December’s Geminid meteor shower promises to be best of 2007

By William Atkins
Monday, 03 December 2007 19:10

Science - Space

Around 10 p.m. local time Thursday is the beginning of the Geminids in North America. The number of meteors should increase around midnight, with more coming per hour until dawn brings a maximum of a couple hundred per hour traveling across the early morning sky.
A sky chart of the position of the Geminids with surrounding constellations appears at the Space.com website Sky Map.

The show that the Geminids put on in December has been brighter and more numerous in recent years, as up to 180 meteors per hour have been sometimes seen at its peak.

The Geminids were first observed about 150 years ago. They are called “Geminids” because they appear to come out of the constellation Gemini ("The Twins"). The meteors will appear yellowish in color as they travel about 20 to 24 miles (32 to 39 kilometers) per second across the night sky.

The Geminid meteor shower originates from an asteroid, 3200 Phaethon, instead of a comet, as is usually the case. The orbit of the asteroid is highly elliptical. Its closest approach to the Sun (perihelion) is about half the distance of planet Mercury to the Sun, the closest planet in the solar system to the Sun. This closest approach happens once every 1.4 years or so.

When 3200 Phaethon gets this close, its surface temperature rises dramatically—reaching upwards to about 1385 degrees Fahrenheit (752 degrees Celsius). This relationship to the Sun caused it to be named after Phaethon, the son of the Greek sun god Helios.

Astronomers aren’t sure how 3200 Phaethon came to be. Theories include it colliding with another asteroid and it previously being a comet that’s now gone extinct.

Asteroid 3200 Phaethon was discovered in 1983 by astronomers Simon F. Green and John K. Davies while using the Infrared Astronomical Satellite (IRAS). It is classified as a potentially hazardous asteroid (PHA) because it comes as close as 2 million miles (3.2 million kilometers) to Earth—a very close distance with respect to distances in the solar system.

The asteroid, itself, is about 3.2 miles (5.1 kilometers) in width. Thus, it is possible to see it with good binoculars or an average backyard telescope a few days before the Geminid meteor shower. In fact, on December 10th, 3200 Phaethon will be about 11 million miles (18 million kilometers) from Earth as it flies through the constellation Virgo.

An orbital map of 32 Phaethon appears at the NASA Jet Propulsion Lab website called "32 Phaethon (1983 TB)."