"Year's Best" Meteor Shower Peaks Tonight

Brian Handwerk
for National Geographic News

Updated December 13, 2004

Attention skywatchers: Grab a lawn chair and bundle up, because what experts believe will be this year's best meteor shower peaks tonight. In the hours around midnight the Geminids will streak across the night sky at rates of a meteor per minute or more.

"I think that the Geminids should be the best shower this year," said Bill Cooke, a meteor-shower expert with the Space Environment Group at NASA's Marshall Space Flight Center in Huntsville, Alabama. "There's no moon so conditions will be perfect—as long as you don't mind freezing a bit."

While most meteor showers are at their best only in the early morning hours, the Geminids aid the sleepy by appearing in good numbers before midnight.

"You can begin to see the Geminids almost as soon as it gets dark," Cooke said. "You won't see many but you'll see them and you can see them all night."

Like many recurring meteor showers, the Geminids are named for the constellation from which they appear to originate.

Meteors will be seen all over the sky, but seem to radiate from the constellation Gemini, known as "the twins" and anchored by two of the sky's brightest stars (Castor and Pollux).

Gemini will climb above the eastern horizon from 5:00 to 7:00 p.m. local time, when viewers can spot occasional "Earthgrazers." These long colorful streaks travel horizontally across the atmosphere.

Peak times will be after midnight, when locales such as Boston could see as many as 80 meteors per hour. During peak hours in North America, Gemini will be found high overhead next to the bright and visible Saturn and to the left of the distinctive constellation of Orion (the hunter). Southern Hemisphere stargazers can also spot the Geminids, just a bit lower in the sky and in slightly reduced numbers.

This year a nearly new moon will cooperate with stargazers and provide dark skies for optimal viewing. Avoiding man-made lights will make the shower even more impressive—fleeing the city's glare can enable viewers to see as many as ten times more meteors.

The showy sky scene is of ancient origin.

"The best information we have to date indicates that asteroid Phaethon stopped producing Geminids about six centuries ago," Cooke said. "So all the Geminids you see are older than six hundred years."

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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