SKY & TELESCOPE'S NEWS BULLETIN
APRIL 13, 2001
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=========================================================== SKY & TELESCOPE'S NEWS BULLETIN - APRIL 13, 2001 =========================================================== For images and Web links for these items, visit http://www.skypub.com =========================================================== VISIT SKY & TELESCOPE'S ONLINE IMAGE GALLERY Sky & Telescope's Web site now features dozens of stunning celestial vistas from ground- and space-based telescopes. Visit the Gallery of Images at http://www.skypub.com/imaging/gallery/ =========================================================== JUPITER'S LIGHT SHOW Already recognized as the most potent system of its kind in the solar system, it appears that Jupiter's aurora can also put on quite a dazzling -- and impromptu -- light show. On September 21, 1999, as the Hubble Space Telescope looked on, the planet's north polar region erupted with ultraviolet light that brightened 30-fold in just 70 seconds. Then, almost as quickly, the outburst abated. Although space physicists have been monitoring the Jovian aurora with HST for more than a decade, nothing this intense or abrupt has ever been witnessed. Unlike terrestrial auroras, which are powered by solar-wind interactions with Earth's magnetic bubble, those on Jupiter draw their energy largely from the breakneck, 9.9-hour rotation of the planet and its inner magnetosphere. Trapped electrons spiral down the magnetic field lines and slam into the planet's upper atmosphere, causing hydrogen atoms to glow in a bright oval of ultraviolet light. However, the 1999 flare occurred poleward of the ubiquitous auroral oval, implying a source region farther out in the magnetosphere, some 3 or 4 million kilometers from the planet's sunward-facing "morning" quadrant. The HST observers, led by J. Hunter Waite Jr. (Southwest Research Institute), can't yet explain what caused the outburst, but they suspect an external trigger. As they note in the April 12th issue of Nature, the Jovian magnetosphere likely reacted to the arrival of a high-density pulse of solar wind. Because the interplanetary conditions were not unusually stormy that day, the team suggests that "such flares, if indeed triggered by changes in solar-wind pressure, may not be uncommon." AURORA WATCHES CONTINUE And speaking of auroras, you may get another opportunity to see some northern (or southern) lights this weekend. During the latter half of the past week, the Sun had several large eruptions directed toward the Earth. Auroral warnings are up once again, so watch the skies this weekend. COMET LINEAR'S EXTENDED OUTBURST When a faint comet suddenly flares to prominence, astronomers are grateful for the easy viewing but instinctively wary -- usually the outburst wanes quickly, and the comet may fizzle. So far that hasn't been the case with Comet LINEAR (C/2001 A2), a recent find that brightened dramatically over several days in late March. (This is not the "Christmas" Comet LINEAR that had an outburst of hype in February. That one is designated C/2000 WM1.) The story of C/2001 A2 begins back in mid-January, when the MIT Lincoln Laboratory team (LINEAR) in Socorro, New Mexico, captured images of a 19th-magnitude object in Cancer that did not appear to be moving like a typical main-belt asteroid. Follow-up observations at two observatories in the Czech Republic revealed a fuzzy rather than a point-source image. The orbit calculated by Brian G. Marsden, and the brightness observations available in January, suggested the comet would brighten slowly to perhaps 13th or 12th magnitude by early April, ultimately reaching about 9th magnitude in June. However, starting on March 26th, Michael Mattiazzo of Wallaroo, South Australia, noticed the comet was much brighter than expected. By April 1st some observers reported that Comet LINEAR had reached magnitude 7.5, and it has hovered near 8th magnitude since then. The comet remains an easy evening-sky target in a small telescope, though for Northern Hemisphere observers it is sinking fast toward the southwest horizon as twilight ends. This coming week, it moves from Monoceros into Lepus, and is a few degrees away from the 2nd-magnitude star Saiph, the eastern foot of Orion. The farther south you live, the higher the comet appears in your sky. If the comet doesn't fizzle, it could attain naked-eye visibility by the time it rounds perihelion in late May and early June. Here are coordinates for Comet LINEAR at 0 hours Universal Time for the coming week: R.A. Dec. Apr 14 5h 58m -10.5 deg. Apr 16 5 57 -11.1 Apr 18 5 57 -11.7 Apr 20 5 