How does a comet start?
A comet is a big wad of rocks and debris with, perhaps, ice and frozen gases. It travels a long, narrow orbit around the sun, and no one knows for sure how its life began. Most of the time, it is a cold, dark lump of matter far, far from the sun. One end of the orbit loops close in around the sun, and this is when the ccmet seems to come to life. For a short while, the rocky core becomes a radiant head and behind it streams a filmy trail of golden hair. But all this glory is just the reflection of the sun, and it soon vanishes. A big comet comes into view soon after it crosses the orbit of Mars, when it is close enough to borrow some of the glory of the sun.
