"Stars fell like rain" was how ancient Chinese astronomers described the first Leonid meteor storm in AD 902. Subsequent stargazers likened the celestial display to a "night of raining fire." Others believed it surely heralded Judgment Day.
While Leonid outbursts happen every year, their intensity and conditions on Earth don't often combine to make them easy to view. But tomorrow and Wednesday, astronomers anticipate a visually epic event. At the height of the storm, as many as 10,000 meteors per hour will flit across the sky like celestial fireflies.
"It is an amazing thing to see," says Catharine Garmany, director of Fiske Planetarium at the University of Colorado in Boulder. The eye of the storm is expected to occur during daylight hours in the United States, but predawn viewing should produce a worthy spectacle.
Meteors, commonly called shooting stars, are streaks of light that appear when a comet's contrails evaporate in the earth's upper atmosphere. The Leonids, so named because they seem to emanate from the constellation Leo, are in fact the long tail of the comet Tempel-Tuttle, which orbits the sun every 33 years. As the earth passes through the comet's wake, the Leonid showers are visible for several days as particles speed across the sky at up to 160,000 miles per hour.
Astronomers can't say exactly what the Leonids will produce this year. But the showers hit peak activity only about once a century, and many believe 1998 will be the year. Still others say November 1999 could bring the best show.
But not everyone is excited about the meteor event: Some 500 satellites are in orbit around the earth and could be damaged by rocketing debris. Meteors range in size from a grain of sand to a pebble, and one whack from a larger particle could knock out a satellite. Because these bits move through space at such terrific velocities, even the smallest bits pose a threat. The speed can cause an electrically charged cloud called a plasma, which could upset sensitive electronics.
"Even a grain of sand will do a great deal of damage when it's traveling on the order of 40 miles per sec," says Ian Stewart, senior research associate at the Laboratory for Astrophysical and Space Programs at the University of Colorado. "That would cross the country in 15 minutes." It would also pack a wallop comparable to a blast from a Colt 45.
Satellite operators - including the US military - are taking precautions, such as angling solar panels in the least vulnerable positions. The Pentagon considers the threat to its spy, communications, and other satellites as "elevated but not serious" - not enough to change any military preparations in the Persian Gulf.
For space scientists, the Leonid storm provides more than just visual entertainment: It is a rare opportunity to learn more about meteors. The US is flying two research aircraft over Japan during the storm's peak, at altitudes as high as 40,000 feet. The $870,000 mission is a joint project of the National Aeronautics and Space Administration, the National Center for Atmospheric Research in Boulder, and the National Science Foundation.
"What the return of Halley's comet was to comet studies, the return of a Leonid storm will be to meteor astronomy," says Peter Jenniskens, a lead scientist at NASA's Ames Research Center at Moffett Field, Calif. "The Leonid showers' historic role cannot be overemphasized, but scientific observations have been very few."
NASA's Electra aircraft will tote state-of-the-art observing equipment to measure the density and fluorescence of the molecules as they vaporize. This could help researchers estimate the weight of a meteor, and may even provide clues about the origin and prevalence of life in the universe.
* Best place to view the storm: Eastern Asia and Australia. (But don't worry, even in North America, clear skies should allow for a good show, even without binoculars.)
* Set your alarms: The best viewing will be around 2 a.m. (in observer's time zone) on Nov. 17 and 18. Next chance to view a Leonid storm may not be until 2098 or 2131.
* Viewing tips: Get away from city lights. Focus on the darkest part of the sky, about 50 degrees up from the eastern horizon.