NationMaster - Encyclopedia: Celestial objects

Mosaic of the planets of the solar system, excluding Pluto, and including Earths Moon. Note: planets are not portrayed in the same scale. The Solar System consists of the Sun and all the objects that orbit around it, including asteroids, comets, moons, and planets). The Earth is the third... Solar system	Extrasolar objects
	Simple objects	Compound objects	Extended objects
The Sun (occasionally referred to as Sol) is the star at the centre of our solar system. Planet Earth orbits the Sun, as do innumerable other bodies including other planets, asteroids, meteoroids, comets and dust. In common usage, the primary stellar body around which an object orbits is called its... Sun A planet (from the Greek πλανήτης, planetes or wanderers) is a body of considerable mass that orbits a star and that produces very little or no energy through nuclear fusion. Prior to the 1990s only nine were known (all of them in our... Planets Atmospheric characteristics Atmospheric pressure trace Potassium 31.7% Sodium 24.9% Atomic Oxygen 9.5% Argon 7.0% Helium 5.9% Molecular Oxygen 5.6% Nitrogen 5.2% Carbon dioxide 3.6% Water 3.4% Hydrogen 3.2% Mercury is the closest planet to the Sun, and the second-smallest... Mercury (*min temperature refers to cloud tops only) Atmospheric characteristics Atmospheric pressure 9321.9 kPa Carbon dioxide 96% Nitrogen 3% Sulfur dioxide Water vapor Carbon monoxide Argon Helium Neon Carbonyl sulfide Hydrogen chloride Hydrogen fluoride trace Venus is the second planet from the Sun, named after the Roman goddess Venus. It... Venus Earth, also known as the Earth or Terra, is the third planet outward from the Sun. It is the largest of the solar systems terrestrial planets, and the only planetary body that modern science confirms as harboring life. The planet formed around 4.5 billion (4.5×109) years... Earth For other moons in the solar system see natural satellite. For other uses see Moon (disambiguation). Crust composition Oxygen 43% Silicon 21% Aluminium 10% Calcium 9% Iron 9% Magnesium 5% Titanium 2% Nickel 0.6% Sodium 0.3% Chromium 0.2% Potassium 0.1% Manganese 0.1% Sulfur 0.1... Moon Mars is the fourth planet from the Sun in the solar system, named after the Roman god of war (the counterpart of the Greek Ares), on account of its blood red color as viewed in the night sky. This feature also earned it the name of Red Planet. Mars has... Mars Phobos is the larger and innermost of Mars two moons, named after Phobos, son of Ares (Mars) from Greek Mythology. Phobos orbits closer to a (major) planet than any other moon in the solar system, less than 6000 km above the surface of Mars. It is also one of the... Phobos Deimos (DAY mos) is the smaller and outermost of Mars two moons, named after Deimos from Greek Mythology. Phobos and Deimos were both discovered by American astronomer Asaph Hall. The names were suggested by Henry Madan (1838–1901), Science Master of Eton, from Book XV of the Iliad, where... Deimos Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0.1% Water vapor 0.1% Ammonia 0.02% Ethane 0.0002% Phosphine 0.0001% Hydrogen sulfide <0.0001% Jupiter is the fifth planet from the Sun and by far the largest within our solar system; some have... Jupiter satellites Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0.2% Water vapor 0.1% Ammonia 0.01% Ethane 0.0005% Phosphine 0.0001% Saturn is the sixth planet from the Sun. It is a gas giant, the second-largest planet in the solar system after... Saturn The Saturnian System (photographic montage) Saturn Rings and Satellites. ESA Saturn has a large number of natural satellites. Introduction The precise number of Saturns moons will never be certain as the orbiting chunks of ice in Saturns rings are all technically moons, and it is difficult to draw... satellites Atmospheric characteristics Atmospheric pressure 120 kPa Hydrogen 83% Helium 15% Methane 1.99% Ammonia 0.01% Ethane 0.00025% Acetylene 0.00001% Carbon monoxide Hydrogen sulfide trace Uranus (pronounced yər-AYN-us, or YOOR-ə-nus) is the seventh planet from the Sun. It is a gas giant... Uranus satellites Atmospheric characteristics Atmospheric pressure 100-300 kPa Hydrogen >84% Helium >12% Methane 2% Ammonia 0.01% Ethane 0.00025% Acetylene 0.00001% Neptune is the eighth planet from the sun, and the outermost gas giant in our solar system. Due to Plutos eccentric orbit, Neptune is sometimes... Neptune satellites Atmospheric characteristics Atmospheric pressure 0.15-0.30 Pascal Composition Nitrogen,Methane Pluto is the ninth planet from the Sun in our solar system. Because Pluto is also the smallest planet in our solar system and has a highly eccentric orbit (which takes it inside the orbit of Neptune) there... Pluto Charon is the only known satellite of Pluto. It was discovered by astronomer James Christy on June 22, 1978 by carefully examining highly magnified images of Pluto on photographic plates taken a couple of months before and noticing that a slight bulge appeared periodically. Later, the bulge was confirmed on... Charon An asteroid is a small, solid object in our Solar System, orbiting the Sun. An asteroid is an example of a minor planet (or planetoid), which are much smaller than planets. Most asteroids are believed to be remnants of the protoplanetary disc which were not incorporated into planets during the... Asteroids Near-Earth asteroids (NEAs) are asteroids whose orbit intersects Earths orbit and which may therefore pose a collision danger, as well as being most easily accessible for spacecraft from Earth. In fact, some near-Earth asteroids can be reached with much less ΔV than it takes to reach... Near-Earth asteroids " Vulcanoids are hypothetical asteroids that may orbit in a dynamically stable zone between 0.08 and 0.21 astronomical units from the Sun, well within the orbit of Mercury. They take their name from the hypothetical planet Vulcan, which eighteenth-century astronomers fruitlessly searched for to explain