This past week we touched on the resurgence of the Andromedid meteor shower and learned that Comet ISON may even gift us with dusty sprinkles next month. These one-off meteor blasts are certainly worth following, but if it’s reliability and numbers you’re looking for, the Geminids are your shower. No speculating here. No maybes. From a dark sky, anywhere from 60-120 Geminids an hour will zip past starting Friday night through dawn Saturday.
Every year in mid-December, Earth’s orbital path crosses that of 3200 Phaethon (FAY-eh-thon), a 3.2 mile diameter (5.1 km) asteroid with an orbit takes it only 13 million miles from the sun every 1.4 years – almost three times closer than Mercury. That has consequences as we’ll soon see.
Most meteor showers are the offspring of comets, which drop dust and small rocks along their orbits after getting roasted by the sun. Phaethon’s sometimes referred to as a “rock comet”. Normally a quiet, well-behaved asteroid, Phaethon brightened by a factor of two and was caught spewing jets of dust when nearest the sun in 2009, 2010 and 2012. Apparently the intense heat of the sun either fractured the surface or heated rocks to the point of desiccation, creating enough dust to form temporary tails like a comet.
While it may look like an asteroid most of the time, Phaethon may really be a comet that’s still occasionally active. Either way, this originator of the Geminids produces a reliable meteor shower.
This year the Geminids will be at their best overnight Dec. 13-14 with maximum activity forecast for around 8 p.m. CST (2 a.m. Greenwich time Dec. 14) Friday night. At that time, the radiant will be low or will not have risen for western hemisphere skywatchers, but that shouldn’t be a problem – the shower’s active all night. The later it gets, the more meteors you’ll see as the radiant rises ever higher in the sky.
There are two times for viewing the Geminids. You can go out around 9 or 10 Friday evening and face east toward brilliant Jupiter in Gemini, which by good fortune shines close to the shower radiant. Because the bright, waxing gibbous moon will be out, its light will cut the number of meteors you’ll see about in half. That’s why it’s a good idea to hide the moon from view if you can, so its glare isn’t a bother.
If you want to see more Geminids, you can set your alarm for just before 5 a.m. That’s when the moon sets and leaves about an hour of dark sky before the start of morning twilight. Because of the much later hour, the Earth will have “rotated” Gemini and Jupiter into the western sky. Just take that lawn chair and turn it to face the south-southwest for the best view.
The Geminids are medium-speed meteors, hitting the atmosphere at 70 miles overhead at 35 km/sec and often leave chalky-white “trains” or streaks of what looks like glowing smoke when they burn up. If you get one that lingers a while, consider examining it with binoculars. Sometimes you’ll see swirls and loops in the fading train.
The Geminids are now the richest annual meteor shower, even beating out the August Perseids. Their only drawback? They happen at the coldest time of year. So layer up, heat up the coffee and don’t let the cold rob you of what should be one of 2013’s astronomical highlights.