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Italian astrophotographer Lorenzo Lovato imaged this Leonid fireball on Nov. 17, 1998.


This illustration, among the most famous depictions of the 1833 Leonid meteor shower, was produced some 50 years after the event. The depiction is through the eyes of a government civil servant on his way from Florida to New Orleans.


Norwegian astrophotographer Arne Danielsen captured this spectacular Leonid fireball on November 18, 1999.
The Power of a Shooting Star
Earthgrazers and Fireballs: The Strange Side of the Leonids
By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
16 November 2001

leonids_commentary_011116

Editor's Note: This article was written in 2001 but its principles apply to subsequent years.

The Leonid meteor shower is a strange show. Its meteors are among the fastest known. It is notoriously difficult to predict. And it is a total night owl, refusing to show its best stuff until well after midnight.

Moreover, there are some strange characters to look for as the shower's source ekes above the eastern horizon late at night and into the early morning hours of the annual peak.

A handful of meteors will first zoom across the horizon for long stretches of time. Earthgrazers, they're called. And if you're real lucky, you might spot some fireballs -- larger meteors that explode upon impact with Earth's atmosphere, generating spectacular blazes of light (not to mention fear of alien spacecraft and calls to local law enforcement offices).

Earthgrazers

Leonid meteors will take their time arriving the night before the peak. Wherever you are on Earth, you're viewing location has to rotate into the stream of space dust that causes the Leonids. The shooting stars will appear to emanate from a point in the sky known as the radiant, which for the Leonids happens to be in the constellation Leo (hence the name).

No knowledge of this is needed to find an earthgrazer. Just go out and look to the east. The timing depends on where you live. Figure mid-evening for high northern latitudes, such as Canada; late evening hours for mid-northern latitudes, as in most of the United States; and after midnight for equatorial regions and the Southern Hemisphere.

What might you see?

"When the radiant lies near the horizon the Leonid meteors cannot penetrate far into the Earth's atmosphere," explains Robert Lunsford of the American Meteor Society. "At this time they are only able to skim the upper atmosphere."

These earthgrazers, as scientists call them, often last several seconds and can span a great distance of the sky, Lunsford said.

To see an earthgrazer, you'll need an unobstructed view of the eastern horizon.

Later, as Earth continues rotating, the Leonid radiant moves higher into the sky, along with its host constellation and all the stars. Meteors will strike the atmosphere at a more direct angle, Lunsford explains, creating shorter paths. But the paths will still span much of the sky, so you don't need to face East. In fact, the best views will be everywhere but directly East.

Just go out, look up.

Fireballs

Most Leonid meteors are created by sand-sized grains of dust that vaporize about 60 miles up due to the heating caused by Earth's atmosphere. But Tempel-Tuttle, the comet that has left all this Leonid raw material in space, also deposits a few larger chunks of itself each time it swings around the Sun (which it does every 33 years).

A comet fragment the size of a marble can generate a glorious fireball of light as it burns up. Instead of slicing through the atmosphere like a small bit of dust, such a pebble sometimes goes splat upon meeting up with a certain density of air.

"The Leonids can have fireballs, but they're not especially noted for them," said Bill Cooke, a meteor researcher at NASA's Marshall Space Flight Center. Cooke said the number of fireballs each year depends in part on which streams of cometary debris Earth plows through.

In 1998, observers noted several fireballs when the planet moved through a stream that comet Tempel-Tuttle had deposited in the 14th Century. The Sun's radiation had blown much of that ancient dust into a widely dispersed region of space, so the 1998 Leonids did not produce a great number of shooting stars.

But the larger material -- fireball material -- was still relatively concentrated. In fact, Cooke said, scientists are learning that gravity acts on these larger fragments, causing them to be huddled more closely together over time. They call the process "gravitational focusing."

No one can say how many fireballs might be visible this year, but one thing is for sure: With the Moon outshining many meteors, fireballs stand to be even more conspicuous.

Full coverage: Leonids Special Report

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