Comets are icy planetesimals usually from 1 to 50 km across and containing bits of fragile dust resembling carbonaceous chondrite material. They probably formed among the outer planets and were ejected into the Oort cloud, from which they occasionally reenter the inner solar system.

When a reentering comet reaches a distance of about 2 to 4 AU from the sun, material begins to sublime off its surface, producing a gaseous coma and a gas-and-dust tail that is blown outward by the solar wind. The solid debris become meteoroids strewn along the comet's orbit, since they leave the comet at too low a speed to change orbit very much.

These particles are affected by Poynting-Robertson and radition forces and occasionally hit Earth, producing meteors or their larger cousins, fireballs.

Comets age slowly as more and more gas and dust are lost. Some of them may burn out, leaving inert residues of stony material-possibly cataloged in some cases as Apollo asteroids of spectral class C, P or D. Comets in their various states would provide interesting targets for close investigation by spacecraft.

Hollywood tried to personify this with their asteroidal adventure - Armageddon, more recently NASA theorized the possibilities using remote robot landings.
Comet Periodicity

Most comets have an elliptical orbit around the Sun, whose period can vary enormously. Comets are generally defined as being short-period if their orbit is less than 200 years, the remainder being known as long-period comets.

Short-period comets tend to remain within the orbit of Jupiter and close to the plane of the Solar System ecliptic. The shortest known period is Encke's comet, which orbits every 3.3 years. The long-period comets may have an aphelion well outside the orbit of Pluto and can be inclined at all angles to the plane of the ecliptic. These are sometimes thought of as belonging to Jupiter's family. B. G. Marsden's Catalogue of Cometary Orbits (1972) lists 97 short-period comets and 503 long-period ones.

Other comets are not orbiting the Sun at all, and move in on hyberbolic paths, only to disappear again. For others, their orbits are too long to calculate - possibly disappearing for tens of thousands of years.


Most comets are named after their discoverers and denoted by letters in the order of discovery (see Amateur Astronomer for examples). After that, they are numbered in order of their perihelion passage (for example, the Arend–Roland Comet was 1956h but became 1957 III). New comets are being discovered at the rate of 10-12 a year, many of them by amateurs.


Astronomers have come to the conclusion that there may be two distinct types of comet - one rich in methanol and one low in methanol. This is supported by observations of the spectrum of Comet Hyakutake. The continuing study of comets will undoubtedly add to our understanding of the nature of our own solar system.

A member of the Legion of Super Pets.

Biron is the real name of Comet the Super Horse. Originally a centaur in ancient Greece, Biron lived the "normal" life of a half-man/half-horse until the day that he rescued the legendary sorceress Circe from an enemy. In gratitude for his help, Circe granted Biron a single wish. Biron, obviously tired of straddling the line between humanity and equinity, took the bit in his mouth and requested to be turned fully human. Circe complied, but an unknown enemy made her spell go awry, turning Biron into a horse. Circe was able to allow Biron to change into a human, but because of the vaguaries of magic, he is only able to do so when a comet is in the sky. Hence, Biron became known as Comet.

Comet's powers are magically-based, so he does not have the same weaknesses that Kryptonians have to Kryptonite, magic, and the rays of a red sun. Comet's only power was that he could fly. Biron occasionally was romantically involved with Supergirl. This only took place when he was in human form to avoid a Comics Code debacle.

Comet, along with Krypto, Streaky, and Beppo came together to help the Legion of Super-Heroes. In recognition of their help, the Legion established them as the Legion of Super Pets.

We always presume that a comet is a big fat icy glowing ball whose magnificent and dusty tail trails behind it, but this is incorrect. A comet tail always points away from the Sun. So the tail (or tails) stream behind the comet as it looms towards the Sun, but when the same comet is retreating back out into the solar system, the tail actually leads the way.

Com"et (?), n. [L. cometes, cometa, from Gr. comet, prop. long-haired, fr. to wear long hair, fr. hair, akin to L. coma: cf. F. comete.] Astron.

A member of the solar system which usually moves in an elongated orbit, approaching very near to the sun in its perihelion, and receding to a very great distance from it at its aphelion. A comet commonly consists of three parts: the nucleus, the envelope, or coma, and the tail; but one or more of these parts is frequently wanting. See Illustration in Appendix.


© Webster 1913.

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