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

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 474
light cylinder
  استوانه‌ی ِ نور   
ostovâne-ye nur

Fr.: cylindre de lumière   

A cylinder of radius cP/(2π) around a → pulsar's spin axis, where P is the pulsar period and c the → speed of light. At this surface, the velocity of a hypothetical object that corotates with the → neutron star would reach the speed of light.

light; → cylinder.

light deflection
  واچفت ِ نور   
vâcaft-e nur

Fr.: déflexion de la lumière   

The deviation of a light ray by the gravitational field of a massive body. For example, stellar light passing near the Sun will be deviated by 1''.75 at the Sun's limb.

light; → deflection.

light echo
  پژواک ِ نوری   
pažvâk-e nuri (#)

Fr.: écho de lumière   

Reflection of light from a stellar outburst by successively more distant clouds of dust surrounding the star. For example, the light echoes from two shells of dust near supernova 1987A, or those of star V838 Mon.

light; → echo.

light element
  بن‌پار ِ سبک   
bonpâr-e sabok (#)

Fr.: élément léger   

In astrophysics, a chemical element that has an atomic number of one, two, or three, such as hydrogen, helium, and lithium; sometimes also beryllium and boron.

light; → element.

light pollution
  آلودگی ِ نوری   
âludegi-ye nuri (#)

Fr.: pollution lumineuse   

The inappropriate or excessive use of artificial light. It brightens the sky and has a particularly damaging effect on astronomical observations. More generally, light pollution can have serious environmental consequences for humans, wildlife, and our climate. Types of light pollution include: → glare, → skyglow, → light trespass, and → light clutter.

light; → pollution.

light ray
  پرتو ِ نور   
partow-e nur

Fr.: rayon de lumière   

An imaginary line directed along the path that the light follows. In other words, light pictured simply in terms of straight lines.

light; → ray.

light trespass
  ترارفت ِ نوری   
tarâraft-e nuri

Fr.: lumière intrusive   

A type of → light pollution which is light falling where it is not wanted or needed. Light trespass occurs when poorly shielded or poorly aimed fixtures cast light into unwanted areas, such as buildings, neighboring property, and homes. This light is a main contributor to → skyglow which interferes with astronomical instruments.

light; → trespass.

light year
  نور-سال، سال ِ نوری   
nur-sâl (#), sâl-e nuri (#)

Fr.: année-lumière   

light-year

light; → year.

light-gathering power
  توان ِ گرد‌آوری ِ نور   
tavân-e gerdâvari-ye nur (#)

Fr.: pouvoir collecteur de lumière   

The most important function of an astronomical telescope, which is directly related to the area (or to the square of the diameter) of the main mirror or lens.

light; gathering, from O.E. gadrian, gædrian "to gather, collect;" → power.

Tavân, → power; gerdâvari, verbal noun of gerd âvardan, from gerd "round; around" (Mid.Pers. girt "round, all around," O.Iranian *gart- "to twist, to wreathe," cf. Skt. krt "to twist threads, spin, to wind, to surround," kata- "a twist of straw;" Pali kata- "ring, bracelet;" Gk. kartalos "a kind of basket," kyrtos "curved") + âvardan "to bring," Mid.Pers. âwurtan, âvaritan; Av. ābar- "to bring, to possess," from prefix ā- + Av./O.Pers. bar- "to bear, carry," bareθre "to bear (infinitive)," bareθri "a female that bears (children), a mother;" Mod.Pers. bordan "to carry;" Skt. bharati "he carries;" Gk. pherein; L. fero "to carry;" nur, → light.

light-second
  نور-ثانیه، ثانیه‌ی ِ نوری   
nur-sâniyé, sâniye-ye nuri

Fr.: second-lumière   

The distance travelled by light in free space in one second. It is equivalent to 2.997924580 × 108 m or 2.998 × 105 km. This unit of length is mainly used in astronomy, telecommunications, and relativistic physics. Some quantities expressed in this unit are as follows. The mean diameter of the Earth: about 0.0425 light-seconds. The average distance from the Earth to the Moon: about 1.282 light-seconds. The diameter of the Sun: about 4.643 light-seconds. The average distance from the Earth to the Sun: 499.0 light-seconds.

light; → second.

light-time
  نور-زمان، زمان ِ نوری   
nur-zamân, zamân-e nuri (#)

