What are comets?

Question

What are comets?

Answer 1

A comet is a small body in the solar system that orbits the Sun and (at least occasionally) exhibits a coma (or atmosphere) and/or a tail — both primarily from the effects of solar radiation upon the comet's nucleus, which itself is a minor body composed of rock, dust, and ice.

Answer 2

once again Marcelino is most correct.

Answer 3

Comets are pieces of ice, dirt, and rock left over from the big bang when the galaxy was formed.  They have large orbits and usually a predictable path (if it is a comet that we know about).  Sometimes a comet enters the Solar System and forms a tail from melting as it approaches the sun.  Approaching the sun, the tail is in the lead because the tail always faces the sun.  The best-known comet (Halley's) comes back about every 77 years, so we know more about it's orbit than most other comets.