For example, Halley's comet returns every 76 years. It was first seen in 240 BC by the Chinese. For example Halley's comet is 16 x 8 km. The comet also develops a tail of ionized gasesand dust that may be millions of km long. As the comet moves away from the sun, the tail preceeds the head.
Comets have no light of their own, but reflect sunlight.
Meteor showers are associated with comets.