Synonyms of 'Astronomy terms'
achondritea rare stony meteorite that consists mainly of silicate minerals and has the texture of igneous rock but contains no chondrules aerolitea stony meteorite consisting of silicate minerals aerospacethe atmosphere and space beyond aerospherethe entire atmosphere surrounding the earth albedoalmucantar or almacantaran instrument for measuring altitudes altitudethe angular distance of a celestial body from the horizon measured along the vertical circle passing through the body analemmaannular eclipsean eclipse of the sun in which the moon does not cover the entire disc of the sun, so that a ring of sunlight surrounds the shadow of the moon antheliona faint halo sometimes seen in polar or high altitude regions around the shadow of an object cast onto a thick cloud bank or fog aphelionthe point in its orbit when a planet or comet is at its greatest distance from the sun apocynthionthe point at which a spacecraft in lunar orbit is farthest from the moon apolunethe point in a lunar orbit when a spacecraft is at its greatest distance from the moon appulsea very close approach of two celestial bodies so that they are in conjunction but no eclipse or occultation occurs apoapsisapsis or apseeither of two points lying at the extremities of an eccentric orbit of a planet, satellite, etc, such as the aphelion and perihelion of a planet or the apogee and perigee of the moon. The line of apsides connects two such points and is the principal axis of the orbit asteroidany of numerous small celestial bodies that move around the sun mainly between the orbits of Mars and Jupiter. Their diameters range from 930 kilometres (Ceres) to less than one kilometre asteroid beltthe concentrations of asteroids that move around the sun mainly between the orbits of Mars and Jupiter astroblemea mark on the earth's surface, usually circular, formed by a large ancient meteorite impact atmosphereaureola or aureoleauroraaurora australisthe aurora seen around the South Pole aurora borealisthe aurora seen around the North Pole azimuththe angular distance usually measured clockwise from the north point of the horizon to the intersection with the horizon of the vertical circle passing through a celestial body barycentrea centre of mass, esp of the earth-moon system or the solar system basinbinary stara double star system comprising two stars orbiting around their common centre of mass. A visual binary can be seen through a telescope. A spectroscopic binary can only be observed by the spectroscopic Doppler shift as each star moves towards or away from the earth black dropblack holean object in space so dense that its escape velocity exceeds the speed of light blue stragglerbolidea large exceptionally bright meteor that often explodes brown dwarfa type of celestial body midway in mass between a large planet and a small star burstcataclysmic variableCepheid variableany of a class of variable stars with regular cycles of variations in luminosity (most ranging from three to fifty days). There is a relationship between the periods of variation and the absolute magnitudes, which is used for measuring the distance of such stars Chandrasekhar limitthe upper limit to the mass of a white dwarf, equal to 1.44 solar masses. A star having a mass above this limit will continue to collapse to form a neutron star chemospherechondritea stony meteorite consisting mainly of silicate minerals in the form of chondrules chromospherea gaseous layer of the sun's atmosphere extending from the photosphere to the corona and visible during a total eclipse of the sun circumlunarcircumpolarcircumsolarcircumstellarcislunarclusteran aggregation of stars or galaxies moving together through space collapsara collapsed star, either a white dwarf, neutron star, or black hole colour indexthe difference between the apparent magnitude of a star measured in one standard waveband and in a longer standard waveband, indicating its colour and temperature colureeither of two great circles on the celestial sphere, one of which passes through the celestial poles and the equinoxes and the other through the poles and the solstices comathe luminous cloud surrounding the frozen solid nucleus in the head of a comet, formed by vaporization of part of the nucleus when the comet is close to the sun cometa celestial body that travels around the sun, usually in a highly elliptical orbit: thought to consist of a solid frozen nucleus part of which vaporizes on approaching the sun to form a gaseous luminous coma and a long luminous tail companionthe fainter of the two components of a double star conjunctionthe position of a planet or the moon when it