Photograph by Jonathan Blair, Corbis
Published December 12, 2011
A holiday light show is on offer for sky-watchers this week, as the annual Geminid meteor shower peaks during the overnight hours of December 13 and 14.
This year's Geminid shower should be filled with colorful shooting stars and fireballs—but catching the spectacle will be a matter of timing, astronomers say.
"The best times are probably before the moon rises, around 9 p.m. local time, when it will be dark still," said Geza Gyuk, an astronomer at the Adler Planetarium in Chicago. Once it rises, the mostly full moon will drown out fainter meteors.
If you're out under clear skies, "face northeast and look for meteors racing out from the shower's radiant—its namesake constellation, Gemini, which will be low on the horizon," Gyuk said.
"The other best chance will be in the very early morning of December 14, around 2 a.m., when the shower's radiant will be very high overhead," he said.
"At that point, my advice will be to face west away from the moon and look for meteors streaking down from the sky."
The Geminids peak will feature rates of up to 30 to 40 meteors an hour as seen from suburban locations and up to 100 meteors an hour from the dark countryside.
Despite this bounty, the Geminids don't usually get as much fanfare as the August Perseids, perhaps because the December shower falls close to the holiday season and during frosty weather in the Northern Hemisphere, where most of the shooting stars will be visible.
For those willing to brave the cold, Gyuk suggests wearing warm clothes, using reclining deck chairs, and being prepared to stay a while.
"Meteor observing needs patience, and it helps to be in a group, so bring friends to help catch meteors that the others might have missed."
Slow-Moving Geminids Easy to Spot
While the shower's peak will last only a few hours each night, dozens of shooting stars will be visible over the course of the entire week.
Geminid meteors are fairly slow travelers, moving less than half the speeds of meteors in other showers.
"This means the meteors tend to zip across the sky more slowly and can be caught by eye more easily," Gyuk said.
And despite the glare of the waning moon, the Geminids may have a few surprises in store for observers, Gyuk said.
The Geminids have a good reputation for producing fireballs, which are much brighter than average meteors and occasionally explode.
(Related: "'Major,' Green Meteor Lights Midwest Night Sky" [April 2010].)
Finally, the Geminids can be quite colorful compared with other showers, with some yellow and even occasionally red, green, and blue streaks, Gyuk said.
Meteors Come From Mystery Object
Meteors are mostly sand grain-size particles that enter Earth's atmosphere at high speed, burning up and superheating the air around them, which creates the characteristic short-lived streaks of light.
Most annual showers occur when Earth passes through clouds of debris left behind by passing comets, causing tons of cosmic dust to rain down on the planet in short periods of time.
The Geminids are unusual, though, because they're thought to be the only annual meteor shower created by a mysterious asteroid-like object dubbed 3200 Phaethon.
Discovered in 1983 by a NASA satellite, Phaethon is a roughly three-mile-wide (five-kilometer-wide) space rock. Its year-and-a-half-long orbit precisely matches the appearance of the Geminids, making the body a prime candidate for the source of the meteors.
Unlike icy comets, Phaethon doesn't release gases or produce a visible tail of debris as it nears the sun. But it's possible that's because the body has been thoroughly baked by its frequent passages close to our star's intense heat, Gyuk said.
And fairly recently, astronomers detected anomalous brightenings of Phaethon whenever it approached the sun, which suggests that the space rock might be releasing small caches of frozen gases that had been trapped until now.
So although 3200 Phaethon is widely considered to be an asteroid, "it might in fact be better to classify it as a nearly dead comet," Gyuk said.
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