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Encyclopedia > Comet
Comet Hale-Bopp
Comet Hale-Bopp

Comets are small Solar System bodies that orbit the Sun and, when close enough to the Sun, exhibit a visible coma (or atmosphere) and/or a tail — both primarily from the effects of solar radiation upon the comet's nucleus. Comet nuclei are themselves loose collections of ice, dust and small rocky particles, measuring a few kilometres or tens of kilometres across. Image:Comet-Hale-Bopp-29-03-1997 hires adj. ... Image:Comet-Hale-Bopp-29-03-1997 hires adj. ... Comet Hale-Bopp (formally designated C/1995 O1) was probably the most widely observed comet of the twentieth century, and one of the brightest seen for many decades. ... Download high resolution version (800x1174, 790 KB) ©  This image is copyrighted. ... Download high resolution version (800x1174, 790 KB) ©  This image is copyrighted. ... Comet West formally designated C/1975 V1, 1976 VI, and 1975n, was a spectacular comet, sometimes considered to qualify for the status of great comet. It was discovered by Richard M. West on August 10, 1975 and reached peak brightness in March 1976. ... Comet can refer to: An astronomical comet. ... This article is about the Solar System. ... Sol redirects here. ... The comet Ikeya-Zhang exhibiting a bright, condensed coma (march 2002) In astronomy, the nebulous envelope around the nucleus of a comet is called its coma (from the Latin word for hair). It is formed when the comet passes close to the sun on its highly elliptical orbit; as the... The solid, central part of a comet is known as the comet nucleus. ...


Comets have a variety of different orbital periods, ranging from a few years, to hundreds of thousands of years, while some are believed to pass through the inner Solar System only once before being thrown out into interstellar space. Short-period comets are thought to originate in the Kuiper Belt, which lies beyond the orbit of Neptune. Long-period comets are believed to originate at a very much greater distance from the Sun, in a cloud (the Oort cloud) consisting of debris left over from the condensation of the solar nebula. Comets are thrown from these outer reaches of the Solar System inwards towards the Sun by gravitational perturbations from the outer planets (in the case of Kuiper Belt objects) or nearby stars (in the case of Oort Cloud objects), or as a result of collisions. The Kuiper belt, derived from data from the Minor Planet Center. ... For other uses, see Neptune (disambiguation). ... Artists rendering of the Oort cloud and the Kuiper Belt. ... For other uses, see Condensation (disambiguation). ... This article or section does not cite any references or sources. ...


Comets are distinguished from asteroids by the presence of a coma and/or tail, though very old comets that have lost all their volatile materials may come to resemble asteroids.[1] Asteroids are also believed to have a different origin from comets, having formed in the inner Solar System rather than the outer Solar System.[2] Recent findings have, however, somewhat blurred the distinction between asteroids and comets;[3] see also Asteroid: Terminology. For other uses, see Asteroid (disambiguation). ... The ability of a liquid to evaporate quickly and at relatively low temperatures. ... For other uses, see Asteroid (disambiguation). ...


There are a reported 3,354 known comets as of November 2007,[4] of which several hundred are short-period. This number is steadily increasing. However, this represents only a tiny fraction of the total potential comet population: the reservoir of comet-like bodies in the outer solar system may number one trillion.[5] The number of naked-eye comets averages to roughly one per year,[6] though many of these are faint and unspectacular. When a historically bright or notable naked-eye comet is witnessed by many people, it is often considered a Great comet. Great Comet West A Great Comet is a comet which becomes particularly bright and it is very spectacular to be noticed by a casual observer. ...


The word "comet" came to the English language through Latin cometes from the Greek word komē, meaning "hair of the head"; Aristotle first used the derivation komētēs to depict comets as "stars with hair." The astronomical symbol for comets () accordingly consists of a disc with a hairlike tail. The English language is a West Germanic language that originates in England. ... For other uses, see Latins and Latin (disambiguation). ... Greek ( IPA: or simply IPA: — Hellenic) has a documented history of 3,500 years, the longest of any single natural language in the Indo-European language family. ... For other uses, see Aristotle (disambiguation). ... Chinese Celestial symbols on an antique bronze mirror Astronomical symbols are symbols used to represent various celestial objects, theoretical constructs and observational events. ...

Contents

Physical characteristics

Nucleus of comet Tempel 1 imaged by the Deep Impact impactor. The nucleus measures about 6 kilometres across.
Nucleus of comet Tempel 1 imaged by the Deep Impact impactor. The nucleus measures about 6 kilometres across.

Comet nuclei are in a range from 1/2 kilometer to 50 kilometers across and are composed of rock, dust, water ice, and frozen gases such as carbon monoxide, carbon dioxide, methane and ammonia.[7] They are often popularly described as "dirty snowballs", though recent observations have revealed dry dusty or rocky surfaces, suggesting that the ices are hidden beneath the crust (see Debate over comet composition). Comets also contain a variety of organic compounds; in addition to the gases already mentioned, these may include methanol, hydrogen cyanide, formaldehyde, ethanol and ethane, and perhaps more complex molecules such as long-chain hydrocarbons and amino acids.[8][9][10] Comet nuclei are irregularly shaped: they have insufficient mass (and hence gravity) to become spherical. Image File history File links Tempel_1_Deep_Impact_5min. ... Image File history File links Tempel_1_Deep_Impact_5min. ... Tempel 1 is a periodic comet (formally designated 9P/Tempel 1). ... Illustration of the Deep Impact space probe after impactor separation (artists conception) Deep Impact is a NASA space probe designed to study the composition of the interior of the comet Tempel 1. ... Image File history File linksMetadata Size of this preview: 648 × 519 pixelsFull resolution (648 × 519 pixel, file size: 107 KB, MIME type: image/jpeg)Taken by nasa as stated here [1]. Retiono Virginian 15:51, 24 April 2007 (UTC) File history Legend: (cur) = this is the current file, (del) = delete... Image File history File linksMetadata Size of this preview: 648 × 519 pixelsFull resolution (648 × 519 pixel, file size: 107 KB, MIME type: image/jpeg)Taken by nasa as stated here [1]. Retiono Virginian 15:51, 24 April 2007 (UTC) File history Legend: (cur) = this is the current file, (del) = delete... Comet Hyakutake (Japanese: 百武彗星 Hyakutake suisei, IPA ; formally designated C/1996 B2) is a comet that was discovered in January 1996, which passed very close to Earth in March of that year. ... Carbon monoxide, with the chemical formula CO, is a colorless, odorless, and tasteless gas. ... Carbon dioxide (chemical formula: ) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Methane is a chemical compound with the molecular formula . ... For other uses, see Ammonia (disambiguation). ... Benzene is the simplest of the arenes, a family of organic compounds An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. ... Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naphtha or wood spirits, is a chemical compound with chemical formula CH3OH (often abbreviated MeOH). ... R-phrases , , , , . S-phrases , , , , , , , , . Flash point −17. ... Formaldehyde is the chemical compound with the formula H2CO. It is the simplest aldehyde-- an organic compound containing a terminal carbonyl group: it consists of exactly one carbonyl. ... Grain alcohol redirects here. ... This article is about a chemical compound. ... In chemistry, a hydrocarbon is a cleaning solution consisting only of carbon (C) and hydrogen (H). ... In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. ...


In the outer solar system, comets remain frozen and are extremely difficult or impossible to detect from Earth due to their small size (though some observations of comet nuclei in the Kuiper Belt have been made[11]). As a comet approaches the inner solar system, solar radiation causes the water, frozen gases and other volatile materials within the comet to vaporise and stream out of the nucleus, carrying dust away with them. The streams of dust and gas thus released form a huge, extremely tenuous atmosphere around the comet called the coma, and the force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous tail to form, which points away from the sun. The outer solar system (as opposed to the outer planets) is that part of the Solar System which begins at roughly the orbit of Neptune and terminates at maximum orbit distance, approximately one Light Year from the sun in terms of orbital measurements. ... An inner planet is any one of the Solar systems rocky planets that lie inside the asteroid belt: Mercury (planet), Venus (planet), Earth (planet) and Mars (planet). ... Solar irradiance spectrum at top of atmosphere. ... “Space dust” redirects here. ... The comet Ikeya-Zhang exhibiting a bright, condensed coma (march 2002) In astronomy, the nebulous envelope around the nucleus of a comet is called its coma (from the Latin word for hair). It is formed when the comet passes close to the sun on its highly elliptical orbit; as the... Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. ... The plasma in the solar wind meeting the heliopause The solar wind is a stream of charged particles (i. ...


The streams of dust and gas each form their own distinct tail, pointing in slightly different directions. The tail of dust is left behind in the comet's orbit in such a manner that it often forms a curved tail. At the same time, the ion tail, made of gases, always points directly away from the Sun, as this gas is more strongly affected by the solar wind than is dust, following magnetic field lines rather than an orbital trajectory. While the solid nucleus of comets is generally less than 50 km across, the coma may be larger than the Sun, and ion tails have been observed to extend 1 astronomical unit (150 million km) or more.[12] The astronomical unit (AU or au or a. ...


Both the coma and tail are illuminated by the Sun and may become visible from Earth when a comet passes through the inner solar system, the dust reflecting sunlight directly and the gases glowing from ionisation. Most comets are too faint to be visible without the aid of a telescope, but a few each decade become bright enough to be visible with the naked eye. Occasionally a comet may experience a huge and sudden outburst of gas and dust, during which the size of the coma temporarily greatly increases in size. This happened in 2007 to Comet Holmes. This article is about Earth as a planet. ... This article is about the electrically charged particle. ... This article does not cite any references or sources. ... 17P/Holmes is a periodic comet in our solar system, discovered by the British amateur astronomer Edwin Holmes on November 6, 1892. ...


