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: 218
Weyl's principle
  پروز ِ ویل   
parvaz-e Weyl

Fr.: principe de Weyl   

The → world lines of galaxies form in the 4D space-time a bundle of non-intersecting → geodesics orthogonal to a series of space-like hyperstructures (e.g. Narlikar 2002, An Introduction to Cosmology, 3rd Edition, Cambridge Univ. Press). Expressed differently: The world lines of galaxies, or "fundamental particles," form (on average) a space-time filling family of non-intersecting geodesics converging toward the past (Rugh & Zinkernagel, 2010, astro-ph/1006.5848). The statement is sometimes denoted postulate, assumption, or hypothesis. The importance of Weyl's principle is that it asserts that cosmic matter moves according to certain regularity requirements. See also → cosmological principle.

First introduced by the German mathematician Hermann Weyl (1885-1955) in 1923 in his Raum, Zeit, Materie; → principle.

Wezen
  وزن   
Vazn (#)

Fr.: Wezen   

The star δ Canis Majoris, magnitude 1.84. It is an F8 supergiant 1800 light-years away. Among bright stars, Wezen is one of the most distant and luminous. Its luminosity is 50,000 times that of the Sun. Other designations: Alwazn, Wesen, HR 2693, HD 54605.

From Ar. Al-wazn (الوزن) "weight."

Vazn, from Ar. Al-wazn, as above.

whale
  وال، نهنگ   
vâl, nahang (#)

Fr.: balleine   

1) Any of the larger ocean mammals, excluding the porpoises and dolphins, that breathe through a blowhole on the top of their head and have front flippers, no hind limbs, and a flat horizontal tail.
2) The constellation → Cetus.

M.E., O.E. hwæl, cf. O.S. hwal, O.N. hvalr, Swed. val, M.Du. wal, Du. walvis, O.H.G. wal, Ger. Wal, probably cognate with L. squalus and Pers. vâl, as below.

1) Mod.Pers. vâl, wâl, related to Mid.Pers. kar (mâhig) "whale (fish);" Av. kara- "a mythological fish;" also Mod.Pers. kuli "a kind of fish;" cf. L. squalus "a kind of large sea fish;" PIE (s)kwalo- "a large fish."
2) Pers. nahang originally "crocodile," from Mid.Pers. nihang "crocodile; hippopotamus," ultimately from Proto-Iranian *ni-θanj- "to drag down," since crocodiles drag down their preys underwater and drown them, from ni- "down, below," → ni- (PIE) , + θanj- "to draw, pull" (cf. Pers. farhang; sanjidan, etc.).

Wheatstone bridge
  پل ِ ویتستون   
pol-e Wheatstone

Fr.: pont de Wheatstone   

An device consisting of four → resistances in series, used to determine the value of an unknown electrical resistance when the other three resistances are known.

Named after Charles Wheatstone (1802-1875), British physicist, who extensively used the circuit (1843) but was not its inventor. Such an arrangement of four resistances was first used by Samuel Hunter Christie (1784-1865) in 1833; → bridge.

wheel
  چرخ   
carx (#)

Fr.: roue   

1) A solid disk or a rigid circular ring arranged to turn around an axle passed through the center.
2) Anything like a wheel in shape or function.

M.E. whel(e), O.E. hweol, hweogol, from PIE *k(w)e-k(w)lo- "wheel, circle;" cf. Gk. kyklos "circle, wheel;" L.L. cyclus; Mod.Pers. carx "wheel;" Av. caxra- "wheel;" Skt. cakra- "wheel, circle;" Rus. koleso "wheel."

Carx "wheel," akin to wheel, as above.

Wheeler-DeWitt equation
  هموگش ِ ویلر-دویت   
hamugeš-e Wheeler-DeWitt

Fr.: équation de Wheeler-DeWitt   

In → quantum gravity, an equation that describes the → wave function of the → Universe. It is an adaptation of the → Schrodinger equation but includes the curved space attributes of → general relativity.

Named after American theoretical physicists John Archibald Wheeler (1911-2008) and Bryce Seligman DeWitt (1923-2004).

whirl
  ۱) چرخیدن، گردیدن؛ ۲) چرخش، گردش   
1) carxidan, gardidan; 2) carxeš, gardeš

Fr.: 1) tourbillonner, tournoyer; 2) tourbillon, tournoiement   

1) To turn around or spin rapidly.
2) The act of whirling; rapid rotation. → whirlwind, → whirlpool, → dust whirl.

