STAR Party: The 2007 Geminids Meteor Shower December 13, 2007

GEMINIDS [maximum December 13, 11pm EST (December 14, 4h UT)]

Best viewing windows: Friday morning, December 14; the last couple of hours before morning twilight. Also, the entire night of Thursday evening/Fridayednesday morning, December 13/14 after about 8pm local time.

The Geminids are a beautiful, prolific and reliable shower. Dry, clear air will help a lot with the lunar glare, but it will be difficult to achieve maximum rates of 20 Geminids/hour even at the best sites. The Moon will be high in the sky for most of the night. In the last couple of hours before morning twilight, it's fairly low. During those hours, you may be able to put it behind you and out of your field of view. During the rest of the night, you'll need to find some way to block the Moon and the bright sky surrounding it without obstructing the rest of your field of view. I've used objects like my hand, chairs, cars, trees and telescopes to do so during past showers.

Geminids are medium-speed meteors. Most of them don't leave glowing trains, but the brighter ones are often colored (yellow, green and blue are most common). The shower has a skew rate profile, with activity dropping quickly after maximum. At the same time, the proportion of bright meteors is higher during and after maximum than on pre-maximum nights. The Geminids are worth watching for one or two mornings before the peak; there will be slightly less moonlight interference, and some locations will get a short moonless period before morning twilight.

The point from where the Geminid meteors appear to radiate is located within the constellation Gemini and is referred to as the radiant. The radiant is located in the northern portion of that constellation near Gemini's two brightest stars, Castor and Pollux. These meteors tend to move moderately fast, when compared to other meteor showers, and Geminids tend to be rather bright.

For Northern Hemisphere observers, the Geminid radiant is above the horizon for nearly all hours of darkness and the optimum observing point shifts throughout the night. Early in the evening the best observing position is to point your feet northward, westward, or southward and look straight up. Late in the evening your orientation could remain unchanged, but you should shift the center of your gaze to about 45° above the horizon. By about 2:00 a.m. you can point your feet in any direction, with your gaze centered about 45° above the horizon. By late morning, the best vantage point would be to point your feet towards the north, east, or south and set your gaze to a point about 45° above the horizon. In the Southern hemisphere, the radiant stays in the northern sky. It would be best to point your feet northward and center your gaze between 45° above the horizon and straight overhead.

Geminid History:
http://comets.amsmeteors.org/meteors/showers/geminidhistory.html