Surprisingly, cometary nuclei are among the darkest objects known to exist in the solar system. The Giotto probe found that Comet Halley's nucleus reflects approximately 4% of the light that falls on it, and Deep Space 1 discovered that Comet Borrelly's surface reflects only 2.4% to 3% of the light that falls on it; by comparison, asphalt reflects 7% of the light that falls on it. It is thought that complex organic compounds are the dark surface material. Solar heating drives off volatile compounds leaving behind heavy long-chain organics that tend to be very dark, like tar or crude oil. The very darkness of cometary surfaces allows them to absorb the heat necessary to drive their outgassing. Darkness is the absence of light. ... In this artists concept, Giotto points its white high-gain antenna dish towards earth with the ring of solar cells facing the sun. ... This article is about the comet. ... The spacecraft Deep Space 1 was launched October 24, 1998 on top of a Delta II rocket. ... Comet Borrelly (formally designated 19P/Borrelly) is a periodic comet, which was visited by the space craft Deep Space 1. ... The term asphalt is often used as an abbreviation for asphalt concrete. ... Tar can be produced from corn stalks by heating in a microwave. ... Petro redirects here. ...


In 1996, comets were found to emit X-rays.[13] These X-rays surprised researchers, because their emission by comets had not previously been predicted. The X-rays are thought to be generated by the interaction between comets and the solar wind: when highly charged ions fly through a cometary atmosphere, they collide with cometary atoms and molecules. In these collisions, the ions will capture one or more electrons leading to emission of X-rays and far ultraviolet photons.[14] An X-ray picture (radiograph), taken by Wilhelm Röntgen in 1896, of his wife, Anna Bertha Ludwigs[1] hand X-rays (or Röntgen rays) are a form of electromagnetic radiation with a wavelength in the range of 10 to 0. ... ...


The fate of comets

Eventually – typically after many orbits of the Sun – all the volatile material contained in a comet nucleus evaporates away, and the comet either disintegrates into a trail of dust or becomes a small, dark, inert lump of rock or rubble[15] that may come to resemble an asteroid. Comets are also known to break up into large fragments, as happened with Comet Schwassmann-Wachmann 3 in 2006. This breakup may be triggered by tidal gravitational forces from the Sun or a large planet, by an "explosion" of volatile material, or for other reasons not fully explained. For other uses, see Asteroid (disambiguation). ... 73P/Schwassmann-Wachmann, also known as Schwassmann-Wachmann 3, is a periodic comet in our solar system which is in the process of disintegrating. ...


Some comets meet a more spectacular end – either falling into the Sun,[16] or smashing into a planet or other body. Collisions between comets and planets or moons were common in the early Solar System: some of the many craters on the Earth's Moon, for example, may have been caused by comets. A recent collision of a comet with a planet occurred in 1994 when Comet Shoemaker-Levy 9 broke up into pieces and collided with Jupiter. This article is about Earths moon. ... Hubble Space Telescope image of Comet Shoemaker-Levy 9, taken on May 17, 1994. ... For other uses, see Jupiter (disambiguation). ...


Many comets and asteroids collided into Earth in its early stages. Many scientists believe that comets bombarding the young Earth (about 4 billion years ago) brought the vast quantities of water that now fill the Earth's oceans, or at least a significant proportion of it. But other researchers have cast doubt on this theory.[17] The detection of organic molecules in comets has led some to speculate that comets and/or meteorites may have brought the precursors of life – or even life itself – to Earth.[18] There are still many near-Earth comets, although a collision with an asteroid is more likely than with a comet. Willamette Meteorite A meteorite is a natural object originating in outer space that survives an impact with the Earths surface without being destroyed. ...


It is suspected that comet impacts have, over long timescales, also delivered significant quantities of water to the Earth's Moon, some of which may have survived as lunar ice. This article is about Earths moon. ... The continuous bombardment of the Moon by comets and meteoroids have added some amount of water to the lunar surface. ...


Orbital characteristics

Orbits of Comet Kohoutek (red) and Earth (blue), illustrating the high eccentricity of the orbit and more rapid motion when closer to the Sun.
Orbits of Comet Kohoutek (red) and Earth (blue), illustrating the high eccentricity of the orbit and more rapid motion when closer to the Sun.
Histogram of the aphelia of the 2005 comets, showing the giant planet comet families. The abscissa is the natural logarithm of the aphelion expressed in AUs.
Histogram of the aphelia of the 2005 comets, showing the giant planet comet families. The abscissa is the natural logarithm of the aphelion expressed in AUs.

Most comets have elongated elliptical orbits that take them close to the Sun for a part of their orbit, and then out into the further reaches of the Solar System for the remainder. Comets are often classified according to the length of their orbital period; the longer the period the more elongated the ellipse. Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... Orbits of Comet Kohoutek and Earth Comet Kohoutek, formally designated C/1973 E1, 1973 XII, and 1973f, was first sighted on March 7, 1973 by Czech astronomer Luboš Kohoutek. ... This article is about Earth as a planet. ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ... Sol redirects here. ... Image File history File links Download high resolution version (721x853, 3 KB)Histogram of the aphelia of the 186 comets listed by the MPC in June 2005. ... Image File history File links Download high resolution version (721x853, 3 KB)Histogram of the aphelia of the 186 comets listed by the MPC in June 2005. ... For the histogram used in digital image processing, see Color histogram. ... elements of an orbit. ... Abscissa means the x coordinate on an (x, y) graph; the input of a mathematical function against which the output is plotted. ... The natural logarithm, formerly known as the hyperbolic logarithm, is the logarithm to the base e, where e is an irrational constant approximately equal to 2. ... The astronomical unit (AU or au or a. ... In astrodynamics or celestial mechanics a elliptic orbit is an orbit with the eccentricity greater than 0 and less than 1. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ...

  • Short-period comets are generally defined as having orbital periods of less than 200 years. They usually orbit more-or-less in the ecliptic plane in the same direction as the planets. Their orbits typically take them out to the region of the outer planets (Jupiter and beyond) at aphelion; for example, Comet Halley's aphelion is a little way beyond the orbit of Neptune. At the shorter extreme, Comet Encke has an orbit which never places it farther from the Sun than Jupiter. Short-period comets are further divided into the Jupiter family (periods less than 20 years) and Halley family (periods between 20 and 200 years).
  • Long-period comets have highly eccentric (elongated) orbits and periods ranging from 200 years to thousands or even millions of years. (However, by definition they remain gravitationally bound to the Sun; those comets that are ejected from the solar system due to close passes by major planets are no longer properly considered as having "periods".) Their orbits take them far beyond the outer planets at aphelia, and the plane of their orbits need not lie near the ecliptic.
  • Single-apparition comets are similar to long-period comets, but have parabolic or hyperbolic trajectories which will cause them to permanently exit the solar system after passing the Sun once.
  • Some authorities use the term periodic comet to refer to any comet with a periodic orbit (that is, all short-period comets plus all long-period comets),[19] while others use it to mean exclusively short-period comets.[20] Similarly, although the literal meaning of non-periodic comet is the same as single-apparition comet, some use it to mean all comets that are not "periodic" in the second sense (that is, to also include all comets with a period greater than 200 years).
  • Recently-discovered main-belt comets form a distinct class, orbiting in more circular orbits within the asteroid belt.[21][22]

Based on their orbital characteristics, short-period comets are thought to originate in the Kuiper belt – a disk of objects in the transneptunian region – whereas the source of long-period comets is thought to be the far more distant spherical Oort cloud (after the Dutch astronomer Jan Hendrik Oort who hypothesised its existence).[23] Vast swarms of comet-like bodies are believed to orbit the Sun in these distant regions in roughly circular orbits. Occasionally the gravitational influence of the outer planets (in the case of Kuiper Belt objects) or nearby stars (in the case of Oort cloud objects) may throw one of these bodies into an elliptical orbit that takes it inwards towards the Sun, to form a visible comet. Unlike the return of periodic comets whose orbits have been established by previous observations, the appearance of new comets by this mechanism is unpredictable. The following is the IAUs list of periodic comets that have a number designation. ... The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... Comet Halley, officially designated 1P/Halley, more generally known as Halleys Comet after Edmond Halley, is a comet that can be seen every 75-76 years. ... For other uses, see Neptune (disambiguation). ... Comet Encke (officially designated 2P/Encke) is a periodic comet, named after Johann Franz Encke, who through laborious study of its orbit and many calculations was able to link multiple observations in 1786 (2P/1786 B1), 1795 (2P/1795 V1), 1805 (2P/1805 U1) and 1818 (2P/1818 W1) to... For other uses, see Jupiter (disambiguation). ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ... In astrodynamics or celestial mechanics a parabolic trajectory is an orbit with the eccentricity equal to 1. ... In astrodynamics or celestial mechanics a hyperbolic trajectory is an orbit with the eccentricity greater than 1. ... Unlike most comets which originate in the Oort cloud, main-belt comets have near-circular orbits within the asteroid belt and may have been the source of Earths water[1]. Category: ... For other uses, see Asteroid (disambiguation). ... The Kuiper belt, derived from data from the Minor Planet Center. ... Artists rendering of the Oort cloud and the Kuiper Belt. ... Jan Hendrik Oort (April 28, 1900 – November 5, 1992) was an internationally famous Dutch astronomer. ... Sol redirects here. ...


Since their elliptical orbits frequently take them close to the giant planets, comets are often subject to further gravitational perturbations. Short period comets display a tendency for their aphelia to coincide with a giant planet's orbital radius, with the Jupiter family of comets being the largest, as the histogram shows. It is clear that comets coming in from the Oort cloud often have their orbits strongly influenced by the gravity of giant planets as a result of a close encounter. Jupiter is the source of the greatest perturbations, being more than twice as massive as all the other planets combined, in addition to being the swiftest of the giant planets. These perturbations may sometimes deflect long-period comets into shorter orbital periods (Halley's Comet being a possible example). A diagram of Keplerian orbital elements. ... Metroplex (in shadow) and Giant Planet Gigantion, or Giant Planet, is a fictional planet home to giant Transformers in the animated television program, Transformers: Cybertron; it is referred to as Gigalonia in Transformers: Galaxy Force, the Japanese version of the show. ... For the histogram used in digital image processing, see Color histogram. ... This article is about the comet. ...


Early observations have revealed a few genuinely hyperbolic (i.e. non-periodic) trajectories, but no more than could be accounted for by perturbations from Jupiter. If comets pervaded interstellar space, they would be moving with velocities of the same order as the relative velocities of stars near the Sun (a few tens of kilometres per second). If such objects entered the solar system, they would have positive total energies, and would be observed to have genuinely hyperbolic trajectories. A rough calculation shows that there might be four hyperbolic comets per century, within Jupiter's orbit, give or take one and perhaps two orders of magnitude.