the excess precession... Vulcanoids" " Apohele asteroids are a subclass of Aten asteroids. They have not only their perihelion at less than one AU (within Earths orbit), but also their aphelion; that is, their entire orbit is within Earths. As of July 2004 there are only two confirmed Apoheles: 2003 CP20 and 2004... Apoheles" " The Arjuna asteroids are a class of near-Earth asteroids whose orbits are very Earth-like in character, having low inclination, orbital periods close to one Earth year, and low eccentricity. Arjunas are very uncommon, but of significance owing to the extremely low delta V required to reach them from... Arjunas" The Aten asteroids are a group of near-Earth asteroids, named after the first of the group to be discovered (2062 Aten, discovered January 7, 1976 by Eleanor F. Helin). They have semi_major axes of less than one astronomical unit, placing them inside the orbit of Earth. Nearly all known... Atens The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, the first asteroid of this group to be discovered. They are Earth-crosser asteroids that have orbital semi-major axes greater than that of the Earth. Some can get very close to the Earth, making them... Apollos The Amor asteroids are a group of near-Earth asteroids named after the asteroid 1221 Amor. They approach the orbit of the Earth from beyond, but do not cross it. Most Amors do cross the orbit of Mars. The two moons of Mars, Deimos and Phobos, may be Amor asteroids... Amors A Mars-crosser asteroid is an asteroid whose orbit crosses that of Mars. The known numbered Mars-crossers are listed here. Buried in the list are two peculiar asteroids: 5261 Eureka, the only numbered Martian Trojan, and (26677) 2001 EJ18, Mars only other numbered co-orbital. Notes: ¹ inner-grazer; ² outer... Mars-crossers The asteroid belt is a region of the solar system falling roughly between the planets Mars and Jupiter where the greatest concentration of asteroid orbits can be found. It is termed the main belt when contrasted with other concentrations of minor planets, since these may also be termed asteroid belts... Asteroid belt Hungarias Phocaeas Nysas The Alinda asteroids are a group of asteroids with a semi-major axis of about 2.5 AU and an orbital eccentricity approximately between 0.4 and 0.65. The namesake is 887 Alinda, discovered by Max Wolf in 1918. These objects are held in this region by the 1... Alindas Hilda asteroids are asteroids with a semi-major axis between 3.7 AU and 4.2 AU, an eccentricity greater than 0.07, and an inclination less than 20°. They do not form a true asteroid family, in the sense that they do not descend from a common parent object... Hildas Pallas Marias Koronis Eos Themis Griquas Cybeles Thule As originally defined, Trojan asteroids have a semi-major axis between 5.05 AU and 5.40 AU, and lie in elongated, curved regions around the two Lagrangian points 60° ahead and behind of Jupiter. The term is sometimes used to refer to minor bodies with similar relationships to other... Trojan asteroids Mars trojans Jupiter trojans Neptune trojans Outer planet crossers Damocloids are asteroids such as 5335 Damocles and (16746) 1996 PW that have long-period highly eccentric orbits typical of periodic comets such as 1P/Halley, but without showing a cometary coma or tail. The object 2001 OG108 was thought to be a Damocloid, but as it approached perihelion it... Damocloids The centaurs are a class of icy planetoids that orbit the Sun between Jupiter and Neptune, named after the mythical race of centaurs. The first centaur to be discovered, 2060 Chiron was found to display a coma upon its approach to perihelion, and is now officially classified as both a... Centaurs A trans-Neptunian object (TNO) is any object in the solar system with all or most of its orbit beyond that of Neptune. The Kuiper belt and Oort cloud are names for some subdivisions of that volume of space. Pluto and its moon Charon are trans-Neptunian objects, and if... Trans-Neptunian objects The Kuiper belt (KYE per) is an area of the solar system extending from within the orbit of Neptune (at 30 AU) to 50 AU from the sun, at inclinations consistent with the ecliptic. Origins The first astronomers to suggest the existence of this belt were Frederick C. Leonard in... Kuiper Belt A cubewano is any substantial Kuiper belt object, orbiting beyond about 41 AU and not controlled by resonances with the outer planets. The odd name is derived from the first trans-Neptunian object found, (15760) 1992 QB1. Later objects were called QB1-os, or cubewanos. Objects identified as cubewanos include... Cubewanos In astronomy, a plutino is a Pluto-like object, insofar as it has the same relative orbit as Pluto. These orbits are stabilized by an orbital resonance with Neptune, similar to Plutos 3:2 orbital resonance. This means that plutinos complete 2 orbits around the sun in the time... Plutinos Twotinos A scattered disk object (or scattered disc object or SDO) is a trans-Neptunian object of the Kuiper belt with a very eccentric orbit. An SDOs distance to the Sun varies enormously and can reach billions of kilometres. Most of the time they are found in the outer areas... Scattered Disk Objects 90377 Sedna is a trans-Neptunian object, discovered by Mike Brown (Caltech), Chad Trujillo (Gemini Observatory) and David L. Rabinowitz (Yale University) on November 14, 2003. Its discovery was the farthest distance at which any natural object in the solar system has ever been observed. Sedna is described as a... Sedna Comet Hale-Bopp, showing a white dust tail and blue gas tail (February 1997) Comet (disambiguation). A comet is a small astronomical object similar to an asteroid but composed largely of ice. Comets typically move in highly elliptical orbits, the aphelia of which may be many times more distant than... Comets Periodic comets Long-period comets Lost comets This diagram shows the presumed distance of the Oort cloud compared to the rest of the solar system. The