Who discovered comets? How is the tail formed?

Comets have been known to mankind since eons, hence it cannot be said that comets were discovered by any single individual. A comet, like planets and asteroids, orbits around the sun – with the orbital period varying from a few years to thousands of years. A comet is formed of rock, ice, dust and a few frozen gases like carbon dioxide, carbon monoxide and methane. When a comet is close to the sun, the radiation from the sun causes the volatile matter in the comet to vaporize and spread out into space in the form of its tail, its dust particles and ions glowing due to sunlight falling on it.