A number of periodic comets discovered in earlier decades or previous centuries are now "lost." Their orbits were never known well enough to predict future appearances. However, occasionally a "new" comet will be discovered and upon calculation of its orbit it turns out to be an old "lost" comet. An example is Comet 11P/Tempel-Swift-LINEAR, discovered in 1869 but unobservable after 1908 because of perturbations by Jupiter. It was not found again until accidentally rediscovered by LINEAR in 2001.[24] 11P/Tempel-Swift-LINEAR is a periodic comet in our solar system. ... For other uses, see Linear (disambiguation). ...


Comet nomenclature

The names given to comets have followed several different conventions over the past two centuries. Before any systematic naming convention was adopted, comets were named in a variety of ways. Prior to the early 20th century, most comets were simply referred to by the year in which they appeared, sometimes with additional adjectives for particularly bright comets; thus, the "Great Comet of 1680" (Kirch's Comet), the "Great September Comet of 1882," and the "Daylight Comet of 1910" ("Great January Comet of 1910"). After Edmund Halley demonstrated that the comets of 1531, 1607, and 1682 were the same body and successfully predicted its return in 1759, that comet became known as Comet Halley. Similarly, the second and third known periodic comets, Comet Encke[25] and Comet Biela,[26] were named after the astronomers who calculated their orbits rather than their original discoverers. Later, periodic comets were usually named after their discoverers, but comets that had appeared only once continued to be referred to by the year of their apparition. The Great Comet of 1680, formally known as C/1680 V1 or Kirchs Comet, has the distinction of being the first comet discovered by telescope. ... Photograph of the comet as seen from Cape Town The Great Comet of 1882 (modern formal designation: C/1882 R1) was a comet which became very bright in September 1882. ... The Great Daylight Comet of 1910 was a great comet which upstaged the much-anticipated appearance of Halleys Comet in the same year. ... Edmond Halley. ... Comet Halley, officially designated 1P/Halley, more generally known as Halleys Comet after Edmond Halley, is a comet that can be seen every 75-76 years. ... Comet Encke (officially designated 2P/Encke) is a periodic comet, named after Johann Franz Encke, who through laborious study of its orbit and many calculations was able to link multiple observations in 1786 (2P/1786 B1), 1795 (2P/1795 V1), 1805 (2P/1805 U1) and 1818 (2P/1818 W1) to... 3D/Biela is the official designation for a lost periodic comet discovered in 1826 by Wilhelm von Biela. ...


In the early 20th century, the convention of naming comets after their discoverers became common, and this remains so today. A comet is named after up to three independent discoverers. In recent years, many comets have been discovered by instruments operated by large teams of astronomers, and in this case, comets may be named for the instrument. For example, Comet IRAS-Araki-Alcock was discovered independently by the IRAS satellite and amateur astronomers Genichi Araki and George Alcock. In the past, when multiple comets were discovered by the same individual, group of individuals, or team, the comets' names were distinguished by adding a numeral to the discoverers' names (but only for periodic comets); thus Comets Shoemaker-Levy 1–9. Today, the large numbers of comets discovered by some instruments (in August 2005, SOHO discovered its 1000th comet[27]) has rendered this system impractical, and no attempt is made to ensure that each comet has a unique name. Instead, the comets' systematic designations are used to avoid confusion.[28] Comet IRAS-Araki-Alcock (C/1983 H1) was a small comet that, in 1983, made the closest approach to the earth (about 5,000,000 km) of any comet in 200 years. ... The Infrared Astronomical Satellite (IRAS) was a space-based observatory that performed a survey of the entire sky at infrared wavelengths. ... George Eric Deacon Alcock (August 28, 1912 – December 15, 2000) was a British astronomer. ... Hubble Space Telescope image taken on May 17, 1994. ... The Solar and Heliospheric Observatory (SOHO) is a spacecraft that was launched on an Atlas IIAS launch vehicle on 2 December 1995 to study the Sun, and began normal operations in May 1996. ...


Until 1994, comets were first given a provisional designation consisting of the year of their discovery followed by a lowercase letter indicating its order of discovery in that year (for example, Comet 1969i (Bennett) was the 9th comet discovered in 1969). Once the comet had been observed through perihelion and its orbit had been established, the comet was given a permanent designation of the year of its perihelion, followed by a Roman numeral indicating its order of perihelion passage in that year, so that Comet 1969i became Comet 1970 II (it was the second comet to pass perihelion in 1970)[29] The provisional designation of comets and asteroids are similar to each other: they both follow a pattern set in 1925 by the Minor Planet Center of the IAU. Historical designations At first, astronomers strove to assign symbols to the minor planets: 1 Ceres a stylized sickle 2 Pallas a lozenge... Comet Bennett, formally known as C/1969 Y1, was one of two brilliant comets to grace the 1970s, along with Comet West. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... The system of Roman numerals is a numeral system originating in ancient Rome, and was adapted from Etruscan numerals. ... Comet Bennett, formally known as C/1969 Y1, was one of two brilliant comets to grace the 1970s, along with Comet West. ...


Increasing numbers of comet discoveries made this procedure awkward, and in 1994 the International Astronomical Union approved a new naming system. Comets are now designated by the year of their discovery followed by a letter indicating the half-month of the discovery and a number indicating the order of discovery (a system similar to that already used for asteroids), so that the fourth comet discovered in the second half of February 2006 would be designated 2006 D4. Prefixes are also added to indicate the nature of the comet: IAU redirects here. ... For other uses, see Asteroid (disambiguation). ...

  • P/ indicates a periodic comet (defined for these purposes as any comet with an orbital period of less than 200 years or confirmed observations at more than one perihelion passage);
  • C/ indicates a non-periodic comet (defined as any comet that is not periodic according to the preceding definition);
  • X/ indicates a comet for which no reliable orbit could be calculated (generally, historical comets);
  • D/ indicates a comet which has broken up or been lost;
  • A/ indicates an object that was mistakenly identified as a comet, but is actually a minor planet.

After their second observed perihelion passage, periodic comets are also assigned a number indicating the order of their discovery.[30] So Halley's Comet, the first comet to be identified as periodic, has the systematic designation 1P/1682 Q1. Comet Hale-Bopp's designation is C/1995 O1. Comets which first received a minor planet designation keep the latter, which leads to some odd names such as P/2004 EW38 (Catalina-LINEAR). Minor planets, or asteroids or planetoids, are minor celestial bodies of the Solar system orbiting the Sun (mostly Small solar system bodies) that are smaller than major planets, but larger than meteoroids (commonly defined as being 10 meters across or less[1]), and that are not comets. ... Comet Halley as taken with the Halley Multicolor Camera on the ESA Giotto mission. ... Comet Hale-Bopp (formally designated C/1995 O1) was probably the most widely observed comet of the twentieth century, and one of the brightest seen for many decades. ...


There are only five objects that are cross-listed as both comets and asteroids: 2060 Chiron (95P/Chiron), 4015 Wilson-Harrington (107P/Wilson-Harrington), 7968 Elst-Pizarro (133P/Elst-Pizarro), 60558 Echeclus (174P/Echeclus), and 118401 LINEAR (176P/LINEAR (LINEAR 52)). 2060 Chiron (IPA: ) is an object in the outer solar system with an orbit between those of Saturn and Uranus and a radius of 71±5 km [1]. Although it was initially classified as an asteroid, later dispute arose as to whether it was an asteroid or actually a comet. ... 2060 Chiron (KEYE ron) is an object in the outer solar system with an orbit between those of Saturn and Uranus and a radius of 71±5 km [1]. Although it was initially classified as an asteroid, later dispute arose as to whether it was an asteroid or actually a... Comet Wilson-Harrington is a periodic comet (formally designated 107P/Wilson-Harrington). ... Comet Wilson-Harrington is a periodic comet (formally designated 107P/Wilson-Harrington). ... Comet Elst-Pizarro is a periodic comet (formally designated 133P/Elst-Pizarro). ... Comet Elst-Pizarro is a periodic comet (formally designated 133P/Elst-Pizarro). ... 60558 Echeclus is a centaur in the outer solar system. ... 60558 Echeclus is a centaur in the outer solar system. ... 118401 LINEAR (provisional designation 1999 RE70) is an asteroid and main-belt comet (176P/LINEAR, also known as LINEAR 52) which was discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) 1-metre telescopes in Socorro, New Mexico on September 7, 1999. ... 118401 LINEAR (provisional designation 1999 RE70) is an asteroid and main-belt comet (176P/LINEAR, also known as LINEAR 52) which was discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) 1-metre telescopes in Socorro, New Mexico on September 7, 1999. ...


History of comet study

Early observations and thought

Comet Halley depicted on the Bayeux Tapestry which shows King Harold I being told of Halley's Comet before the Battle of Hastings in 1066.
Comet Halley depicted on the Bayeux Tapestry which shows King Harold I being told of Halley's Comet before the Battle of Hastings in 1066.

Before the invention of the telescope, comets seemed to appear out of nowhere in the sky and gradually vanish out of sight. They were usually considered bad omens of deaths of kings or noble men, or coming catastrophes, or even interpreted as attacks by heavenly beings against terrestrial inhabitants. From ancient sources, such as Chinese oracle bones, it is known that their appearances have been noticed by humans for millennia. Some authorities interpret references to "falling stars" in Gilgamesh, the Book of Revelation and the Book of Enoch as references to comets, or possibly bolides. Image File history File links Tapestry_of_bayeux10. ... Image File history File links Tapestry_of_bayeux10. ... Comet Halley, officially designated 1P/Halley, more generally known as Halleys Comet after Edmond Halley, is a comet that can be seen every 75-76 years. ... The Bayeux Tapestry (French: Tapisserie de Bayeux) is a 50 cm by 70 m (20 in by 230 ft) long embroidered cloth which depicts the events leading up to the 1066 Norman invasion of England as well as the events of the invasion itself. ... Examples of omens from the Nuremberg Chronicle (1493): natural phenomena and strange births. ... Replica of an oracle bone -- turtle shell Oracle bones (Chinese: 甲骨; pinyin: jiǎgǔpiàn) are pieces of bone or turtle shell used in royal divination from the mid Shang to early Zhou dynasties in ancient China, and often bearing written inscriptions in what is called oracle bone script. ... For other uses, see Gilgamesh (disambiguation). ... Visions of John of Patmos, as depicted in the Très Riches Heures du Duc de Berry. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... The term bolide (from the Greek βολις, bolis, missile) can refer to either an extraterrestrial body that collides with the Earth, or to an exceptionally bright, fireball-like meteor regardless of whether it ultimately impacts the surface. ...