Oort cloud (sometimes called the Öpik-Oort Cloud) is a postulated spherical cloud of comets situated about 50,000 to 100,000 AU from the Sun. This is approximately 1000 times... Oort Cloud A meteoroid is a relatively small (sand- to boulder-sized) fragment of debris in the Solar System. When entering the Earths atmosphere, the light phenomenon created by the ram pressure against the air (Despite the commonly held belief, friction is not at work here) and the resulting ionization of... Meteoroids A meteor is the visible path of a meteoroid that enters the Earths (or another bodys) atmosphere, commonly called a shooting star. The visibility is due to the heat produced by the atmospheric entry. A very bright meteor, brighter than the apparent magnitude of Venus, may be called... Meteors Categories: Planetology \| Astronomy stubs ... Meteor showers	Infrared Image of a possible extrasolar planet (lower left) in the Constellation Taurus, taken by the Hubble Space Telescope. Subsequently proven to be a background star, but heavily used by the media nonetheless. An extrasolar planet (or exoplanet) is a planet which orbits a star other than the Sun, and... Exoplanets Very hot Jupiters Artists impression of roaster extrasolar planet HD 209458b (Osiris). Hot Jupiter is a class of extrasolar planets whose mass is close to or exceeds that of Jupiter , but unlike in our own solar system, where Jupiter orbits at 5 AU, the planet referred to orbits within approximately 0.05... Hot Jupiters Eccentric Jupiters Pulsar planets are planets that are found orbiting pulsars. Pulsars are rapidly rotating neutron stars. The first ever planets discovered around another star, were discovered around a millisecond pulsar. Pulsar planets are discovered through pulsar timing measurements, to detect anomalies in the pulsation period. Any bodies orbiting the pulsar will... Pulsar planets Hot Neptunes / Super-Earths Transiting planets A rogue planet is a planet that either has an extremely elongated orbit around its star so that it is not on the same orbital plane as the other planets in the system, or it is an interstellar planet, a planet that drifts freely through space and doesnt orbit... Rogue / An interstellar planet is a hypothetical type of rogue planet that has been ejected from its solar system by a proto-gas giant to become an outcast, drifting in interstellar space. Theoretical ideas on the atmospheres of interstellar exoplanets In 1998, David J. Stevenson authored a paper entitled Possibility of... Interstellar planets Hypothetical planet types Chthonian planets Oceanic planets Trojan planets Brown dwarfs are sub-stellar objects (~13 to 75 Jupiter masses) that never fuse hydrogen into helium in their cores, as do stars on the main sequence. They do fuse deuterium. A useful criterion for telling brown dwarfs from low mass stars is obtained through testing for lithium, which is... Brown dwarfs Lithium dwarfs Methane dwarfs Sub-brown dwarfs For alternate meanings see star (disambiguation) Hundreds of stars are visible in this image taken by the Hubble Space Telescope of the Sagittarius Star Cloud in the Milky Way Galaxy. A star (Greek astron) is any massive gaseous celestial body in outer space. Stars appear as shining points in the... Stars by In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequenly refined in terms of other characteristics. Stellar temperatures can be classified by using Wiens displacement law; but this poses difficulties for distant stars. Stellar spectroscopy offers a way... spectral type Blue stars Blue-white stars White stars Yellow-white stars Yellow stars Orange stars Red stars In astrophysics, peculiar stars have distinctly unusual metal abundances. Chemically peculiar stars are common among hot main sequence (hydrogen-burning) stars. These hot peculiar stars have been divided into 4 main classes: helium-weak (He-weak), mercury-manganese (HgMn), Ap, and metallic lined (Am). The class names give a good... Peculiar stars A carbon star is a red giant (or occasionally red dwarf) star whose atmosphere contains more carbon than oxygen; the two elements combine in the upper layers of the star, forming carbon monoxide and other carbon compounds. The abundance of carbon is thought to be a product of helium fusion... Carbon stars C-type stars S-type stars Shell stars Wolf-Rayet stars are evolved, hot, massive stars, that exhibit high mass-loss caused by strong stellar winds. Consequently, they are short-lived, and therefore rare. The surface composition is usually mainly helium based with characteristic broad emission lines of carbon, nitrogen or oxygen. They usually have thermal radio emitters... Wolf-Rayet stars Peculiar A-type stars Metallic A-type stars Barium stars P Cygni stars Blue stragglers are stars in open or globular clusters that are hotter and bluer than other cluster stars having the same luminosity. Thus, they are separate from other stars on the clusters Hertzsprung_Russell diagram. Blue straggler stars appear to violate standard theories of stellar evolution, in which all stars... Blue stragglers For alternate meanings see star (disambiguation) Hundreds of stars are visible in this image taken by the Hubble Space Telescope of the Sagittarius Star Cloud in the Milky Way Galaxy. A star (Greek astron) is any massive gaseous celestial body in outer space. Stars appear as shining points in the... Stars by In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequenly refined in terms of other characteristics. Stellar temperatures can be classified by using Wiens displacement law; but this poses difficulties for distant stars. Stellar spectroscopy offers a way... luminosity class A subdwarf star, sometimes denoted by sd, is luminosity class VI under the Yerkes spectral classification system. They are defined as stars with luminosity 1.5 to 2 magnitudes lower than that of main-sequence stars of the same spectral type; this is due to subdwarfs having lower metallicity than... Subdwarf