A comet is a small body orbiting our Sun, usually at great distance from Earth and with a highly elliptical orbit. They are composed of 'ices' and dust. As a comet approaches the inner solar system, the heat of the Sun vapourises volatile material from the surface and pushes the material directly away from the Sun. This gives rise to the 'ion tail', usually a ghostly blue colour and quite straight, it always points directly away from the Sun and has nothing to do with the direction of motion of the comet. A second tail exists, usually white and curved. This is dust which falls off the comet and is left in track of its orbit. Here is a photo of comet Hale-Bopp, taken from Hoswick, Shetland in 1998. Scientists recently deliberately crashed a space probe onto the surface of a comet in order to learn more.
Comets and their dust tails give rise to regular meteor showers.
Image copyright C.McGinlay, may be used for non-commercial educational purposes. 20 second exposure onto 1000ASA Kodak Ektar, taken 13/14 April 1997 2357GMT. Set2/3A