In the first book of his Meteorology, Aristotle propounded the view of comets that would hold sway in Western thought for nearly two thousand years. He rejected the ideas of several earlier philosophers that comets were planets, or at least a phenomenon related to the planets, on the grounds that while the planets confined their motion to the circle of the Zodiac, comets could appear in any part of the sky.[31] Instead, he described comets as a phenomenon of the upper atmosphere, where hot, dry exhalations gathered and occasionally burst into flame. Aristotle held this mechanism responsible for not only comets, but also meteors, the aurora borealis, and even the Milky Way.[32] // Meteorology (from Greek: μετέωρον, meteoron, high in the sky; and λόγος, logos, knowledge) is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting. ... For other uses, see Aristotle (disambiguation). ... This article is about the astronomical term. ... For other uses, see Zodiac (disambiguation). ... Air redirects here. ... Photo of a burst of meteors with extended exposure time A meteor is the visible path of a meteoroid that enters the Earths (or another bodys) atmosphere, commonly called a shooting star or falling star. ... Aurora borealis Polar aurorae are optical phenomena characterized by colorful displays of light in the night sky. ... For other uses, see Milky Way (disambiguation). ...


A few later classical philosophers did dispute this view of comets. Seneca the Younger, in his Natural Questions, observed that comets moved regularly through the sky and were undisturbed by the wind, behavior more typical of celestial than atmospheric phenomena. While he conceded that the other planets do not appear outside the Zodiac, he saw no reason that a planet-like object could not move through any part of the sky, humanity's knowledge of celestial things being very limited.[33] However, the Aristotelian viewpoint proved more influential, and it was not until the 16th century that it was demonstrated that comets must exist outside the earth's atmosphere. Bust, traditionally thought to be Seneca, now identified by some as Hesiod. ...


One very famous old recording of a comet is the appearance of Halley's Comet on the Bayeux Tapestry, which records the Norman conquest of England in AD 1066.[34] This article is about the comet. ... The Bayeux Tapestry (French: Tapisserie de Bayeux) is a 50 cm by 70 m (20 in by 230 ft) long embroidered cloth which depicts the events leading up to the 1066 Norman invasion of England as well as the events of the invasion itself. ... Bayeux Tapestry depicting events leading to the Battle of Hastings The Norman Conquest of England was the conquest of the Kingdom of England by William the Conqueror (Duke of Normandy), in 1066 at the Battle of Hastings and the subsequent Norman control of England. ... For other uses, see England (disambiguation). ...


In 1577, a bright comet was visible for several months. The Danish astronomer Tycho Brahe used measurements of the comet's position taken by himself and other, geographically separated, observers to determine that the comet had no measurable parallax. Within the precision of the measurements, this implied the comet must be at least four times more distant from the earth than the moon.[35] This article is about the astronomer. ... For other uses, see Parallax (disambiguation). ...


Orbital studies

The orbit of the comet of 1680, fit to a parabola, as shown in Isaac Newton's Principia.
The orbit of the comet of 1680, fit to a parabola, as shown in Isaac Newton's Principia.

Although comets had now been demonstrated to be in the heavens, the question of how they moved through the heavens would be debated for most of the next century. Even after Johannes Kepler had determined in 1609 that the planets moved about the sun in elliptical orbits, he was reluctant to believe that the laws that governed the motions of the planets should also influence the motion of other bodies—he believed that comets travel among the planets along straight lines. Galileo Galilei, although a staunch Copernicanist, rejected Tycho's parallax measurements and held to the Aristotelian notion of comets moving on straight lines through the upper atmosphere.[36] Download high resolution version (1506x701, 130 KB) This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... Download high resolution version (1506x701, 130 KB) This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... A parabola A graph showing the reflective property, the directrix (light blue), and the lines connecting the focus and directrix to the parabola (blue) In mathematics, the parabola (from the Greek: παραβολή) (IPA pronunciation: ) is a conic section generated by the intersection of a right circular conical surface and a plane... Sir Isaac Newton FRS (4 January 1643 – 31 March 1727) [ OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist. ... For Whitehead and Russells axiomatic work on mathematics, see Principia Mathematica. ... Kepler redirects here. ... For other uses, see Ellipse (disambiguation). ... Illustration of Keplers three laws with two planetary orbits. ... Galileo redirects here. ... Nicolaus Copernicus (in Latin; Polish Mikołaj Kopernik, German Nikolaus Kopernikus - February 19, 1473 – May 24, 1543) was a Polish astronomer, mathematician and economist who developed a heliocentric (Sun-centered) theory of the solar system in a form detailed enough to make it scientifically useful. ...


The first suggestion that Kepler's laws of planetary motion should also apply to the comets was made by William Lower in 1610.[35] In the following decades other astronomers, including Pierre Petit, Giovanni Borelli, Adrien Auzout, Robert Hooke, Johann Baptist Cysat, and Giovanni Domenico Cassini all argued for comets curving about the sun on elliptical or parabolic paths, while others, such as Christian Huygens and Johannes Hevelius, supported comets' linear motion.[36] Pierre Petit (1832-1909) was a French photographer born in the south of France. ... Giovanni Borelli ( 1608- 1679), born in Pisa, Italy, was a Renaissance physicist and mathematician. ... Adrien Auzout ( January 28th, 1622– May 23rd, 1691) was a French astronomer. ... Robert Hooke, FRS (July 18, 1635 – March 3, 1703) was an English polymath who played an important role in the scientific revolution, through both experimental and theoretical work. ... Johann Baptist Cysat, holding a Jacobs staff Johann Baptist Cysat (Latinized as Cysatus; in French, Jean-Baptiste Cysat) (ca. ... Giovanni Domenico (Jean-Dominique) Cassini Portrait Giovanni Domenico Cassini (June 8, 1625–September 14, 1712) was an Italian astronomer, engineer, and astrologer. ... Christiaan Huygens Christiaan Huygens (approximate pronunciation: HOW-khens; SAMPA /h9yGEns/ or /h@YG@ns/) (April 14, 1629–July 8, 1695), was a Dutch mathematician and physicist; born in The Hague as the son of Constantijn Huygens. ... Johannes Hevelius Johannes Hevelius (Latin), also called Johann Hewelke, Johannes Höwelcke or Johannes Hewel (in German), or Jan Heweliusz (in Polish), (born January 28, 1611 – died January 28, 1687), was a councillor and mayor in Danzig (GdaÅ„sk). ...


The matter was resolved by the bright comet that was discovered by Gottfried Kirch on November 14, 1680. Astronomers throughout Europe tracked its position for several months. In 1681, the Saxon pastor Georg Samuel Doerfel set forth his proofs that comets are heavenly bodies moving in parabolas of which the sun is the focus. Then Isaac Newton, in his Principia Mathematica of 1687, proved that an object moving under the influence of his inverse square law of universal gravitation must trace out an orbit shaped like one of the conic sections, and he demonstrated how to fit a comet's path through the sky to a parabolic orbit, using the comet of 1680 as an example.[37] The Great Comet of 1680, formally known as C/1680 V1 or Kirchs Comet, has the distinction of being the first comet discovered by telescope. ... Gottfried Kirch (Kirche, Kirkius) (December 18, 1639—July 25, 1710) was a German astronomer. ... is the 318th day of the year (319th in leap years) in the Gregorian calendar. ... Events First Portuguese governor was appointed to Macau The Swedish city Karlskrona was founded as the Royal Swedish Navy relocated there. ... Location Time zone CET/CEST (UTC+1/+2) Administration Country NUTS Region DED Capital Dresden Minister-President Georg Milbradt (CDU) Governing parties CDU / SPD Votes in Bundesrat 4 (from 69) Basic statistics Area  18,416 km² (7,110 sq mi) Population 4,252,000 (11/2006)[1]  - Density 231 /km... A parabola A graph showing the reflective property, the directrix (light blue), and the lines connecting the focus and directrix to the parabola (blue) In mathematics, the parabola (from the Greek: παραβολή) (IPA pronunciation: ) is a conic section generated by the intersection of a right circular conical surface and a plane... Sir Isaac Newton FRS (4 January 1643 – 31 March 1727) [ OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist. ... For Whitehead and Russells axiomatic work on mathematics, see Principia Mathematica. ... In physics, an inverse-square law is any physical law stating that some quantity is inversely proportional to the square of the distance from a point. ... Gravity is a force of attraction that acts between bodies that have mass. ... Wikibooks has more on the topic of Conic section Types of conic sections Table of conics, Cyclopaedia, 1728 In mathematics, a conic section (or just conic) is a curve that can be formed by intersecting a cone (more precisely, a right circular conical surface) with a plane. ...


In 1705, Edmond Halley applied Newton's method to twenty-four cometary apparitions that had occurred between 1337 and 1698. He noted that three of these, the comets of 1531, 1607, and 1682, had very similar orbital elements, and he was further able to account for the slight differences in their orbits in terms of gravitational perturbation by Jupiter and Saturn. Confident that these three apparitions had been three appearances of the same comet, he predicted that it would appear again in 1758–9.[38] (Earlier, Robert Hooke had identified the comet of 1664 with that of 1618,[39] while Jean-Dominique Cassini had suspected the identity of the comets of 1577, 1665, and 1680.[40] Both were incorrect.) Halley's predicted return date was later refined by a team of three French mathematicians: Alexis Clairaut, Joseph Lalande, and Nicole-Reine Lepaute, who predicted the date of the comet's 1759 perihelion to within one month's accuracy.[41] When the comet returned as predicted, it became known as Comet Halley or Halley's Comet (its official designation is 1P/Halley). Its next appearance will be in 2061. Edmond Halley FRS (IPA: ) (November 8, 1656 – January 14, 1742) was an English astronomer, geophysicist, mathematician, meteorologist, and physicist. ... The elements of an orbit are the parameters needed to specify that orbit uniquely, given a model of two ideal masses obeying the Newtonian laws of motion and the inverse-square law of gravitational attraction. ... For other uses, see Jupiter (disambiguation). ... This article is about the planet. ... Alexis Claude Clairault (or Clairaut) ( May 3, 1713 - May 17, 1765) was a French mathematician. ... Joseph Jérôme Lefrançais de Lalande (July 11, 1732 – April 4, 1807) was a French astronomer. ... Nicole-Reine Étable de la Brière Lepaute (1723-1788) was a French astronomer. ... Comet Halley, officially designated 1P/Halley, more generally known as Halleys Comet after Edmond Halley, is a comet that can be seen every 75-76 years. ...


