Comet Hale-Bopp

Comet West

A comet is a small body in the solar system that orbits Sun and (at least occasionally) exhibits a coma (or atmosphere) and/or a tail — both primarily from the effects of solar radiation upon the comet's nucleus, which itself is a minor body composed of rock, dust, and ice. Comets' orbits are constantly changing: their origins are in the outer solar system, and they have a propensity to be highly affected (or perturbed) by relatively close approaches to the major planets. Some are moved into Sun-grazing orbits that destroy the comets when they near the Sun, while others are thrown out of the solar system forever. 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. ... The Sun (Latin: Sol) is the star at the center of the Solar System. ... 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. ...

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 by analysing online the mountains of images accumulated by some satellite observatories such as SOHO.^[1][2] Soho is an area of central Londons West End, in the borough of the City of Westminster. ...

Most comets are believed to originate in a cloud (the Oort cloud) at large distances from the Sun consisting of debris left over from the condensation of the solar nebula; the outer edges of such nebulae are cool enough that water exists in a solid (rather than gaseous) state. Asteroids originate via a different process, but very old comets which have lost all their volatile materials may come to resemble asteroids. This image is an artists rendering of the Oort cloud and the Kuiper Belt. ... Water vapor condensing over a cup of hot tea Condensation is the change in matter of a substance to a denser phase, such as a gas (or vapor) to a liquid. ... This article or section does not cite any references or sources. ... Fig. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... For other uses, see Solid (disambiguation). ... This article does not cite any references or sources. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... 253 Mathilde, a C-type asteroid. ... The ability of a liquid to evaporate quickly and at relatively low temperatures. ...

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 tail of hair. The English language is a West Germanic language that originates in England. ... Latin is an ancient Indo-European language originally spoken in Latium, the region immediately surrounding Rome. ... Aristotle (Greek: AristotélÄ“s) (384 BC – 322 BC) was a Greek philosopher, a student of Plato and teacher of Alexander the Great. ... Chinese Celestial symbols on an antique bronze mirror Astronomical symbols are symbols used to represent various celestial objects, theoretical constructs and observational events. ...

Physical characteristics

Comet Hyakutake

Long-period comets are believed to originate in a distant cloud known as the Oort cloud (after the astronomer Jan Hendrik Oort who hypothesised its existence).^[3] They are sometimes perturbed from their distant orbits by gravitational interactions, falling into extremely elliptical orbits that can bring them very close to the Sun. One theory holds that as a comet approaches the inner solar system, solar radiation causes part of its outer layers, composed of ice and other materials, to melt and evaporate, but this has not been proven, due to its distance. 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, and passed very close to the Earth in March of that year. ... This image is an 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. ... In astrodynamics or celestial mechanics a elliptic orbit is an orbit with the eccentricity greater than 0 and less than 1. ... The Sun (Latin: Sol) is the star at the center of the Solar System. ... 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. ...

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 streams of dust and gas each form their own distinct tail, pointed 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 body of comets (called the nucleus) 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."^[4] Porous chondrite interplanetary dust particle. ... 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 For the British comic, see Solar Wind (comic). ... The solid, central part of a comet is known as the comet nucleus. ... The astronomical unit (AU or au or a. ...

Both the comet 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. 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. From ancient sources, such as Chinese oracle bones, it is known that their appearances have been noticed by humans for millennia. 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.^[5] Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... An electrostatic potential map of the nitrate ion (NO3−). Areas coloured red are lower in energy than areas colored yellow An ion is an atom or group of atoms which have lost or gained one or more electrons, making them negatively or positively charged. ... A telescope (from the Greek tele = far and skopein = to look or see; teleskopos = far-seeing) is an instrument designed for the observation of remote objects. ... now. ... Replica of an oracle bone -- turtle shell Replica of an oracle bone -- ox scapula Oracle bones (甲骨片 pinyin: jiÇŽgÇ”piàn) are pieces of bone or turtle shell used in royal divination in the mid Shang to early Zhou dynasties in ancient China, and often bearing written inscriptions in what... Halleys Comet, officially designated 1P/Halley and also referred to as Comet Halley 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, as well as, the Norman invasion of England in 1066. ... 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. ... Motto (French) God and my right Anthem No official anthem - the  United Kingdom anthem God Save the Queen is commonly used England() – on the European continent() – in the United Kingdom() Capital (and largest city) London (de facto) Official languages English (de facto) Unified  -  by Athelstan 927 AD  Area  -  Total 130...

