SIGHTINGS


 
November Comet Dust
Cloud And Meteor Shower
Pose Threat To Satellites
By Tim Radford
The Guardian
From Scripps Howard News Service
10-5-98
 
 
November 17, 1998 will be one of the more spectacular periodic encounters with a dust cloud from a comet.
 
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.
 
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.
 
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.
 
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."
 
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.
 
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.
 
"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."
 
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.
 
"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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