Lists of comets

Non-periodic comets are seen only once. They are usually on near-parabolic orbits that will not return to the vicinity of the Sun for thousands of years, if ever.

Coin showing Caesar's Comet as a star with eight rays, tail upward

Periodic comets usually have elongated elliptical orbits, and usually return to the vicinity of the Sun after a number of decades.

The official names of non-periodic comets begin with a "C"; the names of periodic comets begin with "P" or a number followed by "P". Comets that have been lost or disappeared have names with a "D". Comets whose orbit has not been determined are designated with a "X" prefix.