"as lying before the mouth of a Big Fish, an Arabic constellation. This ""cloud"" was apparently commonly known to the Isfahan astronomers, very probably before 905. The first recorded mention of the Large Magellanic Cloud was also given in the ""Book of Fixed Stars"". These were the first galaxies other than the Milky Way to be observed from Earth. The Great Andromeda Nebula he observed was also the first true nebula to be observed, as distinct from a star cluster. He probably also cataloged the Omicron Velorum star cluster as a ""nebulous star"", and an additional ""nebulous object"" in Vulpecula,"
"the convention ""Chhmm±ddd"", always beginning with the prefix ""C"", where ""h"", ""m"", and ""d"" represent the approximate coordinates of the cluster center in hours and minutes of right ascension, and degrees of declination, respectively, with leading zeros. The designation, once assigned, is not to change, even if subsequent measurements improve on the location of the cluster center. The first of such designations were assigned by Gosta Lynga in 1982. Star cluster Star clusters are groups of stars. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds or thousands of very old stars which are"
"The term ""fixed stars"" generally refers to the background of celestial objects that do not appear to move relative to each other in the night sky, generally including all stars other than the sun, nebulae and other star-like objects. Though ""fixed"", such objects were proven to have proper motion by Edmund Halley in 1718. Apparently referring to proper motion, Smith said that Kolob moves ""swifter than the rest of the twelve fixed stars"". Also, the Book of Abraham refers to ""fixed planets"", thereby including planets in the set of celestial objects that may be ""fixed"". He also refers to the"
"Fixed stars The fixed stars () comprise the background of astronomical objects that appear to not move relative to each other in the night sky compared to the foreground of Solar System objects that do. Generally, the fixed stars are taken to include all stars other than the Sun. Nebulae and other deep-sky objects may also be counted among the fixed stars. Exact delimitation of the term is complicated by the fact that no celestial objects are in fact fixed with respect to each other. Nonetheless, extrasolar objects move so slowly in the sky that the change in their relative"
"the four main groups were formalised in 1958 at the tenth general assembly of the International Astronomical Union (IAU). The General Catalogue of Variable Stars (GCVS) has updated the definitions with some additional information and provided newer reference stars where old examples such as S Vul have been re-classified. The semiregular variable stars, particularly the SRa and SRb sub-classes, are often grouped the Mira variables under the long-period variable heading. In other situations, the term is expanded to cover almost all cool pulsating stars. The semi-regular giant stars are closely related to the Mira variables: Mira stars generally pulsate in"
"relatively bright stars for which it is named. The four are often identified as A, B, C, and D in order of increasing right ascension. The brightest of the four stars is C, or Theta Orionis C, with an apparent magnitude of 5.13. Both A and B have been identified as eclipsing binaries. Infrared images of the Trapezium are better able to penetrate the surrounding clouds of dust, and have located many more stellar components. About half the stars within the cluster have been found to contain evaporating circumstellar disks, a likely precursor to planetary formation. In addition, brown dwarfs"
"""T"", ""O"" and ""O"" constitute 32 crystallographic point groups. An abbreviated form of the Hermann–Mauguin notation commonly used for space groups also serves to describe crystallographic point groups. Group names are Crystallographic point group In crystallography, a crystallographic point group is a set of symmetry operations, like rotations or reflections, that leave a central point fixed while moving other directions and faces of the crystal to the positions of features of the same kind. For a periodic crystal (as opposed to a quasicrystal), the group must also be consistent with maintenance of the three-dimensional translational symmetry that defines crystallinity. The"
"""Alpha Centauri C"". In 10 August 2018, IAU approved the name ""Toliman"" for ""Alpha Centauri B"". Alpha Centauri is a triple star system, with its two main stars, Alpha Centauri A and Alpha Centauri B, being binary components. The ""AB"" designation, or older ""A×B"", denotes the mass centre of a main binary system relative to companion star(s) in a multiple star system. ""AB-C"" refers to the component of Proxima Centauri in relation to the central binary, being the distance between the centre of mass and the outlying companion. Because the distance between Proxima (C) and either of Alpha Centauri A"
