For the week including December 11, 2009

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THE GEMINIDS ARRIVE

Over the course of a year, there are dozens of meteor showers that can be watched from your backyard.  Most of them pass unnoticed primarily because the numbers of meteors falling aren’t increased much beyond the one or two an hour that come down randomly every day. For instance, last week I didn’t get a single email regarding the Puppids meteor shower that was going on. Maybe it’s because they only fall at the rate of four to five an hour. On the night of Sunday, the 13th, we have something much different.

Of all the many meteor showers available, everyone’s favorite appears to be the Geminids, so called because the meteors seem to issue from the constellation of Gemini, the Twins. This shower peaks Sunday and the current estimates are that the meteors will come down a couple of times a minute. With no moonlight to obscure them, the meteor shower will be evident soon after the Sun goes down.

Meteor showers occur when the Earth passes through the tail debris left behind by a passing comet. The Perseid shower is associated with Comet Swift-Tuttle and stream from the constellation of Perseus – the Orionids are associated with Halley’s Comet and come out of Orion. The Geminid meteor shower first showed up with a very nice display in December of 1863. Since then, year after year, we’ve been treated to a great meteor shower, but nobody was able to find the comet that caused it.

That was until October of 1983 when the Infrared Astronomical Satellite (IRAS), picked up a large asteroid in space whose orbit exactly matched that of the Geminid meteor debris stream. It shocked everyone that this rock, not a comet, was responsible for the Geminids until astronomers understood what they were really seeing. This asteroid, named Phaethon, was actually a dead comet – the stony remnant left after the Sun had blown away all the dusty material that gave the comet its tail. Phaethon recently passed the Earth’s orbit and we are now running into the remains of its tail which still trail it through space. When the tiny debris particles, traveling at a hundred thousand miles per hour, hit the Earth’s atmosphere, they vaporize and create a wonderfully bright streak in the night sky. You don’t have to worry about being conked on the head by one of these meteors, most are smaller than a grain of sand and disintegrate long before they could hit the ground.

If you’d like to watch the meteor shower, dress warmly and head to a dark place tonight where you have an unrestricted view to the east. A lawn chair, thermos of coffee, and a blanket aren’t bad ideas either. When you’re all set up, look to the east and you will see the bright twin stars Castor and Pollux of Gemini rising above the horizon. The meteors will stream from a broad area of the eastern sky, but if you trace their paths backward, they will seem to be streaming from the area circled in our illustration.