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 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.

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 ).

" He might have had the comet tail phenomenon in mind when he wrote those words, although his publications on comet tails came several years later.

Gibbs also applied his vector methods to the determination of planetary and comet orbits, and he developed the concept of mutually reciprocal triads of vectors which later proved to be of importance in crystallography.

Although he had suspected that two comets that had appeared in succession in 1680 and 1681 were the same comet before and after passing behind the Sun ( he was later found to be correct ; see Newton's Comet ), he was unable to completely reconcile comets into his model.

In 1066, the comet was seen in England and thought to be an omen: later that year Harold II of England died at the Battle of Hastings ; it was a bad omen for Harold, but a good omen for the man who defeated him, William the Conqueror.

Although it was initially called an asteroid and classified as a minor planet, it was later found to exhibit behavior typical of a comet.

* The Aurigid shower parent comet C / 1911 N1 ( Kiess ) returns to the inner solar system and sheds the dust particles that one revolution later cause the 1935, 1986, 1994, and 2007 Aurigid meteor outbursts on Earth.

* ISEE-3 – 12 August 1978 – Solar wind investigations ; later redesignated International Cometary Explorer and performed Comet Giacobini-Zinner and Comet Halley flybys – First comet flyby

He speculated that the planet Venus is a former " comet " which was ejected from Jupiter and subsequently 3, 500 years ago made two catastrophic close passes by Earth, 52 years apart, and later interacted with Mars, which then had a series of near collisions with Earth which ended in 687 B. C., before settling into its current orbit.

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.

On the album Autobahn, which appeared a few months later, the track title was shortened to " Kometenmelodie " ( comet melody ).

The bright areas would later turn out to be two jets emitting from the comet.

Based on these calculations, Heinrich Wilhelm Matthäus Olbers made a prediction that the comet would go on to become extremely bright later that year.

However the periodicity of comets was probably unknown in Eilmer's time, and so his remark " It is long since I saw you " could have referred to a different, later comet.

* A comet is observed, which later becomes known as Comet Halley, after Edmund Halley successfully predicts its return in 1758.

* Johannes Kepler records the appearance and motion of a comet, later to be known as Comet Halley.

In these papers, he proposed the " icy conglomerate " hypothesis of comet composition ( later called the " dirty snowball " hypothesis ).

The basic features of this hypothesis were later confirmed, however the exact amount ( and thus the importance ) of ices in a comet is an active field of research, with most of the recently obtained data pointing to a low contribution of ices to a comet's mass ( dubbed the " icy dirtball " hypothesis ).

He found his second comet later the same year and a third in 1882.

A few days later, it became known that Eugène Joseph Delporte at the Royal Observatory, Belgium, also had found the comet on August 19, so he was added to the list of discoverers.

A few weeks later, news from Paul Ahnert at Sonneberg, Thuringia, Germany, reached Harvard that he also observed the new comet on July 22, but it was too late to recognize his contribution.

The asteroid was used as a target to practice the flyby technique that the Stardust space probe would later use on the comet Wild 2.

The latter he had discovered at Nice on September 4, 1896, but it was not seen on its return, a little less than 7 years later, and was considered a lost comet and consequently designated D / 1896 R2.

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

* September 7 – A large comet is observed in Japan ( it's Japan's oldest observation record of the Halley's Comet ).

During its 1986 apparition, Halley became the first comet to be observed in detail by spacecraft, providing the first observational data on the structure of a comet nucleus and the mechanism of coma and tail formation.

This calculation enabled him, after examining historical records, to determine that the orbital elements of a second comet which had appeared in 1682, were nearly the same as those of two comets which had appeared in 1531 ( observed by Petrus Apianus ) and 1607 ( observed by Johannes Kepler ).

The comet was also observed from space by the International Cometary Explorer.

The telescopes observed Halley, at the faintest and furthest any comet has ever been imaged, in order to verify a method for finding very faint trans-Neptunian objects.

The first observation of a major impact event occurred in 1994: the collision of the comet Shoemaker-Levy 9 with Jupiter ; to date, no such events have been observed on Earth.

Observations of comet C / 1999 S4 ( LINEAR ) with the Chandra satellite in 2000 determined that X-rays observed from that comet were produced predominantly by charge exchange collisions between highly charged carbon oxygen and nitrogen minor ions in the solar wind, and neutral water, oxygen and hydrogen in the comet's coma.

As the comet passed the earth, a large puff or blob of material was observed being ejected in the sunward direction every 6. 23 hours.

These dust trails are sometimes observed in comet images taken at mid infrared wavelengths ( heat radiation ), where dust particles from the previous return to the Sun are spread along the orbit of the comet ( see figures ).

He observed Halley's comet in 1835 from Landulph and the following year started to make his own astronomical calculations, predictions and observations, engaging in private tutoring to finance his activities.

This comet was observed by the crew of Skylab 4 and Soyuz 13, thus becoming the first comet to be observed by a manned spacecraft.

This agrees with the observed orbits of planets and comets, to a reasonably good approximation, although if a comet passes close to the Sun, then it is also influenced by other forces, such as the solar wind and radiation pressure, which modify the orbit, and cause the comet to eject material into space.