Leonid meteors promise a particularly bright night

By , Staff writer for The Christian Science Monitor

For lovers of the starry night, the Leonid meteors return each November like galactic swallows. Normally, they build from a few per hour to peak at numbers plentiful enough to be called a "shower" (possibly 100 or more in an hour).

That wasn't the case last year. We saw a meteor "storm." As astronomers accurately predicted, millions of people were dazzled by hundreds, if not thousands, of streaking, flaming, exploding fireballs.

This year, our solar system is giving us a second chance to be totally awestruck. There are two "storms" predicted for the 2002 Leonids. The first is on Nov. 18 about 11 p.m. Eastern time. The second peak will occur 6-1/2 hours later, around 5:30 a.m., EST. Predictions are for peaks of up to several thousand per hour.

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Don't miss it. A Leonid storm (at night) won't happen again until early in the 22nd century.

The Leonids are dross from the Comet Temple- Tuttle. It orbits the sun every 33 years (keep this number in mind, as it is a key reason why astronomers predict a meteor storm rather than a shower).

Residue from the comet strings out along its entire elliptical orbit, forming a "river" of space dust made up of millions of tiny particles no bigger than fine ash. These particles elliptically orbit the Sun. Earth crosses paths with this debris every year in mid-November – like bugs against a windshield. The particles, traveling at more than 140,000 m.p.h., collide with Earth's atmosphere some 80 miles up and incandesce.

The point of impact is referred to as the radiant. The radiant for the Leonids occurs close to the constellation Leo, hence their name.

Why a meteor storm rather than a shower?

The answer is simple and complex at the same time. Comets are giant snowballs with stellar dust frozen inside. The comet's ice encases the dust.

But as a comet travels closest to the sun, the ice particles on the surface of the comet heat up and vaporize.

As the ice turns to gas, dust particles in the ice escape in one big cloud and float free. Those dust particles, like the gas, continue to orbit in the gravitational trail of the comet. This escape process is not one seamless trickle. It is a burst. It happens every 33 years, (the time it takes for Temple-Tuttle to travel closest to the sun).

Over time – we're talking eons here – the cloud dissipates into a thin stream of particles. It is these particles that provide the material for a meteor shower each November. But before it dissipates, the cloud of particles continues in orbit as well. Every 33 years, as Earth collides with Temple-Tuttle's debris, it bulldozes through this cloud. The result is a meteor storm.

Best viewing of the first peak will be the night of the Nov. 18 in Europe and North Africa with meteors visible low to the east-northeast in North America at 11 p.m., EST.

The peak of the second storm offers the best viewing for North America.

The early morning event on Nov. 19 at 5:30 a.m., EST, will be visible high in the sky to the southeast. Jupiter, also in the southeast, will be the second-brightest object in the night sky (magnitude –2.21) after the moon.

Venus will rise in the east, just before dawn, blocking any view of the Leonids on Nov. 19.

• NASA's Marshall Space Flight Center has produced a forecast for 58 cities around the world: http://science.nasa.gov/headlines/y2002/09oct_leonidsforecast.htm?list85848)

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