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Wishing "All" clear skies,
Bob
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- To: skyline@gs1.revnet.com
- Subject: S&T's News Bulletin for July 17, 1998
- From: John Wagoner <stargate@gtedot net>
- Date: Fri, 17 Jul 1998 23:14:26 -0500
SKY & TELESCOPE'S NEWS BULLETIN JULY 17, 1998 CLOSE-UPS OF GANYMEDE On July 15th, the Jet Propulsion Laboratory released a bevy of new images of Jupiter's largest moon Ganymede taken by the Galileo spacecraft. The pictures show fine details on the icy world, including fresh impact scars and terrain of varying brightness and roughness. Among the more intriguing images was one showing a 150-kilometer-long (90-mile-long) chain of craters. Three such features are known to exist on the satellite, and more than a dozen can be found on the surface of Callisto. Crater chains are believed to arise when a comet or asteroid comes too close to Jupiter and is disrupted by tidal forces produced by its tremendous gravity. The resulting pieces travel closely together, and sometimes wind up hitting something larger -- in this instance, Ganymede, or as in the case of Comet Shoemaker-Levy 9 in July 1994, Jupiter itself. SNAPSHOTS OF THE EARLIEST STELLAR NURSERIES? Two international research teams have just taken a key step toward answering one of cosmology's biggest questions: when did the universe's stars and galaxies turn on? Earlier this year, Cosmic Background Explorer (COBE) measurements showed that many of the universe's earliest stars have evaded even the deepest visible-light surveys. That's because the stars were shrouded by clouds of dust that absorbed their light and turned it into infrared radiation. But COBE couldn't pin down when and where the universe's unseen stars began to shine. Enter SCUBA, the Submillimeter Common User Bolometer Array, which "photographs" the sky's appearance at submillimeter wavelengths from the focal plane of the James Clerk Maxwell Telescope on Mauna Kea. Yesterday's issue of Nature contains SCUBA images of the Hubble Deep Field and two other sky patches in Ursa Major and Canes Venatici. While relatively crude, the images do contain a handful of submillimeter-wave "hot spots," presumably the redshifted glows of star- warmed dust clouds in newborn galaxies. According to their discoverers, the blobs are bright enough to account for a significant fraction of the sky's far-infrared glow (assuming they cover the entire sky in like numbers). The next step -- unambiguously associating the hot spots with galaxies of known redshift -- may require the higher resolution of an orbiting telescope or ground-based interferometer that operates at submillimeter wavelengths. NASA TO OPEN OFFICE FOR HAZARDOUS OBJECTS The commotion from last March's "brush with an asteroid" has generated fallout from NASA. The space agency announced July 14th that the Jet Propulsion Laboratory will be home for the Near-Earth Object Program Office, to be headed by Donald Yeomans. The department will be responsible for detecting, tracking, and studying potentially hazardous comets and asteroids. Its goal is to find at least 90 percent of the estimated 2,000 objects larger than about 1 kilometer in diameter that approach the Earth, and do so by 2010. In addition, according to B. Carl Pilcher, science director for Solar System Exploration in NASA's Office of Space Science, the new office will also take charge of reporting findings to the public, should a potentially hazardous objects be found. NEW MMT UPDATE TO HOG THE ROAD The formerly Multiple-Mirror Telescope atop Mt. Hopkins in Arizona has been out of service since March. The six 1.8-meter mirrors were removed to make room for a single 6.5-meter primary, and modifications to the telescope structure are nearly complete. On July 23rd, the mirror and mirror cell combination will be separated so the mirror cell can be transported to the mountain. The cell weighs 120 metric tons and consists of 100 arms that support the mirror. On the morning of the 27th, the 7.5-meter-wide (25- foot-wide) support mechanism will hog Interstate 19 as it lumbers from Tucson to Amado, Arizona. The mirror itself is to be moved to the mountain in November and aluminized in December, with first light expected shortly thereafter. Astronomical observations will begin early next spring. THIS WEEK'S "SKY AT A GLANCE" Some daily events in the changing sky, from the editors of SKY & TELESCOPE. JULY 19 -- SUNDAY * West Coast telescope users can try to observe the waning crescent Moon occulting the 1st-magnitude star Aldebaran in broad daylight this afternoon. You'll need a very clear, deep blue sky; the Moon and Aldebaran will be in the west, not very high, with the Sun about 48 degrees to their upper left. See the timetable in the January Sky & Telescope, page 97. JULY 20 -- MONDAY * 29th anniversary of the Apollo 11 landing on the Moon. * The waning crescent Moon pairs up with Venus low in the east-northeast during dawn on Tuesday morning. Little Mars is 8 degrees to Venus's lower left. JULY 21 -- TUESDAY * Vega is the brightest star nearly overhead after dark at this time of year. Just face east and look very high up. If your sky is fairly dark, also look for the little triangle-and-parallelogram pattern of the constellation Lyra dangling from Vega, to its lower right. Aside from Vega, Lyra's stars are only as bright as 3rd or 4th magnitude. * Venus shines 0.3 degree north of the 3.7-magnitude star Eta Geminorum Wednesday morning. JULY 22 -- WEDNESDAY * The red long-period variable stars R Bootis, T Ursae Majoris, and W Andromedae should be at their maximum light (7th or 8th magnitude) around this date. JULY 23 -- THURSDAY * Venus is 0.5 degree from 2.9-magnitude Mu Geminorum Friday morning. JULY 24 -- FRIDAY * The brightest star rather low in the south after dark around this time of year is Antares, colored fire-orange. Antares is a red supergiant about 700 times bigger than the Sun. It's about 500 light-years distant. Antares qualifies as the biggest single object that most people can easily see (at least at this time of year). Show it to someone tonight! JULY 25 -- SATURDAY * The thin waxing crescent Moon is low in the west in early dusk, just to the upper left of Regulus and dwindling little Mercury. Try looking for them about 30 minutes after sunset. Spotting all three may be a challenging observation even with binoculars. ============================ THIS WEEK'S PLANET ROUNDUP ============================ MERCURY is disappearing into the glow of sunset. Early in the week, scan for it with binoculars very low in the west about 30 minutes after the Sun goes down. Mercury is to the lower right of Regulus; don't confuse the two! VENUS shines brightly (magnitude -3.9) low in the east-northeast during dawn. MARS is emerging from the glow of sunrise to the lower left of Venus. It's faint (magnitude +1.6), so binoculars will help. JUPITER rises around 11 p.m. daylight saving time. It's the brilliant "star" (magnitude -2.7) shining in the southeastern sky during early morning hours and high in the south at dawn. Jupiter is at the Pisces-Aquarius border. SATURN (in eastern Pisces) rises around 12:30 a.m. It's the dimmer "star" (magnitude +0.2) far to Jupiter's lower left during the night's latest hours. It's almost directly left of Jupiter by morning twilight. (The two planets appear about 35 degrees apart, 3 or 4 fist-widths at arm's length.) URANUS and NEPTUNE, magnitudes 5.7 and 7.8 respectively, are in Capricornus, well up in the south-southeast by midnight. See the finder chart in the May Sky & Telescope, page 96. PLUTO, magnitude 13.7, is near the Ophiuchus-Scorpius border in the south right after dark. See the finder chart in the May Sky & Telescope, page 97. The charts for Uranus, Neptune, and Pluto are also at http://www.skypub.com/whatsup/urnepl98.html. (All descriptions that relate to the horizon or zenith are written for the world's midnorthern latitudes. Descriptions that also depend on longitude are for North America. Eastern Daylight Time, EDT, equals Universal Time minus 4 hours.) More details, sky maps, and news of other celestial events appear each month in SKY & TELESCOPE, the essential magazine of astronomy. See our enormous Web site at http://www.skypub.com/. Clear skies! SKY & TELESCOPE, P.O. Box 9111, Belmont, MA 02478 * 617-864-7360 (voice) ======================================================================= Copyright 1998 Sky Publishing Corporation. S&T's Weekly News Bulletin and Sky at a Glance stargazing calendar are provided as a service to the astronomical community by the editors of SKY & TELESCOPE magazine. Widespread electronic distribution is encouraged as long as these paragraphs are included. But the text of the bulletin and calendar may not be published in any other form without permission from Sky Publishing (contact permissions@skypub.com or phone 617-864-7360). Illustrated versions, including active links to related Internet resources, are available via SKY Online on the World Wide Web at http://www.skypub.com/. In response to numerous requests, and in cooperation with the Astronomical League (http://www.mcsdot net/~bstevens/al/) and the American Association of Amateur Astronomers (http://www.corvus.com/), S&T's Weekly News Bulletin and Sky at a Glance are available via electronic mailing list too. For a free subscription, send e-mail to skyline@gs1.revnet.com and put the word "join" on the first line of the body of the message. To unsubscribe, send e-mail to skyline@gs1.revnet.com and put the word "unjoin" on the first line of the body of the message.
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