Don't Miss the Geminids!
Best Meteor Shower of 2007 Peaks Dec. 13
By Joe Rao
SPACE.com Skywatching Columnist
What could be the best meteor display of the year will reach its peak on the night of Dec.13-14.
Here is what astronomers David Levy and Stephen Edberg have written of the annual Geminid Meteor Shower: "If you have not seen a mighty Geminid fireball arcing gracefully across an expanse of sky, then you have not seen a meteor."
The Geminids get their name from the constellation of Gemini, the Twins, because the meteors appear to emanate from a spot in the sky near the bright star Castor in Gemini.
Also in Gemini this month is the planet Mars, nearing a close approach to the Earth later this month, and shining brilliantly with yellow-orange hue. To be sure, Mars is certain to attract the attention of prospective Geminid watchers this upcoming week.
The Geminid Meteors are usually the most satisfying of all the annual showers, even surpassing the famous Perseids of August.
Studies of past find the "Gems" have a reputation for being rich both in slow, bright, graceful meteors and fireballs as well as faint meteors, with relatively fewer objects of medium brightness.
They are of medium speed, encountering Earth at 22 miles per second (35 kps). They are bright and white, but unlike the Perseids, they leave few visible trails or streaks. They are four times denser than most other meteors, and have been observed to form jagged or divided paths.
Geminids also stand apart from the other meteor showers in that they seem to have been spawned not by a comet, but by 3200 Phaethon, an Earth-crossing asteroid. Then again, the Geminids may be comet debris after all, for some astronomers consider Phaethon to really be the dead nucleus of a burned-out comet that somehow got trapped into an unusually tight orbit. Interestingly, on December 10, Phaethon will be passing about 11 million miles (18 million kilometers) from Earth, its closest approach since its discovery in 1983.
The prospects for this year
The Geminids perform excellently in any year, but British meteor astronomer, Alastair McBeath, has categorized 2007 as a "great year."
Last year's display was hindered somewhat by the moon, two days past last quarter phase. But this year, the moon will be at new phase on Dec. 9. On the peak night, the moon will be a fat crescent, in the south-southwest at dusk and setting soon after 8 p.m. That means that the sky will be dark and moonless for the balance of the night, making for perfect viewing conditions for the shower.
According to McBeath, the Geminids are predicted to reach peak activity on Dec. 14 at 16:45 GMT. That means those places from central Asia eastwards across the Pacific Ocean to Alaska are in the best position to catch the very crest of the shower, when the rates conceivably could exceed 120 per hour.
"But," he adds, "maximum rates persist at only marginally reduced levels for some 6 to 10 hours around the biggest ones, so other places (such as North America) should enjoy some fine Geminid activity as well.
Indeed, under normal conditions on the night of maximum activity, with ideal dark-sky conditions, at least 60 to 120 Geminid meteors can be expected to burst across the sky every hour on the average (Light pollution greatly cuts the numbers).
The Earth moves quickly through this meteor stream producing a somewhat broad, lopsided activity profile. Rates increase steadily for two or three days before maximum, reaching roughly above a quarter of its peak strength, then drop off more sharply afterward. Late Geminids, however, tend to be especially bright. Renegade forerunners and late stragglers might be seen for a week or more before and after maximum.
What to do
Generally speaking, depending on your location, Gemini begins to come up above the east-northeast horizon right around the time evening twilight is coming to an end. So you might catch sight of a few early Geminids as soon as the sky gets dark.
There is a fair chance of perhaps catching sight of some "Earth-grazing" meteors. Earth grazers are long, bright shooting stars that streak overhead from a point near to even just below the horizon. Such meteors are so distinctive because they follow long paths nearly parallel to our atmosphere.
The Geminids begin to appear noticeably more numerous in the hours after 10 p.m. local time, because the shower's radiant is already fairly high in the eastern sky by then. The best views, however, come around 2 a.m., when their radiant point will be passing very nearly overhead.
The higher a shower's radiant, the more meteors it produces all over the sky.
But keep this in mind: At this time of year, meteor watching can be a long, cold business. You wait and you wait for meteors to appear. When they don't appear right away, and if you're cold and uncomfortable, you're not going to be looking for meteors for very long! The late Henry Neely (1878-1963), who for many years served as a lecturer at New York's Hayden Planetarium, once had this to say about watching for the Geminids: "Take the advice of a man whose teeth have chattered on many a winter's night – wrap up much more warmly than you think is necessary!"
Hot cocoa or coffee can take the edge off the chill, as well as provide a slight stimulus. It's even better if you can observe with friends. That way, you can keep each other awake, as well as cover more sky. Give your eyes time to dark-adapt before starting.
Bundle up and good luck!
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Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.