Strong Leonid meteor showers expected Nov. 17

By Joe Rao

updated 4:03 p.m. ET Nov. 2, 2009

Circle Nov. 17 on your calendar, for early that morning a moderate to possibly very strong showing of annual Leonid meteor shower is likely.

The very strong display will favor those living across most of central and eastern Asia.  In this region, meteor rates might briefly rise to a few hundred per hour (the time frame for the most intense activity is anticipated sometime around 21:40 GMT). 

A far more modest, but still potentially enjoyable display of a few dozen Leonid meteors per hour is expected to favor North America. In the United States and Canada, eastern observers will be particularly well-positioned for maximum activity, expected sometime between 3:30 and 5:30 a.m. EST, when the radiant of the Leonid shower will be well up in the dark southeastern sky.

A meteor shower's radiant is the perspective point from which all the meteors would appear to originate if their paths were traced backward far enough. The higher the radiant is, the more meteors flash into view all over the sky (though meteors can appear anywhere in the sky, so focusing on the radiant is not necessary).

The Leonid radiant is within the so-called "Sickle" of Leo; a backwards question-mark pattern of stars that outlines the head and mane of the constellation Leo, the Lion. Hence the meteors are known as "Leonids."

Not in the East? Don't fret. Observers all across North America may experience a good Leonid show with "shooting stars" streaking across the sky every few minutes.

INTERACTIVE Your guide to the meteor show A look at meteor showers and how to view them

Also a big plus in 2009 is the lack of any interference from the moon.  New moon is on Nov. 16, so skies will be dark for catching the fainter meteor streaks. And the first light of dawn will not break until shortly after 5 a.m. local time.

Europe and Africa appear largely out of luck. This year's first round of expected enhanced activity will happen chiefly during their daylight hours. The second, stronger outburst will occur during early evening, but that's hours before Leo comes above the horizon. Europeans might try watching before sunrise on the morning of Nov. 17, but are not likely to see more than 10 or 15 Leonids per hour.  

Cosmic garbage
It may not sound sexy, but simply put, the reason for this year's anticipated good Leonid showing is due to cosmic garbage.

The Leonids are known to be made up of cosmic litter from a small — 2.2 mile — dusty comet discovered by two astronomers in the late 19th century and christened Tempel-Tuttle. The Leonid meteors are thought to be the dusty legacy of Comet Tempel-Tuttle because the dust is moving around the sun in virtually the same orbit as the comet. 

As the Earth encounters the debris left behind by the comet's previous passes through our orbit, these tiny fragments of the comet — typically no bigger than a sand grain or the occasional pea — impact our atmosphere at speeds of up to 45 miles per second, causing them to blaze briefly but brightly in the night sky.

The Leonids are not a one-night stand. The dust from Tempel-Tuttle spangles the sky for a few nights every year in mid-November. This year, the peak is expected during the predawn hours of Nov. 17, but early-morning hours on the dates surrounding Nov. 17 could provide a decent show, too. 

Tempel-Tuttle last passed near the sun and Earth more than a decade ago (in 1998) and for several years thereafter the Leonids put on some spectacular displays, producing many hundreds – even thousands of meteors per hour. But with the departed comet now cruising through the outer part of the solar system, we typically would not expect to see more than 8 or 10 Leonids during an hour's watch.

Yet if several meteor scientists are correct, this year will be atypical. The researchers have produced various models of the Leonid stream and all of them are indicating that the Earth will intersect a few "rivers of rubble" left behind by Comet Tempel-Tuttle.

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