"individually. The star positions ""α, δ"" are compiled in several star catalogues of different volume and accuracy. ""Absolute"" and very precise coordinates of 1000-3000 stars are collected in fundamental catalogues, starting with the FK (Berlin ~1890) up to the modern FK6. ""Relative"" coordinates of numerous stars are collected in catalogues like the Bonner Durchmusterung (Germany 1852-1862, 200.000 rough positions), the SAO catalogue (USA 1966, 250.000 astrometric stars) or the Hipparcos and Tycho catalogue (110.000 and 2 million stars by space astrometry). Star position Star position is the apparent location of any given star in the sky, which seems fixed onto"
"Castor Moving Group The Castor Moving Group is a moving group of stars sharing similar velocities. The stars that have been identified as part of the group include Castor, Fomalhaut, Vega, α Cephei and α Librae. While the reported group members are young (typically with ages of hundreds of millions of years), recent results suggest that the velocity differences amongst the moving group stars are too large for them to have possibly shared a common origin. The moving group was first proposed by J. P. Anosova, and V. V. Orlov in 1990. Anosova and Orlov originally proposed 15 members. In"
"The Magnificent Seven (neutron stars) The Magnificent Seven is the informal name of a group of isolated young cooling neutron stars at a distance of 120 to 500 parsecs from Earth. These objects are also known under the names XDINS (X-ray Dim Isolated Neutron Stars) or simply XINS. The first to fit this classification was RX J1856.5-3754, which was discovered by Walter et al. in 1992, and confirmed as a neutron star in 1996. The term ""Magnificent Seven"" was initially applied to the sources RX J1856.5-3754, RBS1556, RBS1223, RX J0806.4-4132, RX J0720.4-3125, RX J0420.0-5022 and MS 0317.7-6647. However, it was"
"CH star CH stars are particular type of carbon stars which are characterized by the presence of exceedingly strong absorption bands due to CH (methylidyne) in their spectra. They belong to the stellar population II, meaning they are metal poor and generally pretty middle-aged stars, and are under-luminous compared to the classical C–N carbon stars. The term 'CH star' was coined by Philip C. Keenan in 1942 as a sub-type of the C classification, which he used for carbon stars. The main molecular feature used in identifying the initial set of five CH stars lies in the Fraunhaufer G band."
"Compact star In astronomy, the term ""compact star"" (or ""compact object"") refers collectively to white dwarfs, neutron stars, and black holes. It would grow to include exotic stars if such hypothetical dense bodies are confirmed. Most compact stars are the endpoints of stellar evolution, and thus often referred to as stellar remnants, the form of the remnant depending primarily on the mass of the star when it formed. All of these objects have a high mass relative to their radius, giving them a very high density. The term ""compact star"" is often used when the exact nature of the star"
"stars and duals: In terms of group theory, if ""G"" is the symmetry group of a polyhedral compound, and the group acts transitively on the polyhedra (so that each polyhedron can be sent to any of the others, as in uniform compounds), then if ""H"" is the stabilizer of a single chosen polyhedron, the polyhedra can be identified with the orbit space ""G""/""H"" – the coset ""gH"" corresponds to which polyhedron ""g"" sends the chosen polyhedron to. There are eighteen two-parameter families of regular compound tessellations of the Euclidean plane. In the hyperbolic plane, five one-parameter families and seventeen isolated"
"stellar discoveries, laboratory experiments (with co-workers James R. Heath, Sean C. O'Brien, Yuan Liu, Robert Curl and Richard Smalley at Rice University) which simulated the chemical reactions in the atmospheres of the red giant stars demonstrated that stable C molecules could form spontaneously from a condensing carbon vapour. The co-investigators directed lasers at graphite and examined the results. The C molecule is a molecule with the same symmetry pattern as a football, consisting of 12 pentagons and 20 hexagons of carbon atoms. Kroto named the molecule buckminsterfullerene, after Buckminster Fuller who had conceived of the geodesic domes, as the dome"
"subset of stars which showed forbidden emission lines from ionised iron and some other elements. These stars were all considered to be distinct from the classical main sequence Be stars, although they appeared to consist of a wide range of different types of star. The term B[e] star was coined to group these stars. One type of B[e] star was readily identified as being highly luminous supergiants. By 1985, eight dust-shrouded B[e] supergiants were known in the Magellanic Clouds. Others were found to be definitely not supergiants. Some were binaries, others proto-planetary nebulae, and the term ""B[e] phenomenon"" was used"
"the stable anchor points by which all other stars' spectra would be classified. There followed a hiatus of 30 years, until a cluster of works representing renewed interest in the star appeared around the year 1990. The items in this subsection all refer to works in the film, television, and print franchise originated by Gene Roddenberry. Deneb is referred to as a location in space or the center of a planetary system unusually often in fiction. For a list containing many stars and planetary systems that have a less extensive list of references, see Stars and planetary systems in fiction."