Among the comets with short enough periods to have been observed several times in the historical record, Comet Halley is unique in consistently being bright enough to be visible to the naked eye. Since the confirmation of Comet Halley's periodicity, many other periodic comets have been discovered through the telescope. The second comet to be discovered to have a periodic orbit was Comet Encke (official designation 2P/Encke). Over the period 1819–1821 the German mathematician and physicist Johann Franz Encke computed orbits for a series of cometary apparitions observed in 1786, 1795, 1805, and 1818, concluded that they were same comet, and successfully predicted its return in 1822.[42] By 1900, seventeen comets had been observed at more than one perihelion passage and recognized as periodic comets. As of April 2006, 175 comets have achieved this distinction, though several have since been destroyed or lost. In ephemerides, comets are often denoted by the symbol . This article does not cite any references or sources. ... Comet Encke (officially designated 2P/Encke) is a periodic comet, named after Johann Franz Encke, who through laborious study of its orbit and many calculations was able to link multiple observations in 1786 (2P/1786 B1), 1795 (2P/1795 V1), 1805 (2P/1805 U1) and 1818 (2P/1818 W1) to... Johann Franz Encke (23 September 1791 – 26 August 1865) was a German astronomer, born in Hamburg. ... An ephemeris (plural: ephemerides) (from the Greek word ephemeros= daily) was, traditionally, a table providing the positions (given in a Cartesian coordinate system, or in right ascension and declination or, for astrologers, in longitude along the zodiacal ecliptic), of the Sun, the Moon, and the planets in the sky at...


Studies of physical characteristics

Comets have highly elliptical orbits. Note the two distinct tails:Cyan for gas tail, grey for dust tail.

Isaac Newton described comets as compact and durable solid bodies moving in oblique orbits, and their tails as thin streams of vapor emitted by their nuclei, ignited or heated by the sun. Newton suspected that comets were the origin of the life-supporting component of air. Newton also believed that the vapors given off by comets might replenish the planets' supplies of water (which was gradually being converted into soil by the growth and decay of plants), and the sun's supply of fuel — Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... In astrodynamics or celestial mechanics a elliptic orbit is an orbit with the eccentricity greater than 0 and less than 1. ... Sir Isaac Newton FRS (4 January 1643 – 31 March 1727) [ OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist. ... The solid, central part of a comet is known as the comet nucleus. ...

From his huge vapouring train perhaps to shake
Reviving moisture on the numerous orbs,
Thro' which his long ellipsis winds; perhaps
To lend new fuel to declining suns,
To light up worlds, and feed th' ethereal fire."

 
James Thomson , "The Seasons" (1730; 1748)

As early as the 18th century, some scientists had made correct hypotheses as to comets' physical composition. In 1755, Immanuel Kant hypothesized that comets are composed of some volatile substance, whose vaporization gives rise to their brilliant displays near perihelion.[43] In 1836, the German mathematician Friedrich Wilhelm Bessel, after observing streams of vapor in the 1835 apparition of Comet Halley, proposed that the jet forces of evaporating material could be great enough to significantly alter a comet's orbit and argued that the non-gravitational movements of Comet Encke resulted from this mechanism.[44] James Thomson (September 11, 1700 – August 27, 1748) was a Scottish poet. ... Kant redirects here. ... Friedrich Wilhelm Bessel (July 22, 1784 – March 17, 1846) was a German mathematician, astronomer, and systematizer of the Bessel functions (which, despite their name, were discovered by Daniel Bernoulli). ... the lizard king ... Comet Encke (officially designated 2P/Encke) is a periodic comet, named after Johann Franz Encke, who through laborious study of its orbit and many calculations was able to link multiple observations in 1786 (2P/1786 B1), 1795 (2P/1795 V1), 1805 (2P/1805 U1) and 1818 (2P/1818 W1) to...


However, another comet-related discovery overshadowed these ideas for nearly a century. Over the period 1864–1866 the Italian astronomer Giovanni Schiaparelli computed the orbit of the Perseid meteors, and based on orbital similarities, correctly hypothesized that the Perseids were fragments of Comet Swift-Tuttle. The link between comets and meteor showers was dramatically underscored when in 1872, a major meteor shower occurred from the orbit of Comet Biela, which had been observed to split into two pieces during its 1846 apparition, and was never seen again after 1852.[45] A "gravel bank" model of comet structure arose, according to which comets consist of loose piles of small rocky objects, coated with an icy layer. Giovanni Virginio Schiaparelli (March 14, 1835 – July 4, 1910) was an Italian astronomer. ... The Perseids (pûrsÄ“-Ä­dz, or [pʰɝsijɪdz] in IPA) are a prolific meteor shower[1] associated with the comet Swift-Tuttle. ... Photo of a burst of meteors with extended exposure time A meteor is the visible path of a meteoroid that enters the Earths (or another bodys) atmosphere, commonly called a shooting star or falling star. ... Comet Swift-Tuttle (formally designated as 109P/Swift-Tuttle) was independently discovered by Lewis Swift on July 16, 1862 and by Horace Parnell Tuttle on July 19, 1862. ... 3D/Biela is the official designation for a lost periodic comet discovered in 1826 by Wilhelm von Biela. ...


By the middle of the twentieth century, this model suffered from a number of shortcomings: in particular, it failed to explain how a body that contained only a little ice could continue to put on a brilliant display of evaporating vapor after several perihelion passages. In 1950, Fred Lawrence Whipple proposed that rather than being rocky objects containing some ice, comets were icy objects containing some dust and rock.[46] This "dirty snowball" model soon became accepted. It was confirmed when an armada of spacecraft (including the European Space Agency's Giotto probe and the Soviet Union's Vega 1 and Vega 2) flew through the coma of Halley's comet in 1986 to photograph the nucleus and observed the jets of evaporating material. The American probe Deep Space 1 flew past the nucleus of Comet Borrelly on September 21, 2001 and confirmed that the characteristics of Comet Halley are common on other comets as well. Fred Lawrence Whipple (November 5, 1906 – August 30, 2004) was an American astronomer. ... The Space Shuttle Discovery as seen from the International Space Station. ... ESA redirects here. ... In this artists concept, Giotto points its white high-gain antenna dish towards earth with the ring of solar cells facing the sun. ... The Vega mission was a Venus mission which also took advantage of the appearance of Comet Halley in 1986. ... The Vega mission was a Venus mission which also took advantage of the appearance of Comet Halley in 1986. ... The spacecraft Deep Space 1 was launched October 24, 1998 on top of a Delta II rocket. ... Comet Borrelly (formally designated 19P/Borrelly) is a periodic comet, which was visited by the space craft Deep Space 1. ... is the 264th day of the year (265th in leap years) in the Gregorian calendar. ... This article is about the year. ...


Although comets formed in the outer Solar System, radial mixing of material during the early formation of the Solar System is thought to have redistributed material throughout the proto-planetary disk,[47] so comets also contain crystalline grains which were formed in the hot inner Solar System. This is seen in comet spectra as well as in sample return missions.

Comet Wild 2 exhibits jets on lit side and dark side, stark relief, and is dry.
Comet Wild 2 exhibits jets on lit side and dark side, stark relief, and is dry.

The Stardust spacecraft, launched in February 1999, collected particles from the coma of Comet Wild 2 in January 2004, and returned the samples to Earth in a capsule in January 2006. Claudia Alexander, a program scientist for Rosetta from NASA's Jet Propulsion Laboratory who has modeled comets for years, reported to space.com about her astonishment at the number of jets, their appearance on the dark side of the comet as well as on the light side, their ability to lift large chunks of rock from the surface of the comet and the fact that comet Wild 2 is not a loosely-cemented rubble pile.[48] Image File history File links Released by NASA to the public domain. ... Image File history File links Released by NASA to the public domain. ... An enhanced image of Comet 81P/Wild, from the Stardust spacecraft, showing surface detail and plumes of gas. ... An artists rendering of Stardust (NASA image) The Stardust capsule with cometary and interstellar samples landed at the U.S. Air Force Utah Test and Training Range at 10:10 UTC (15 January 2006) in the Bonneville Salt Flats. ... Comet 81P/Wild, also known as Wild 2, is a comet named after Swiss astronomer Paul Wild (pronounced Vilt), who discovered it in 1978. ...


Forthcoming space missions will add greater detail to our understanding of what comets are made of. In July 2005, the Deep Impact probe blasted a crater on Comet Tempel 1 to study its interior. And in 2014, the European Rosetta probe will orbit comet Comet Churyumov-Gerasimenko and place a small lander on its surface. Illustration of the Deep Impact space probe after impactor separation (artists conception) Deep Impact is a NASA space probe designed to study the composition of the interior of the comet Tempel 1. ... Tempel 1 is a periodic comet (formally designated 9P/Tempel 1). ... Conceptual drawing of the Rosetta orbiter and Philae lander Rosetta is a European Space Agency-led unmanned space mission launched in 2004 intended to study the comet 67P/Churyumov-Gerasimenko. ... 67P/Churyumov-Gerasimenko is the designation of a comet with a current orbital period of 6. ...


Rosetta observed the Deep Impact event, and with its set of very sensitive instruments for cometary investigations, it used its capabilities to observe Tempel 1 before, during and after the impact. At a distance of about 80 million kilometres from the comet, Rosetta was the only spacecraft other than Deep Impact itself to view the comet.


Debate over comet composition

Comet Borrelly exhibits jets, yet is hot and dry.

