Jimmy Westlake: Get ready for the Geminid meteor shower
December 8, 2014
Steamboat Springs — Get ready for the best meteor shower of the year. It's the Geminid meteor shower and it could bring as many as 120 shooting stars per hour to our sky.
Geminid meteors are so named because they seem to spring from the stars of our constellation of Gemini, the Twins. Each bright streak that you see is caused by a tiny bit of space dust entering the Earth's atmosphere at high speed and burning up about 60 miles high.
Most of the particles are so small that you could hold a thousand of them in the cupped palm of your hand. Under ideal, dark sky conditions, a single observer can expect to see as many as 120 meteors per hour on the night of peak activity.
First observed in the year 1862, Geminid meteors are unique for a number of reasons, foremost of which is their unusual source. Most other meteor showers are produced by fluffy little pieces of comet dust, but Geminid meteors are tough little bits of rock, shed by a rocky asteroid named Phaethon.
Once every 17 months, Phaethon makes a close pass by the sun, inside the orbit of the planet Mercury. This causes its parched surface to crack, fracture and spew dusty particles into space. For this unusual behavior, Phaethon has been described as a "rock comet."
Earth plows through Phaethon's dust-filled orbit in mid-December each year, and, as a result, we are treated to the Geminid meteor shower. Because the particles from Phaethon are rocky, they can penetrate deeper into the Earth's atmosphere before burning up, so Geminid meteor streaks tend to be long, slow and bright.
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Last year, the Geminids had to compete with a nearly full moon in the sky and were mostly washed out, but conditions are much better this year. The third quarter moon won't rise until 11:47 p.m. on the night of peak activity, Saturday, so meteor watching can commence as early as 8 p.m., when the constellation of Gemini breaks the northeast horizon.
The next night will be nearly as good, and the moon will rise an hour later, around 12:25 a.m. In general, meteor counts tend to increase in the hours after midnight, but the rising moon likely will reduce those counts somewhat.
Geminid meteors can be seen for several nights before and after the peak, so take advantage of any clear night this week and next. In fact, the biggest, brightest Geminid fireballs tend to show up in the nights after the night of the peak activity.
If you have a tripod-mounted camera and are feeling lucky, you might be able to record the streak of a bright Geminid meteor. Use a wide angle lens to capture as large a patch of sky as possible, set to a low aperture setting to let in as much light as possible. Set your camera's ISO sensitivity to at least 800, mount it on a stable tripod and then take brief time exposures of the sky.
If the moon is not up, you can try exposures of from 30 seconds up to several minutes, but once the moon is up, you'll probably have to cut those down to 30 seconds or they will be overexposed by the moonlight.
Geminid meteors will shoot across all parts of the sky, so it won't really matter where you aim your camera. If you are lucky, one or more bright meteors might shoot through your chosen patch of sky.
So, bundle up against the cold, grab a thermos of your favorite warm beverage and get out there under the stars to watch Mother Nature's free fireworks show — the annual December Geminid meteor shower.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His “Celestial News” column appears weekly in the Steamboat Today newspaper, and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Check out Jimmy's new "2015 Cosmic Calendar" of sky events on his website at http://www.jwestlake.com. It features 12 of his best astrophotographs and a day-by day listing of cool celestial events that you and your family can enjoy watching in 2015. Proceeds from the sale of Cosmic Calendars help to support the CMC SKY Club.
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