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

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

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 de-excitation   فرو انگیزش   foru-angizešFr.: désexcitation   Transition from an excited energy state to a lower energy level, as in spectral line formation or particle emission from an atomic nucleus.From → de- + → excitation. de-projection   وا-فراشانش   vâ-farâšânešFr.: déprojection   A method for estimating the real orientation of a field and/or related velocities/separations from two-dimensional images.→ de-; → projection. decagon   ده‌بر، ده‌گوش   dahbar (#), dahguš (#)Fr.: décagone   A ten-sided → polygon. A decagon that is equilateral and equiangular is called a regular decagon. Each angle of a regular decagon is 144°. The central angle subtending any side is 36°. The ratio of the radius to the side of a regular decagon forms the → golden ratio.→ deca-; → -gon. decay constant   پایای ِ تباهی   pâyâ-ye tabâhiFr.: constante de désintégration   A constant of proportionality occurring in the formula expressing spontaneous → decay of → radionuclides. The number of atoms decaying is given by N = N0e-kt, where N0 is the number of nuclei in the given volume of the substance at instant t = 0, N is the number of nuclei at t, and k is decay constant. Decay constant is related to → half-life by τ = ln2/k, roughly 0.693/k.→ decay; → constant. deceleration   واشتاب   vâšetâb (#)Fr.: décéleration   The act or process of moving, or of causing to move, with decreasing speed. Sometimes called negative acceleration.Verbal noun of decelerate. deceleration parameter   پارامون ِ واشتاب   pârâmun-e vâšetâbFr.: paramètre de décéleration   A parameter designating the rate at which the expansion of the Universe would slow down owing to the braking gravitational effect of the matter content of the Universe. It is expressed by: q(t) = -R(t)R ..(t)/R .2(t), where R(t) represents the size of the Universe at time t. See also → expansion parameter; compare with → acceleration parameter.→ deceleration; → parameter. decimal fraction   برخه‌ی ِ دهدهی   barxe-ye dahdahiFr.: fraction décimale   A fraction expressed by using → decimal representation, as opposed to a vulgar fraction. For example, 2/5 is a vulgar fraction; 0.40 is a decimal fraction.→ decimal; → fraction. decimal representation   نمایش ِ دهدهی   nemâyeš-e dahdahiFr.: représentation décimale   A representation of a real number between 0 and 1, as written a = d1d2d3 ..., where each di is one of the digits 0, 1, 2, ..., 9. This means that a = d1 x 10-1 + d2 x 10-2 + d3 x 10-3+ ... decision   واسون   vâsunFr.: décision   The act or process of deciding. → rule of decision.Verbal noun of → decide. declaration   روناگش   runâgešFr.: déclaration   The act of declaring; announcement. 2) Something that is announced or proclaimed.Verbal noun of → declare. declension   واکیله   vâkiléFr.: déclinaison   The → inflection of nouns, pronouns, or adjectives for case, number, and gender.M.E. declenson, declynson (with suffix later assimilated to -sion), from O.Fr. declinaison, from L. declinatio, → declination declination   واکیلش   vâkilešFr.: déclinaison   1) Angular distance (symbol δ) from the celestial equator. One of the coordinates, with → right ascension, that defines the position of a heavenly body in the equator system. Declination is measured positively (+) north or negatively (-) south of the celestial equator from 0° to 90°. 2) Angle between geographic North and magnetic North (symbol D).Verbal noun of → decline; → -tion. declination axis   آسه‌ی ِ واکیلش   âse-ye vâkilešFr.: axe de déclinaison   The axis to which the telescope tube is fastened in an → equatorial mounting.→ declination; → axis. declination circle   پرهون ِ واکیلش، دایره‌ی ِ ~   parhun-e vâkileš, dâyeré-ye ~Fr.: cercle de déclinaison   For a telescope with an → equatorial mounting, a graduated circle attached to the → declination axis that shows the → declination to which the telescope is pointing.→ declination; → circle. decomposition   واهمنهش   vâhamnehešFr.: décomposition   The process or the state of breaking down a physical entity or an organic material.From → de- + → composition. decompression   واتنجش   vâtanješFr.: décompression   1) A gradual decrease in surrounding → pressure, especially the controlled decrease in pressure that divers undergo after working in deep water or breathing compressed air. 2) Computers: The restoration of compressed electronic data to their full size.→ de- + → compression. deconvolution   واهماگیش   vâhamâgišFr.: déconvolution   A mathematical operation that allows to restore the original input signal, such as an astronomical image or spectrum, to its state before being affected by the → atmospheric turbulence and the → transfer function of the instrument. → convolution.From → de- + → convolution. deconvolution algorithm   خوارزمیک ِ واهماگیش   xârazmik-e vâhamâgišFr.: logiciel de déconvolution, algorithme ~ ~   An algorithm used to improve the resolution of an image particularly when the convolving function is well defined. Also called deconvolution code. deconvolve   واهماگیشیدن   vâhamâgišidanFr.: déconvoluer   Verbal form of → deconvolution.From → de- + → convolve. decretion   وابال   vâbâlFr.: décrétion   A physical process that is contrary to accretion, referring to the outward direction of the mass flow from a star to its environment.From → de- "reversal, removal," + -cretion, from L. accretionem (nom. accretio, gen. accretionis) "a growing larger," from stem of accrescere, → accretion.