stars Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. Stars located on this band are known as main-sequence stars or dwarf stars. The coolest dwarfs are the red dwarfs. This line is so pronounced... Dwarf ( Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. Stars located on this band are known as main-sequence stars or dwarf stars. The coolest dwarfs are the red dwarfs. This line is so pronounced... Main sequence) For alternate meanings see star (disambiguation) Hundreds of stars are visible in this image taken by the Hubble Space Telescope of the Sagittarius Star Cloud in the Milky Way Galaxy. A star (Greek astron) is any massive gaseous celestial body in outer space. Stars appear as shining points in the... stars Subgiant stars According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giants. Examples include Aldebaran and Arcturus. They are believed to be stars of solar mass or higher which... Giant stars Bright giant stars A supergiant is a very large type of star which is ~10 to 50 solar masses on the Hertzsprung-Russell diagram. Supergiants can have radii in excess of 1000 solar radii. Because of their extreme masses they have short lifespans of only 10 to 50 million years and are only... Supergiant stars Hypergiant stars For alternate meanings see star (disambiguation) Hundreds of stars are visible in this image taken by the Hubble Space Telescope of the Sagittarius Star Cloud in the Milky Way Galaxy. A star (Greek astron) is any massive gaseous celestial body in outer space. Stars appear as shining points in the... Stars by Stars can be grouped into two general types called Population I and Population II. The criteria for classification include space velocity, location in the galaxy, age, chemical composition, and differences in distribution on the Hertzsprung-Russell diagram. Population I stars contain significant amounts of elements heavier than helium (termed metals... population Population III stars are a hypothetical population of extremely massive stars that are believed to have been formed in the early universe. They have not been observed directly, but are thought to be components of faint blue galaxies. Their existence is necessary to account for the fact that heavy elements... Population III stars Stars can be grouped into two general types called Population I and Population II. The criteria for classification include space velocity, location in the galaxy, age, chemical composition, and differences in distribution on the Hertzsprung-Russell diagram. Population I stars contain significant amounts of elements heavier than helium (termed metals... Population II stars The galactic halo is a region of space surrounding spiral galaxies, including our galaxy, the Milky Way. The galactic halo is believed to consist largely of stars, gas and dark matter. Halo stars The bulk of the stars in a spiral galaxy are located either close to a single plane... Halo stars Thick disk stars Stars can be grouped into two general types called Population I and Population II. The criteria for classification include space velocity, location in the galaxy, age, chemical composition, and differences in distribution on the Hertzsprung-Russell diagram. Population I stars contain significant amounts of elements heavier than helium (termed metals... Population I stars Most stars are of nearly constant luminosity. Our own Sun is a good example of one which goes through relatively little variation in brightness (usually about 0.1% over an 11 year solar cycle). Many stars, however, undergo significant variations in luminosity, and these are known as variable stars. Variable... Variable stars Intrinsic variables Pulsating variables A Cepheid variable is a member of a particular class of variable stars, notable for a fairly tight correlation between their period of variability and absolute stellar luminosity. Because of this correlation (discovered by Henrietta Swan Leavitt in 1912), Cepheid variables can be used as a standard candle to determine... Cepheid variables A W Virginis variable is a variable star similar to a Cepheid variable. W Virginis are different because they are population II stars, and so have a lower mass (less than our Sun), and lower metallicity. Their luminosity is, on average, about 1.5 magnitudes less than classical Cepheids. The... W Virginis variables Delta Scuti variables RR Lyrae variables are variable stars often used as standard candles. An RR Lyrae is a pulsating Horizontal_branch star, with a mass about half of our Sun. It pulses in a manner similar to Cepheid variables, but some important differences exist. RR Lyrae are old, relatively low mass stars. Therefore... RR Lyrae variables Mira variables are a class of pulsating variable stars characterized by very red colors, pulsation periods longer than 100 days, and light amplitudes greater than one magnitude. They are red giant stars in the very late stages of stellar evolution (the asymptotic giant branch) that will expel their outer envelopes... Mira variables Semiregular variable stars are giants or supergiants of intermediate and late spectral type showing considerable periodicity in their light changes, accompanied or sometimes interrupted by various irregularities. Periods lie in the range from 20 to more than 2000 days, while the shapes of the light curves may be rather different... Semiregular variables An irregular variable is a type of variable star in which variations in brightness show no regular periodicity. There are two main sub-types of irregular variable - eruptive irregular variables and pulsating irregular variables. Categories: Variable stars \| Irregular variables \| Stub ... Irregular variables Beta Cephei variables Alpha Cygni variables RV Tauri variables An eruptive variable is a variable star characterised by sudden extreme increases in luminosity. There are many different types of eruptive variables, with an enormous range of increases in luminosity and recurrence timescales. Examples