Debate continues about how much ice is in a comet. In 2001, NASA's Deep Space 1 team, working at NASA's Jet Propulsion Lab, obtained high-resolution images of the surface of Comet Borrelly. They announced that comet Borrelly exhibits distinct jets, yet has a hot, dry surface. The assumption that comets contain water and other ices led Dr. Laurence Soderblom of the U.S. Geological Survey to say, "The spectrum suggests that the surface is hot and dry. It is surprising that we saw no traces of water ice." However, he goes on to suggest that the ice is probably hidden below the crust as "either the surface has been dried out by solar heating and maturation or perhaps the very dark soot-like material that covers Borrelly's surface masks any trace of surface ice".[49] Image File history File links Released by NASA to the public domain. ... Image File history File links Released by NASA to the public domain. ... Comet Borrelly (formally designated 19P/Borrelly) is a periodic comet, which was visited by the space craft Deep Space 1. ... The spacecraft Deep Space 1 was launched October 24, 1998 on top of a Delta II rocket. ... Comet Borrelly (formally designated 19P/Borrelly) is a periodic comet, which was visited by the space craft Deep Space 1. ...


The recent Deep Impact probe has also yielded results suggesting that the majority of a comet's water ice is below the surface, and that these reservoirs feed the jets of vaporised water that form the coma of Tempel 1.[50] Illustration of the Deep Impact space probe after impactor separation (artists conception) Deep Impact is a NASA space probe designed to study the composition of the interior of the comet Tempel 1. ...


However, more recent data from the Stardust mission show that materials retrieved from the tail of comet Wild 2 were crystalline and could only have been "born in fire."[51][52] More recent still, the materials retrieved demonstrate that the "comet dust resembles asteroid materials."[53][54][55] These new results have forced a rethink about the very nature of comets and their distinction from asteroids.[56] An artists rendering of Stardust (NASA image) The Stardust capsule with cometary and interstellar samples landed at the U.S. Air Force Utah Test and Training Range at 10:10 UTC (15 January 2006) in the Bonneville Salt Flats. ...


Notable comets

Great comets

Main article: Great Comet

While hundreds of tiny comets pass through the inner solar system every year, very few are noticed by the general public. About every decade or so, a comet will become bright enough to be noticed by a casual observer — such comets are often designated Great Comets. In times past, bright comets often inspired panic and hysteria in the general population, being thought of as bad omens. More recently, during the passage of Halley's Comet in 1910, the Earth passed through the comet's tail, and erroneous newspaper reports inspired a fear that cyanogen in the tail might poison millions, while the appearance of Comet Hale-Bopp in 1997 triggered the mass suicide of the Heaven's Gate cult. To most people, however, a great comet is simply a beautiful spectacle. Great Comet West A Great Comet is a comet which becomes particularly bright and it is very spectacular to be noticed by a casual observer. ... Great Comet West A Great Comet is a comet which becomes particularly bright and it is very spectacular to be noticed by a casual observer. ... This article is about the comet. ... Except where noted otherwise, data are given for materials in their standard state (at 25 Â°C, 100 kPa) Infobox disclaimer and references Cyanogen is the chemical compound with the formula (CN)2. ... Comet Hale-Bopp (formally designated C/1995 O1) was probably the most widely observed comet of the twentieth century, and one of the brightest seen for many decades. ... The logo used by the Heavens Gate group Heavens Gate was the name of a cult co-led by Marshall Applewhite and Bonnie Nettles. ...


Predicting whether a comet will become a great comet is notoriously difficult, as many factors may cause a comet's brightness to depart drastically from predictions. Broadly speaking, if a comet has a large and active nucleus, will pass close to the Sun, and is not obscured by the Sun as seen from the Earth when at its brightest, it will have a chance of becoming a great comet. However, Comet Kohoutek in 1973 fulfilled all the criteria and was expected to become spectacular, but failed to do so. Comet West, which appeared three years later, had much lower expectations (perhaps because scientists were much warier of glowing predictions after the Kohoutek fiasco), but became an extremely impressive comet.[57] Orbits of Comet Kohoutek and Earth Comet Kohoutek, formally designated C/1973 E1, 1973 XII, and 1973f, was first sighted on March 7, 1973 by Czech astronomer Luboš Kohoutek. ... Comet West formally designated C/1975 V1, 1976 VI, and 1975n, was a spectacular comet, sometimes considered to qualify for the status of great comet. It was discovered by Richard M. West on August 10, 1975 and reached peak brightness in March 1976. ...


The late 20th century saw a lengthy gap without the appearance of any great comets, followed by the arrival of two in quick succession — Comet Hyakutake in 1996, followed by Hale-Bopp, which reached maximum brightness in 1997 having been discovered two years earlier. The first great comet of the 21st century was Comet McNaught, which became visible to naked eye observers in January 2007. It was the brightest in over 40 years. Comet Hyakutake (Japanese: 百武彗星 Hyakutake suisei, IPA ; formally designated C/1996 B2) is a comet that was discovered in January 1996, which passed very close to Earth in March of that year. ... C/2006 P1, also known as Comet McNaught, is a non-periodic comet discovered on August 7, 2006 in Australia by Robert H. McNaught[1]. It made perihelion on January 12, 2007, and has become easily visible to the naked eye. ...


Sungrazing comets

Main article: Sungrazing comet
The Great Comet of 1882, is a member of the Kreutz group
The Great Comet of 1882, is a member of the Kreutz group

A Sungrazing comet is a comet that passes extremely close to the Sun at perihelion, sometimes within a few thousand kilometres of the Sun's surface. While small sungrazers can be completely evaporated during such a close approach to the Sun, larger sungrazers can survive many perihelion passages. However, the strong tidal forces they experience often lead to their fragmentation. SOHO spots a Kreutz Sungrazer with a prominent tail, plunging towards the Sun A Sungrazing comet is a comet that passes extremely close to the Sun at perihelion - sometimes within a few thousand kilometres of the Suns surface. ... Image File history File links Download high resolution version (918x798, 54 KB)Photograph of the Great Comet of 1882 from South Africa by Her Majestys Astronomer at the Cape, David Gill. ... Image File history File links Download high resolution version (918x798, 54 KB)Photograph of the Great Comet of 1882 from South Africa by Her Majestys Astronomer at the Cape, David Gill. ... The Great Comet of 1882 was a comet which became very bright in September 1882. ... SOHO spots a Kreutz Sungrazer with a prominent tail, plunging towards the Sun The Kreutz Sungrazers are a family of comets characterized by orbits taking them extremely close to the Sun at perihelion. ... Sol redirects here. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... The tidal force is a secondary effect of the force of gravity and is responsible for the tides. ...


About 90% of the sungrazers observed with SOHO are members of the Kreutz group, which all originate from one giant comet that broke up into many smaller comets during its first passage through the inner solar system.[58] The other 10% contains some sporadic sungrazers, but four other related groups of comets have been identified among them: the Kracht, Kracht 2a, Marsden and Meyer groups. The Marsden and Kracht groups both appear to be related to Comet 96P/Machholz, which is also the parent of two meteor streams, the Quadrantids and the Arietids.[59] The Solar and Heliospheric Observatory (SOHO) is a spacecraft that was launched on an Atlas IIAS launch vehicle on 2 December 1995 to study the Sun, and began normal operations in May 1996. ... SOHO spots a Kreutz Sungrazer with a prominent tail, plunging towards the Sun The Kreutz Sungrazers are a family of comets characterized by orbits taking them extremely close to the Sun at perihelion. ... An inner planet is any one of the Solar systems rocky planets that lie inside the asteroid belt: Mercury (planet), Venus (planet), Earth (planet) and Mars (planet). ... This article about a comet includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ... A meteor shower, some of which are known as a meteor storm or meteor outburst, is a celestial event where a group of meteors are observed to radiate from one point in the sky. ... The Quadrantids are a meteor shower. ... The Arietids are a strong meteor shower that lasts from May 22 to July 2 each year, and peaks on June 7. ...


Unusual comets

Of the thousands of known comets, some are very unusual. Comet Encke orbits from outside the main asteroid belt to inside the orbit of Mercury while Comet 29P/Schwassmann-Wachmann travels in a nearly circular orbit entirely between Jupiter and Saturn.[60] 2060 Chiron, whose unstable orbit keeps it between Saturn and Uranus, was originally classified as an asteroid until a faint coma was noticed.[61] Similarly, Comet Shoemaker-Levy 2 was originally designated asteroid 1990 UL3.[62] Roughly six percent of the near-earth asteroids are thought to be extinct nuclei of comets which no longer experience outgassing.[63] Comet Encke (officially designated 2P/Encke) is a periodic comet, named after Johann Franz Encke, who through laborious study of its orbit and many calculations was able to link multiple observations in 1786 (2P/1786 B1), 1795 (2P/1795 V1), 1805 (2P/1805 U1) and 1818 (2P/1818 W1) to... This article is about the planet. ... The comet Schwassmann-Wachmann 1 Source: Nasa Comet Schwassmann-Wachmann 1 is thought to be a member of a relatively new class of objects called Centaur, of which 45 objects are known. ... This article is about the planet. ... 2060 Chiron (IPA: ) is an object in the outer solar system with an orbit between those of Saturn and Uranus and a radius of 71±5 km [1]. Although it was initially classified as an asteroid, later dispute arose as to whether it was an asteroid or actually a comet. ... For other uses, see Uranus (disambiguation). ... Computer model of the Apollo Asteroid 6489 Golevka Near-Earth asteroids (NEAs) are asteroids whose orbits are close to Earths orbit. ...


Some comets have been observed to break up during their perihelion passage, including great comets West and Ikeya-Seki. Comet Biela was one significant example, breaking into two during its 1846 perihelion passage. The two comets were seen separately in 1852, but never again afterward. Instead, spectacular meteor showers were seen in 1872 and 1885 when the comet should have been visible. A lesser meteor shower, the Andromedids, occurs annually in November, and is caused by the Earth crossing Biela's orbit.[64] Comet West formally designated C/1975 V1, 1976 VI, and 1975n, was a spectacular comet, sometimes considered to qualify for the status of great comet. It was discovered by Richard M. West on August 10, 1975 and reached peak brightness in March 1976. ... Comet Ikeya-Seki, formally designated C/1965 S1, 1965 VIII, and 1965f, was a comet discovered independently by Kaoru Ikeya and Tsutomu Seki. ... 3D/Biela is the official designation for a lost periodic comet discovered in 1826 by Wilhelm von Biela. ... Categories: Planetology | Astronomy stubs ... The Andromedids meteor shower is associated with the comet 3D/Biela, which was last observed in 1852. ...


