Comets are members of the solar system; that is to say, they travel in orbits around the Sun in a manner fundamentally the same as that of the planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto), the asteroids (tiny, rocky, minor planets of which the solar system contains many thousand), and meteors. Many appear regularly. One, Encke’s comet, returns every three years, while others are calculated to return at intervals of thousands of years. Some suddenly appear in the sky or are observed through a telescope as they approach. They travel in a curved path around the Sun and disappear again in the recesses of the solar system, far beyond the range of observation.
Their origin is uncertain; why intermittent wandered suddenly appear in the region of the Sun has yet to be fully explained. The existence of comets, however, has been known for centuries; one of the earliest records dates from about 1770 B.C. Although many ancient civilizations possessed fine astronomers, before the seventeenth century there were no instruments capable of making the observations needed to compute the speed and distance of a comet, and it was not until 1682 that the successive return of the same comet was finally established. After the invention of the telescope, many more comets were discovered, their behavior examined, and their orbit calculated.
For the purposes of recording, cataloging, and discussing comets, there is now a standard method of nomenclature. When a comet is discovered, it is designated by the order of its discovery in that year; thus Comet 1961e was the fifth to be discovered in 1961. When its orbit has been calculated, a Roman numeral is substituted for the letter, denoting the order of the comet according to its distance from the Sun at its closest approach to the Sun (the perihelion distance). Comet 1950v was the fifth closest to the Sun in that year. Comets are usually also named after their discoverer – Comet 1961e is known as Comet Humason or Humason’s comet.