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. ... Halleys Comet, officially designated 1P/Halley and also referred to as Comet Halley after Edmond Halley, is a comet that can be seen every 75–76 years. ... 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. ... Base layer of asphalt concrete in a road under construction. ... 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 and hydrogen; therefore, carbides, carbonates, carbon oxides and elementary carbon are not organic (see below for more on the definition controversy... Tar can be produced from corn stalks by heating in a microwave. ... Pumpjack pumping an oil well near Lubbock, Texas Ignacy Łukasiewicz - inventor of the refining of kerosene from crude oil. ...

In 1996, comets were found to emit X-rays.^[6] 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.^[7] In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... ...

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.

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.

Comets are sometimes classified according to the length of their orbital periods. Short-period comets, also called periodic comets, have orbital periods of generally 30 years or less (though some take the very arbitrary figures of 50, 100, or even 200 years), while long-period comets have longer orbital timespans but remain gravitationally bound to the Sun by definition (those comets that are ejected from the solar system due to close passes by major planets are no longer properly considered as having "periods"), and main-belt comets orbit within the asteroid belt.^[8] Single-apparition comets have parabolic or hyperbolic orbits which will cause them to permanently exit the solar system after passing the Sun once. Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... Comet by naked-eye 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 LuboÅ¡ Kohoutek. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ... The Sun (Latin: Sol) is the star at the center of the Solar System. ... 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. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... 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 details on the physical properties of bodies in the asteroid belt see Asteroid and Main-belt comet. ... A parabola A parabola (from the Greek: παραβολή) is a conic section generated by the intersection of a cone, and a plane tangent to the cone or parallel to some plane tangent to the cone. ... For hyperbole, the figure of speech, see hyperbole. ...

Early observations have revealed a few genuinely hyperbolic orbits, 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 orbits. A rough calculation shows that there might be 4 hyperbolic comets per century, within Jupiter's orbit, give or take one and perhaps two orders of magnitude.

On the other extreme, the short period Comet Encke has an orbit which never places it farther from the Sun than Jupiter. Short-period comets are thought to originate in the transneptunian region (called by some the "Kuiper belt"), whereas the source of long-period comets is thought to be the Oort cloud. 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... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... The Kuiper belt, derived from data from the Minor Planet Center. ... This image is an artists rendering of the Oort cloud and the Kuiper Belt. ...

Since their elliptical orbits frequently take them close to the giant planets, cometary orbits are often perturbed. 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. 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. ... Example of a histogram of 100 normally distributed random values. ...

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.^[9] 11P/Tempel-Swift-LINEAR is a periodic comet in our solar system. ... The word linear comes from the Latin word linearis, which means created by lines. ...

Comet nomenclature

Comet McNaught

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^[10] and Comet Biela,^[11] 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. Image File history File links Download high-resolution version (1600x1067, 309 KB) Comet P1 McNaught, taken from Swifts Creek, Victoria, Australia at approx 10:10 pm. ... Image File history File links Download high-resolution version (1600x1067, 309 KB) Comet P1 McNaught, taken from Swifts Creek, Victoria, Australia at approx 10:10 pm. ... For other uses, see Comet McNaught (disambiguation). ... 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^[12]) 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.^[13] 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)^[14] 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, with P/ indicating a periodic comet, C/ indicating a non-periodic comet, X/ indicating a comet for which no reliable orbit could be calculated (generally, historical comets), D/ indicating a comet which has broken up or been lost, and A/ indicating 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.^[15] 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). Logo of the IAU The International Astronomical Union (French: Union astronomique internationale) unites national astronomical societies from around the world. ... 253 Mathilde, a C-type asteroid. ... 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