include flare stars, which are very faint stars on the main sequence; novae and dwarf novae... Eruptive variables Flare stars T Tauri variables FU Orionis variables R Coronae Borealis variables Luminous blue variables Artists conception of a cataclysmic variable system Cataclysmic variables are a class of binary stars containing a white dwarf and a companion star. The companion star is usually a red dwarf, although in some cases it is another white dwarf or a slightly evolved star (subgiant). Several hundreds of... Cataclysmic variables Symbiotic variables Dwarf novae A nova is a cataclysmic nuclear explosion caused by the accretion of hydrogen onto the surface of a white dwarf star. When a white dwarf has a close companion star, the companion will often begin to have its outer atmosphere drawn away from it by the white dwarfs gravity... Novae Remnant of Keplers Supernova, SN 1604. A supernova is a type of stellar explosion which appears to result in the creation of a new star upon the celestial sphere. (Nova is Latin for new). The super prefix distinguishes this from a nova, which also involves a star increasing in... Supernovae Remnant of Keplers Supernova, SN 1604. A supernova is a type of stellar explosion which appears to result in the creation of a new star upon the celestial sphere. (Nova is Latin for new). The super prefix distinguishes this from a nova, which also involves a star increasing in... Type I supernovae Type II supernovae In astronomy, gamma-ray bursts (GRBs) are flashes of gamma rays that last from seconds to hours, the longer ones being followed by several days of X-ray afterglow. They occur at apparently random positions in the sky several times each day. As of summer 2003, one of the more... Gamma ray bursts Long GRBs Collapsars A hypernova is a theoretical type of supernova produced when exceptionally large stars collapse at the end of their lifespan. In a hypernova, the core of the star collapses directly into a black hole and two extremely energetic jets of plasma are emitted from its rotational poles at nearly light... Hypernovae Short GRBs Dark GRBs Extrinsic variables Rotating variables Alpha2 CVn stars Rotating ellipsoidal variables An eclipsing binary star is a binary star in which the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. In the case where the binary is also a spectroscopic binary and the parallax of the... Eclipsing binaries Algol stars Beta Lyrae stars W Ursae Majoris stars In astronomy, a compact star (sometimes called a compact object) is a star that is a white dwarf, a neutron star, a strange star, or a black hole. Compact star is often used when the exact nature of the star is not known, but evidence suggests it is very massive... Compact stars A white dwarf is an astronomical object which is produced when a low to medium mass star dies. These stars are not heavy enough to generate the core temperatures required to burn carbon in nucleosynthesis reactions, and after they have become a red giant during their helium-burning phase, they... White dwarfs A black dwarf is the remains of a Sun-sized star which has evolved to a white dwarf and subsequently cooled down such that it no longer gives out radiation. None are known to exist in our universe, as the time taken for a white dwarf to cool to such... Black dwarfs This article is about the celestial body. Neutron Star was a 1966 Hugo award winning short story by Larry Niven A neutron star is a compact star in which the weight of the star is carried by the pressure of free neutrons. It is also called a degenerate star. The... Neutron stars A magnetar is a neutron star with an extremely strong magnetic field, the decay of which powers the emission of copious amounts of high-energy electromagnetic radiation, particularly X-rays and gamma-rays. The theory regarding these objects was formulated by Robert Duncan and Christopher Thompson in 1992. In the... Magnetars Composite Optical/X-ray image of the Crab Nebula pulsar, showing surrounding nebular gases stirred by the pulsars magnetic field and radiation. Pulsars are rotating neutron stars that are observable as sources of electromagnetic radiation. The radiation is observed to consist of a regular series of pulses, believed to... Pulsars A strange star or quark star is a hypothetical type of star composed of strange matter. This is an ultra-dense phase of matter that is theorized to form inside particularly massive neutron stars. It is theorized that when the neutronium which makes up a neutron star is put under... Strange stars This article is about an object in astrophysics. For other uses, see Black hole (disambiguation). An artists impression of a black hole with a closely orbiting companion star that exceeds its Roche limit. In falling matter forms an accretion disk, with some of the matter being ejected in highly... Black holes Top: artists conception of a supermassive black hole drawing material from a nearby star. Bottom: images believed to show a supermassive black hole devouring a star in galaxy RXJ 1242-11. Left: X-ray image, Right: optical image. Webpage: chandra.harvard.edu/photo/2004/rxj1242/ A supermassive black hole... Supermassive black holes	A binary star system consists of two stars both orbiting around their barycenter. The term binary star was apparently first coined by Sir William Herschel in 1802 to designate a real double star —the union of two stars that are formed together in one system by the laws... Multiple stars A binary star system consists of two stars both orbiting around their barycenter. The term binary star was apparently first coined by Sir William Herschel in 1802 to designate a real double star —the union of two stars that are formed together in one system by the laws... Binary stars This topic is about the astronomical phenomenon. For other uses, see double star (disambiguation). When two stars are so nearly in the same direction as seen from Earth that they appear to be a single star to the naked eye