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

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

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 dispersion   پاشش   pâšeš (#)Fr.: dispersion   1) The resolution of white light into its component wavelengths, either by → refraction or by → diffraction. Dispersion is actually an effect in which radiations having → different wavelengths travel at different speeds in the medium. Since the → angle of refraction of each radiation vary as a function of its → wavelength, the component waves deviate from each other. 2) The rate of change of → refractive index with wavelength: dn/dλ. → Cauchy's equation shows that dispersion varies approximately as the inverse cube of the wavelength. 3) The selective → retardation of → radio waves when they propagate through a → plasma. As a result, higher → frequency waves from a → pulsar will arrive at the Earth before the lower frequencies due to the presence of → intervening → ionized gas in the → interstellar medium. → dispersion measure. 4) Statistics: The spread of values of a → variable around the → mean or → median of a → distribution.Verbal noun of → disperse. dispersion curve   خم ِ پاشش   xam-e pâšešFr.: courbe de dispersion   A graph displaying the variation of the → refractive index of a substance against the wavelength of the electromagnetic wave passing through the substance.→ dispersion; → curve. dispersion equation   هموگش ِ پاشش   hamugeš-e pâšešFr.: équation de dispersion   An equation representing the variation of → refractive index as a function of → wavelength; for example → Cauchy's equation and → Sellmeier's equation.→ dispersion; → equation. dispersion measure   اندازه‌ی ِ پاشش   andâze-ye pâšešFr.: mesure de dispersion   A parameter used in radio astronomy which describes the amount of dispersion in a radio signal due to its passage through an intervening plasma. It is proportional to the product of the interstellar electron density and the distance to the source.→ dispersion; → measure. dispersion relation   بازانش ِ پاشش   bâzâneš-e pâšešFr.: relation de dispersion   An equation that describes how the → angular frequency, ω, of a wave depends on its → wave number, k. For the simplest of waves, where the speed of propagation, c, is a constant, ω(k) = ck. If the → phase velocity depends on k, that is for a dispersive medium, the function ω(k) is nonlinear.→ dispersion; → relation. dispersive   پاشنده، پاششی   pâšandé, pâšešiFr.: dispersif   Tending or serving to disperse.From → disperse + → -ive. dispersive index   دیشن ِ پاششی   dišan-e pâšešiFr.: indice de dispersion   The reciprocal of the → dispersive power.→ dispersive; → index. dispersive medium   مدیم ِ پاشنده   madim-e pâšandéFr.: milieu dispersif   A medium in which the → phase velocity is a function of → wave number (→ frequency).→ dispersive; → medium. dispersive power   توان ِ پاشش   tâvân-e pâšešFr.: pouvoir dispersif   A measure of the ability of a medium to separate different colors of light. It is defined by: (n2 - n1)/(n - 1), where  n1 and n2 are refractive indices at two specified widely differing wavelengths, and n is the → index of refraction for the average of these wavelengths.→ dispersive; → power. displacement   جا-به-جایی   jâ-be-jâyi (#)Fr.: déplacement   Physics: A vector quantity that specifies the change of position of a body or particle from the mean position or position of rest. Geology: The offset of rocks caused by movement along a fault.From displace, from → dis- + place + -ment.Jâ bé jâyi, noun of jâ bé jâ literally "place to place," from jâ "place," from Mid.Pers. giyag "place," O.Pers. ā-vahana- "place, village," Av. vah- "to dwell, stay," vanhaiti "he dwells, stays," Skt. vásati "he dwells," Gk. aesa (nukta) "to pass (the night)," Ossetic wat "room; bed; place," Tokharian B wäs- "to stay, wait;" PIE base ues- "to stay, live, spend the night." displacement current   جریان ِ جا-به-جایی   jarayân-e jâ-be-jâyi (#)Fr.: courant de déplacement   In electromagnetism, a quantity which is not a real current (movement of charge), but has the units of current and has an associated magnetic field. The physical meaning of this displacement current is that a changing electric field makes a changing magnetic field.→ displacement; → current. display   ۱) نمودن، نمایاندن، نمایش‌دادن؛ ۲) نمایش   1) nemudan, nemâyândan, nemâyeš dâdan; 2) nemâyeš (#)Fr.: 1) visualiser; 2) visualisation   1a) To show; make visible. 1b) Of computers, to show the output data on a screen. 2a) The act of displaying. 2b) Of computers, a visual representation of information.From O.Fr. despleier "to unfold, spread out," from L. displicare "to scatter," from → dis- "un-, apart" + plicare "to fold, twist," from PIE base *plek- "to plait, twist" (cf. Gk. plekein "to plait," L. plectere "to plait, braid, intertwine," Av. frašna- "helmet" (in ərəzatô.frašna- "having a silver helmet" (epithet of Mithra), Skt. praśna- "turban," O.H.G. flehtan "to plait," Russ. plesti "to plait").Nemudan, nemâyândan "to show, display," from Mid.Pers. nimūdan, present stem nimây- "to show," from O.Pers./Av. ni- "down; into," → ni-, + māy- "to measure," cf. Skt. mati "measures," matra- "measure," PIE base *me- "to measure;" cf. Gk. metron "measure," L. metrum. displease   وازوشیدن   vâzušidanFr.: déplaire   1) To incur the dissatisfaction, dislike, or disapproval of; offend; annoy. 2) To be unpleasant; cause displeasure (Dictionary.com).→ dis-; → please. displeasure   وازوشه   vâzušéFr.: mécontentement, déplaisir   Dissatisfaction, disapproval, or annoyance.→ dis-; → pleasure. disqualification   واچونایش   vâcunâyešFr.: disqualification   An act or instance of disqualifying; the state of being disqualified.→ disqualify; → -tion. disqualified   واچوناییده، واچونامند   vâcunâyide, vâcunâmandFr.: non qualifié   (of a person) declared ineligible for an office, activity, or competition because of an offence or infringement (OxfordDictionaries.com).→ dis-; → qualified. disqualify   واچوناییدن، واچونامند کردن   vâcunâyidan, vâcunâmand kardan,Fr.: disqualifier   To deprive of qualification or fitness; render unfit; incapacitate (Dictionary.com).→ dis-; → qualify. disruption   گسیخت   gosixtFr.: rupture   Forcible division into pieces of an object. → tidal disruption.From L. disruptio "a breaking asunder," noun of action from p.p. stem of disrumpere "break apart, split, shatter, break to pieces," from → dis- "apart" + rumpere "to break."Gosixt, past stem of gosixtan "to tear away, to beark off." dissect   واسکنجیدن   vâsekanjidanFr.: disséquer   1) To cut apart (an animal body, plant, etc.) to examine the structure, relation of parts, or the like. 2) To examine minutely part by part; analyze: to dissect an idea (Dictionary.com).L. dissectus, p.p. of dissecare "to cut to pieces," from dissecare "cut in pieces," from → dis- "apart" + secare "to cut," → section.Vâsekanjidan, from vâ- "apart," → dis-, + sekanjidan "to cut to pices," cognate with šekastan "to break," → section. dissection   واسکنجش   vâsekanješFr.: dissection   The act of dissecting.→ dissect; → -tion.