G 800 Plus film, 5-second exposure Lunar Eclipse Sequence Canon TX camera, 50-millimeter lens, Fujichrome Velvia film pushed +1 stop to ISO 100, sequence exposures at 5-minute intervals Partial-phase exposures at f/16 with a 2-stop neutral-density filter ranged from seconds near mideclipse to 21⁄2 seconds at ends of sequence Mideclipse exposure at f/2.8 (no filter) was 10 seconds and recorded several bright stars as “points.” Final exposure made before dawn with Moon in west illuminating foreground, f/2.8 with light orange “warming” filter, minutes and shows stars as trails Copeland’s “Christmas Tree” Astro-Physics 5-inch f/9 refractor, gas-hypersensitized Kodak Technical Pan 2415 film, 3-hour exposure Field 11⁄4° wide centered at 6h 41m, +10°; north is up IC 410 and IC 405 in Auriga Astro-Physics 5-inch refractor working at f/4.5, gashypered Fujicolor HG 400 film.Two 1-hour exposures were digitized and combined Field 21⁄2° wide centered at 5h 19m, +33° 45'; north is up The Crab Nebula 12 1⁄2-inch f/9 Ritchey-Chrétien reflector, gas-hypered Kodak Technical Pan 2415 film, hydrogen-alpha filter with a 150-angstrom-wide bandpass, 3-hour exposure Field 10' wide centered at 5h 34.5m, +22° 01'; north is up Circumpolar Comet Hale-Bopp 16-mm f/2.8 Zeiss fisheye lens, ScotchChrome 400 film, eight 1-minute exposures separated by 1-hour intervals ©1997 Sky Publishing Corp All rights reserved Sky & Telescope September 1997 115 [...]... far away our object was then, consider that as the photons traveled toward us, each light-year of the journey was smaller at the time of emission, by an amount given by the twothirds-power law The original distance of the object is thus the sum, or integral, of the incremental “distances then” covered by the light on each step of its journey to us, from t then to t now : ∫ tthen 20 REM by Thomas A... incorporating these equations into a BASIC program, I’ve created a handy conversion tool so you can discover their significance A Program Walk-Through The program’s only assumption is that the scale factor of the universe has grown at a rate of the 2⁄3 power of time since shortly (about 300,000 years) after the Big Bang.* Therefore, the scale of the universe now (tnow) versus then (tthen) is (tnow/tthen)2/3... yet available, but the worst is feared: the February 5th fire began in the library basement, where the rarest portion of the collection was stored The only positive note is that, at the start of World War II, several of the library’s rarest holdings were removed to the relative safety of the Academy of SciRussia’s Pulkovo Observatory, seen here as it appeared in 1974, was the scene of a devastating ences... emitted the light we see today! The object’s distance at any other time t is the distance then times the increase in scale factor of the universe at t versus tthen Line 330 determines tnow by solving Distance = 3c tthen[(tnow/tthen)1/3 –1](t/tthen)2/3 Since the scale factor of the universe is 6.08 times as large now as it was then, our sample object is now more than 26 billion light-years away! The diagram... age of the universe THEN in billions of years? 1 Age of the universe NOW = 15.0000 billion years Age of the universe THEN = 1.0000 billion years Light travel time = 14.0000 billion years Scale of the universe NOW versus THEN = 6.082 Redshift of the light we see NOW = 5.082 Distance of object THEN = 4.399 billion light-years Distance of object NOW = 26.753 billion light-years Speed away from us THEN =... and ered during the MACHO Small Magellanic Clouds microlensing survey of the The principal issue behind these searchLarge Magellanic Cloud The es — unraveling the nature of dark matter light curves of the variables — remains unresolved The amplitude of closely mimic those produced a given microlensing event depends on the by microlensing events but separation of the source and lens on the are slightly... one or more ways to indicate the distance of an object: its redshift, its age, its distance (then or now), or the speed with which it moves away from us (then or now) How do all these quantities interrelate, and how are they associated with other cosmological characteristics, such as the value of the Hubble parameter (H0) or the age of the universe? The relationships between these values can be summarized... the shell’s 260° Vela remnant 5° 0° -5° ©1997 Sky Publishing Corp All rights reserved center Note that the southern section of the remnant is much fainter than the northern and central regions The visible-light image of Vela (below), showing only the lower-right edge of the remnant (outlined on the radio image), details intricate loops and filaments This emission is produced mainly where the edge of. .. quasar-pair studies Most of the atoms in each cloud were ionized by diffuse ultraviolet radiation, which Quasar 2 most likely came from quasars accompanying the clouds The typical mass of a cloud is only a few hundred times that of the Sun The number of such clouds in space is large, but the fraction of space filled with them is small Yet the indications are that at early times, most of the universe’s particulate... shadows cast by ethereal gas clouds that lie between Earth and the distant quasars These invisible clouds hold important clues to the birth of the first stars and galaxies The first visible-light spectra of quasars, taken in the 1960s, contained narrow, dark lines caused by pockets of cool gas somewhere along the sight lines to the distant beacons Soon there was a consensus that most of these absorption