but may be separated by the use of telescopes, they... Optical binaries A visual binary star is a binary star for which the angular separation between the two components is great enough to permit them to be observed as a double star in a telescope. The resolving power of the telescope is an important factor in the detection of visual binaries, and... Visual binaries An astrometric binary star is a binary star for which only one of its component stars could be visually observed. The visible stars position is carefully measured and detected to have a wobble, due to the gravitational influence from its counterpart. From astrometric measurements of the movement of the... Astrometric binaries A spectroscopic binary star is a binary star which cannot be resolved as a visual binary, even with telescopes of the highest existing resolving power. In such binaries the separation between the stars is usually very small, and the orbital velocity very high. Unless the plane of the orbit happens... Spectroscopic binaries An eclipsing binary star is a binary star in which the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. In the case where the binary is also a spectroscopic binary and the parallax of the... Eclipsing binaries Close binaries Detached binaries are a kind of binary stars where each component is within its Roche lobe. The stars have no major effect on each other, and essentially evolve separately. Most binaries belong to this class. Example: Sirius Categories: Astronomy \| Binary stars \| Astronomy stubs ... Detached binaries Semidetached binary stars are the ones where one of the components fills its Roche lobe and the other does not. Gas from the surface of the Roche lobe filling component (donor) is transferred to the other star (accretor). The mass transfer dominates the evolution of the system. In many cases... Semidetached binaries Contact binaries are a type of binary stars where both components of the binary fill their Roche lobes. The uppermost part of the stellar atmospheres forms a common envelope that surrounds both stars. As the friction of the envelope brakes the orbital motion, the stars coalesce in the future, unless... Contact binaries Unresolved binaries X-ray bursters are a class of binary stars which have periodic outbursts luminous in X-rays. They contain a neutron star and an accreting companion. When a star in a binary fills its Roche lobe (either due to being very large or very close to its companion), it begins... X-ray bursters A triple star system consists of three gravitationally bound stars. The stars are in orbits around a common center of mass, usually so that two of the stars form a close binary star and the third is further away. This configuration is often called a hierarchical triple star. Multiple stars... Triple stars Stellar groupings Star clusters are physically bound systems of stars. In order of low compactness to high compactness (and in some sense also age) they range from stellar associations to open clusters to globular clusters. Star clusters may evolve into moving groups. Globular Cluster M92 in the Hercules constellation. General information Star... Star clusters A stellar association is a very loose star cluster, looser than both open clusters and globular clusters. Discovered by Viktor Ambartsumian in 1947. Categories: Stub \| Star clusters \| Stellar associations ... Stellar associations An open cluster is a group of stars (star cluster) that were born at the same time from a molecular cloud, and are still near to each other. They are also called galactic clusters since they exist within the galaxys disk. NGC 3603 is home to an open cluster... Open clusters A globular cluster is a spherical bundle of stars (star cluster) that orbits a galaxy as a satellite. Globular clusters are very tightly gravitationally bound, which gives them their spherical shape, and extremely dense (in relative terms) towards their core. The Globular Cluster M80. General information Globular clusters are usually... Globular clusters Orion is a remarkable constellation, visible from most places on the globe (but not always the whole year long). A constellation is a group of stars visibly related to each other in a particular configuration. In three-dimensional space, most of the stars we see have little relation to one... Constellations For other meanings of asterism, see asterism. In astronomy, an asterism is a recognized pattern of stars seen in Earths sky. Asterisms are considered to be distinct from constellations, although the origin of most constellations is also a recognizable pattern of stars. Examples of asterisms include: the Big Dipper... Asterisms This article is about a celestial body. For alternate meanings see galaxy (disambiguation). Seen behind a veil of foreground stars which lie within our own galaxy, this face-on Spiral Galaxy ESO 269-57 is about 150 million light-years away and 200,000 light-years across. Stars are almost... Galaxy components In astronomy, a bulge is a huge, tightly packed group of stars. The term commonly refers to the central group of stars found in most spiral galaxies. The bulge in galaxy spirals is usually composed of Population II stars, small, red and old. This is because all stars were born... Galactic bulges Galactic bars Galactic rings A spiral galaxy presents a face-on view of its spiral arms. Spiral arms are regions of stars that extend from the center of spiral and barred spiral galaxies. These long, thin regions resemble a spiral and thus give spiral galaxies their name. The existence of spiral arms has puzzled... Spiral arms Thin disks Thick disks The galactic halo is a region of space surrounding spiral galaxies, including our galaxy, the Milky Way. The galactic halo is believed to consist largely of stars, gas and dark matter. Halo stars The bulk of the stars in a spiral galaxy are located either close to a single plane... Galactic halos Categories: Stub ... Galactic coronae This article is about a celestial