Celestial News: Geminid meteors compete with full moon
The best annual meteor shower of the year is in progress this week and rising toward a spectacular peak before dawn Wednesday. It’s the Geminid meteor shower and, under ideal dark sky conditions, it can bring as many as 120 shooting stars per hour to our sky.
This year, however, the peak of the Geminid meteor shower coincides with the night of December’s long night full moon, so the numbers will be diminished.
Geminid meteors are so named because they seem to spring from the stars of the constellation of Gemini the Twins. The radiant for this shower is very near the bright star Castor; Geminid meteors will spring out in all directions from this point. Each bright Geminid shooting star 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 you could hold a thousand of them in the cupped palm of your hand.
The Geminid meteor shower is a relative newcomer to our skies. No one reported seeing any Geminid meteors before the year 1862, but every December since that year, the Geminid shower has appeared on schedule and seems to be getting stronger and better every year.
The Geminid meteors are also unique, because their parent body seems to be a rocky asteroid rather than an icy comet. In 1983, the IRAS satellite spotted a small object, about three miles across orbiting along the same path as the dust swarm that generates the Geminid meteor shower. Now named Phaethon, this object might well be a burned out comet disguised as an asteroid, that is, a comet that has lost all its ice after many passes around the Sun and is now only the rocky skeleton of a once-active comet.
The trail of dust particles that follows Phaethon around the Sun could be a leftover from its comet days. Because the particles from Phaethon are rocky, they can penetrate deeper into our atmosphere before burning up, so Geminid meteor streaks are often long, slow, and bright.
The constellation of Gemini is visible above the northeastern horizon by 7:30 p.m. this week, so the meteor action starts at a reasonable hour and builds through the night. The full moon will definitely put a crimp in meteor watching, but there will still be plenty of bright Geminids that will shine through the moonlight. Just keep the bright moon to your back or hidden behind a building, then kick back and watch the fireworks.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Steamboat Springs Campus. His Celestial News column appears weekly in Steamboat Today. Check out Westlake’s new 2017 Cosmic Calendar of sky events on his website, jwestlake.com. It features 12 of his best astro-photos and a day-by day listing of cool celestial events you and your family can enjoy watching all year.
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