March, April, May
Fick Calendar Home

April 2003

Closeup of a Comet

This close-up view of the head of Comet Ikeya-Zhang gives the impression that it is speeding through our sky. Indeed, comets travel tens of thousands of miles per hour as they pass close to the Sun, but at their large distance from the Earth (70 million miles in this case), they appear to move quite slowly through our sky The color technique used to make this image is evident as a result of the motion of the comet. The telescope remained pointed at the comet, which moved slightly between the blue, red, and green filtered exposures. Thus the background stars appear as short three-color streaks

The features of a comet head are the nucleus (the bright spot at lower right) and coma (the more diffuse material surrounding the nucleus). The tail of the comet points (generally) away from the Sun. Though they can extend for many millions of miles, the entire comet has a mass comparable to a small mountain. The nucleus is composed of rock and ice (a "dirty snowball") and the tail contains nuclear material that has been vaporized by the heat and light of the Sun.