"Year's Best" Meteor Shower Peaks Tonight

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Though the Geminids we see are ancient, the shower's appearance to earthbound observers is relatively recent.

"The Geminids are neat because they are sort of a new meteor shower," said Gary Kronk, a St. Louis, Missouri, science writer who was the author of Cometography and maintains the Comets and Meteor Showers Web site. "They weren't first observed until the 1860s, and since that time they have steadily increased in intensity."

Many periodic showers were observed and recorded in the ancient records of Chinese and Muslim astronomers. The Lyrids, for example, were observed in China as early as the 7th century BC.

"People have tried to find references to [the Geminids] in historical records but there is no trace," Kronk continued. "Just about every other major shower is found in historical records going back hundreds of years at the least."

Uncertain Origins

Like other annual meteor showers, the Geminids occur when our orbiting planet intersects with a cosmic debris path of tiny dust particles. The miniscule flecks become streaking meteors when they enter Earth's atmosphere at speeds of 80,000 miles per hour (129,000 kilometers per hour). The speed creates friction that heats up atmospheric gases and causes them to glow in much the same manner as neon signs.

Unlike other known showers, however, Geminids appear to stem from an asteroid rather than a comet. Asteroid 3200 Phaethon is the only asteroid to be associated with a meteor shower.

When orbiting comets pass near the sun, that star's tremendous heat strips them of a layer of ice and dust. The resulting debris field spreads out along the comet's orbit. When Earth passes through the orbiting debris a meteor shower ensues.

But asteroids are primarily rocky and do not generally trail "tails" of debris. Thus the exact origin of the Geminids remains a mystery—but theories abound.

Some speculate that asteroid 3200 Phaethon, a near-Earth object some three miles (4.8 kilometers) across, collided with another asteroid while in the asteroid belt. The cosmic crash could have created a trailing debris field similar to that found behind comets.

An alternate theory suggests that 3200 Phaethon is in fact a dead comet—blasted clear of its ice by repeated trips close to the sun. With its ice vaporized, the comet would have become a rocky ball trailing a bit of dust.

But Cooke believes that 3200 Phaethon is indeed an asteroid.

"If you look at its orbit and calculate what its orbit was in the past, it's tough to justify [the extinct comet theory]. Based on the orbit it does appear to be an asteroid," he explained.

Recently, another theory has been proposed.

"Most asteroids are regarded almost as a pile of gravel held together by gravity," Cooke explained. "As you can imagine, they can only spin so fast before they fly apart. The theory suggests that maybe asteroid Phaethon was spinning so fast that it slung parts of itself out into space and then for some reason it slowed. It still is very much a mystery."

Whatever its exact origins, the Geminid stream is slowly moving away from Earth and will eventually disappear. There's controversy about whether the showers have yet reached their peak. For now, however, the viewing is great.

"You get the crisp clear December nights, so even though rates are comparable to the Perseids of August the Geminids seem to stand out more. They are a great meteor shower to watch," Kronk said.

For would-be watchers the process is simple. Dress warmly, get to the darkest locale possible, relax, and keep looking up!

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