56 -12.4 THIS WEEK'S "SKY AT A GLANCE" Some daily events in the changing sky, by the editors of Sky & Telescope. APRIL 15 -- SUNDAY * Last-quarter Moon (exact at 11:31 a.m. Eastern Daylight Time). * The naked-eye eclipsing variable star Algol should be in one of its periodic dimmings, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 9:38 p.m. EDT. Algol takes several additional hours to fade and to brighten. APRIL 16 -- MONDAY * Jupiter shines 5 degrees north of Aldebaran in the west during and after dusk. APRIL 17 -- TUESDAY * Jupiter is the brightest of the many winter stars and planets departing into the west at nightfall. To Jupiter's left is Orion, tilting now with his Belt horizontal. A similar distance left of Orion is bright Sirius. APRIL 18 -- WEDNESDAY * As dawn begins to brighten Thursday morning, look very low in the east-southeast for the waning crescent Moon. Look well to its left, due east, for Venus. APRIL 19 -- THURSDAY * Find bright Jupiter in the west in early evening and look far to its upper right to spot Capella. Equally far to Capella's upper left are Castor and Pollux. APRIL 20 -- FRIDAY * Very high in the south right after dark is the Sickle pattern of the constellation Leo. It looks like a backward question mark. Its brightest star is its bottom one, Regulus. APRIL 21 -- SATURDAY * The brightest star on the eastern side of the sky at this time of year is the Spring Star, Arcturus. As evening grows late, look low in the northeast for the Summer Star, Vega, already risen into good view. ============================ THIS WEEK'S PLANET ROUNDUP ============================ MERCURY is hidden in the glare of the Sun. VENUS is low in the glow of sunrise. Look for it just above the horizon due east about 45 minutes before sunup. MARS (magnitude -0.6) rises in the southeast around 11:30 p.m. and shines yellow-orange in the south before and during dawn. Well to its right is similarly-colored but much dimmer Antares. In a telescope Mars is 12 arcseconds wide and growing; it will reach 21 arcseconds when nearest to Earth in June. See the observing guide to Mars in the May Sky & Telescope, page 102. JUPITER and SATURN (magnitudes -2.1 and -0.2, respectively) shine rather low in the west during and after dusk. Jupiter is the brightest "star" there; look for yellowish Saturn well to its lower right. Closer to Jupiter's lower left is orange Aldebaran. To the upper right of Saturn are the Pleiades. URANUS and NEPTUNE (6th and 8th magnitude, respectively, in Capricornus) are very low in the southeast before dawn. PLUTO (magnitude 14; invisible without a large telescope) is in Ophiuchus in the south before the first light of dawn. (All descriptions that relate to the horizon or zenith -- including the words up, down, right, and left -- 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 [GMT] minus 4 hours.) More celestial events, sky maps, observing projects, and news of the world's astronomy research appear each month in SKY & TELESCOPE, the essential magazine of astronomy. See our enormous Web site and astronomy bookstore at http://www.skypub.com/ . Clear skies! SKY & TELESCOPE, 49 Bay State Rd., Cambridge, MA 02138 * 617-864-7360 =========================================================== Copyright 2001 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). Updates of astronomical news, including active links to related Internet resources, are available via SKY & TELESCOPE's site on the World Wide Web at http://www.skypub.com/. In cooperation with 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. For a free subscription, send e-mail to join@astromax.com and put the word "join" on the first line of the body of the message. To unsubscribe, send e-mail to unjoin@astromax.com and put the word "unjoin" on the first line of the body of the message. If you should have any problems either subscribing to or unsubscribing from the list, send a message to list administrator John Wagoner at stargate@gte.net for assistance. --------------------------------------------------------------------- SKY & TELESCOPE, the Essential Magazine of Astronomy, is read by more than 200,000 enthusiasts each month. It is available on newsstands worldwide. For subscription information, or for a free copy of our catalog of fine astronomy books and products, please contact Sky Publishing Corp., 49 Bay State Rd., Cambridge, MA 02138-1200, U.S.A. Phone: 800-253-0245 (U.S. and Canada); 617-864-7360 (International). Fax: 617-864-6117. E-mail: custserv@skypub.com. WWW: http://www.skypub.com/. Clear skies! ===========================================================
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