These terms have historically been applied to any astronomical object orbiting the Sun that did not show the disk of a planet and was not observed to have the characteristics of an active comet, but as small objects in the outer Solar System were discovered, their volatile-based surfaces were found to more closely resemble comets, and so were often distinguished from traditional asteroids.

SOHO's 2000th comet was discovered by Polish amateur astronomer Michał Kusiak on 26 December 2010, and the numbers are expected to continue rising steadily for the foreseeable future.

It was especially noted that the birth and death of some notable persons coincided with separate appearances of the comet, such as with writers Mark Twain ( who correctly speculated that he'd " go out with the comet " in 1910 ) and Eudora Welty, to whose life Mary Chapin Carpenter dedicated the song Halley Came to Jackson.

Comet Shoemaker – Levy 9 ( formally designated D / 1993 F2 ) was a comet that broke apart and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of Solar System objects.

This generated a large amount of coverage in the popular media, and the comet was closely observed by astronomers worldwide.

The comet was discovered by astronomers Carolyn and Eugene M. Shoemaker and David Levy.

It was the first comet observed to be orbiting a planet, and had probably been captured by the planet around 20 – 30 years earlier.

The comet was later observed as a series of fragments ranging up to in diameter.

The comet was thus a serendipitous discovery, but one that quickly overshadowed the results from their main observing program.

Comet Shoemaker – Levy 9 was the ninth periodic comet ( a comet whose orbital period is 200 years or less ) discovered by the Shoemakers and Levy, hence its name.

It was their eleventh comet discovery overall including their discovery of two non-periodic comets, which use a different nomenclature.

The discovery image gave the first hint that comet Shoemaker – Levy 9 was an unusual comet, as it appeared to show multiple nuclei in an elongated region about 50 arcseconds long and 10 arcseconds wide.

Brian Marsden of the Central Bureau for Astronomical Telegrams noted that the comet lay only about 4 degrees from Jupiter as seen from Earth, and that while this could of course be a line of sight effect, its apparent motion in the sky suggested that it was physically close to the giant planet.

Orbital studies of the new comet soon revealed that it was orbiting Jupiter rather than the Sun, unlike all other comets known at the time.

Before the comet was captured by Jupiter, it was probably a short-period comet with an aphelion just inside Jupiter's orbit, and a perihelion interior to the asteroid belt.

Each fragment of the comet was denoted by a letter of the alphabet, from " fragment A " through to " fragment W ", a practice already established from previously observed broken-up comets.

More exciting for planetary astronomers was that the best orbital solutions suggested that the comet would pass within of the center of Jupiter, a distance smaller than the planet's radius, meaning that there was an extremely high probability that SL9 would collide with Jupiter in July 1994.

The discovery that the comet was likely to collide with Jupiter caused great excitement within the astronomical community and beyond, as astronomers had never before seen two significant Solar System bodies collide.

Because of this, he suggested that the Shoemakers and David Levy had discovered the fragments of a comet that had been disrupted by Jupiter's gravity.

Johannes Kepler observed that comet tails point away from the Sun and suggested that the sun caused the effect.

* It is suggested that the original comet associated with the Kreutz Sungrazers family of comets passes perihelion at this time.

His " definitive orbit " for the Leonids coincided with that of the comet 55P / Tempel-Tuttle and therefore suggested the, later widely accepted, close relationship between comets and meteors.

The comet's past orbital evolution became a point of interest as several astronomers suggested early on that the comet might be a return of the then lost periodic comet Spitaler ( aka 113P / Spitaler ).

Mexican astronomers have suggested that a comet may have split into several pieces around 1883 and that Earth barely avoided multiple Tunguska events or even a mass extinction.

He also suggested in 1978 that the Tunguska event was a fragment of the periodic comet Encke.

Chernobrov suggested that the Vitim event could be caused by a comet nucleus with a diameter about 50 – 100 meters.

The impact of a comet or another extraterrestrial body has also been suggested.

* Dyson tree, a hypothetical tree that can grow on a comet as suggested by Freeman Dyson

Some astronomers suggested that perhaps they were all one comet, whose orbital period was somehow being drastically shortened at each perihelion passage, perhaps by retardation by some dense material surrounding the Sun.

A Dyson tree is a hypothetical genetically-engineered plant, ( perhaps resembling a tree ) capable of growing in a comet, suggested by the physicist Freeman Dyson.

He suggested that such plants could produce a breathable atmosphere within hollow spaces in the comet ( or even within the plants themselves ) utilising solar energy and cometary materials, thus providing self-sustaining habitats for humanity in the outer solar system.

This glass is probably formed from Libyan Desert sands by comet or stony-meteorite impact.

A monster will also become angry if either player collects a skull ( the only negative item in the game ), and the monster is hit by the resulting comet crossing the screen.

Such a spectrometer will also be used by the Philae lander of the Rosetta spacecraft to probe the surface of the 67P / Churyumov-Gerasimenko comet.

The type of display presented by the comet depends on its composition and how close it comes to the Sun.

At this time a number of researchers, most notably Eugene M. Shoemaker, ( co-discoverer of the comet Shoemaker-Levy 9 ), conducted detailed studies of a number of craters and recognized clear evidence that they had been created by impacts, specifically identifying the shock-metamorphic effects uniquely associated with impact events, of which the most familiar is shocked quartz.

Several other observers found images of the comet in precovery images obtained before March 24, including Kin Endate from a photograph exposed on March 15, S. Otomo on March 17, and a team led by Eleanor Helin from images on March 19.

The comet had apparently passed extremely close to Jupiter on July 7, 1992, just over above the planet's cloud topsa smaller distance than Jupiter's radius of, and well within the orbit of Jupiter's innermost moon Metis and the planet's Roche limit, inside which tidal forces are strong enough to disrupt a body held together only by gravity.

Although the comet had approached Jupiter closely before, the July 7 encounter seemed to be by far the closest, and the fragmentation of the comet is thought to have occurred at this time.

Observers hoped that the impacts would give them a first glimpse of Jupiter beneath the cloud tops, as lower material was exposed by the comet fragments punching through the upper atmosphere.

The others usually begin with the world rushing to catastrophe, until people realise a better way of living: whether by mysterious gases from a comet causing people to behave rationally and abandoning a European war ( In the Days of the Comet ( 1906 )), or a world council of scientists taking over, as in The Shape of Things to Come ( 1933, which he later adapted for the 1936 Alexander Korda film, Things to Come ).

Hyperbolas arise in practice in many ways: as the curve representing the function in the Cartesian plane, as the appearance of a circle viewed from within it, as the path followed by the shadow of the tip of a sundial, as the shape of an open orbit ( as distinct from a closed and hence elliptical orbit ), such as the orbit of a spacecraft during a gravity assisted swing-by of a planet or more generally any spacecraft exceeding the escape velocity of the nearest planet, as the path of a single-apparition comet ( one travelling too fast to ever return to the solar system ), as the scattering trajectory of a subatomic particle ( acted on by repulsive instead of attractive forces but the principle is the same ), and so on.

The stream comprises solid particles, known as meteoroids, ejected by the comet as its frozen gases evaporate under the heat of the Sun when it is close enough – typically closer than Jupiter's orbit.

The meteoroids left by the comet are organized in trails in orbits similar to though different from that of the comet.