... Bad Astronomy . ... Bitesize Astronomy . ... Keep Bad Astronomy close to your heart, and help make me filthy rich. ... As the comet approaches the Sun, that ice melts and even vaporizes. It boils off the comet head and the moving comet leaves it behind. ... Plus, there must be a large pocket of gas just under the surface of the comet. ... Finally, the tail is streaming off the comet head, but appears to be off to one side since the comet's motion around the Sun makes it leave behind that material. ...