http://www.space.com/spacewatch/comet_neat_030131.html
Promising New Comet Called NEAT Graces Evening Sky By Joe Rao space.com 31 January 2003 During the next few weeks skywatchers can look for a recently discovered comet that may become plainly visible in the evening sky, and could possibly shine very brightly, just before a close encounter with the Sun. Officially catalogued as C/2002 V1, the comet is currently visible with a pair of binoculars. Astronomers who attempt to forecast the future characteristics and behavior of these cosmic vagabonds have found this one to be particularly capricious. It may not brighten much more. Or it may soon be visible to the naked eye. There has even been talk that it might shine so brightly as to be visible during broad daylight, though such high hopes have dimmed in recent days. The comet is commonly referred to as NEAT, for its discovery in November by NASA's Near Earth Asteroid Tracking program at the Jet Propulsion Laboratory (JPL). Comets brighten, and display a head and tail, because the Sun boils surface material away, which then glows with reflected sunlight. But the process in not completely understood, and each comet tends to behave a bit differently. Some even come apart as they approach the Sun. Comet NEAT has already shown itself to be an oddball, so before projecting what NEAT might do, a little history is in order. NEAT History The first word about this new C/2002 V1 reached the astronomical community on a routine announcement card from the Smithsonian Astrophysical Observatory (SAO), Cambridge, Massachusetts, the clearinghouse in the United States for astronomical discoveries. The SAO also serves in that capacity as an agency of the International Astronomical Union. The I.A.U. Circular No. 8010, dated Nov. 6, 2002, stated that Steven H. Provdo of NASA's Jet Propulsion Laboratory reported the discovery of a new comet as part of NASA's Jet Propulsion Laboratory's NEAT program. NEAT is an autonomous celestial observatory searching for and studying asteroids and comets that roam the same region of the solar system through which Earth orbits. The NEAT system, using a 1.2-meter (4-foot) telescope, is located in Hawaii and is a cooperative effort with the U.S. Air Force. The following day on I.A.U. Circular 8011 a preliminary orbit for the new comet was published. The comet was then about 217 million miles (349 million kilometers) from the Sun. It was projected to make its closest approach to the Sun (called "perihelion") at a distance of 9.2 million miles (14.8 million kilometers) on Feb. 18, 2003. That's just under one-tenth the Earth's average distance from the Sun. At the time of its discovery, the comet shone at a very feeble magnitude of +17.3 - which is about 25,000 times dimmer than the faintest stars that can be perceived with the unaided eye. Astronomers use positive numbers for dim objects. The faintest star visible shines at about magnitude 6.5, but can only be seen under absolutely dark sky conditions away from all local lighting. The brightest objects achieve zero or negative magnitudes. The first predictions indicated that the comet would dutifully brighten as it approached the Sun, possibly reaching second magnitude (the brightness of Polaris, the North Star) at perihelion. At that time however, the comet would be positioned just six degrees from the Sun in our sky and would be hopelessly drowned-out by the brilliant solar glare. But during December, a curious thing began to happen. Erratic behavior Comet NEAT started brightening very rapidly late last year, far outpacing even the most optimistic brightness forecasts. Were it to continue brightening in the same manner as it approached the Sun, the comet would have likely evolved into an amazingly brilliant object, perhaps briefly becoming visible even in broad daylight, a feat commonly achieved only by the Sun, the Moon and the planet Venus (for experienced skywatchers) But by early January the level of brightening slowed considerably. Suggestions were then put forward that comet NEAT might actually start to fizzle out as it crossed the Earth's orbit on its inbound approach to the Sun; perhaps its brightening would stop completely, or it might even start getting dimmer. Were it just a small comet, NEAT would certainly become well cooked at its close approach to the Sun and, in addition, might be subjected to great disruptive forces that could break it up or even destroy it totally. But in mid January, a new orbit calculated for NEAT demonstrated that it is moving around the Sun in a highly elliptical orbit, taking roughly 37,000 years to make one complete revolution around the Sun. That means the comet likely has been through the inner solar system at least once before - probably more than once - suggesting that it has survived previous close brushes with the Sun. ---------------------------------------------------------------------------- See NEAT now Currently, comet NEAT is shining at around magnitude +5.5 and might actually