is in line with the sun as seen from the earth. The inner planets are in inferior conjunction when the planet is between the earth and the sun and in superior conjunction when the sun lies between the earth and the planet constellationany of the 88 groups of stars as seen from the earth and the solar system, many of which were named by the ancient Greeks after animals, objects, or mythological persons cooordinate systemCopernican systemthe theory published in 1543 by Copernicus which stated that the earth and the planets rotated around the sun and which opposed the Ptolemaic system coronathe outermost region of the sun's atmosphere, visible as a faint halo during a solar eclipse cosmiccosmogonythe study of the origin and development of the universe or of a particular system in the universe, such as the solar system cosmologythe branch of astronomy concerned with the evolution and structure of the universe cratera similarly shaped depression formed by the impact of a meteorite or exploding bomb crescentthe curved shape of the moon in its first or last quarters crustculminationthe highest or lowest altitude attained by a heavenly body as it crosses the meridian cuspeither of the points of a crescent moon or of a satellite or inferior planet in a similar phase dwarfdynamicseccentricecospherethe planetary ecosystem, consisting of all living organisms and their environment effective temperatureejectamatter thrown out of a crater by an erupting volcano or during a meteorite impact ellipseelongationemersionthe reappearance of a celestial body after an eclipse or occultation ephemerisa table giving the future positions of a planet, comet, or satellite epochequatorthe great circle of the earth with a latitude of 0°, lying equidistant from the poles; dividing the N and S hemispheres escape velocityequinoxevectionevolved starexospherethe outermost layer of the earth's atmosphere. It extends from about 400 km above the earth's surface extinctionthe dimming of light from a celestial body as it passes through an absorbing or scattering medium, such as the earth's atmosphere or interstellar dust faculaany of the bright areas on the sun's surface, usually appearing just before a sunspot and subject to the same 11-year cycle farsidefilamenta long structure of relatively cool material in the solar corona fireballflareshort for solar flare flocculusa marking on the sun's surface or in its atmosphere, as seen on a spectroheliogram. It consists of calcium when lighter than the surroundings and of hydrogen when darker galactic centregalactic equatorgalactic rotationgalaxyany of a vast number of star systems held together by gravitational attraction in an asymmetric shape (an irregular galaxy) or, more usually, in a symmetrical shape (a regular galaxy), which is either a spiral or an ellipse giantgravitationthe force of attraction that bodies exert on one another as a result of their mass heliocentricheliospherethe region around the sun outside of which the sun's influence is negligible and interstellar space begins immersion or ingressthe disappearance of a celestial body prior to an eclipse or occultation inclinationthe angle between a line on a graph and the positive limb of the x-axis inequalityinertiainferior planeteither of the planets Mercury and Venus, whose orbits lie inside that of the earth inner planetany of the planets Mercury, Venus, earth, and Mars, whose orbits lie inside the asteroid belt insolationthe quantity of solar radiation falling upon a body or planet, esp per unit area interplanetaryinterstellarionospherea region of the earth's atmosphere, extending from about 60 kilometres to 1000 km above the earth's surface, in which there is a high concentration of free electrons formed as a result of ionizing radiation entering the atmosphere from space jeta long thin feature extending from an active galaxy and usually observed at radio wavelengths light yeara unit of distance used in astronomy, equal to the distance travelled by light in one year, i.e. 9.4607 × 1012 kilometres or 0.3066 parsecs limblodestar or loadstara star, esp the North Star, used in navigation or astronomy as a point of reference luminositya measure of the radiant power emitted by a star lunarlunar eclipsemagnetospheremagnitudethe apparent brightness of a celestial body expressed on a numerical scale on which bright stars have a low value. Values are measured by eye (visual magnitude) or more accurately by photometric or photographic methods, and range from –26.7 (the sun), through 1.5 (Sirius), down to about +30. Each integral value represents a brightness 2.512 times greater than the next highest integral value major