"4.7 arcminutes (or 0.08°) on the sky. The brighter group contains Xi Scorpii A, B, and C. A and B are both yellow-white F-type stars. A is slightly brighter and warmer. They are separated by 0.744 arcseconds on average, and orbit around a common center once every 45.9 years. The dimmer, seventh-magnitude Xi Scorpii C orbits this pair at about ten times the distance, having a separation of around 7.6 arcseconds. The second group contains Xi Scorpii D and E. Both D and E are K-type main-sequence stars, which are separated by about 11.9 arcseconds. They are known to be"
"C-N is hypothesized to be a sequence of increased carbon abundance with age for carbon stars in the asymptotic giant branch. The class D (for Degenerate) is the modern classification used for white dwarfs – low-mass stars that are no longer undergoing nuclear fusion and have shrunk to planetary size, slowly cooling down. Class D is further divided into spectral types DA, DB, DC, DO, DQ, DX, and DZ. The letters are not related to the letters used in the classification of other stars, but instead indicate the composition of the white dwarf's visible outer layer or atmosphere. The white"
"keep the same relative arrangement over time. The other group contained the naked eye planets, which they called ""wandering stars"". (The Sun and Moon were sometimes called planets as well.) The planets seem to move and change their position over short periods of time (weeks or months). They always seem to move within the band of stars called the zodiac by Westerners. The planets can also be distinguished from fixed stars because stars tend to twinkle, while planets appear to shine with a steady light. However, fixed stars do have parallax, which is a change in apparent position caused by"
"now know, the fixed stars are not ""fixed"". The concept of inertial frames of reference is no longer tied to either the fixed stars or to absolute space. Rather, the identification of an inertial frame is based upon the simplicity of the laws of physics in the frame, in particular, the absence of fictitious forces. Law of inertia holds for Galilean coordinate system which is a hypothetical system relative to which fixed stars remain fixed. Fixed stars The fixed stars () comprise the background of astronomical objects that appear to not move relative to each other in the night sky"
"the accretion disk when its rotation is in resonance with the orbital period of the binary. Cataclysmic variable star Cataclysmic variable stars (CV) are stars which irregularly increase in brightness by a large factor, then drop back down to a quiescent state. They were initially called novae, from the Latin 'new', since ones with an outburst brightness visible to the naked eye and an invisible quiescent brightness appeared as new stars in the sky. Cataclysmic variable stars are binary stars that consist of two components; a white dwarf primary, and a mass transferring secondary. The stars are so close to"
"Catalogues of Fundamental Stars The Catalogue of Fundamental Stars is a series of six astrometric catalogues of high precision positional data for a small selection of stars to define a celestial reference frame, which is a standard coordinate system for measuring positions of stars. The six volumes in the fundamental catalogue series are as follows: The ""Fundamental-Catalog"" (FC) was compiled by Auwers and published in two volumes. The first volume, published in 1897, contains 539 stars and the second, published in 1883, contains 83. The ""Neuer Fundamentalkatalog"" (NFK) was compiled by J. Peters and contained 925 stars. The ""Third Fundamental"
"sequence O, B, A, F, G, K and M. (A popular mnemonic for memorizing this sequence of stellar classes is ""Oh Be A Fine Girl/Guy, Kiss Me"".) The luminosity class ranged from I to V, in order of decreasing luminosity. Stars of luminosity class V belonged to the main sequence. In April 2018, astronomers reported the detection of the most distant ""ordinary"" (i.e., main sequence) star, named Icarus (formally, MACS J1149 Lensed Star 1), at 9 billion light-years away from Earth. When a protostar is formed from the collapse of a giant molecular cloud of gas and dust in the"
"a galaxy cluster. They are tabulated below: Stars, Star clusters, Galaxies, Galaxy clusters, Super clusters Galaxy cluster A galaxy cluster, or cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity with typical masses ranging from 10–10 solar masses. They are the largest known gravitationally bound structures in the universe and were believed to be the largest known structures in the universe until the 1980s, when superclusters were discovered. One of the key features of clusters is the intracluster medium (ICM). The ICM consists of heated gas between"
