Best meteor shower of 2010 arrives starting Dec. 13

Slower-moving Geminids won’t require binoculars or a telescope to see

What should be the best meteor shower of 2010 will occur beginning on the evening of Monday, Dec. 13.

Like most meteor showers, the Geminids will be at their best after midnight (early on the morning of Dec. 14), when the Earth is heading directly into the meteoroid stream. But some will be visible earlier in the night, on the evening of Dec. 13, because the meteors radiant —where they appear to originate — is nearly circumpolar, so they will stay in view above the horizon all night.

What causes a meteor shower?
Most meteor showers are caused by fragments of old comets scattered along a comets orbit. When the Earth passes through a comets orbit, it sweeps up the fragments, which are heated by friction with the Earth’s atmosphere to incandescence, and are visible as bright streaks of light. The Geminid shower is unique in being associated not with a comet, but with an asteroid — 3200 Phaethon.

Phaethon is a very odd asteroid indeed. Its orbit brings it closer to the sun than any other known asteroid, well inside Mercury’s orbit. Its orbit is more like that of a comet than an asteroid, but it has never exhibited any of the features which characterize comets: no coma, no gas jets, no dust tail.

When we look toward the radiant of this meteor shower, we are looking into the line of Phaethon’s orbit. The meteors appear to radiate from this point in the sky, but this is an effect of perspective, much as railroad tracks appear to diverge as they get closer to us.

The Geminids’ radiant is, as the name implies, in the in the direction of the constellation Gemini, just north of the northernmost of Gemini’s two brightest stars, Castor. In the early evening of Dec. 13, the radiant is low in the northeast. By 1 a.m. ET, after the date has changed to Dec. 14, the radiant is almost directly overhead. By 6.a.m., when the shower is at its peak in the Eastern time zone, the radiant is low in the west.