# 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: 316 Search : act
 Lorentz contraction   ترنگش ِ لورنتز   terengeš-e LorentzFr.: contraction de Lorentz   The decrease in the length of a body moving in the direction of its length as measured by an observer situated in that direction. The shortening factor is [1 - (v/c)2]1/2, where v is the relative velocity and c light speed.→ Lorentz; → contraction. Lorentz factor   کروند ِ لورنتز   karvand-e LorentzFr.: facteur de Lorentz   In → special relativity, an important parameter which appears in several equations, including → time dilation, → length contraction, and → relativistic mass. It is defined as γ = 1 / [1 - (v/c)2]1/2 = dt/dτ, where v is the velocity as observed in the reference frame where time t is measured, τ is the proper time, and c the → velocity of light. Same as Lorentz γ factor.→ Lorentz; → factor. mass fraction   برخه‌ی ِ جرم   barxe-ye jermFr.: fraction de masse   The fractional amount (by mass) of a given → chemical element or → nuclide in a given → chemical composition. In chemical composition studies of astrophysical objects the mass fractions of → hydrogen, → helium, and all the remaining chemical elements are usually denoted by the parameter X, Y, and Z, respectively. Their sum is defined as X + Y + Z = 1. The parameter Z is usually referred to as → heavy elements or → metals.→ mass; → fraction. meteoritic impact   برخورد ِ شخانه‌ای   barxord-e šaxâne-yiFr.: impact météoritique   A striking of a meteorite against another body, especially the solar system planets or satellites.→ meteoritic; → impact. nuclear reaction   واژیرش ِ هسته‌ای   vâžireš-e haste-yiFr.: réaction nucléaire   A process in which the energy, composition, or structure of an atomic nucleus changes.→ nuclear; → reaction. nuclear reactor   واژیرگر ِ هسته‌ای   vâžirgar-e haste-yiFr.: réacteur nucléaire   A device in which a nuclear fission chain reaction is maintained and controlled for the production of nuclear energy or radioactive isotopes.→ nuclear; → reactor. nulling fraction (NF)   برخه‌ی ِ نولش   barxe-ye nulešFr.: fraction de phase d'arrêt   The fraction of time that a → pulsar undergoes → pulse nulling. For most → nulling pulsars this fraction can range from zero (for the → Vela pulsar) to more than 50%.→ null; → -ing; → fraction. optical activity   ژیرندگیِ نوری   žirandegi-ye nuriFr.: activité optique   The property possessed by some substances and their solutions of rotating the plane of vibration of → polarized light. When a beam of → linearly polarized light is sent through an optically active substance, such as crystalline quartz and sugar solution, the direction of vibration of the emerging linearly polarized light is found to be different from the original direction. Those which rotate the → plane of polarization to the right, for an observer looking in the incoming beam, are called → dextrorotatory or right handed; those which rotate it to the left, → levorotatory or left handed. Optical activity may be due to an asymmetry of molecules of a substance (solutions of cane sugar) or it may be a property of a crystal as a whole (crystalline quartz).→ optical; → activity. optically active   نورانه ژیرا   nurâné žirâFr.: optiquement actif   Relating to → optical activity.→ optically; → active. packing fraction   برخه‌ی ِ انباشتگی   barxe-ye anbÃ¢štegi (#)Fr.: coefficient de tassement   The difference between the isotopic mass of a nuclide and its mass number divided by its mass number. The packing fraction is a measure of the stability of the nucleus.Packing, from the verb pack "to put together in a pack," from the noun pack, from M.E. pak, packe, from M.D. pac or perhaps M.L.G. pak; → fraction.Barxé, → fraction; anbÃ¢štegi quality noun of anbÃ¢štan, anbÃ¢rdan "to fill, to replete;" Mid.Pers. hambāridan "to fill;" from Proto-Iranian *ham-par-, from prefix ham- + par- "to fill;" cf. Av. par- "to fill," parav-, pauru-, pouru- "full, much, many;" O.Pers. paru- "much, many;" Mid.Pers. purr "full;" Mod.Pers. por "full, much, very;" PIE base *pelu- "full," from *pel- "to be full;" cf. Skt. puru- "much, abundant;" Gk. polus "many," plethos "great number, multitude;" O.E. full. parallactic   دیدگشتی   didgaštiFr.: parallactique   Of or pertaining to a parallax.Adj. form of → parallax. parallactic angle   زاویه‌ی ِ دیدگشتی   zâviye-ye didgaštiFr.: angle parallactique   Of an object in the sky, the angle between the → celestial pole, the object, and the → zenith. Since parallactic angle describes the orientation on the sky of the object for a particular observer, it can be an important quantity in some observations.→ parallactic; → angle. parallactic ellipse   بیضی ِ دیدگشت   beyzi-ye didgaštFr.: ellipse de parallaxe   The path on the sky of the apparent position of a star as seen from the Earth, due to the Earth's annual motion around the Sun.→ parallactic; → ellipse. parallactic inequality   ناهموگی ِ دیدگشتی   nâhamugi-ye didgaštiFr.: inégalité parallactique   An irregularity in the Moon's motion caused by the Sun's gravitational attraction, which sets the Moon ahead or behind its normal orbital position. The Moon is about 2 arcminutes ahead of its expected position at first quarter, and a similar amount behind at last quarter. parallactic motion   جنبش ِ دیدگشتی   jonbeš-e didgaštiFr.: mouvement parallactique   The proper motion of a star due to the effect of the Sun's motion relative to the → local standard of rest.→ parallactic; → motion. perigalactic   پیراکهکشانی   pirâkahkešâniFr.: périgalactique   Of or pertaining to a → perigalacticon.→ peri-; → galactic. perigalacticon   پیراکهکشان   pirâkahkešânFr.: périgalacticon   The point in an object's orbit around a galaxy when the object lies closest to the galactic center; opposite of → apogalacticon.→ peri- + → galaxy. polarization fraction   برخه‌ی ِ قطبش   barxe-ye qotbešFr.: fraction de polarisation   The ratio expressed by P = (Ipar - Iper) / (Ipar + Iper), where Ipar and Iper are the light intensities with the electric field vector respectively parallel and perpendicular to the incident beam.→ polarization; → fraction. practicable   ورز‌پذیر، ورزیدنی   varzpazir, varzidaniFr.: praticable   That can be done or used or put into practice.→ practice; → -able. practical   ورزال   varzâlFr.: pratique   Concerned with practice, as opposed to → theory.→ practice; → -al.