Several comets, especially the brighter ones, have been discovered not by professional astronomers, but by amateurs using simple telescopes or even binoculars. The comets found by professional astronomers are usually faint ones that show up in photographic plates of the skies, not necessarily related to comet research. Amateurs tend to scan those parts of the sky generally ignored by astronomers -- the low, western sky in the evening and the eastern horizon before dawn, regions in which bright comets are most likely to be found. Some comets are discovered by spacecraft.

When a comet -- either a new one or a returning one -- is spotted, it is assigned a designation consisting of the year and a letter in alphabetical order. Under this system, introduced in 1870, the first comet discovered in 1994 will be designated 1994a and the second 1994b. If more than 26 comets are reported, the letters are used again with numerical subscripts.

A permanent name for a comet is finalised after a few years, after its perihelion -- the closest point to the sun. This is because a comet sighting can occur in one year and pass perihelion in another. These designations use the year and Roman numerals, 1994 I, 1994 II and so on. They generally include the names of the discoverer(s).

Some comets, like Halley's and Encke's, are named after those who have done substantial work on them. Comets so bright that they are noticed by several astronomers at about the same time are given impersonal names, like Brilliant Comet (1882 II) or Eclipse Comet (1948 XI). Satellites which discover comets give their names to comets, as in 1983 VII IRAS-Araki-Alcock.

Comets are also categorised according to the size and shape of their orbits. Short-period comets move in elliptical orbits, each taking less than 200 years. Most of the 135 short-period comets have orbits that take between 3 and 9 years and at least 120 of them have aphelia -- points farthest from the sun -- close to Jupiter's orbit. Long-period comets have parabolic-shaped orbits that take up to hundreds of thousands of years to complete. At least 613 of these exist, and are all well out of reach of giant planets.

Not the Shoemaker-Levy, though. This one seems to be one destined to poke a hole through the giant planets veil of secrecy.