Fr.: temps-lumière   

The time it takes for light, travelling at about 300 000 km per second, to travel a certain distance.

light; → time.

light-travel distance
  اپست ِ سفر ِ نور   
apest-e safar-e nur

Fr.: distance du voyage de la lumière   

The distance traversed by a photon between the time it is emitted and the time it reaches the observer. It is also referred to as the → look-back time.

light; → travel; → distance.

light-year
  نور-سال، سال ِ نوری   
nur-sâl (#), sâl-e nuri (#)

Fr.: année-lumière   

The distance that light travels in one year at about 300,000 km per second, i.e. 9.5 x 1012 km. It is equal to about 63,000 → astronomical units. See also → parsec.

light; → year.

lightguide
  نوربَر   
nurbar

Fr.: faisceau de fibres optiques; guide d'ondes optique   

A bundle of optical fibers arranged randomly for the purpose of transmitting energy, not an image.

light; → guide.

lightlike
  نورسان   
nursân

Fr.: genre lumière   

Of, pertaining to, or describing an → event on the → light cone.

light; → -like.

lightlike interval
  اندروار ِ نورسان   
andarvâr-e nursân

Fr.: intervalle genre lumière   

The space-time interval between two events if it is zero, i.e. ds2 = 0.

lightlike; → interval.

lightning
  آذرخش   
âzaraxš (#)

Fr.: foudre   

A → flash of light produced by an → electric discharge in response to the buildup of an → electric potential between → cloud and → Earth's surface, or between different portions of the same cloud.

Lightning, pr.p. of lightnen "make bright," extended form of O.E. lihting, from leht, → light.

Âzaraxš, from âzar "fire," variants âtaš, taš (Mid.Pers. âtaxš, âtur "fire;" Av. ātar-, āθr- "fire," singular nominative ātarš-; O.Pers. ātar- "fire;" Av. āθaurvan- "fire priest;" Skt. átharvan- "fire priest;" cf. L. ater "black" ("blackened by fire"); Arm. airem "burns;" Serb. vatra "fire;" PIE base *āter- "fire") + raxš "lightning, reflection of light," raxšidan "to shine, flash," variant deraxš, deraxšidan "to shine, radiate" (O.Pers. raucah-, Av. raocah- "light" (cf. Skt. roka- "brightness, light," Gk. leukos "white, clear," L. lux "light" (also lumen, luna), E. light, Ger. Licht, Fr. lumière; PIE base *leuk- "light, brightness"); cognate with Mod.Pers. words ruz "day," rowšan "bright, clear," foruq "light," and afruxtan "to light, kindle").

likelihood
  شدواری   
šodvâri

Fr.: vraisemblance   

1) The state of being likely or probable; a probability or chance of something.
2) In technical language likelihood is not synonymous for probability. Same as → likelihood function.

From → likely + -hood a suffix denoting state, condition, character, nature, etc., from M.E. -hode, -hod, O.E. -hād (cf. Ger. -heit).

Šodvâri, noun of šodvâr, → likely.

likelihood function
  کریای ِ شدواری   
karyâ-ye šodvâri

Fr.: fonction de vraisemblance   

A function that allows one to estimate unknown parameters based on known outcomes. Opposed to → probability, which allows one to predict unknown outcomes based on known parameters. More specifically, a probability refers to the occurrence of future events, while a likelihood refers to past events with known outcomes.

likelihood; → function.

likely
  شدوار   
šodvâr

Fr.: vraisemblable   

Probably or apparently destined; having a high probability of occurring or being true.

Perhaps from O.N. likligr "likely," from likr "like" (adj.).

Šodvâr, from šod past stem of šodan "to become, to be, to be doing, to go, to pass" + -vâr a suffix with several meanings "resembling, like, in the manner of; having, endowed with." The first element from Mid.Pers. šudan, šaw- "to go;" Av. šiyav-, š(ii)auu- "to move, go," šiyavati "goes," šyaoθna- "activity; action; doing, working;" O.Pers. šiyav- "to go forth, set," ašiyavam "I set forth;" cf. Skt. cyu- "to move to and fro, shake about; to stir," cyávate "stirs himself, goes;" Gk. kinein "to move;" Goth. haitan "call, be called;" O.E. hatan "command, call;" PIE base *kei- "to move to and fro."

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