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11232Fwd = Leonids: Imperfect Storm 'Casting

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  • Frits Westra
    Dec 1, 2001
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      Forwarded by: fwestra@... (Frits Westra)
      URL: http://www.wired.com/news/technology/0,1282,48671,00.html
      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 [52]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
      period.

      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
      thunder.

      [Part 2 of this story at:]
      http://www.wired.com/news/technology/0,1282,48671-2,00.html

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