[Gk. kome, hair.] A wandering class of heavenly bodies. As seen through a powerful telescope, a comet consists of an ill-defined mass of light called the head, which is much brighter towards the centre, presenting the appearance of a nucleus like a star or planet. Surrounding the nucleus there are certain definite layers of luminous material, which seems to unite behind the head, and from which a luminous train called the tail proceeds. The direction in which the tail points is always opposite to that of the sun. There are many comets revolving round the sun in very elliptic orbits, almost touching the sun at one end of the orbit and very distant at the other. Other comets are supposed to come from the depths of space. Some of them break up into fragments and form meteoric rings.