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: the December 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, 2008 will see the moon will turn full on Dec. 12 and as
such will seriously hamper — if not all but prevent — observation of the peak of
the Geminids, which is predicted to occur for the night of Dec. 13-14. Bright
moonlight will flood the sky through much of that night, and will certainly play
havoc with any serious attempts to observe these meteors.
The Geminids are already around, having been active only in
a very weak and scattered form from 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
both in slow, bright, meteors as
well as rather faint meteors, with relatively few of medium brightness. Many
Geminids appear yellowish in hue.
Great balls of fire
But 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 to attract attention even in bright
moonlight. In their book, "Observe Meteors," published by the
Astronomical League, astronomers David Levy and Stephen Edberg note 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 those nights after the night of full moon.
That's when the constellation Gemini (from where the meteors get their name)
will be rising above the east-northeast horizon.
Catch an earthgrazer on Sunday
In fact, early on Sunday evening, December 14, there will be
a "window of opportunity" to look for Geminids in a dark, moonless
sky. Between the times 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.
Much better in 2009
In the absence of moonlight a single observer might see upwards
to 120 meteors per hour on the peak night, a number that sadly can not be hoped
to be approached 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!"
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other
publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.
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