Last year's Geminids were mooned out. This summer's Perseids took a beating from moonlight. Our patience will finally get its reward this week with the return of the Geminid meteor shower under dark skies. Expect a great show.
Under ideal circumstances — no light pollution with the shower's radiant high overhead — we might see up to 120 meteors an hour, but since few of us live in this perfect world, expect closer to 60 per hour or a meteor a minute. Hey, I'll take it.
While meteor numbers will peak overnight (around midnight Central time), the Geminids are one of the few showers you don't necessarily have to get up at 2 a.m. to see best. The radiant, the spot in the sky from which the meteors will appear to stream from, is high enough in the eastern sky by 9 p.m. local time. That means you can even take the kids out for a look. For sure, there will be few meteors at that hour, but you'll definitely see some activity before bedtime.
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The later you stay up, the higher the radiant rises, and the more Geminids will come flashing down. When the radiant is low, you lose about half the usual number of meteors because they're cut off by the horizon. Hard-core Geminid-watchers will trundle out around 1 a.m. local time, when the radiant stands high overhead, to see the shower around the time of full strength.
There are two best times for viewing the shower depending on your schedule and how much sleep deprivation you can handle.
- Civilized observing: Wednesday night Dec. 13 from 9-11 p.m. Find as dark a place as possible, dress warmly and tuck yourself under a blanket or sleeping bag. I've sprawled on the ground under a sleeping bag, but a reclining lawn chair is MUCH more comfortable. Face east, kick back and wait for the sparks to fly. Don't be surprised if you see two meteors appear simultaneously or have to wait a few minutes between bursts. For fun, I always keep an informal count of how many meteors I see. If you can only spend a half-hour, that's fine. You'll still see a few.
- Mad Max observing: Plan on being out from about 1-3 a.m. Dec. 14 to see the maximum number of meteors and then going to work or school later that morning a little dazed. It's for a good cause, after all. Stay warm and face south or southwest if you're out during the wee hours.
Besides Geminids you'll also see random or sporadic meteors. You can easily tell the two apart by tracing their paths backwards. If they point back to Gemini, they're Geminids. Shower members are small bits of rock and dust, many about one millimeter across, shed by the asteroid 3200 Phaethon (FAY-uh-thon).
Most showers originate from debris sloughed off by comets as the sun boils ice and dust from their surfaces, but the Geminids are different. Their "parent" is an asteroid 3.1 miles (5.1 km) across that passes very close to the sun during its 1.4-year-long orbit. It's thought that the tremendous heat Phaethon experiences disrupts its crust, cracking it and releasing bits and pieces of rock that trail along its orbit. Every mid-December, Earth's orbit intersects Phaethon's and the debris slams into our atmosphere at 22 miles per second (35 km/sec), vaporizing in a shower of meteor streaks.
Each meteor shower, and there are many, has its own unique qualities based on speed, the density of the particles along its orbit and other factors. The Geminids arrive at "medium speed" (they're slower than the Perseids) and have a habit of producing nice fireballs, defined as meteors that are as bright as Jupiter or brighter (about magnitude –3).
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Coincidentally, the Geminids' parent asteroid is making a historically close approach to Earth at the same time as shower maximum. Normally, Phaethon shines around 15th magnitude and is only visible in larger amateur telescopes. This time around it peaks at magnitude 10.7, bright enough to spot in a small 4.5-inch telescope. If you'd like to watch it dash across Auriga and Perseus in the coming nights, check out my article on the Sky & Telescope website. There are several excellent maps there to help you find it. Note that the map times are in UT or Universal Time. Subtract 5 hours for Eastern time; 6 for Central; 7 for Mountain and 8 for Pacific.
You can still see a modest number of Geminids through Friday morning, but the shower will basically be over after that. If bad weather prevails, Italian astronomer Gianluca Masi will webcast the event live on his Virtual Telescope Project site at two different times: Dec. 13 starting at 4 p.m. Central Time (22:00 UT) from Italy and on Dec. 14 starting at 4 a.m. Central Time ( 10:00 UT) from Arizona.I
I know I've wished you all clear skies before, but I'm wishing it twice as hard now because this should be a great shower.
