Meteor Shower to Peak on Saturday

John Roach
for National Geographic News
December 11, 2002

If clouds and a bright moon obscured your view of last month's Leonids meteor shower, take heart. Meteor gazers have another chance to catch a show this year. The annual Geminid meteor shower is reaching peak force, streaking from a mysterious object known as 3200 Phaethon.

The shower began on December 7 and is predicted to reach peak intensity of 120 meteors per hour at 10:00 Universal Time (5:00 a.m. ET) on December 14, according to Bill Cooke, an astronomer at the Marshall Spaceflight Center in Huntsville, Alabama.

While the Geminids can be seen in the Northern Hemisphere from 10:00 p.m. local time on, astronomers suggest the best time to view the shower is from 2:00 a.m. until dawn. That is the time when the local sky is pointed directly into the meteor stream.

The Geminid meteor shower originates from the constellation Gemini. Astronomers consider it to be one of the best each year, topping even the more well-known Perseids, which occur in August.

In addition, the Geminids hold the allure of being something out of the "Twilight Zone," said Cooke. Astronomers are not sure whether to call the source of the meteor shower, 3200 Phaethon, a comet, an asteroid, or something else yet defined by science.

"It has become obvious in recent years that our nomenclature in astronomy is not keeping pace with the discoveries," said Cooke. "We like to place objects in nice, well-defined categories, even in light of the knowledge that Mother Nature makes no such distinctions."

Defining Geminids

Most meteor showers result from debris that boils off a comet's nucleus when it passes close to the sun. This debris orbits the sun along with the comet, forming a long, thin stream of debris. When this debris hits Earth's atmosphere, it burns up, an event popularly known as a shooting star.

When the Geminids suddenly appeared in the night sky in 1862, astronomers started searching for the comet that was the source of the meteor shower. For more than a century, astronomers found nothing. Then, in 1983, scientists using NASA's Infrared Astronomical Satellite discovered a curious object moving in the same orbit as the Geminid meteors.

There was just one catch: the object didn't look like a comet. Rather, it was several kilometers wide and looked more like a rocky asteroid. Indeed, 3200 Phaethon has an orbit that is characteristic of an asteroid and its meteors are about four times denser than meteors produced by well-known comet showers, said Cooke.

Brian Marsden, an astronomer with the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, suggests that 3200 Phaethon could be bombarded by other rocks as it passes through the main asteroid belt, causing a tail of ice and dust.

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