planeta planet of the solar system, as opposed to an asteroid (minor planet) maremassmass lossmass transfermergermeridianone of the imaginary lines joining the north and south poles at right angles to the equator, designated by degrees of longitude from 0° at Greenwich to 180° meridian passagemesospherethe atmospheric layer lying between the stratosphere and the thermosphere, characterized by a rapid decrease in temperature with height metallicitymetal ratiometeora very small meteoroid that has entered the earth's atmosphere. Such objects have speeds approaching 70 kilometres per second meteoritea rocklike object consisting of the remains of a meteoroid that has fallen on earth. It may be stony (chondrite), iron, or stony iron (pallasite) meteoroidany of the small celestial bodies that are thought to orbit the sun, possibly as the remains of comets. When they enter the earth's atmosphere, they become visible as meteors meteoroid streammeteor showera transient rain of meteors, such as the Perseids, occurring at regular intervals and coming from a particular region in the sky. It is caused by the earth passing through a large number of meteoroids (a meteor swarm) missing massmolecular clouda cool dense interstellar region composed of a wide variety of molecules, mainly hydrogen, plus some dust, in which stars are forming moonquakemoving clustermultiple stara system of three or more stars associated by gravitation nadirthe point on the celestial sphere directly below an observer and diametrically opposite the zenith naked singularityan infinitely dense point mass without a surrounding black hole nearsidenebulaany substance for use in an atomizer spray neutron stara star that has collapsed under its own gravity to a diameter of about 10 to 15 km. It is composed mostly of neutrons, has a mass of between 1.4 and about 3 times that of the sun, and a density in excess of 1017 kilograms per cubic metre new moonthe moon when it appears as a narrow waxing crescent nodeeither of the two points at which the orbit of a body intersects the plane of the ecliptic. When the body moves from the south to the north side of the ecliptic, it passes the ascending node; moving from the north to the south side, it passes the descending node north celestial polenorthern hemispherethat half of the globe lying north of the equator northern lightsnorthingnorth polar distancenovaa variable star that undergoes a cataclysmic eruption, observed as a sudden large increase in brightness with a subsequent decline over months or years; it is a close binary system with one component a white dwarf nucleosynthesisthe formation of heavier elements from lighter elements by nuclear fusion in stars nucleusthe central portion in the head of a comet, consisting of small solid particles of ice and frozen gases, which vaporize on approaching the sun to form the coma and tail nutationa periodic variation in the precession of the earth's axis causing the earth's poles to oscillate about their mean position oblatenessobliquitythe angle between the plane of the earth's orbit and that of the celestial equator, equal to approximately 23° 27′ at present observatoryoccultationoctantany of the eight parts into which the three planes containing the Cartesian coordinate axes divide space open clusteroppositionthe position of an outer planet or the moon when it is in line or nearly in line with the earth as seen from the sun and is approximately at its nearest to the earth orbitthe curved path, usually elliptical, followed by a planet, satellite, comet, etc, in its motion around another celestial body under the influence of gravitation orbital elementsorbital velocitythe velocity required by a spacecraft, satellite, etc, to enter and maintain a given orbit oscillating universeouter planetany of the planets Jupiter, Saturn, Uranus, Neptune, and (formerly) Pluto, whose orbit lies outside the asteroid belt parallaxthe angle subtended at a celestial body, esp a star, by the radius of the earth's orbit. Annual or heliocentric parallax is the apparent displacement of a nearby star resulting from its observation from the earth. Diurnal or geocentric parallax results from the observation of a planet, the sun, or the moon from the surface of the earth partial eclipsepenumbral eclipseperiapsisthe closest point to a central body reached by a body in orbit periastronthe point in the orbit of a body around a star when it is nearest to the star, esp applied to double-star systems percentreperigeethe point in its orbit around the earth when the moon or an artificial satellite is nearest the earth perihelionthe point in its orbit when a planet or comet is nearest