Astronomers estimated that the visible fragments of SL9 ranged in size from a few hundred metres to two kilometres across, suggesting that the original comet may have had a nucleus up to acrosssomewhat larger than Comet Hyakutake, which became very bright when it passed close to the Earth in 1996.

However, the discovery of the object 1996 PW, an asteroid in an orbit more typical of a long-period comet, suggests that the cloud may also contain rocky objects.

The 1301 apparition may have been seen by the artist Giotto di Bondone, who represented the Star of Bethlehem as a fire-colored comet in the Nativity section of his Arena Chapel cycle, completed in 1305.

Some believe the dome may be related to an ancient meteor or comet impact, part of the 38th parallel structures, which are a string of geological features running west to Kansas.

The parent body of the Quadrantids was recently tentatively identified ( in a paper by Peter Jenniskens ) as the minor planet 2003 EH < sub > 1 </ sub >, which in turn may be the same object as the comet C / 1490 Y1 2003 EH < sub > 1 </ sub > Is the Quadrantid Shower Parent Comet that was observed by Chinese, Japanese and Korean astronomers some 500 years ago.

It was created by the impact of an asteroid or comet some 65 million years ago which may have caused the Cretaceous – Paleogene extinction event, which led to the demise of the dinosaurs.

He treated in a masterly manner ( Bulletin astronomique, 1889 ) the theory of the capture of comets by the larger planets, and in this connection published his valuable Criterion for establishing the identity of a periodic comet, whatever may have been the perturbations brought about in its orbit, between successive appearances, by the action of a planet.

Fragments of the comet may have barely missed Earth in 1883.

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.

Davies has had a longstanding association with the problem of time ’ s arrow, and was also a early proponent of the theory that life on Earth may have come from Mars cocooned in rocks ejected by asteroid and comet impacts.

Although the 1949 images show cometary features, all subsequent images show only a stellar image, suggesting it may be an inactive comet that undergoes only infrequent outbursts.

In some cases, such as the Great Comet of 1882, a comet develops a visible antitail or dust tail, which points in a different direction and when the viewing angle and parallax are just right may appear to point in the opposite direction from the normal ion tail.

Computing the best-fit orbit for this long-period comet is made more difficult since it underwent a splitting event which may have caused a non-gravitational perturbation of the orbit.

It belonged to the Jupiter comet family, whose comets can be short-lived so it may not exist any longer today.

Given that it is more likely that the main mass loss occurred near aphelion before the 1845 apparition, it seems possible that fragment A at least may still exist as a ' dormant ' comet.

For example, if a scientist discovered a comet about to kill the planet in a matter of weeks, it may cause more happiness to suppress the truth than to allow society to discover the impending danger.

Its orbital elements indicate that may be an extinct comet.

Linked comet orbits suggest that both Marsden and Kracht groups have a small period, on the order of five years, but the Meyer group may have intermediate-or long-period orbits.

Further control mechanisms may also exist, considering that p31 < sup > comet </ sup > is not present in lower eukaryotes.

As well as functioning as a regulator of the C-MAD2 positive feedback loop, p31 < sup > comet </ sup > also may act as a deactivator of the SAC.

The low-temperature interior of this crater functions as a cold trap that may capture and freeze volatiles shed during comet impacts on the Moon.

* As of October 2009, the heliosphere may be bubble, not comet shaped.

However, occasionally a comet may brighten to naked eye visibility, and even more rarely it may become as bright or brighter than the brightest stars.

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.

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

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.

When the comet passed Jupiter in the late 1960s or early 1970s, it happened to be near its aphelion, and found itself slightly within Jupiter's Hill sphere.

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.

Some goldfish varieties, such as the common goldfish, comet goldfish, and shubunkin have body shapes and coloration that are similar to koi, and can be difficult to tell apart from koi when immature.

Whereas previously it was hazardous to guess if there would be a storm or little activity, the predictions of Asher and McNaught timed bursts in activity down to ten minutes by narrowing down the clouds of particles to individual streams from each passage of the comet, and their trajectories amended by subsequent passage near planets.

In 1950, the idea was independently revived by Dutch astronomer Jan Hendrik Oort as a means to resolve a paradox: over the course of the Solar System's existence, the orbits of comets are unstable ; eventually, dynamics dictate that a comet must either collide with the Sun or a planet, or else be ejected from the Solar System by planetary perturbations.

* June 2 – Donati's Comet, the first comet to be photographed, is discovered by Giovanni Battista Donati and remains visible for several months afterwards.

* 2135-2136 Halley's comet will be at perihelion.

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.

Moreover, if a fragment of an icy comet were to strike the Earth, the most likely outcome, due to the low tensile strength of such bodies, would be for it to disintegrate in the upper atmosphere, leading to an air burst explosion analogous to that of the Tunguska event.

There were multiple ideas of how to spread Max's immunity to humanity, including: an air burst that would spread the antibody and dispersed through the human race and save everyone from the comet or, the immunity would be attached to the viruses associated with the common cold and thus spread through the common cold ( he detailed how a scene would show original Cindy sneezing as part of the beginning of the immunity spread ).

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.

These observations supported a number of longstanding hypotheses about comet construction, particularly Fred Whipple's " dirty snowball " model, which correctly predicted that Halley would be composed of a mixture of volatile ices – such as water, carbon dioxide and ammonia – and dust.

Halley was the first comet to be recognized as periodic.

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.

However, observations conducted around the time of Halley's Comet's appearance in 1986 suggest that the Eta Aquarid meteor shower might not originate from Halley's Comet, though it might be perturbed by the comet.

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.

The comet is represented on the Bayeux Tapestry as a fiery star, and the surviving accounts describe it as appearing to be four times the size of Venus and shining with a light equal to a quarter of that of the Moon.

It will be the greatest disappointment of my life if I don't go out with Halley's comet.

A planet ( or asteroid or comet ) is simply said to be in conjunction, when it is in conjunction with the Sun, as seen from the Earth.

Impact breccias are thought to be diagnostic of an impact event such as an asteroid or comet striking the Earth, and are usually found at impact craters.