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- November 17, 1998 will be one of the
more spectacular periodic encounters with a dust cloud from a comet.
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- Tiny fragments of stardust -- the size
of a grain of sand or rice -- will hit the Earth's atmosphere at 41 miles
a second, and burn up in a blaze of glory in the early morning sky, at
the rate of at least one a second when Earth runs head-on into the Leonids.
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- Rocket launches will be suspended, the
Hubble space telescope will look away and satellites' solar panels will
be moved out of the line of fire.
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- Meteor storms and showers are predictable
-- as with the Perseids last month. But every 33 years, a group called
the Leonids provide a series of spectacular autumn encounters.
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- If this year is a disappointment, then
pin your hopes on Nov. 18, 1999, says Mark Littmann, professor of astronomy
at the University of Tennessee at Knoxville. "Back in 1966, they were
estimated at as high as 40 meteors a second. This time around, a meteor
a second would be very impressive. People who saw it in 1833 said it was
like the heavens were on fire. It is like nothing else that can be seen
in the night time sky."
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- People in the Far East will probably
get the best show when the constellation Leo rises over the horizon after
midnight. "Don't watch for just a minute or two, because it can come
in spurts," he said.
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- The encounter is with a ribbon of dust
shed by Comet Tempel-Tuttle. Meteors that burn up in the atmosphere and
meteorites that hit the ground are a fact of life. Shooting stars appear
every night. The guess is that Earth collects an average of 500 tons of
stones, dust, water and gases from space every day.
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- "Over the 4 billion years the Earth
has been in existence," Littmann says, "we have added 16 million
million million tons, but even so we have added less than 1 percent to
the Earth's mass."
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- But the Leonids are the fastest arrivals
of all, because the Earth runs into them almost head on. Humans are in
no danger. But the radio region of the upper sky will fizz, crackle and
pop, and instruments orbiting above the atmosphere will be at extra risk.
NASA engineers and satellite operators have been meeting to work out just
how big that risk will be.
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- "Even though we are dealing with
something the size of a grain of sand or smaller, traveling at 150,000
mph, it's like a bullet," Littmann said.
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