body. For alternate meanings see galaxy (disambiguation). Seen behind a veil of foreground stars which lie within our own galaxy, this face-on Spiral Galaxy ESO 269-57 is about 150 million light-years away and 200,000 light-years across. Stars are almost... Galaxies This article is about a celestial body. For alternate meanings see galaxy (disambiguation). Seen behind a veil of foreground stars which lie within our own galaxy, this face-on Spiral Galaxy ESO 269-57 is about 150 million light-years away and 200,000 light-years across. Stars are almost... Galaxies by morphology A spiral galaxy is a type of galaxy in the Hubble sequence which is characterized by the following physical properties: Spiral Galaxy M74 presents a face-on view of its spiral arms. It contains about 100 billion stars, 30 million light-years away toward the constellation Pisces. A considerable total... Spiral galaxies NGC 253, a barred spiral starburst gallery (2MASS). A barred spiral galaxy is a spiral galaxy with a band of bright stars emerging from the center and running across the middle of the galaxy. Spiral arms appear to emerge from the ends of the bar in these galaxies, whereas they... Barred spiral galaxies The Spindle Galaxy (NGC 5866), a lenticular galaxy in the Draco constellation. A lenticular galaxy is a type of galaxy which is an intermediate between an elliptical galaxy and a spiral galaxy in the Hubble sequence classification scheme. Lenticular galaxies are disc galaxies (like spirals galaxies) which have used up... Lenticular galaxies An elliptical galaxy is a type of galaxy in the Hubble sequence characterized by the following physical properties: The giant elliptical galaxy NGC 4881 (the spherical glow at upper left) lies at the edge of the Coma Cluster of Galaxies. No or at most inconsiderable amount of angular momentum. No... Elliptical galaxies A ring galaxy is a galaxy with a ring-like appearance. The ring consists of massive, relatively young blue stars, which are extremely bright. The central region contains relatively little luminous matter. Astronomers believe that ring galaxies are formed when a smaller galaxy passes through the center of a larger... Ring galaxies An irregular galaxy is a galaxy that does not fall into the Hubble classification for galaxies. These are galaxies that feature neither spiral nor elliptical morphology. There are two Hubble types of irregular galaxies. An Irr-I galaxy (Irr I) is an irregular galaxy that features some structure but not... Irregular galaxies This article is about a celestial body. For alternate meanings see galaxy (disambiguation). Seen behind a veil of foreground stars which lie within our own galaxy, this face-on Spiral Galaxy ESO 269-57 is about 150 million light-years away and 200,000 light-years across. Stars are almost... Galaxies by size Giant diffuse galaxies Giant ellipticals A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Ways 200-400 billion stars. The Large Magellanic Cloud, containing over 30 billion stars, is sometimes classified as a dwarf galaxy. There are many dwarf galaxies in... Dwarf galaxies Ultracompact dwarfs An active galaxy is a galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy: stars, dust and interstellar gas. This energy, depending on the active galaxy type, can be emitted across most of the electromagnetic spectrum, as infrared, radio waves... Active galaxies This view, taken with infrared light, is a false-color image of a quasar-starburst tandem with the most luminous starburst ever seen in such a combination. The quasar-starburst was found by a team of researchers from six institutions. A quasar (from quasi-stellar radio source) is an astronomical... Quasars A blazar is a galaxy with a very compact and highly variable energy source at the center of the host galaxy. Blazars are among the most violent phenomena in the universe and are an important topic in extragalactic astronomy. Blazars are members of a larger group of Active Galaxies, also... Blazars An active galaxy is a galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy: stars, dust and interstellar gas. This energy, depending on the active galaxy type, can be emitted across most of the electromagnetic spectrum, as infrared, radio waves... Radio galaxies Seyfert galaxies are spiral or irregular galaxies containing an extremely bright nucleus, most likely caused by a supermassive black hole, that can sometimes outshine the surrounding galaxy. The light from the central nucleus varies in less than a year, which implies that the emitting region must be less than one... Seyfert galaxies A starburst galaxy is a galaxy in the process of an intense burst of stellar formation, often as a result of a collision or close encounter between two galaxies. Known starburst galaxies include M82 and IC 10. A subtype of starburst galaxy is the Wolf-Rayet galaxy, where a large... Starburst galaxies Dark galaxies Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. Matter throughout the visible Universe has, over the course of the Universes history, aggregated into a range of large-scale structures under the influence of gravity. Groups and clusters may contain from ten to... Galaxy clusters In astronomy, a galaxy cluster cloud is a denser part of a galaxy supercluster, consisting of several galaxy clusters. The most well-known example is the Canes Venatici cloud of the Virgo supercluster, which harbours our own galaxy, the Milky Way. See also Large-scale structure of the cosmos Galaxy... Galaxy cluster clouds Superclusters are large groups of smaller galaxy groups and clusters, and are among the largest structures of the cosmos. The superclusters dictates that the galaxies in our Universe are not uniformly distributed; most of them are grouped together in groups and clusters, with groups containing up to 50 and clusters... Superclusters In astronomy, filaments are one of the largest known structures in the Universe, thread-like structures with a typical length