Tuesday, December 11, 2007
Best Meteor Shower of the Year on the 13th
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.
According to the experts, 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).