EIU Astro

Geminid Meteor Shower December 12, 2010

The Geminid meteor shower, which peaks this year on Dec. 13th and 14th, is the most intense meteor shower of the year. It lasts for days, is rich in fireballs, and can be seen from almost any point on Earth.

The Geminids is the final major meteor shower of the year; it’s also one of the most eye-catching! To observe the Geminids look anywhere from 50 degrees to 60 degrees above the horizon and about 20 degrees away from the constellation Gemini. The Geminids meteor shower can be seen all over the world, but the best viewing opportunities are for those in the Northern Hemisphere (above the equator). Those in the Southern Hemisphere will still have a worthwhile viewing experience.

For the best viewing experience, find an area unobstructed by structures and that is far away from city lights. Using binoculars or telescores is not recommended – you’ll be more likely to miss a hooting star whizzing by. Just gaze the skies with your eyes.

credit: Wally-Pacholka

Most meteor showers come from comets, which spew ample meteoroids for a night of ‘shooting stars.’ The Geminids are different. The parent is not a comet but a weird rocky object named 3200 Phaethon that sheds very little dusty debris—not nearly enough to explain the Geminids.”Of all the debris streams Earth passes through every year, the Geminids’ is by far the most massive,” says Cooke. “When we add up the amount of dust in the Geminid stream, it outweighs other streams by factors of 5 to 500.”

This makes the Geminids the 900-lb gorilla of meteor showers. Yet 3200 Phaethon is more of a 98-lb weakling.

3200 Phaethon was discovered in 1983 by NASA’s IRAS satellite and promptly classified as an asteroid. What else could it be? It did not have a tail; its orbit intersected the main asteroid belt; and its colors strongly resembled that of other asteroids. Indeed, 3200 Phaethon resembles main belt asteroid Pallas so much, it might be a 5-kilometer chip off that 544 km block.

“If 3200 Phaethon broke apart from asteroid Pallas, as some researchers believe, then Geminid meteoroids might be debris from the breakup,” speculates Cooke. “But that doesn’t agree with other things we know.”

Researchers have looked carefully at the orbits of Geminid meteoroids and concluded that they were ejected from 3200 Phaethon when Phaethon was close to the sun—not when it was out in the asteroid belt breaking up with Pallas. The eccentric orbit of 3200 Phaethon brings it well inside the orbit of Mercury every 1.4 years. The rocky body thus receives a regular blast of solar heating that might boil jets of dust into the Geminid stream.

“We just don’t know,” says Cooke. “Every new thing we learn about the Geminids seems to deepen the mystery.”

This month Earth will pass through the Geminid debris stream, producing as many as 120 meteors per hour over dark-sky sites. The best time to look is probably between local midnight and sunrise on Tuesday, Dec. 14th, when the Moon is low and the constellation Gemini is high overhead, spitting bright Geminids across a sparkling starry sky.

Bundle up, go outside, and savor the mystery.

Credit: NASA Science, Dr. T. Phillips