of 70 to 150 megaparsec that form the boundaries between large voids in the universe. Filaments consist of galaxies; parts where a large number of galaxies are very close to... Filaments / In astronomy, voids are the empty spaces between filaments, one of the largest-scale structures in the Universe that contain none or hardly any galaxies. Voids typically have a diameter of 11 to 150 Mpc; particularly large voids, defined by the absence of rich superclusters, are sometimes called supervoids. A... Voids	Circumstellar matter Dust disks The interplanetary medium is the material which fills the solar system and through which all the larger solar system bodies such as planets, asteroids and comets move. Composition and physical characteristics The interplanetary medium includes interplanetary dust, cosmic rays and hot plasma from the solar wind. The temperature of the... Interplanetary medium A protoplanetary disc (also protoplanetary disk, proplyd) is an accretion disc surrounding a T Tauri star. They differ from the discs surrounding the primary components close binary systems in their size and temperature. Protoplantary discs have radii up to 1000 Astronomical Units and rather cool. Only their innermost parts reach... Protoplanetary disks The interstellar medium (or ISM) is a term used in astronomy to describe the rarefied gas and dust that exists between the stars (or their immediate circumstellar environment) within a galaxy. The matter normally consists of about 99% gas particles and usually 1% of dust. This compound is usually extremely... Interstellar medium The Triangulum Emission Nebula NGC 604 lies in a spiral arm of Galaxy M33, 2.7 million light-years from Earth. This nebula is a region in which stars are forming. A nebula (Latin for mist; plur. nebulae) is an interstellar cloud of dust and gas. Originally nebula was a... Nebulae NGC 6543, the Cats Eye Nebula A planetary nebula is an astronomical object consisting of a glowing shell of gas formed by certain types of stars at the end of their lives. They are in fact unrelated to planets; the name originates from a supposed similarity in appearance to... Planetary nebulae The Crab Nebula is an expanding cloud of gas created by the 1054 supernova. Remnant of Keplers Supernova, SN 1604. 1987A supernova remnant A supernova remnant (SNR) is made up of the materials left behind by the gigantic explosion of a star in a supernova. There are two possible... Supernova remnants A plerion (Greek full) is also called pulsar wind nebula. Plerions have been found inside the shell of supernova remnants. Usually they emit synchrotron radiation powered by a pulsar. A classical example is the Crab Nebula. Categories: Astronomy stubs ... Plerions Bright nebulae An emission nebula is a cloud of ionized gas emitting light of various colors. The most common source for ionization are high-energy photons emitted from a nearby hot star. Among the several different types of emission nebula are H II regions, in which star formation is taking place and... Emission nebulae In astronomy, reflection nebulae are clouds of dust which are simply reflecting the light of a nearby star or stars. The nearby star or stars are not hot enough to cause ionization in the gas of the nebula like in emission nebulae but are bright enough to give sufficient scattering... Reflection nebulae NGC 604, a giant H II region in the Triangulum Galaxy. An H II region is a cloud of glowing gas, sometimes several hundred light years across, in which star formation is taking place. Young, hot, blue stars which have formed from the gas emit copious amounts of... H II regions A dark nebula is a large cloud which appears as star-poor regions where the dust of interstellar medium seems to be concentrated. Molecular Cloud Barnard 68 is a dark nebula, not a hole in space. No stars are visible in the center which indicates that Barnard 68 is relatively... Dark nebulae A Molecular cloud is a type of interstellar clouds whose density and size permits the formation of molecular hydrogen, H2. However, this molecule is difficult to detect, and the molecule most used to trace the H2 is CO (carbon monoxide). The ratio between CO luminosity and H2 mass is roughly... Molecular clouds Bok globules H I regions Intergalactic space is the physical space between galaxies. Generally free of dust and debris intergalactic space is very close to a vacuum with an average density of less than one atom per cubic meter. The primary method of energy transfer in intersteller space is by radiation as opposed to convection... Intergalactic medium WMAP image of the CMB anisotropy,Cosmic microwave background radiation(June 2003) The cosmic microwave background radiation (CMB) is a form of electromagnetic radiation that fills the whole of the universe. It has the characteristics of black body radiation at a temperature of 2.725 kelvins. It has a frequency... Cosmic microwave background radiation Dark matter is matter that cannot be detected by its emitted radiation but whose presence can be inferred from gravitational effects on visible matter such as stars and galaxies. Estimates of the amount of matter in the universe based on gravitational effects consistently suggest that there is far more matter... Dark matter Massive compact halo objects, or MACHOs, is a general name for any kind astronomical body which might explain the apparent presence of dark matter in galaxy halos. A MACHO is a small chunk of normal baryonic matter, which emits little or no radiation and drifts through interstellar space unassociated with... MACHOs This article is about the hypothetical class of particles. For other uses of the term, see wimp (disambiguation). In astrophysics, WIMPs, or weakly interacting massive particles, are hypothetical particles which figure into one explanation of the dark matter problem. These particles only interact through the weak nuclear force and gravity... WIMPs

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