An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Lorentz contraction
  ترنگش ِ لورنتز   
terengeš-e Lorentz

Fr.: 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 Lorentz

Fr.: 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 jerm

Fr.: 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-yi

Fr.: 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-yi

Fr.: 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-yi

Fr.: 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 nuleš

Fr.: 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 nuri

Fr.: 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 žirâ

Fr.: optiquement actif   

Relating to → optical activity.

optically; → active.

packing fraction
  برخه‌ی ِ انباشتگی   
barxe-ye anbâštegi (#)

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; anbâštegi quality noun of anbâštan, anbârdan "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   
didgašti

Fr.: parallactique   

Of or pertaining to a parallax.

Adj. form of → parallax.

parallactic angle
  زاویه‌ی ِ دیدگشتی   
zâviye-ye didgašti

Fr.: 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 didgašt

Fr.: 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 didgašti

Fr.: 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; → inequality.

parallactic motion
  جنبش ِ دیدگشتی   
jonbeš-e didgašti

Fr.: 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   
pirâkahkešâni

Fr.: périgalactique   

Of or pertaining to a → perigalacticon.

peri-; → galactic.

perigalacticon
  پیراکهکشان   
pirâkahkešân

Fr.: 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 qotbeš

Fr.: 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, varzidani

Fr.: praticable   

That can be done or used or put into practice.

practice; → -able.

practical
  ورزال   
varzâl

Fr.: pratique   

Concerned with practice, as opposed to → theory.

practice; → -al.

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