for National Geographic News
This week marks the return of the Leonid meteor shower. The heavenly show is expected to peak on Friday, November 19, at 1:40 a.m. ET for sky-watchers in North America. The spectacle looks to be the second-to-last chance to see the shower in this century.
The Leonids, which recur each November, had a spectacular run between 1999 and 2002. The meteor showers of those years approached the intensity of "meteor storms," a threshold generally marked when viewers can see a thousand meteors an hour.
"Those terrific years have passed, and we're now back to a more normal level," said Kelly Beatty, executive editor of Sky and Telescope magazine and editor of Night Sky magazine. "Still, at a good dark site, you might see 15 [meteors] per hour."
A second peak around, also on the 19th, will treat Asian observers to some 60 meteors per hour.
Astronomers say the show should be a good one. They note, however, that predicting meteor shower intensity is not always an exact science.
"There's always a chance for a surprise," said Bill Cooke, a meteor-shower expert with the Space Environment Group at NASA's Marshall Space Flight Center in Huntsville, Alabama.
"The art of meteor forecasting has been around for only a few years," Cooke added. "We do very well on the timing. We can nail that to within a few minutes. But we're not always as good on the intensity."
While the frequency of the 2004 Leonid shower may not match that of previous years, the show will still pack quite a punch, observers say.
The meteors will zip into our atmosphere at 44 miles a second (71 kilometers a second). Most will vaporize between 56 to 62 miles (90 to 100 kilometers) above the Earth's surface.
"They are the fastest meteors in a known shower," said Beatty, the Sky and Telescope editor. "They tend to be very bright, and they leave behind a kind of glowing trail for a few seconds that a lot of other meteors do not."
The glowing "trains," sometimes compared to the visible exhaust plumes of rockets, hang in the sky for a few seconds before fading.
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