Leonids 2000: Predicted Flurries
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A note about time: UT=Universal Time; EST=Eastern Standard Time, the time on the US east coast.

Leonid meteor outbursts happen when Earth passes close to dusty debris trails laid down by comet Tempel-Tuttle. The comet returns to the inner solar system every 33 years --the last time was in 1998-- but it never follows the same path twice. Gravitational perturbations by the planets, particularly Jupiter, nudge it into slightly different orbits each time around. As a result, no two of its debris trails are in the same spot. They are laid out in a complex pattern that has baffled astronomers for many years. Lately, though, researchers have figured out where many of the dust streams are located and can predict when Earth will pass through one.

Above: Earth's path through space is shown in blue. Auburn-colored ellipses denote dust streams laid down by comet Tempel-Tuttle in the indicated years. Until they disperse after a few centuries, these narrow trails are regions that have a high density of meteoroids and so there is a meteor storm if the Earth passes through one. This year our planet will pass close to trails deposited in 1932, 1733 and 1866. Courtesy of Dr. David Asher (copyright 2000, all rights reserved). [more information]

This year Earth will glide through the outskirts of three debris streams, but we won't hit any dead center. The result could be modest outbursts at the following times:

Friday, Nov. 17.
Time: 7:50 am UT (2:50 am EST)
Earth will approach material ejected from comet Tempel-Tuttle in 1932. The most optimistic models suggest an outburst of 800 meteors per hour; 100 per hour is a more likely maximum. Bright moonlight might reduce the number of meteors visible in a single hour to no more than 25% of these values.

Date: Saturday, Nov. 18.
Time: 3:44 am UT (10:44 pm EST on Friday)
Earth will approach material ejected from comet Tempel-Tuttle in 1733. Experts say this is the most likely time to see a Leonids outburst in 2000. Models suggest as many as 700 meteors per hour under ideal conditions, although bright moonlight could reduce that number by 75%. If it occurs, this outburst might last for a few hours centered around the time of the peak.

Observers in the United States are not favorably placed for this potential flurry. The constellation Leo, as seen from the US east coast, will be just below the horizon at the time. However, east-coast observers could spot a special type of meteor called an Earthgrazer. These are long, bright shooting stars that streak overhead from just below the horizon. They often display colorful halos and long-lasting trails. Earthgrazers are so distinctive because they follow a path nearly parallel to our atmosphere.

Date: Saturday, Nov. 18.
Time: 7:51 am UT (2:51 am EST)
Earth will approach material ejected by comet Tempel-Tuttle in 1866. The most optimistic predictions suggest 700 meteors per hour; 100 per hour is more likely. Like the other peaks, this one will be less dazzling because of bright moonlight that will substantially reduce the number of visible meteors. The NASA meteor balloon will reach the stratosphere during this peak. Don't miss the live webcast!

What if it's a dud?

One of the greatest uncertainties in these predictions is the width of comet Tempel-Tuttle's dust streams. For instance, on Nov. 18th Earth will pass approximately 0.3 lunar distances (LD) from the 1733 and 1866 debris trails. But how wide are those trails? No one knows. If observers see substantial outbursts at the predicted times, researchers can conclude that the trails are at least 0.3 LD wide. On the other hand, if this year's Leonids are a dud, we can surmise that the relevant trails are much narrower than our near-miss distances in 2000.

Note: One "lunar distance," or LD, equals 384 thousand km, the average distance between Earth and the Moon.

For more information about Leonid dust streams and meteor outbursts, please visit Leonid Meteors 2000 from the Armagh Observatory.

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