Photographer Tony Eckersley shot this amazing composite photo of seven meteors over San Francisco during a one-hour period of the Geminid meteor shower Thursday night. "I saw around 30 total," Tony explains, "shame I only caught seven in the camera." And now, we go to NASA to learn more about this rock comet meteor shower:

Most meteor showers are caused by icy comets, which spew jets of meteoroids when they are heated by sunlight. The Geminids are different. The parent is not a comet but a weird rocky object named 3200 Phaethon.

When 3200 Phaethon was discovered in 1983 by NASA's IRAS satellite, astronomers quickly realized that they had found the source of the Geminids. The orbit of 3200 Phaethon was such a close match to that of the Geminid debris stream, no other conclusion was possible. Yet here was a puzzler: Everything about 3200 Phaethon suggests it is an asteroid. [...]

There is, however, another possibility: Perhaps 3200 Phaethon is a "rock comet."
A "rock comet" is a new kind of object being discussed by some astronomers. It is, essentially, an asteroid that comes very close to the sun--so close that solar heating scorches dusty debris right off its rocky surface. Rock comets could thus grow comet-like tails made of gravely debris that produce meteor showers on Earth.

The meteor shower peaked last night, with astronomers predicting a rate of about 100 meteors per hour. With little moonlight tonight, local observers ought to be able to catch a glimpse of a shooting star or two tonight if the cloud cover clears.