Historically, comets were thought to be unlucky, or even interpreted as attacks by heavenly beings against terrestrial inhabitants. 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. Gilgamesh, according to the Sumerian king list, was the fifth king of Uruk (Early Dynastic II, first dynasty of Uruk), the son of Lugalbanda, ruling circa 2650 BC. He is also the central character in the Epic of Gilgamesh, which says that his mother was Ninsun, (whom some call Rimat... 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.^[16] 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.^[17] Satellite image of Hurricane Hugo with a polar low visible at the top of the image. ... Aristotle (Greek: Aristotélēs) (384 BC – 322 BC) was a Greek philosopher, a student of Plato and teacher of Alexander the Great. ... The eight planets and three dwarf planets of the Solar System. ... It has been suggested that this article be split into multiple articles. ... Layers of Atmosphere - not to scale (NOAA)[3] Earths atmosphere is a layer of gases surrounding the planet Earth and retained by the Earths gravity. ... 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. ... It has been suggested that Andromeda-Milky Way collision be merged into this article or section. ...

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.^[18] 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. ...

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 measureable 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.^[19] Tycho Brahe Monument of Tycho Brahe and Johannes Kepler in Prague Tycho Brahe, born Tyge Ottesen Brahe (December 14, 1546 – October 24, 1601), was a Danish nobleman from the region of Scania (in modern-day Sweden), best known today as an early astronomer, though in his lifetime he was also... This does not adequately cite its references or sources. ...

Orbital studies

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.^[20] 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, (4 January 1643 – 31 March 1727) [ OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist, regarded by many as the greatest figure in the history of science. ... Newtons own copy of his Principia, with handwritten corrections for the second edition. ... Johannes Kepler (December 27, 1571 – November 15, 1630) was a German Lutheran mathematician, astronomer and astrologer, and a key figure in the 17th century astronomical revolution. ... For other uses, see Ellipse (disambiguation). ... Johannes Keplers primary contributions to astronomy/ astrophysics were the three laws of planetary motion. ... Galileo Galilei (15 February 1564 – 8 January 1642) was an Italian physicist, mathematician, astronomer, and philosopher who is closely associated with the scientific revolution. ... 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.^[19] 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.^[20] 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.^[21] 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. ... November 14 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. ... The Free State of Saxony (German: Freistaat Sachsen; Sorbian: Swobodny Stat Sakska) is the easternmost federal state of Germany. ... 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, (4 January 1643 – 31 March 1727) [ OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist, regarded by many as the greatest figure in the history of science. ... Newtons own copy of his Principia, with handwritten corrections for the second edition. ... 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.^[22] (Earlier, Robert Hooke had identified the comet of 1664 with that of 1618,^[23] while Jean-Dominique Cassini had suspected the identity of the comets of 1577, 1665, and 1680.^[24] 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.^[25] 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. Portrait of Edmond Halley painted around 1687 by Thomas Murray (Royal Society, London) Portrait of Edmond Halley Bust of Edmond Halley in the Museum of the Royal Greenwich Observatory Edmond Halley FRS (sometimes Edmund, 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. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ... 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 they were same comet, and successfully predicted its return in 1822.^[26] 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 ☄. A telescope (from the Greek tele = far and skopein = to look or see; teleskopos = far-seeing) is an instrument designed for the observation of remote objects. ... 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, solid, fixed, and durable bodies: in other words, a kind of planet, which move in very oblique orbits, every way, with the greatest freedom, persevering in their motions even against the course and direction of the planets; and their tail as a very thin, slender vapour, emitted by the head, or nucleus of the comet, ignited or heated by the sun. Comets also seemed to Newton absolutely requisite for the conservation of the water and moisture of the planets; from their condensed vapours and exhalations all that moisture which is spent on vegetations and putrefactions, and turned into dry earth, might be resupplied and recruited; for all vegetables were thought to increase wholly from fluids, and turn by putrefaction into earth. Hence the quantity of dry earth must continually increase, and the moisture of the globe decrease, and at last be quite evaporated, if it have not a continual supply. Newton suspected that the spirit which makes the finest, subtilest, and best part of our air, and which is absolutely requisite for the life and being of all things, came principally from the comets. 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, (4 January 1643 – 31 March 1727) [ OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist, regarded by many as the greatest figure in the history of science. ... The solid, central part of a comet is known as the comet nucleus. ...

