# An Etymological Dictionary of Astronomy and AstrophysicsEnglish-French-Persian

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 155 Search : ratio
 instantaneous acceleration   شتاب ِ لحظه‌ای   šetâb-e lahze-yiFr.: accélération instantanée   The → acceleration of a particle at time t defined by a = lim Δv/Δt = dv/dt. It is the limiting value of Δv/Δt at time t as both Δv and Δt approach zero. integration   دُرُستالش، دُرُستال‌گیری   dorostâleš, dorostâlgiriFr.: intégration   In calculus the operation which consists of finding the areas enclosed by curves through the summations of infinitesimals. The inverse process of differentiation.Verbal noun of → integrate. integration time   زمان ِ دُرُستالش   zamân-e dorostâlešFr.: temps d'intégration   The time during which a detector integrates the incoming photons.→ integration; → time. irrational number   عدد ِ ناوابری   adad-e nâvâbariFr.: nombre irrationnel   A → real number which cannot be exactly expressed as a ratio a/b of two integers. Irrational numbers have decimal expansions that neither terminate nor become periodic. Every → transcendental number is irrational. The most famous irrational number is √ 2.From ir- a prefix meaning "not," a variant of → in-, + → rational; → number. isotopic ratio   وابر ِ ایزوتوپی   vâbar-e izotopiFr.: rapport isotopique   The relative abundances of two isotopes of a given chemical element, such as D/H (deuterium/hydrogen), (carbon) 12C/13C, and (uranium) 235U/238U.→ isotopic; → ratio. iteration   ایترش   itarešFr.: itération   A computational process involving a succession of approximations, which consists of repeating the operation by inputting the outcome of each preceding operation to improve the final result until a desired accuracy is achieved. Compare → repetition.Verbal noun of → iterate. libration   هلازان، رخگرد   halâzân, roxgard (#)Fr.: libration   Small oscillations of a → celestial body about its mean position. The term is used mainly to mean the Moon's libration caused by the apparent wobble of the Moon as it orbits the Earth. The Moon always keeps the same side toward the Earth, but due to libration, 59% of the Moon's surface can be seen over a period of time. This results from three kinds of libration working in combination: → libration in longitude, → libration in latitude, and → diurnal libration. See also: → geometrical libration, → physical libration.L. libration- "a balancing."Halâzân "to and fro motion, oscillation," literally "a swing: a seat suspended by ropes on which a person may sit for swinging," from Gilaki halâcin "a swing," Ilâmi harazân "a swing," variants (Dehxodâ) holucin, holu "a swing," probably from Proto-Ir. *harz- "to send, to set." Roxgard, literally "turning the face," from rox, variant ru(y) "face, surface; aspect; appearance" (Mid.Pers. rôy, rôdh "face;" Av. raoδa- "growth," in plural form "appearance," from raod- "to grow, sprout, shoot;" cf. Skt. róha- "rising, height") + gard "turning, changing," from gardidan "to turn, to change" (Mid.Pers. vartitan; Av. varət- "to turn, revolve;" Skt. vrt- "to turn, roll," vartate "it turns round, rolls;" L. vertere "to turn;" O.H.G. werden "to become;" PIE base *wer- "to turn, bend"). libration in latitude   هلازان ِ ورونایی   halâzân-e varunâ-yiFr.: libration en latitude   A tiny oscillating motion of the Moon arising from the fact that the Moon's axis is slightly inclined relative to the Earth's. More specifically, the Moon's polar axis is tilted nearly 7° with respect to the plane of its orbit around Earth. Hence for half of each orbit we see slightly more of the north pole when its tipped toward us, and for the other half we see slightly more of its south pole. Libration in latitude displaces the mean center of the Moon north-south by between 6°.5 and 6°.9.→ libration; → latitude. libration in longitude   هلازان ِ درژنایی   halâzân-e derežnâyiFr.: libration en longitude   A tiny oscillating motion of the → Moon arising from the fact that the Moon's orbit is not a precise circle but rather an → ellipse. Therefore, Moon is sometimes a little closer to the Earth than at other times, and as a result its → orbital velocity varies a bit. Since the Moon's rotation on its own axis is more regular, the difference appears as a slight east-west oscillation. Libration in longitude is the most significant kind of libration. It varies between about 4°.5 and 8°.1 because of gravitational perturbations in the Moon's orbit caused by the Sun.→ libration; → longitude. linear acceleration   شتاب ِ خطی   šetâb-e xattiFr.: accélération linéaire   The rate of change of the → linear velocity with time. It is defined by the expression Δv/Δt and is equal to the → first derivative of the → linear velocity.