This month Iím not actually featuring a particular constellation but rather a major celestial event, the annual Geminid meteor shower, one of the best of the year. Only the Perseids, seen in early August are as good. This year viewing the Geminids should be fantastic because the moon will set and out the sky be out of the sky by midnight leaving much darker skies for meteor shower watching.
If possible get out in the dark countryside, especially on late Thursday night and Friday morning when Geminids are peaking and you may see 50 to 75 meteors an hour. The very best time to watch for them will be from around midnight to the start of morning twilight. Even if you canít break away from the city lights youíre bound to see at least some decent meteors. Trust me. Itís worth setting the alarm, bundling up, and losing a little sleep.
This shower is called the Geminid meteor shower because all of the meteors in the celestial dome will appear to be streaming from the general direction of the constellation Gemini the Twins, which is in the western half of the sky in the early morning. By no means should you restrict your viewing to just that part of the sky because the meteors will be all over the heavens and I donít want you to miss any! The best thing to do is lay back on a fully reclining lawn chair, rolling your eyes all around and keeping count of how many meteors you see. No binoculars or telescopes needed or wanted. You want to constantly have a wide view of the sky. Meteor shower watching is especially fun with a group of people, because the more eyes in the sky, the more meteors youíll see. Not only that you can give each other moral support for being out in the cold doing something out of the box. It does make memories!
Meteor showers occur when the Earth in its orbit around the sun runs into a debris trail of dust and small pebbles as it orbits around the Sun. For most meteor showers the debris is left behind by a passing comet, but the Geminids are unusual because the debris trail was left behind by an asteroid dubbed by astronomers as 3200 Phaethon. This asteroid was discovered in 1983 and has a diameter of around three miles. It has a highly elliptical orbit that swings it by our part of the solar system every year and a half. Each time it passes it refreshes the debris trail. Itís a real cosmic litterbug! The planet Jupiter has made the Geminids even better over the last few years. Jupiter's gravity has tugged the stream of particles from asteroid 3200 Phaethon, closer to Earth over the centuries.
The individual debris particles 3200 Phaethon are called meteoroids and are tiny. I would say much better than 99% of them are much less than the size of your thumbnail. They slam into our atmosphere about 50 to 80 miles high at speeds that can exceed 40 miles per second. They burn up in our atmosphere due to air friction but no way can we see the actual combustion that high up. The streaks we see are caused by the columns of air becoming temporarily chemically excited by the meteoroids ripping though it.
Meteor showers are best seen after midnight when youíre side of Earth has rotated into the direction of the debris trail. A good analogy is driving on a warm summer evening (isnít that a pleasant thought about now?), you get many more bugs that meet their demise on your front windshield than you do on your rear window. After midnight weíre facing through the ďfront windshieldĒ.
Diagram of Earthís Orbit and Comet Debris...Click