the sun photospherephysical librationplagesplanetarya train of planetary gears planetary alignmentplanetary systemplanetesimalany of a number of small bodies formerly thought to have been drawn from the sun by the close passage of a star to the sun, eventually coalescing to form the planets planetoidplasmaspherepleriona filled-centre supernova remnant in which radiation is emitted by the centre as well as the shell polar axispoleeither of the two antipodal points where the earth's axis of rotation meets the earth's surface precessionthe motion of a spinning body, such as a top, gyroscope, or planet, in which it wobbles so that the axis of rotation sweeps out a cone precession of the equinoxesthe slightly earlier occurrence of the equinoxes each year due to the slow continuous westward shift of the equinoctial points along the ecliptic by 50 seconds of arc per year. It is caused by the precession of the earth's axis around the ecliptic pole, with a period of 25 800 years primarya celestial body around which one or more specified secondary bodies orbit prominencean eruption of incandescent gas from the sun's surface that can reach an altitude of several hundred thousand kilometres. Prominences are visible during a total eclipse. When viewed in front of the brighter solar disc, they are called filaments proper motionthe very small continuous change in the direction of motion of a star relative to the sun. It is determined from its radial and tangential motion protogalaxya cloud of gas in the early stages of its evolution into a galaxy protoplanetprotostara cloud of interstellar gas and dust that gradually collapses, forming a hot dense core, and evolves into a star once nuclear fusion can occur in the core Ptolemaic systemthe theory of planetary motion developed by Ptolemy from the hypotheses of earlier philosophers, stating that the earth lay at the centre of the universe with the sun, the moon, and the known planets revolving around it in complicated orbits. Beyond the largest of these orbits lay a sphere of fixed stars pulsating universepulsating variablequadraturequarterone fourth of the moon's period of revolution around the earth quasarany of a class of extragalactic objects that emit an immense amount of energy in the form of light, infrared radiation, etc, from a compact source. They are extremely distant and their energy generation is thought to involve a supermassive black hole located in the centre of a galaxy quasi-stellar objecta member of any of several classes of astronomical bodies, including quasars (strong radio sources) and quasi-stellar galaxies (no traceable radio emission), both of which have exceptionally large red shifts quietradiantthe point in space from which a meteor shower appears to emanate radio sourcea celestial object, such as a supernova remnant or quasar, that is a source of radio waves rayany of a number of bright streaks that radiate from the youngest lunar craters, such as Tycho; they are composed of crater ejecta not yet darkened, and extend considerable distances reciprocal massred gianta giant star towards the end of its life, with a relatively low temperature of 2000–4000 K, that emits red light red supergiantregolithretardationrevolutionthe orbital motion of one body, such as a planet or satellite, around another ringan enclosed space, usually circular in shape, where circus acts are performed ring plainrisingrotationrupessarossatellitea celestial body orbiting around a planet or star Schwarzschild radiusthe radius of a sphere (Schwarzschild sphere) surrounding a non-rotating uncharged black hole, from within which no information can escape because of gravitational forces scintillationthe twinkling of stars or radio sources, caused by rapid changes in the density of the earth's atmosphere, the interplanetary medium, or the interstellar medium, producing uneven refraction of starlight secondarya celestial body that orbits around a specified primary body sextileSeyfert galaxyany of a class of spiral galaxies having a very bright nucleus, possibly corresponding to an active period in the lives of all spiral galaxies shell stara type of star, usually of spectral type B to F, surrounded by a gaseous shell shepherd satellitesidereal timetime based upon the rotation of the earth with respect to the distant stars, the sidereal day being the unit of measurement singularitya hypothetical point in space-time at which matter is infinitely compressed to infinitesimal volume solarsolar constantthe rate at which the sun's energy is received per unit area at the top of the earth's atmosphere when the sun is at its mean distance from the earth and atmospheric