→ linear; → acceleration. magnetocentrifugal acceleration   شتاب ِ مغنات-مرکزگریز   šetâb-e meqnât-markazgorizFr.: accelération magnetocentrifuge   The acceleration exerted on the plasma particles according to the → magnetocentrifugal model. mass-luminosity ratio   وابر ِ جرم-تابندگی   vâbar-e jerm-tâbandegiFr.: rapport masse-luminosité   The ratio of the mass of a system, expressed in solar masses, to its visual luminosity, expressed in solar luminosities. The Milky Way Galaxy has a mass-luminosity ratio in its inner regions of about 10, whereas a rich cluster of galaxies such as the Coma Cluster has a mass-luminosity ratio of about 200, indicating the presence of a considerable amount of dark matter.→ mass; → luminosity; → ratio. migration   موژش، کوچ   mužeš, kuc (#)Fr.: migration   1) The process or act of migrating; a migratory movement. 2) For an astronomical body, the process or act of changing its place over considerably large distances under the effect of certain physical forces. See, for example, → orbital migration; → Type I migration; → Type II migration. 3) Chem.: A movement or change of position of atoms within a molecule (Dictionary.com).→ migrate; → -tion. Kuc "the act of moving from a dwelling, a place to another, decamping, migration." mixing ratio   وابر ِ آمیزش   vâbar-e âmizešFr.:rapport de mélange   Mass of water vapor per mass of dry air; expressed as grams per kilogram. → humidity→ mixing; → ratio. molar concentration   دبزش ِ مولی   dabzeš-e moliFr.: concentration molaire   Of a gas included in the composition of a → gas mixture, the ratio of the number of moles of this gas to the total number of moles of all the gases in the mixture. Same as mole fraction and mole-fraction concentration.→ molar; → concentration. molecular vibration   شیوش ِ مولکولی   šiveš-e molekuliFr.: vibration moléculaire   The dynamical motion of chemically bound atoms which constantly change their position with each other. The vibration of molecules is treated within → quantum theory. Therefore, the energy of molecular vibration can only take → discrete values. To a first approximation, molecular vibrations can be approximated as → simple harmonic oscillator assigned to each mode.→ molecular; → vibration. National Aeronautics and Space Administration (NASA)   سازمان ِ فضانوردی ِ آمریکا   Sâzmân-e Fazânavardi-ye ÂmrikâFr.: NASA, Administration nationale de l'aéronautique et de l'espace   A federal agency of the United States government founded in 1958 for civil aeronautical research and space exploration, superseding the National Advisory Committee for Aeronautics (NACA). Its goals include improving human understanding of the universe, the solar system, and Earth and establishing a permanent human presence in space. NASA is headquarted at Washington, D.C., and operates several research, development, and test facilities, as follows alphabetically: 1) Ames Research Center; 2) Dryden Flight Research Facility at Edwards, California, used for flight testing and as a landing site for the Space Shuttle; 3) Glenn Research Center at Cleveland, Ohio, concerned with aircraft and rocket propulsion; 4) Goddard Space Flight Center; 5) Jet Propulsion Laboratory; 6) Johnson Space center; 7) Kennedy Space Center; 8) Langley Research Center at Hampton, Virginia, which carries out research in aeronautics and space technology; 9) Marshall Space Flight Center; 10) the Space Telescope Science Institute; 11) Stennis Space Center, near Bay St Louis, Mississippi, for testing rocket engines; and 12) Wallops Flight Facility on Wallops Island, Virginia, which manages NASA's sounding rocket and scientific balloon programs.→ national; → aeronautics; → space; administration, verbal noun of administer, from M.E. amynistre, from O.Fr. aministrer, from L. administrare "to serve, carry out, manage," from → ad- "to" + ministrare "to serve," from minister "servant, priest's assistant," from minus, minor "less," hence "subordinate," + comparative suffix *-teros.Sâzmân, → organization; fazâyi pertaining to fazâ, → space; Âmrikâ "United State of America." obscuration   تیره‌کرد، تیره‌شد   tirekard, tirešodFr.: obscurcissement   1) The act of obscuring. 2) The state of being obscured.→ obscure; → -tion. operation   آپارش   âpârešFr.: opération   1) General: An act or instance, process, or manner of functioning or operating. 2a) Math.: A mathematical process, as addition, multiplication, or differentiation. 2b) The action of applying a mathematical process to a quantity or quantities. 3) Computers: An action resulting from a single instruction.Verbal noun of → operate operational   آپارشی   âpârešiFr.: opérationnel   Pertaining to a process or series of actions for achieving a result.Adj. of → operation.