What is the tail of a Comet?

You cannot see the nucleus of a comet with the naked eye, but you can sometimes see its tail. It appears as a smear of light that moves very gradually across the night sky. As a comet moves closer to the sun, the ice and other frozen gases in its nucleus begin to boil off, producing a long tail of gas and dust. The tail always points away from the sun because light and other forms of radiation from the sun push against the minute particles that are present within the tail.