Another significant cometary disruption was that of Comet Shoemaker-Levy 9, which was discovered in 1993. At the time of its discovery, the comet was in orbit around Jupiter, having been captured by the planet during a very close approach in 1992.[65] This close approach had already broken the comet into hundreds of pieces, and over a period of 6 days in July 1994, these pieces slammed into Jupiter's atmosphere — the first time astronomers had observed a collision between two objects in the solar system.[66] It has also been suggested that the object likely to have been responsible for the Tunguska event in 1908 was a fragment of Comet Encke.[67] Hubble Space Telescope image of Comet Shoemaker-Levy 9, taken on May 17, 1994. ... Trees knocked over by the Tunguska blast. ...


Observation

Example of a comet's path plotted by sky software (Sky Map Pro)

A new comet may be discovered photographically using a wide-field telescope or visually with binoculars. However, even without access to optical equipment, it is still possible for the amateur astronomer to discover a Sun-grazing comet online by downloading images accumulated by some satellite observatories such as SOHO.[68][69] Image File history File links Size of this preview: 800 × 600 pixelsFull resolution (1024 × 768 pixel, file size: 84 KB, MIME type: image/jpeg) Commercial sky software for amateur astronomers allows users to plot the course of comets in the sky. ... Image File history File links Size of this preview: 800 × 600 pixelsFull resolution (1024 × 768 pixel, file size: 84 KB, MIME type: image/jpeg) Commercial sky software for amateur astronomers allows users to plot the course of comets in the sky. ... This article does not cite any references or sources. ... Binocular telescopes, or binoculars, (also known as field glasses) are two identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. ... The Solar and Heliospheric Observatory (SOHO) is a spacecraft that was launched on an Atlas IIAS launch vehicle on 2 December 1995 to study the Sun, and began normal operations in May 1996. ...


Comets visible to the naked eye are fairly infrequent, but comets that put on fine displays in amateur class telescopes (50 mm to 100 cm) occur fairly often — as often as several times a year, occasionally with more than one in the sky at the same time. Commonly available astronomical software will plot the orbits of these known comets. They are fast compared to other objects in the sky, but their movement is usually subtle in the eyepiece of a telescope. However, from night to night, they can move several degrees, which is why observers find it useful to have a sky chart such as the one in the adjoining illustration.


The type of display presented by the comet depends on its composition and how close it comes to the sun. Because the volatility of a comet's material decreases as it gets further from the sun, the comet becomes increasingly difficult to observe as a function of not only distance, but the progressive shrinking and eventual disappearance of its tail and the reflective elements it carries. Comets are most interesting when their nucleus is bright and they display a long tail, which to be seen sometimes requires a large field of view best provided by smaller telescopes. Therefore, large amateur instruments (apertures of 25 cm or larger) that have fainter light grasp do not necessarily confer an advantage in terms of viewing comets. The opportunity to view spectacular comets with relatively small aperture instruments in the 8 cm to 15 cm range is more frequent than might be guessed from the relatively rare attention they get in the mainstream press.


Currently visible comets

Comet 8P/Tuttle, discovered 1858 by Horace Parnell Tuttle, is as of 27 JAN 2008 at about magnitude +7, visible in telescopes to Southern Hemisphere observers in the constellation Eridanus. It was next to spiral galaxy M33 on 30 DEC 2007. Perigee was 2 JAN 2008 at a distance of 0.25 AU. 8P/Tuttle is a periodic comet in our solar system. ... Horace Parnell Tuttle (March 24, 1839 - August 1923) was an American astronomer, and brother of Charles Wesley Tuttle. ... The name Eridanus can refer to: Eridanos (or Eridanus), a river in Greek mythology, associated by Herodotus with the Po. ...


Comet 17P/Holmes, discovered 1892 by Edwin Holmes, is dissipating after a major outburst in October 2007, and remains faintly visible using binoculars in the constellation Perseus. The diameter of the outer coma exceeds 2 degrees of arc. Though total magnitude remains above +5, due to dissipation has a very faint overall appearance, requiring a dark sky to view directly. 17P/Holmes is a periodic comet in our solar system, discovered by the British amateur astronomer Edwin Holmes on November 6, 1892. ... Perseus is a northern constellation, named after the Greek hero who slew the monster Medusa. ...


Comet 46P/Wirtanen, discovered 1948 by Carl A. Wirtanen, currently at about magnitude +9, favoring Northern Hemisphere observers, between Aries and Pisces. 46P/Wirtanen is a short-periodic comet with a current orbital period of 5. ... Carl Alvar Wirtanen (1910 – 1990) was an American astronomer who worked at Lick Observatory. ... Not to be confused with Aeris. ... For the astrological sign, see Pisces. ...


References

  1. ^ "What is the difference between asteroids and comets?", Rosetta FAQ, ESA
  2. ^ Near Earth Object Program FAQ, NASA
  3. ^ "Comet samples are surprisingly asteroid-like", New Scientist, 24 January 2008
  4. ^ Known populations of solar system objects:, Wm. Robert Johnston
  5. ^ How many comets are there?, ESA (Rosetta)
  6. ^ The Rate of Naked-Eye Comets from 101 BC to 1970 AD, A. Lewis Licht, University of Illinois, October 1998
  7. ^ World Book @ NASA
  8. ^ "1997 Apparition of Comet Hale-Bopp: What We Can Learn from Bright Comets", Karen Meech, Planetary Science Research Discoveries, February 14, 1997
  9. ^ "Test boosts notion that comets brought life", CNN, April 6, 2001
  10. ^ "Stardust Findings Suggest Comets More Complex Than Thought", NASA, December 14, 2006
  11. ^ "Hubble Detection of Comet Nucleus at Fringe of Solar System", NASA
  12. ^ Yeomans, Donald K. "Comet World Book Online Reference Center. 2005. Also available from World book @ NASA here.
  13. ^ First X-Rays from a Comet Discovered. Retrieved on 2006-03-05.
  14. ^ Probing space weather with comets. Retrieved on 2006-03-05.
  15. ^ "If comets melt, why do they seem to last for long periods of time?", Scientific American, November 16, 1998
  16. ^ "SOHO analyses a kamikaze comet", ESA, 23 February 2001
  17. ^ "Earth's water brewed at home, not in space", New Scientist Space, 25 September 2007
  18. ^ "Test boosts notion that comets brought life", CNN, April 6, 2001
  19. ^ Comet, Encyclopedia Britannica
  20. ^ Small Bodies: Profile, NASA
  21. ^ IAU bulletin IB74
  22. ^ "New comet class in Earth's backyard", Astronomy, April 3, 2006
  23. ^ Oort, J. H. The structure of the cloud of comets surrounding the Solar System and a hypothesis concerning its origin. Bulletin of the Astronomical Institutes of the Netherlands, Vol XI, No. 408, pg 91–110. 1950.. NASA Astrophysics Data System. Retrieved on 2007-10-15.
  24. ^ Kronk, Gary W. (2001–2005). Cometography. Retrieved on 2006-03-05., '11P/Tempel-Swift-LINEAR'
  25. ^ Kronk, '2P/Encke'
  26. ^ Kronk, '3D/Biela'
  27. ^ The SOHO 1000th Comet Contest. Solar and Heliospheric Observatory (2005). Retrieved on 2006-03-05.
  28. ^ www.cometary.net/searching_for_soho_comets.htm. Retrieved on 2007-07-27.
  29. ^ Arnett, Bill (2000). Astronomical Names. Retrieved on 2006-03-05.
  30. ^ Cometary Designation System. Committee on Small Body Nomenclature (1994). Retrieved on 2007-10-15.
  31. ^ Aristotle (350 B.C.). Meteorologia. , l. 1. c. 6.
  32. ^ Aristotle, l. 1. c. 7.
  33. ^ Carl Sagan & Ann Druyan (1985). Comet. New York: Random House, 23–24. ISBN 0-394-54908-2. 
  34. ^ Britain's Bayeux Tapestry, scene 1. Reading Museum Service (2000–2004). Retrieved on 2005-03-22.
  35. ^ a b (2003) A Brief History of Comets, part I. European Southern Observatory. 
  36. ^ a b Prasar, Vigyan (2001). Development of Cometary Thought, Part II. 
  37. ^ Newton, I.S. (1687). Philosophiæ Naturalis Principia Mathematica. London: Josephi Streater. , Lib. 3, Prop. 41.
  38. ^ Edmundo Halleio (1705). "Astronomiæ Cometicæ Synopsis". Philosophical Transactions 24: 1882–1899. 
  39. ^ Pepys, Samuel (1893). The Diary of Samuel Pepys, M.A., F.R.S.. London: George Bell & Sons. , 1 March 1664/5
  40. ^ Sagan, pp. [42–43 INSERT TITLE]. Retrieved on 2007-07-27.
  41. ^ Sagan, p. [83 INSERT TITLE]. Retrieved on 2007-07-27.
  42. ^ Kronk, '2P/Encke'
  43. ^ Sagan, p. [77 INSERT TITLE]. Retrieved on 2007-07-27.
  44. ^ Sagan, p. [117 INSERT TITLE]. Retrieved on 2007-07-27.
  45. ^ Kronk, '3D/Biela'
  46. ^ F.L. Whipple (1950). "A Comet Model I. The Acceleration of Comet Encke". Astrophysical Journal 111: 375–394. 
  47. ^ van Boekel, Roy. The building blocks of planets within the `terrestrial' region of protoplanetary disks, Nature Vol. 423 page 479. www.nature.com. Retrieved on 2007-01-08.
  48. ^ Britt, Robert Roy. Strange Comet Unlike Anything Known. Space.com. Retrieved on 2006-03-05.
  49. ^ NASA Spacecraft Finds Comet Has Hot, Dry Surface. JPL (2002). Retrieved on 2006-03-05.
  50. ^ NASA’s ‘Deep Impact’ Team Reports First Evidence of Cometary Ice. Retrieved on 2007-07-27.
  51. ^ Comets 'are born of fire and ice' (BBC News, March 14 2006)
  52. ^ NASA's Stardust Comet Samples Contain Minerals Born in Fire (Space.com; March 13, 2006)
  53. ^ Stardust comet dust resembles asteroid materials (Lawrence Livermore National Laboratory; January 24, 2008)
  54. ^ Stardust comet dust resembles asteroid materials (Physorg.com; January 24, 2008)
  55. ^ Surprise! That Comet Is an Asteroid, Sort Of (Wired News; January 25, 2008)
  56. ^ Dust samples prompt rethink about comets
  57. ^ Kronk, 'C/1975 V1 (West)'
  58. ^ M.E. Bailey, Chambers J.E., Hahn G. (1992). "Origin of sungrazers - A frequent cometary end-state". Astronomy and Astrophysics 257: 315–322. 
  59. ^ Ohtsuka K., Nakano S., Yoshikawa M. (2003). "On the Association among Periodic Comet 96P/Machholz, Arietids, the Marsden Comet Group, and the Kracht Comet Group". Publications of the Astronomical Society of Japan 55: 321–324. 
  60. ^ Kronk, '29P/Schwassmann-Wachmann 1'
  61. ^ Kronk, '95P/Chiron'
  62. ^ Kronk, '137P/Shoemaker-Levy 2'
  63. ^ Whitman, Kathryn; Alessandro Morbidelli and Robert Jedicke (2006). "The Size-Frequency Distribution of Dormant Jupiter Family Comets". Retrieved on 2008-02-06. 
  64. ^ The Andromedids ("Bielids"). Gary W. Kronk's Comets & Meteor Showers. Retrieved on 2006-03-05.
  65. ^ seds.lpl.arizona.edu/sl9/sl9.html. Retrieved on 2007-07-27.
  66. ^ Kronk, 'D/1993 F2 Shoemaker-Levy 9'
  67. ^ The Tunguska object - A fragment of Comet Encke. Astronomical Institutes of Czechoslovakia. Retrieved on 2007-10-15.
  68. ^ www.cometary.net/searching_for_soho_comets.htm. Retrieved on 2007-07-27.
  69. ^ http://one.fsphost.com/dvso/. Retrieved on 2007-07-27.

