Spectacular free light show on tonight--Geminid meteor shower

December 13, 1990|By Luther Young

If the skies remain clear tonight and the celestial merry-go-round keeps turning, look for the best meteor performance of the year, as the Geminid meteor shower peaks with as many 75 "shooting stars" per hour.

Thanks to a waning crescent moon which doesn't rise until 5 a.m. tomorrow, the heavens will be dark enough from just after sunset to almost dawn for the annual pre-Christmas fireworks to shine in spectacular fashion.

"The Geminids have a reputation for being particularly bright," said Jim O'Leary, director of the Davis Planetarium at the Maryland Science Center. "And they often feature fireballs," meteors which end in explosive bursts that can sometimes be heard on the ground.

Meteors are tiny bits of cosmic dust that flash into brief incandescence as they enter Earth's atmosphere at 40 miles per second some 60 miles up. The Geminids typically appear white or yellow and are a bit easier to track because they travel more slowly than average.

Observers should look to the east northeast about an hour after sunset, where the constellation Gemini -- meteor showers are named for the constellations from which they appear to radiate -- hangs low on the horizon, to the left of Orion.

"The great thing is that the peak is around 7 p.m. in the evening, and you'll be able to see it," said Geoff Chester of the National Air and Space Museum's Einstein Planetarium. "It's one of the few showers that show an appreciable amount of activity before midnight."

Mr. O'Leary advises meteor-seekers to "find a good, dark place with an unobstructed view of the horizon" and to "stay outside for a while, letting your eyes get accustomed to the dark." They should dress warmly for their long vigil under the stars, he added.

Although the quick flashes emanate from a "radiant point" near Gemini, they can appear all over the sky. The constellation travels as the night progresses, rising to almost overhead in the south by midnight and setting low in the west just before dawn.

The Geminids now hold the title of the brightest and most consistent of the dozen major meteor showers that return annually. Its former challenger, the Perseids in August, has declined in recent years and appears to be disappearing from the skies.

Known as meteoroids until they enter the atmosphere and flame into meteors, the dust specks were left behind along Earth's orbit by comets that visited the inner solar system hundreds or thousands of years ago.

The Perseids owe their existence to Comet Swift-Tuttle, which is supposed to return every 120 years. But it failed to show up as expected in 1981, and the meteor shower may be declining.

And the Geminids are probably the dust children of a comet -- now existing as a cold, dead asteroid labeled 3200 Phaethon -- that first rounded the sun about 15,000 years ago and burned itself out as its layers of ice and dust were peeled away in the intense heat.

"The Geminids were at their best in 1988, with up to 80 an hour, and they've been improving since 1960 or so," Mr. O'Leary said.

The meteor shower was first identified in 1838, and estimates are that it first began crossing the path of Earth in 1750.

Scientists now believe the Geminids will begin declining within the next few decades as the swarm of meteoroids slowly moves out of range. A century from now, the best and brightest meteor shower may be just a memory.

"See it while you can," said Mr. Chester. "It's a free light show courtesy of Mother Nature."

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