11232Fwd = Leonids: Imperfect Storm 'Casting
- Dec 1, 2001Forwarded by: fwestra@... (Frits Westra)
Original Date: Fri, 30 Nov 2001 17:37:50 -0800
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Leonids: Imperfect Storm 'Casting
By Noah Shachtman
2:00 a.m. Nov. 28, 2001 PST
It turns out the scientists predicting meteor showers aren't any more
accurate than the TV talking heads who say when it's going to rain.
The four major forecasts of the timing and strength of mid-November's
Leonid meteor shower "all were wrong," according to Bill Cooke, a
scientist at NASA's Marshall Space Flight Center, who helped make
one of the predictions.
Cooke and the other scientific teams successfully predicted when the
meteors would fall, preliminary evidence and eyewitness accounts
suggest. It's the intensity of the storms that they got wrong.
Peter Jenniskens, from NASA's Ames Research Center, forecasted up
to 4,200 meteors per hour above North America; the real number was
more like 1,000. Cooke said that there would be an hourly peak of
Leonid activity near Hawaii of around 1,300 meteors; instead, only
about 300 per hour fell.
"We sort of blew it there," he said.
Like all meteor showers, the Leonids are caused by the Earth passing
through the ice and dust left behind by a comet -- in this case, Comet
Tempel-Tuttle. Every 33.25 years, Tempel-Tuttle comes close to the
sun. The proximity causes the comet to eject a mass of particles.
These particles then form bands of debris that orbit around the sun.
On Nov. 18, Earth passed through at least three such bands. The ones
from Tempel-Tuttle's solar encounters in 1699 and 1866 went over Asia.
The band from 1767 could be seen over North America.
Despite their less-than-crystal-clear predictions of the Leonid
action, researchers are still heartened by the results. The art of
forecasting meteor showers is extremely young; the first accurate
prediction of a shower's timing came just two years ago, when an 1899
Leonid trail passed over Israel.
"Before that, no one knew when or where on Earth the shower could be
best seen. We only knew what day it would come," said the American
Meteor Society's Robert Lunsford.
Adds Cooke, "It's only in the last half-decade or so that we've had
the computing power to try these forecasts."
Since 1996, Cooke's colleague, Peter Brown, has been assembling a
computer model of 1 million particles from a comet over a 1,000-year
Data from the most recent Leonid shower -- NASA had observers
stationed from Florida to Guam to the Gobi Desert in Mongolia with
specially designed, low-light cameras recording the event -- will be
used to enhance the model, to try to make it more accurate. The other
scientific teams are also using computer modeling in their work, but
they all follow different approaches.
Comets remain objects shrouded in mystery to scientists; the core of a
comet, for example, was viewed for only the second time ever in
September by NASA's Deep Space 1 probe.
One of the biggest mysteries is why people are not only able look at
meteor showers, but can sometimes listen to them as well.
"I just walked outside at 4:46 a.m. EST (on Nov. 18) ... and it's
actually loud. There's a solid stream of hissing.... Is it possible to
hear meteors?" asked Chris Hahn of Lawrence, Massachusetts, in an
e-mail to NASA's Spaceweather.com.
Stranger still, witnesses are reporting no lag between the sight of
the meteor and the sound of it, as there is with lightning and
[Part 2 of this story at:]
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