Another use which he conjectured comets might be designed to serve, is that of recruiting the sun with fresh fuel, and repairing the consumption of his light by the streams continually sent forth in every direction from that luminary —

"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.^[27] 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.^[28] James Thomson (September 11, 1700 – August 27, 1748) was a Scottish poet. ... Immanuel Kant (22 April 1724 – 12 February 1804) was a German philosopher from Königsberg in East Prussia (now Kaliningrad, Russia). ... 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 never seen again after 1852.^[29] 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 are a prolific meteor shower 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.^[30] 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. ... September 21 is the 264th day of the year (265th in leap years) in the Gregorian calendar. ... Year 2001 (MMI) was a common year starting on Monday of the Gregorian calendar. ...

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,^[31] 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.

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.^[32] 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.

As late as 2002, there is conflict on how much ice is in a comet. 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".^[33] 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 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.^[34] 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. ...

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. ... Halleys Comet, officially designated 1P/Halley and also referred to as Comet Halley after Edmond Halley, is a comet that can be seen every 75–76 years. ... Cyanogen is a chemical compound (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.^[35] Comet by naked-eye 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, and passed very close to the 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

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. ... The Sun (Latin: Sol) is the star at the center of the Solar System. ... 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 member 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,^[36] 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.^[37] Soho is an area of central Londons West End, in the borough of the City of Westminster. ... 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. ... The Taurids Meteor Shower 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 orbits in a nearly circular orbit entirely between Jupiter and Saturn.^[38] 2060 Chiron, whose unstable orbit keeps it between Saturn and Uranus, was originally classified as an asteroid until a faint coma was noticed.^[39] Similarly, Comet Shoemaker-Levy 2 was originally designated asteroid 1990 UL₃.^[40] Some near-earth asteroids are thought to be extinct nuclei of comets which no longer experience outgassing. 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. ... Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ... 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. ... Atmospheric characteristics Atmospheric pressure 120 kPa Hydrogen 83% Helium 15% Methane 1. ... 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 Comet 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 after that. 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.^[41] 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 very 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.^[42] 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.^[43] 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.^[44] Hubble Space Telescope image of Comet Shoemaker-Levy 9, taken on May 17, 1994. ... Trees felled by the Tunguska blast. ...

Currently visible comets

• Comet Lovejoy, formally designated C/2007 E2, discovered by Terry Lovejoy on 15 March 2007, is visible telescopically to Northern Hemisphere observers in the constellation Hercules. The discovery is interesting because it was made using a common consumer grade digital camera, and not the usual CCD survey camera. Perihelion was 27 March, perigee was 25 April at a distance of 0.442AU.

• Comet McNaught, formally designated C/2006 P1, discovered by Robert H. McNaught on 7 August 2006, remains visible with telescopes to Southern Hemisphere observers shortly after sunset and shortly before sunrise in the constellation Chamaeleon.^[45]

Comet Lovejoy, formally designated C/2007 E2, is a non-periodic comet discovered by Terry Lovejoy on 15 March 2007. ... Terry Lovejoy is an astronomer, from Brisbane,Queensland, Australia. ... March 15 is the 74th day of the year in the Gregorian calendar (75th in leap years). ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... Hercules (IPA: ) is the fifth largest of the 88 modern constellations. ... This article or section does not cite any references or sources. ... For other uses, see Comet McNaught (disambiguation). ... Robert H. McNaught is an Australian astronomer at the Research School of Astronomy and Astrophysics of the Australian National University. ... August 7 is the 219th day of the year (220th in leap years) in the Gregorian calendar. ... For the Manfred Mann album, see 2006 (album). ... For other uses of the word, see chameleon (disambiguation) Chamaeleon (Latin for chameleon) is a minor southern constellation. ...

