Sky Talk December 2007: The Geminid Meteor Shower

December brings skywatchers one of the year’s two richest displays of “shooting stars” — the Geminids. (No, the other isn’t the famed Perseids in August, as told below!). They’re named for the constellation Gemini from which they appear to radiate or “shoot” across the sky. And unlike most other meteor displays whose host constellations typically don’t rise until the hours after midnight, this one is already above the northeastern horizon after dark making this shower convenient for early evening viewing.

There are two annual meteor showers that stand out among the dozen or so most-observed displays throughout the year. One of these is the Quadrantids in early January and the other this month’s Geminids. Both are richer than the better-known Perseids in August, with peak rates reaching as many as 100 meteors an hour. The Geminids appear to radiate from near the bright star Castor, one of the two “Twin Stars” marking Gemini, the mythological twins (the other being Pollux — use your Edmund Star and Planet Locator (#30092-27) to identify them). The shower will be best viewed on the evening of December 13th into the morning hours of the 14th, with maximum activity predicted for around 2:00 a.m. local time.

The number of meteors seen will increase throughout the night as Gemini continues to rise higher in the sky. But there’s also another significant factor at play here. During the evening hours we’re on the side of our Spaceship Earth “facing away” from the direction the meteors are approaching and so they have to “catch up” with us. But after midnight we’re turned completely toward the direction of the radiant, causing them to slam into the atmosphere at much higher speeds — resulting in many more being seen. So losing some sleep to stay up late watching meteors is definitely worth it!

Observing shooting stars is basically a naked-eye activity in order to canvass as large an area of sky as possible. However, use of your Edmund binoculars is also encouraged for following the trails or “trains” often left behind by many of the brighter meteors. And there’s something here for telescope users as well. Using a low-power, wide-field glass such as the Edmund Astroscan, you may well see faint streaks of light passing through the eyepiece from time-to-time while observing other sights about the sky. Known as telescopic meteors, these are also Geminids that in most cases are much too faint to be seen with the eye alone. Pointing your telescope or binoculars at the radiant itself, you may even see meteors coming directly at you — suddenly appearing from out of nowhere as brightening stars!

This year, little interference will be encountered from the light of a four-day old crescent Moon hanging high above the southwestern horizon at dusk. It sets by mid-evening in any case, leaving a totally dark sky (except, of course, for any manmade light pollution!). A helpful technique here is to face east toward the radiant and concentrate your attention on the sky overhead, preferably reclining comfortably on a lawnchair. And be sure to bundle up against the nighttime chill while you do!

–James Mullaney
Former assistant editor at Sky & Telescope magazine and author of five books on stargazing.

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