absorption has been corrected for. Its value is 1367 watts per square metre solar eclipsesolar spectrumsolar systemthe system containing the sun and the bodies held in its gravitational field, including the planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune), the dwarf planets (Eris, Pluto, and Ceres), the asteroids, and comets solsticesouth celestial polesouthern hemispherethat half of the earth lying south of the equator southern lightssouthingsouth polar distancespacethe region beyond the earth's atmosphere containing the other planets of the solar system, stars, galaxies, etc; universe space-timespectral type or spectral classany of various groups into which stars are classified according to characteristic spectral lines and bands. The most important classification (Harvard classification) has a series of classes O, B, A, F, G, K, M, the series also being a scale of diminishing surface temperature spherulespiculea spiked ejection of hot gas occurring over 5000 kilometres above the sun's surface (in its atmosphere) and having a diameter of about 1000 kilometres spinara fast-spinning star or celestial mass spraystara hot gaseous mass, such as the sun, that radiates energy, esp as light and infrared radiation, usually derived from thermonuclear reactions in the interior, and in some cases as ultraviolet, radio waves, and X-rays. The surface temperature can range from about 2100 to 40 000°C star cloudstellarstellar evolutionthe sequence of changes that occurs in a star as it ages stellar structurestellar windstreams of ionized gas particles constantly emitted in all directions by a star Strömgren spheresublunar pointsubsolar pointsubstellar pointsunspotsunspot cyclesuperclustera giant cluster of galaxies, a cluster consisting of a number of smaller clusters supergiantany of a class of extremely large and luminous stars, such as Betelgeuse, which have expanded to a large diameter and are eventually likely to explode as supernovae superior planetany of the planets (Mars, Jupiter, Saturn, Uranus, Neptune, and (formerly) Pluto) whose orbit lies outside that of the earth supernovaa star that explodes catastrophically owing to either instabilities following the exhaustion of its nuclear fuel or gravitational collapse following the accretion of matter from an orbiting companion star, becoming for a few days up to one hundred million times brighter than the sun. The expanding shell of debris (the supernova remnant) creates a nebula that radiates radio waves, X-rays, and light, for hundreds or thousands of years symbiotic starsynodic periodsyzygyeither of the two positions (conjunction or opposition) of a celestial body when sun, earth, and the body lie in a straight line telluric lineterminatorterrestrial planettidal capturetidal forcetidal frictiontidethe cyclic rise and fall of sea level caused by the gravitational pull of the sun and moon. There are usually two high tides and two low tides in each lunar day total eclipsetotal magnitudethermospherean atmospheric layer lying between the mesosphere and the exosphere, reaching an altitude of about 400 kilometres where the temperature is over 1000°C traintransient lunar phenomenatriple startropical yeartropospherethe lowest atmospheric layer, about 18 kilometres (11 miles) thick at the equator to about 6 km (4 miles) at the Poles, in which air temperature decreases normally with height at about 6.5°C per km universal timeuniversethe aggregate of all existing matter, energy, and space variable starany star that varies considerably in brightness, either irregularly or in regular periods. Intrinsic variables, in which the variation is a result of internal changes, include novae, supernovae, and pulsating stars variationany change in or deviation from the mean motion or orbit of a planet, satellite, etc, esp a perturbation of the moon velocity dispersionvertical circlea great circle on the celestial sphere passing through the zenith and perpendicular to the horizon visual magnitudethe magnitude of a star as determined by visual observation white dwarfone of a large class of small faint stars of enormous density (on average 108 kg/m3) with diameters only about 1 per cent that of the sun, and masses less than the Chandrasekhar limit (about 1.4 solar masses). It is thought to mark the final stage in the evolution of a sun-like star white holea hypothetical portal in space through which matter and energy emerge: thought to be an outlet for black holes and a possible explanation for quasars zenithzenith distance ▷ See astronomy
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Word List of Astronomy terms from the Collins English Word Lists