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See also

Non-periodic comets are seen only once. ...

Further Reading

Schechner, Sara J. Comets, Popular Culture, and the Birth of Modern Cosmology. Princeton, New Jersey: Princeton University Press. 1997.


External links

Wikimedia Commons has media related to:
Comets
Wikiquote has a collection of quotations related to:
Comet
  • Comet C/2001 RX14 (LINEAR) near to galaxy NGC 3726 @ SKY-MAP.ORG, SDSS. Captured on Dec. 14th 2002
  • Cometography.com
  • David Jewitt overview of the comets
  • Comets Page at NASA's Solar System Exploration
  • ESSAY ON COMETS, which gained the first of Dr. Fellowes's prizes, proposed to those who had attended the University of Edinburgh within the last twelve years. By David Milne. Publisher: Edinburgh, Printed for A. Black; 1828. (a searchable facsimile at the University of Georgia Libraries; DjVu & layered PDF format)
  • Everything you wanted to know about comets and asteroids — Provided by New Scientist.
  • Listing of newly discovered comets
  • Comets at the Open Directory Project
  • Seiichi Yoshida's Comet Information website
  • Source of useful comet-related material on the Web
  • Animation and static graphics of current and past comets
  • The Starry Mirror - Comet News
  • Astronomy Cast: Comets

Image File history File links This is a lossless scalable vector image. ... Wikiquote is one of a family of wiki-based projects run by the Wikimedia Foundation, running on MediaWiki software. ... DjVu (pronounced déjà vu) is a computer file format designed primarily to store scanned images, especially those containing text and line drawings. ... New Scientist is a weekly international science magazine covering recent developments in science and technology for a general English-speaking audience. ... The Open Directory Project (ODP), also known as dmoz (from , its original domain name), is a multilingual open content directory of World Wide Web links owned by Netscape that is constructed and maintained by a community of volunteer editors. ... A Small Solar System Body (SSSB) is a term defined in 2006 by the International Astronomical Union to describe objects in the Solar System that are neither planets nor dwarf planets: [1] This encompasses: all minor planets apart from the dwarf planets, : the classical asteroids, (except for 1 Ceres, the... For other uses, see Asteroid (disambiguation). ... Vulcanoids are hypothetical asteroids that may orbit in a dynamically stable zone between 0. ... Computer model of the Apollo Asteroid 6489 Golevka Near-Earth asteroids (NEAs) are asteroids whose orbits are close to Earths orbit. ... For other uses, see Asteroid (disambiguation). ... Image of the Trojan asteroids in front of and behind Jupiter along its orbital path. ... The centaurs are a class of icy planetoids that orbit the Sun between Jupiter and Neptune, named after the mythical race of centaurs. ... Damocloids are asteroids such as 5335 Damocles and 1996 PW that have Halley family or long-period highly eccentric orbits typical of periodic comets such as Comet Halley, but without showing a cometary coma or tail. ... As of March 2007, there are five[1] known Neptune Trojans (named by analogy to the Trojan asteroids) which have the same orbital period as the planet. ... Minor planet is the official term for asteroids and trans-Neptunian objects. ... Minor planet is the official term for asteroids and trans-Neptunian objects. ... 243 Ida and its moon Dactyl An asteroid moon is an asteroid that orbits another asteroid. ... A trans-Neptunian object (TNO) is any object in the solar system that orbits the sun at a greater distance on average than Neptune. ... The Kuiper belt, derived from data from the Minor Planet Center. ... A scattered disk object (or scattered disc object or SDO) is a trans-Neptunian object of the Kuiper belt with a very eccentric orbit. ... Artists rendering of the Oort cloud and the Kuiper Belt. ... Minor planets, or asteroids or planetoids, are minor celestial bodies of the Solar system orbiting the Sun (mostly Small solar system bodies) that are smaller than major planets, but larger than meteoroids (commonly defined as being 10 meters across or less[1]), and that are not comets. ... Meteor redirects here. ... List of asteroids List of comets See also Trans-Neptunian object Categories: Solar System ... 243 Ida & Dactyl. ... Near-Earth objects (NEO) are asteroids, comets and large meteoroids whose orbit intersects Earths orbit and which may therefore pose a collision danger. ... Artists impression of Pluto (background) and Charon (foreground). ... This article is about the astronomical term. ... This article is about the Solar System. ... This page alphabetically lists the first thousand asteroids to be numbered, which are mostly in the main belt. ... This is a list of named asteroids, with links to the Wikipedia articles on the people, places, characters and concepts that they are named after. ... This article is about the Solar System. ... Sol redirects here. ... This article is about the planet. ... For other uses, see Venus (disambiguation). ... This article is about Earth as a planet. ... Adjectives: Martian Atmosphere Surface pressure: 0. ... Spectral type: G[8] Absolute magnitude: 3. ... For other uses, see Jupiter (disambiguation). ... This article is about the planet. ... For other uses, see Uranus (disambiguation). ... For other uses, see Neptune (disambiguation). ... For other uses, see Pluto (disambiguation). ... Absolute magnitude: −1. ... This article is about the astronomical term. ... Artists impression of Pluto (background) and Charon (foreground). ... A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called the primary. ... This article is about Earths moon. ... The relative sizes of and distance between Mars, Phobos, and Deimos, to scale : Phobos (top) and Deimos (bottom). ... Jupiters 4 Galilean moons, in a composite image comparing their sizes and the size of Jupiter (Great Red Spot visible). ... The Saturnian system (photographic montage) Moons of Saturn (photographic montage) Saturn has 60 confirmed natural satellites, plus three hypothetical moons. ... Uranus has twenty-seven known moons. ... Neptune (top) and Triton (bottom), 3 days after the Voyager 2 flyby. ... Hubble image of the Plutonian system Pluto has three known moons. ... Dysnomia (officially designated (136199) Eris I Dysnomia) is a moon of the dwarf planet Eris. ... A Small Solar System Body (SSSB) is a term defined in 2006 by the International Astronomical Union to describe objects in the Solar System that are neither planets nor dwarf planets: [1] This encompasses: all minor planets apart from the dwarf planets, : the classical asteroids, (except for 1 Ceres, the... Meteor redirects here. ... For other uses, see Asteroid (disambiguation). ... 243 Ida and its moon Dactyl An asteroid moon is an asteroid that orbits another asteroid. ... For other uses, see Asteroid (disambiguation). ... The centaurs are a class of icy planetoids that orbit the Sun between Jupiter and Neptune, named after the mythical race of centaurs. ... A trans-Neptunian object (TNO) is any object in the solar system that orbits the sun at a greater distance on average than Neptune. ... The Kuiper belt, derived from data from the Minor Planet Center. ... Eris, the largest known scattered disc object (center), and its moon Dysnomia (left of center). ... Artists rendering of the Oort cloud and the Kuiper Belt. ... Astronomical objects are significant physical entities, associations or structures which current science has confirmed to exist in space. ... Below is a list of solar system objects with diameter >500km: The Sun, a spectral class G2 star Mercury Venus Earth Moon Mars Jupiter Io Europa Ganymede Callisto complete list of Jupiters natural satellites Saturn Tethys Dione Rhea Titan Iapetus complete list of Saturns natural satellites Uranus Ariel... It has been suggested that Planetary-size comparison be merged into this article or section. ... This is a list of solar system objects by mass, in decreasing order. ...


  Results from FactBites:
 
The Columbus Dispatch : John Switzer commentary: Search for tiny owls leads to small comet (501 words)
While we were standing in the darkness waiting for the owls to fly into the nets, we all noticed how bright the stars were out in the country, away from the bright lights of the city.
If you want to try to locate the comet, Perseus is a fall and winter constellation that is now rising in the northeast just after dark, Burns said.
Although Holmes is a rather minor comet, Burns said it's a good experience for stargazers, even if it doesn't look like much to someone without a telescope.
Comet Introduction (1456 words)
Comets are small, fragile, irregularly shaped bodies composed of a mixture of non-volatile grains and frozen gases.
Comet structures are diverse and very dynamic, but they all develop a surrounding cloud of diffuse material, called a coma, that usually grows in size and brightness as the comet approaches the Sun.
When a comet approaches within a few AU of the Sun, the surface of the nucleus begins to warm, and volatiles evaporate.
  More results at FactBites »

 
 

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