This week brings us what usually is considered to be the most satisfying of all the annual meteor displays, even surpassing the famous Perseids of August: December's Geminid meteor shower.
But this year, before making any elaborate plans to view this year's Geminid display, prospective sky watchers should be aware that they will be facing a major obstacle to observe this year's Geminid performance: namely, the moon.
Unfortunately, as luck would have it, the moon turns full on Friday, and as such will seriously hamper — if not all but prevent — observation of the peak of the Geminids, which is predicted to occur late Saturday and early Sunday, Dec. 13-14. Bright moonlight will flood the sky through much of the night, and will certainly play havoc with any serious attempts to observe these meteors.
The Geminids were active only in a very weak and scattered form earlier this month. But a noticeable upswing in Geminid activity has occurred since then, leading up to their peak night this weekend. Historically, this shower has a reputation for being rich in slow, bright, meteors and in rather faint meteors, with relatively few of medium brightness. Many Geminids appear yellowish in hue.
For those who are grasping at straws in light of the poor conditions for Geminid viewing this year, it should be noted that every once in a while, a dazzling Geminid fireball will blaze forth, bright enough to be quite spectacular and more than capable of attracting attention even in bright moonlight.
In their book, "Observe Meteors," published by the Astronomical League, astronomers David Levy and Stephen Edberg say that "if you have not yet seen a mighty Geminid fireball arcing gracefully across an expanse of sky, then you have not seen a meteor."
With this as a background, perhaps the best times to look this year will be during the evening hours on the nights after the full moon. That's when the constellation Gemini (from which the meteors get their name) will be rising above the east-northeast horizon.
Catch an earthgrazer on Sunday
Early on Sunday evening, there will be a "window of opportunity" to look for Geminids in a dark, moonless sky. Between the time that evening twilight ends and the time that the bright waning gibbous moon rises, there will be about an hour of dark sky available.
For most locations, moonrise is around 7 p.m. To find the time of moonrise for your specific location, go to: http://aa.usno.navy.mil/data/docs/RS_OneDay.php
During the moonless interval, there possibly may be an opportunity to catch a glimpse of an unusually beautiful type of meteor called an "Earthgrazer." Earthgrazers are long, bright shooting stars that streak overhead from just below the horizon. They often display colorful halos and long-lasting trails. Earthgrazers are so distinctive because they follow a path nearly parallel to our atmosphere, analogous to a rock skimming across the top of a pond. The Geminid radiant — near to the bright star, Castor — will be near the horizon as our planet is passing through the Geminid stream.
In the absence of moonlight a single observer might see upwards to 120 meteors per hour on the peak night, a number that sadly is out of reach in 2008. Looking ahead to 2009, the Geminids will reach their peak just two days before a new moon, meaning viewing conditions will be nearly perfect. So it appears that this year, Geminid fans will be uttering the same lament that the old Dodger fans in Brooklyn used to:
"Just wait till next year!"