References

For the Manfred Mann album, see 2006 (album). ... is the 186th day of the year (187th in leap years) in the Gregorian calendar. ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... March 22 is the 81st day of the year (82nd in leap years) in the Gregorian calendar. ... For the Manfred Mann album, see 2006 (album). ... This article is about the day. ... For the Manfred Mann album, see 2006 (album). ... This article is about the day. ... For the Manfred Mann album, see 2006 (album). ... This article is about the day. ... For the Manfred Mann album, see 2006 (album). ... This article is about the day. ... For the Manfred Mann album, see 2006 (album). ... This article is about the day. ... For the Manfred Mann album, see 2006 (album). ... This article is about the day. ... is the 60th day of the year (61st in leap years) in the Gregorian calendar. ... Events March 12 - New Jersey becomes a colony of England. ... Nature is one of the most prominent scientific journals, first published on 4 November 1869. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... January 8 is the 8th day of the year in the Gregorian calendar. ... For the Manfred Mann album, see 2006 (album). ... This article is about the day. ... For the Manfred Mann album, see 2006 (album). ... This article is about the day. ... For the Manfred Mann album, see 2006 (album). ... This article is about the day. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... February 15 is the 46th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... January 5 is the 5th day of the year in the Gregorian calendar. ...

External links

• 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
• European Southern Observatory. (2003). "A Brief Hstory of Asteroids." Available online: Part I, Part II.

Major features of the Solar System (not to scale; from left to right): Pluto, Neptune, Uranus, Saturn, Jupiter, the asteroid belt, the Sun, Mercury, Venus, Earth and its Moon, and Mars. ... The Sun (Latin: Sol) is the star at the center of the Solar System. ... This article is about the planet. ... Adjectives: Venusian or (rarely) Cytherean Atmosphere Surface pressure: 9. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... Adjectives: Martian Atmosphere Surface pressure: 0. ... Spectral type: G[8] Absolute magnitude: 3. ... Adjectives: Jovian Atmosphere Surface pressure: 20–200 kPa[4] (cloud layer) Composition: ~86% Molecular hydrogen ~13% Helium 0. ... Adjectives: Saturnian Atmosphere Surface pressure: 140 kPa Composition: >93% hydrogen >5% helium 0. ... Adjectives: Uranian Atmosphere Surface pressure: 120 kPa (at the cloud level) Composition: 83% Hydrogen 15% Helium 1. ... Adjectives: Neptunian Atmosphere Surface pressure: ≫ 100 kPa (cloud level) Composition: 80% ± 3. ... Adjectives: Plutonian Atmosphere Surface pressure: 0. ... Absolute magnitude: −1. ... The eight planets and three dwarf planets of the Solar System. ... Artists impression of Pluto (background) and Charon (foreground). ... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ... Apparent magnitude: up to -12. ... The relative sizes of and distance between Mars, Phobos, and Deimos, to scale. ... Jupiters outer moons and their highly inclined orbits. ... The Saturnian system (photographic montage) Saturn has fifty-six confirmed natural satellites, plus three unconfirmed moons. ... Uranus has 27 known moons. ... Neptune (top) and Triton (bottom), 3 days after the Voyager 2 flyby. ... The planet 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... It has been suggested that micrometeoroid be merged into this article or section. ... 253 Mathilde, a C-type asteroid. ... 243 Ida and its moon Dactyl An asteroid moon is an asteroid that orbits another asteroid. ... For details on the physical properties of bodies in the asteroid belt see Asteroid and Main-belt comet. ... 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. ... The scattered disc (or scattered disk) is a distant region of our solar system, thinly populated by icy planetoids known as scattered disk objects (SDOs), a subset of the broader family of trans-Neptunian objects (TNOs). ... This image is an artists rendering of the Oort cloud and the Kuiper Belt. ... See also Lists of astronomical objects Category: ... 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... This is a list of solar system objects by radius, arranged in descending order of mean volumetric radius. ... This is a list of Solar system objects by mass, in decreasing order. ...