December 612

The flashy Geminid meteor shower

The after-midnight sky this week will be punctuated with shooting stars as the Geminid meteor shower approaches its peak on December 13. Observers may see as many as 50 bright meteors per hour, unless a bright Moon interferes.

Like all meteor showers, the Geminids are named for the constellation or star from which they appear to emanate. Gemini rises around 6:30 p.m. local time and so meteors may be seen in the sky all evening, most coming out of the northeast. Greater numbers of meteors, however, will be seen after midnight and in the morning hours as the night side of Earth faces into its orbit, sweeping up more cosmic debris. By 12:30 a.m., Gemini is directly overhead and this is the direction from which the meteors will emanate.

Typically, Geminid meteors are bright, but only a few leave smoke trails. They are predominantly white in color and can be seen almost anywhere in the sky. To be a true Geminid, as opposed to being a 'sporadic' meteor, its fiery path across the sky must lead back to the constel-

lation Gemini the Twins. Gemini is a distinctive group, hosting two bright stars: white Castor and orange Pollux. These two lie side by side in the sky northeast of the great constellation Orion.

Unlike most other meteor streams, the Geminids are derived from an asteroid, designated 3200 Phaethon, which occasionally swings near Earth. Asteroids are not usually credited with creating the debris trails responsible for meteor showers, but they may be more responsible than previously thought. In 1997, observations of another asteroid, 253 Mathilde, by the Near Earth Asteroid Rendezvous (NEAR) spacecraft, confirmed that it had not only been heavily pummeled by meteors in the past, but that it is also composed of very porous and uniform material. Perhaps, then, particles might easily be blasted away from such a 'fluffy' asteroid, creating debris streams that could result in brief or even long-term meteor showers not unlike the Geminid display.

Also this week:

• In the Southern Hemisphere, the Puppid-Velid meteor shower is active. This shower exhibits several radiants, one in Puppis, one in Vela, and one in Carina. Moreover, it has several peaks. The best time to catch at least one peak may occur this week around December 9. The second occurs later this month on or about December 26. Expect between 5 and 15 meteors per hour. Puppis and Vela rise around 7:30 p.m., but more meteors may be seen when they are higher in the sky, after midnight.

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