Guide to the 2004 Geminids
Post-Geminid Note: The weather wasn't very kind to me, but I got in a couple of off-peak observing hours and also saw lots of Geminids through cloud breaks. For much of the world, this was a well-observed and impressive year for the Geminids. See my Online Observing Log for my experiences. --WS, 12/16/04
I write this article not knowing whether I will see a single Geminid this year. Of course, that uncertainty is due to the often-cruel December weather in Oregon, and by no means reflects some deficiency in the meteor shower. Actually, the Geminids are regarded by many as the most reliable and beautiful of the annual showers. The Moon, sometimes a big light polluter, will be nearly new and of no consequence during this year's Geminids.
The accepted period of Geminid activity runs from December 7-17, but this is really a minor shower before December 10 and after December 15. The radiant is near Castor in the constellation Gemini. This area of the sky culminates at about 2am local time, and is near the zenith for much of North America! The shower can be observed for much of the night, although southerly observers have to wait longer in the evenings.
The necessary equipment for Geminid observing is minimal but important. First and foremost is anything that will make you comfortable when watching the sky for an extended period of time. I have a couple of sleeping bags, an extra blanket, gloves, hat, a couple of pillows and many layers of clothing. Snacks and drinks are good to take if you are planning a long session or are traveling to a remote site. You don't need or want to use binoculars or a telescope when viewing a major meteor shower; your naked eyes will give you the widest field of view and allow you to see the most meteors. I carry a shoestring (for checking the alignment of meteors with shower radiants) and a tape recorder for recording meteor counts and information. A faintly illuminated watch or a talking clock is good for checking the time. Keep a flashlight on hand for emergencies.
If possible, choose an open area that is well away from city lights. From a rural site without ominous light domes looming up from the horizons, you should see more than twice as many meteors as from a typical suburban site just inside one of those light domes. Light pollution will dramatically cut the number of meteors you are able to see. Tall buildings or trees may be a problem if they obstruct your view; as long as you have an open view of the sky, it doesn't matter if they creep in around the very edges of your field of view. If you have a choice, center your field of view about 50-60 degrees above the horizon in the darkest part of the sky. It's probably best not to look right at the Geminid radiant, but keep it somewhere in your field of view.
What can we expect from the Geminids this year? The International Meteor Organization's web site contains complete analyses of the 1993 and 1996 Geminid showers, which were well-observed. Brief reports on the 2000 and 2001 returns are also presented there. Based on those analyses, I offer some rough predictions of hourly rates for a perceptive observer. Because there are so many variables (in addition to the variable nature of the Geminid activity itself), these are guidelines at best. Some observations are going to fall well outside the ranges given here, but I'll stick my neck out.
A final caution is that these values are for someone who is carefully and constantly watching the sky for at least an hour at a time. Meteor activity comes in spurts and lulls, and you have to be looking up in order to see it. Also omitted from these rates are sporadic (random) meteors and those of a few minor showers. These should total ~10-15/hour in the morning and ~5-10/hour in the evening from a dark site. Suburban observers should expect about 1/3 these rates.
Friday morning, December 10 (anywhere in North America). Center your observing time around 2:00am, local standard time, when the radiant is highest. Expect maximum rates of roughly 10 Geminids per hour from a dark rural site (limiting magnitude ~6.5).
Saturday morning, December 11 (anywhere in North America). Under the same timing and conditions suggested for December 10, expect roughly 15 Geminids/hour.
Sunday morning, December 12 (anywhere in North America). With a watch centered on 2:00am, expect ~30 Geminids per hour.
Sunday evening, December 12. The radiant rises soon after twilight ends, so limited observing is possible then. A few long, impressive earthgrazers may be visible at the start of the night, but better rates will be seen later in the night.
9:30-10:30pm local time. From the East Coast of the US, expect ~35-45 Geminids/hour from a dark site. 15-20 Geminids may be seen from suburban sites (limiting magnitude ~5.5) during this hour. From the West Coast, expect ~40-50 Geminids during this hour from a dark site; a little less than half those numbers from a suburban site.
Monday morning, December 13. Rates are rising in advance of maximum activity, which will likely occur during US afternoon hours on December 13. All of the dark hours are good for observing, although the radiant elevation slips just a bit towards morning twilight.
2:00-3:00am local time. From the East Coast of the US, expect 60-80 Geminids per hour from a dark rural site and 25-35 Geminids/hour from a suburban site. From the West Coast, expect 75-85 Geminids/hour from a dark site and ~40 Geminids/hour from a suburban site. Expect similar rates to continue until morning twilight gets too bright.
Monday evening, December 13. ZHRs are near their maximum as twilight falls on the East Coast of the US, and may just be starting to decline 3 hours later as the West Coast gets dark. Unfortunately, not a whole lot will be seen at first because of the low radiant elevation. This will definitely be a good night to watch for long, low and slow "earthgrazers", though. Rates around 7pm local time may approach 20/hour from more northerly locations in the US. Observed rates should improve markedly for several hours thereafter.
9:30-10:30pm local time. From the East Coast of the US, expect 45-75 Geminids/hour from a dark site. From the West Coast, expect 35-50 Geminids/hour from a dark site. About half these numbers should be visible from suburban sites.
Tuesday morning, December 14. ZHRs are just beginning to fall for East Coast observers; initially, the decline is canceled out by the rising radiant elevation. From the West Coast, a decline may be more evident. The Geminid profile has shown some signs of variability; this time window is where an early or late maximum could make a significant difference in observed rates. Data from 2001 seems to show a precipitous drop at this point, while in other years rates have remained quite high. We'll see...
1:30-2:30am local time. From the East Coast of the US, expect 50-80 Geminids/hour from a dark site. From the West Coast, expect 40-70 Geminids/hour from a dark site. Suburban observers should see about half these rates.
Wednesday morning, December 15 (anywhere in North America). The shower is on its way out. Start observing around midnight, and expect 10-15 Geminids/hour for the next few hours (from a dark site).