First we get a rare chance to view the magical colors of the aurora borealis?now we can see the biggest Leonid fireball storm in years.
The Leonid shower of 1998 was extraordinary, but the meteor rates never exceeded a few hundred shooting stars per hour. ?We define a meteor storm to be times when observers can see 1000 or more per hour,? says Bill Cooke from the NASA Marshall Space Flight Center. ?The Leonids of ’98, as spectacular as they were, were not a full-fledged storm.? But this year?s Leonids will be.
Cooke and other experts agree that when the Leonids return later in November, sky watchers in some parts of the world will see a display even better than the one in 1998. Says Cooke, ?What?s coming on Nov. 18th could be the biggest event since 1966 [when North Americans saw a Leonid storm numbering 100,000 shooting stars per hour].?
Observers in North America, Hawaii, Australia and Asian countries along the Pacific Rim will have the best views. Meteor rates in those places could climb as high as 8,000 per hour.
Leonid meteor storms occur when Earth passes through clouds of dusty debris shed by comet 55P/Tempel-Tuttle when it comes close to the Sun every 33 years. This year we will have close encounters with four such clouds, that were shed by the comet long ago, in 1699, 1766, 1799 and 1866.
?Each encounter with a dust cloud will produce an outburst of Leonids over some part of our planet,? says Cooke. ?For example, the best place to view the 1799 meteoroids is Hawaii. That?s where I?ll be.? The 1766 cloud will produce a huge number Leonids over North America, while the 1699 and 1866 clouds will rain meteors over Australia and east Asia.
?These clouds are long and narrow like a comet?s tail,? says Cooke. ?The younger ones are only 10 or so Earth-diameters wide.? In most Novembers we can?t see them at all. The Earth glides between the clouds where there is only a sprinkling of meteoroids. At such times Leonid rates remain as low as only 10 or 15 meteors per hour.
?In 1998 we passed through material shed by the comet in 1333,? says Cooke. ?That filament was old and somewhat spread out,? so rates never climbed to storm levels. It was still spectacular because ?the smallest bits of dust inside that cloud had been blown away long ago by solar radiation pressure. Only the largest meteoroids remained — hence the fireballs. In 2001 we?re running into relatively young clouds, richer in small meteoroids. Observers from ’98 who remember mostly fireballs will be dazzled this year instead by a greater number of ordinary meteors.?
The science of forecasting Leonid meteor storms is still young. The basic techniques were pioneered only three years ago by astronomers David Asher, at Armagh Observatory, and Rob McNaught, at Australian National University. They correctly predicted a brief meteor storm over the Middle East and Europe in 1999. Then, in 2000, they and others used similar methods to forecast the times of three more Leonid storms.
If you want to see the Leonids this year, go someplace away from urban light pollution. Be prepared to watch the sky between midnight and sunrise on Sunday morning, November 18th. Meteor rates will probably be low near midnight, then climb to 10 or 20 per hour by dawn. If you?re lucky you might witness a storm-level outburst and count thousands of shooting stars.
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