be glimpsed by sharp-eyed observers in a dark, clear sky amidst the faint stars of the constellation Pisces. [See map near the top-right of this page or create your own map] For several days it will be located below and to the right of a ring-like pattern of dim stars known as the Western Fish or "Circlet" of Pisces. In the early evening sky it can be readily picked up in binoculars about an hour or so after sunset as a small, circular patch of light with an almost star-like center. In small telescopes the comet's gaseous head or "coma" appears to fill a region of the sky roughly one-fifth of the Moon's apparent diameter as seen from Earth (an actual linear distance of 148,000 miles, or 237,000 kilometers). The comet also displays a short, faint, two-pronged tail composed chiefly of ionized gases. Astronomers are now puzzling over how bright the comet get in the next few weeks as it draws closer to the Sun. ---------------------------------------------------------------------------- Latest Forecast Some veteran observers have watched comet NEAT during the past few weeks and have been impressed with its development. Among those voicing sanguine comments is Clay Sherrod of the Arkansas Sky Observatory. "From observations around the world, NEAT is shaping up to be a remarkable comet and hopefully a showpiece for the public to kickstart their enthusiasm back into mainstream astronomy," Sherrod said recently. "It has been a long dry spell for bright comets." Long-time Australian comet observer Terry Lovejoy points out that during the next couple of weeks comet NEAT will be best placed for observation chiefly from the Northern Hemisphere. "'At the start of February the comet is still 20 degrees up from the western horizon after evening twilight and there is no moonlight interference," Lovejoy says. "It should be magnitude 5, very well condensed, with a faint tail several degrees long, visible with binoculars. The highly evolved complex gas tail will make it an excellent target for astrophotographers." "Realistically," Lovejoy is careful to point out, "the comet might brighten to magnitude +3 or +4 as it drops lower into the evening twilight and might be lost to view sometime around Feb. 10. Predicting the brightness at the February 18 perihelion is really guesswork, but most likely it will be somewhere between magnitude +1 and -2." Misleading so far Another well-known comet expert, John Bortle of Stormville, New York, has also been carefully following comet NEAT. "This object has already proven a bit of an oddball," Bortle says, adding, "its appearance and apparent development have misled many folks so far." Earlier this week, Bortle applied two different brightness formulae to NEAT in an attempt to forecast how it might entertain. In one scenario, the comet brightens to magnitude +5 by February 3, to +4 by February 8 and +3.1 on February 11. On the last date the comet's elongation from the Sun will have been reduced to 18 degrees and it is unlikely to be viewable more than a day or two further. On the day of perihelion passage the comet could attain magnitude -0.4. "Impressive," Bortle says, "but unfortunately not bright enough to glimpse in daylight." But in Bortle's other scenario, he used a special time-dependent formula analysis that suggests that NEAT will get as no brighter magnitude +5 -- barely visible to the naked eye under the darkest sky conditions. Regardless which script the comet ultimately follows, he also believes that the comet's survival after whirling around the Sun on Feb. 18 "could still be something of a toss-up. Caution is going to be the watchword on this one." Watch it on the Web Even is the comet does not brighten dramatically, anyone with an Internet connection will have a chance to watch it as it rounds the Sun, courtesy of the LASCO C3 coronagraph mounted on the SOHO spacecraft. SOHO is a cooperative mission between the European Space Agency and NASA. The spacecraft is stationed in a halo orbit around the Sun-Earth L1 Lagrangian point, a position roughly 930,000 miles (1,500,000 kilometers) sunward of Earth. At this point in space, the orbital period of SOHO exactly matches the orbital period of Earth. From this orbit, SOHO is able to observe the Sun 24 hours a day. Many people used the SOHO web pages to watch another recent comet, called Kudo-Fujikawa (C/2002 X5). It first appeared on SOHO snapshots Jan. 25, looking like a small, white teardrop directly above the Sun, at the top of the circular frame. During the following days, the comet made its way diagonally down to one side of the Sun (which is behind an occulting disk at the center of the field). Comet Kudo-Fujikawa remained within the field of view of SOHO through Jan. 31. Comet NEAT's turn to come within SOHO's camera range will be between Feb. 16 and Feb. 20, allowing ground-based viewers to safely monitor it on their home computers even though it will be very near to the blindingly bright disk of the Sun. ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