"Alpha Centauri Alpha Centauri (α Centauri, abbreviated Alpha Cen or α Cen) is the closest star system to the Solar System at from the Sun. It is a triple star system, consisting of three stars: Alpha Centauri A (officially Rigil Kentaurus), Alpha Centauri B (officially Toliman), and Alpha Centauri C (officially Proxima Centauri). Alpha Centauri A and B are Sun-like stars (Class G and K), and together they form the binary star Alpha Centauri AB. To the naked eye, the two main components appear as a single star with an apparent magnitude of −0.27, forming the brightest point of light"
"known as a stellar association, sometimes also referred to as a ""moving group"". Star clusters visible to the naked eye include the Pleiades (M45), Hyades, and the Beehive Cluster (M44). Globular clusters are roughly spherical groupings of from 10,000 to several million stars packed into regions of from 10 to 30 light years across. They commonly consist of very old Population II stars—just a few hundred million years younger than the universe itself—which are mostly yellow and red, with masses less than two solar masses. Such stars predominate within clusters because hotter and more massive stars have exploded as supernovae,"
"Cataclysmic variable star Cataclysmic variable stars (CV) are stars which irregularly increase in brightness by a large factor, then drop back down to a quiescent state. They were initially called novae, from the Latin 'new', since ones with an outburst brightness visible to the naked eye and an invisible quiescent brightness appeared as new stars in the sky. Cataclysmic variable stars are binary stars that consist of two components; a white dwarf primary, and a mass transferring secondary. The stars are so close to each other that the gravity of the white dwarf distorts the secondary, and the white dwarf"
"Circumpolar constellation In astronomy, a circumpolar constellation is a constellation (group of stars) that never sets below the horizon, as viewed from a location on Earth. Due to Earth's rotation and axial tilt with respect to the Sun, the stars and constellations can be divided into two categories. Those stars and constellations that never rise or set are called ""circumpolar"". The rest are divided into ""seasonal"" stars and constellations. The stars and constellations that are circumpolar depends on the observer's latitude. In the Northern Hemisphere, certain stars and constellations will always be visible in the northern circumpolar sky. The same"
"F-type main-sequence star An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K. This temperature range gives the F-type stars a yellow-white hue. Because a main-sequence star is referred to as a dwarf star, this class of star may also be termed a yellow-white dwarf. Famous examples include Procyon A, Gamma Virginis A and B, and KIC 8462852. The revised Yerkes Atlas system (Johnson & Morgan 1953) listed a dense"
"Chemically peculiar star In astrophysics, chemically peculiar stars (CP stars) are stars with distinctly unusual metal abundances, at least in their surface layers. Chemically peculiar stars are common among hot main sequence (hydrogen-burning) stars. These hot peculiar stars have been divided into 4 main classes on the basis of their spectra, although two classification systems are sometimes used: The class names provide a good idea of the peculiarities that set them apart from other stars on or near the main sequence. The Am stars (CP1 stars) show weak lines of singly ionized Ca and/or Sc, but show enhanced abundances of"
"dwarf, to the current CH-classed star. CH star CH stars are particular type of carbon stars which are characterized by the presence of exceedingly strong absorption bands due to CH (methylidyne) in their spectra. They belong to the stellar population II, meaning they are metal poor and generally pretty middle-aged stars, and are under-luminous compared to the classical C–N carbon stars. The term 'CH star' was coined by Philip C. Keenan in 1942 as a sub-type of the C classification, which he used for carbon stars. The main molecular feature used in identifying the initial set of five CH stars"
"are two other stars, designated AR Cassiopeiae C and D, respectively. They are 76.1″ (or about 1.27′) away from the central system. Their combined spectrum matches that of another B-type main-sequence star. This pair is also designated HD 221237. 67.2″ (1.12′) away from AR Cassiopeiae AB is another pair of stars, F and G, both F-type stars. All four of these stars are known to be common proper motion companions. AR Cassiopeiae AR Cassiopeiae (AR Cas) is a multiple star system in the constellation of Cassiopeia. It is thought to be a septuple star system. It is one of only"