comet
A comet or tailing is a small heavenly body of a few kilometers in diameter, which, at least in the parts of its orbit near the sun, develops a coma produced by outgassing, and usually also a luminous tail. The name comes from altgriech. Κομήτης komētēs, top-of-season ', derived from κόμη kómē for' Haupthaar ',' Mähne '. Comets, like asteroids, are remnants of the formation of the solar system. They formed in the outer, cold regions of the solar system, where the abundant hydrogen compounds condensed to ice. In the vicinity of the sun, the comet ore, which is usually only a few kilometers in size, is surrounded by a diffuse, foggy envelope, called coma, which can reach an extent of 2 to 3 million kilometers. Core and coma together are also called the head of the comet. The most striking characteristic of the comets visible from the earth is, however, the tail, which can reach a length of several hundred million kilometers in large and sun-like objects. Mostly, however, it is only a few tens of millions of kilometers.