The Geminids Are Coming
This is an abridged version of an article that appears in the December Sky & Telescope, page 71.
Geminid meteor
A bright meteor from the 2004 Geminid meteor shower was captured with a tripod-mounted digital camera and a 16-mm lens. It’s a 1-minute exposure at f/2.8 with an ISO setting of 800.
Courtesy Alan Dyer.
The night sky offers many wonderful sights, but few are as magical as meteors. These “shooting stars” are fleeting, unpredictable, and incredibly beautiful. Every time I see one, I feel as though I’ve received a special gift from the cosmos.
Meteors happen all the time. You’re almost sure to see them any time you spend a few hours looking at a clear, dark sky. But you can improve your odds tremendously by going out during one of the annual meteor showers — bursts of meteors that take place on roughly the same dates every year.
The strongest and most reliable meteor showers are the Perseids of August and December’s Geminids. Balmy weather and summer vacations have made the Perseids well known and popular, but the Geminids are actually easier to view from mid-northern latitudes. For one thing, nights are much longer in December. And while the Perseids are best viewed before dawn (as most showers are), the Geminids offer excellent viewing starting in mid- to late evening.
This year, the best time to view the Geminids from North America is the night of December 13–14, with good prospects the following night as well. In Asia, December 14–15 should be better, and in Europe, it’s a tossup between the two.
Your Detailed Local Forecast
This photo shows Geminids streaming away from the shower's radiant near the star Castor. It was made by combining 83 out of 1,256 exposures shot over an 11-hour time span on December 13-14, 2004. Click above for a larger image.
Fred Bruenjes
All the meteors in a shower appear to stream at us from a single spot in the sky: the shower’s radiant. Meteor showers are named after their radiants. For instance, the Geminids stream away from a point in the northeastern corner of the constellation Gemini, which is currently host to brilliant Mars.
All other things being equal, the higher a shower’s radiant is in the sky, the more meteors you’ll see. The Geminid’s radiant is highest around 2 a.m., and it’s already well above the eastern horizon by 9 or 10 p.m. for observers at mid-northern latitudes. That means that the Geminids usually offer excellent shows in the late evening. But there are two more factors to consider.
The darker the sky is, the more meteors you’ll see — and the more spectacular they’ll appear. So it’s usually best to pick a time when the Moon isn’t up. Fortunately, the Moon is a thin waxing crescent during this year’s Geminids, setting before the shower is in full swing and not very bright even while it’s still up.
The final factor is the shower’s inherent strength: the number of meteoroids hitting Earth as a whole, regardless of your own local circumstances. Some showers stretch over many days or even weeks, but the Geminids have a very sharp peak. The curve is also strikingly asymmetric. It takes two days for the rate to climb from one-fifth of the maximum to full strength, but less than one day to drop back to the same level.
This year the Geminids’ peak arrives at 17h Universal Time on Friday, December 14th. That’s great news in East Asia, where the peak coincides with the radiant’s reaching its highest point in the sky, during the early hours of Saturday morning. But in the Americas, the peak falls right in the middle of the day, at noon Eastern Standard Time on Friday. So we’ll miss the very best part of the show.
Because the Geminid rate rises slower than it falls, prospects for North Americans are better before the peak than afterward. Activity should start out modestly around 9 or 10 p.m. on Thursday, December 13th, and then strengthen steadily throughout the night. Just before dawn on Friday morning, you might see a meteor every minute or two from a dark location.
On Friday evening, activity should start about as well as it did on Thursday evening but then decline steadily throughout the night. In fact, the predawn hours of Thursday may offer better viewing, even though they’re more than a day before the shower’s peak.
If you'd like to try not just sightseeing but doing a genuine meteor count, one worth reporting to the International Meteor Organization, see our article "Advanced Meteor Observing". It's easier than it sounds.
