The Perseid meteor shower has comeand gone, but that doesn't mean that there aren't any more good meteor displaysto look forward to. In fact, another potentially good shower is just around thecorner, scheduled to reach its peak during the early hours of Saturday,September 1st: the Aurigid meteors.
The Aurigids get their name fromthe constellation of Auriga, the Charioteer. Themeteors appear to emanate from a spot in the sky near the bright yellowish starCapella in Auriga. The Aurigids, however,are rarely mentioned in most astronomy guidebooks because they are hardly worthmentioning in any given year.
Then why bother about a shower that almost nobody has heardof and that's due this year just days after a bright full moon?
Because in 2007, these unheralded Aurigidsare this summer's wild card.
Unlike the steady and reliable Perseids,little or no activity is usually seen from the Aurigids.Yet, every once in a great while a short-lived outburst ofbright meteors has been reported from the Aurigidshower. Peter Jenniskens of the SETI Institute's Carl Sagan Center has recently shown that theserare outbursts of Aurigid activity were caused by acomet which ejected a trail of dust that very occasionally wanders into theEarth's path.
Outburst in 2007?
Aurigid outbursts are veryinfrequent, having been definitively seen on only three occasions: in 1935,1986 and 1994. There were very few witnesses on each occasion, because thesesudden outbursts were totally unexpected.
But now, for the first time, an alert for an impending Aurigid outburst has been issued.
At the 26th General Assembly of the InternationalAstronomical Union Conference held last August in Prague, Czech Republic,Jenniskens announced that the Aurigidswould likely produce another round of unusual meteor activity on September 1 ofthis year. This forecast is based on calculations made by Jenniskensand colleague Jérémie Vaubaillonof Caltech, and on earlier work in collaboration with amateur astronomer Esko Lyytinen of Finland.
The cometresponsible for the Aurigids is well known: Comet Kiess, which last appeared in 1911. In carefully examining its movements, the meteor scientists havedetermined that prior to 1911, this comet previously swept passed the sunsometime around the year 82 BC (when Julius Caesar was alive). Jenniskens and Vaubailloncalculated that a trail of dust released by the comet at that 82 BC visit willrun smack into Earth's path when our planet passes by on September 1.
Far-western states favored
On Saturday morning, September 1st, in the hour centered onabout 11:37 UT, Earth should encounter the trail of dust released from Comet Kiess.
That moment (4:37 a.m. Pacific Daylight Time) favors thefar-western parts of the United States, where the constellation Auriga will be about two-thirds up in the northeast skyaround the time morning twilight begins. If you live in Portland,San Francisco or Los Angeles, you'll be in perfect position toview the meteors.
Hawaii (1:37 a.m.) and Alaska (2:37 a.m.) willalso be in darkness when the Aurigids arrive,although Auriga will appear much closer to thenortheast horizon. Like the previous outbursts, the upcoming display isexpected to be short-lived: probably lasting no more than an hour or so atmost.
Unfortunately, most of the rest of North America will be out of luck: either bathed in bright twilight ordaylight when the dust trail arrives.
Jenniskens and Vaubaillonare forecasting a ZHR (zenithal hourly rate – the number of meteors seen by asingle observer under a clear, dark sky with the meteors' emanation pointdirectly overhead) of 200. Their outlook is very similar to EskoLyytinen, who predicts a ZHR of 300, but with anadded uncertainty of 1 to 3. Notes Lyytinen,"This would mean something between about 100 and 1,000. Let's hopethis will be around 1,000!"
There is, however, a significant drawback: a bright gibbousmoon will be lighting up the sky on the morning of the shower.
But because the Aurigids ramthrough our atmosphere at exceptionally high speeds of 41 miles per second (66 kps), and since these particles are predicted to be ratherlarge, the display is expected to be rich in bright meteors, with manyappearing as bright as the brightest stars and a few perhaps approaching oreven rivaling Jupiter and Venus. "So," says Jenniskens,"the moon probably won't dim much of the display."
Probably the safest bet is to play it conservative andforecast a rate of perhaps only 20 to 30 per hour, which is what was observedduring the three previous Aurigid outbursts. But ifthose meteors are as bright as the calculations suggest they will be, it couldstill be a memorable – albeit brief show.
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Joe Rao serves as an instructorand guest lecturer at New York'sHayden Planetarium. He writes about astronomy for The New York Times and otherpublications, and he is also an on-camera meteorologist for News 12 Westchester, New York.