Get Ready for the Leonid Meteor Shower

From MSNBC

When people hear about an impending meteor shower, their first impression may be of a sky filled with shooting stars pouring down through the sky like rain. Such meteor storms have actually occurred with the annual Leonid meteor shower of November, such as in 1833 and 1966, when meteor rates of literally tens of thousands per hour were observed.

In more recent years, most notably 1999, 2001 and 2002, lesser Leonid displays of up to a few thousand meteors per hour thrilled skywatchers.

This year will not set any records, but the Leonids - set to peak early Tuesday morning, Nov. 17 - should offer a better-than-average display.

The Leonid meteors are debris shed into space by Comet Tempel-Tuttle, which swings through the inner solar system at intervals of 33.25 years, looping around the sun then heading back into the outskirts of the solar system. During each visit the comet leaves behind a trail of dust in its wake.

Plenty of the comet's old dusty trails litter the mid-November part of Earth's orbit, and the Earth glides through this debris zone every year. But predicting exactly what's out there is tricky.

On special occasions we'll pass directly through an unusually concentrated dust trail, or filament, which can spark a meteor storm resulting in thousands of meteors per hour. That indeed is what transpired in 1999, 2001 and 2002. Since Comet Tempel-Tuttle comet passed near the sun (and in doing so crossed Earth's orbit) in 1998, it was in those years immediately following its passage that the Leonids put on their best show.

But the comet has since receded out to a distance of 1.8 billion miles (2.9 billion kilometers) from the sun, taking most of those dense filaments of dust with it. That's why this year, during the predawn hours of Nov. 17, when the Leonids traditionally should be at their most numerous, we now expect to see no more than 10 meteors per hour, even with the promise of this year's excellent viewing conditions thanks to a new moon.

Still, for some parts of the world, a far more prolific Leonid show could be in the offing this year. For although Comet Tempel-Tuttle is now far removed from the inner solar system, independent studies by several noted meteor scientists suggest that Earth will pass through several notable trails of meteor activity in 2009. We list these encounters below in chronological order, including the prime regions of visibility.

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