M.E. whirlen, from O.N. hvirfla "to whirl," akin to O.E. hwyrflung "turning, revolving."

rotate; → revolve.

whirlpool
  گرداب   
gerdâb (#)

Fr.: tourbillon   

A powerful water current moving rapidly in a circular manner, as that produced by the meeting of opposing currents, sucking down anything that comes within. → Whirlpool galaxy.

From whirl "to turn around," from M.E. whirlen, from O.N. hvirfla "to whirl," cognate with O.E. hweorfan "to turn;" + → pool "a body of water."

Gerdâb "whirlpool," from gerd from gardidan "to turn" (→ -tropic) + âb, → water.

Whirlpool galaxy (M51)
  کهکشان ِ گرداب   
kahkešân-e Gerdâb (#)

Fr.: galaxie du Tourbillon   

A large → spiral galaxy of type Sc seen → face-on in the constellation → Canes Venatici and lying about 31 million → light-years away. Also known as M51 and NGC 5194. It is interacting with a small irregular galaxy NGC 5195.

whirlpool; → galaxy.

whirlwind
  گردباد   
gerdbâd (#)

Fr.: tourbillon de vent   

A general term for a small-scale, rotating column of air. More specific terms are → dust whirl, → dust devil, → waterspout, and → tornado.

whirl; → wind.

whistler
  سوت‌زنی   
sutzani

Fr.: sifflement   

A whistling sound of descending pitch picked up by radio telescopes under certain circumstances. Whistlers are caused by radio waves from distant lightening flashes, which follow the lines of force of the Earth's magnetic field and are reflected back to Earth by the → ionosphere.

From M.E. whistler,; O.E. hwistlere, from hwistlian "whistle."

Sutzani "whistling," from "whistle," probably onomatopoeia + zani verbal noun from zadan "to make, to do," originally "to strike, beat; to do; to play an instrument" (Mid.Pers. zatan, žatan; O.Pers./Av. jan-, gan- "to strike, hit, smite, kill" (jantar- "smiter"); cf. Skt. han- "to strike, beat" (hantar- "smiter, killer"); Gk. theinein "to strike;" L. fendere "to strike, push;" Gmc. *gundjo "war, battle;" PIE *gwhen- "to strike, kill").

white
  سفید   
sefid (#)

Fr.: blanc   

Having the color of fresh snow or milk; reflecting nearly all the rays of sunlight. → white dwarf; → night.

M.E. whit(e); O.E. hwit, from P.Gmc. *khwitaz (cf. O.S., O.Fris. hwit, O.N. hvitr, Du. wit, O.H.G. hwiz, Ger. weiß, Goth. hveits); cognate with Pers. sefid, as below.

Sefid, sepid "white;" Mid.Pers. spêt; Av. spita- "white;" cf. Skt. śveta- "white;" Lith. sviesti "to shine," svaityti "to brighten;" cognate with E. white, as above.

white dwarf
  سفید‌کوتوله، کوتوله‌ی ِ سفید   
sefid kutulé, kutule-ye sefid (#)

Fr.: naine blanche   

A compact star of high surface temperature, low luminosity, and high density (105-108 g cm-3), with roughly the mass of the Sun (mean mass ~ 0.6 Msun) and the radius of the Earth (R ~ 0.01 Rsun), representing the end-point of the evolution of all stars with masses less then ~ 5-9 → solar masses. A white dwarf is what remains after the central star of a → planetary nebula fades and becomes cool. The → Chandrasekhar limit of 1.43 solar masses is the highest mass that a white dwarf can achieve before electron → degeneracy pressure is unable to support it. In the → Hertzsprung-Russell diagram, white dwarfs form a well-defined sequence around 8 magnitudes fainter than the main sequence. They are composed of a core of carbon and oxygen nuclei and degenerate electrons surrounded by a thin shell of helium and an outer skin of hydrogen. White dwarf's radiation is the leftover heat from the star's past when its core was an active nuclear reactor. The star slowly cools as heat escapes through the non-degenerate envelope. → white dwarf crystallization; → cooling time; → Mestel theory. The first white dwarf to be discovered was Sirius B, the → companion of Sirius. White dwarfs are divided into several types, according to their spectral features, which depend on the type of → shell burning that dominated as it became a → planetary nebula: → DA white dwarf; → DB white dwarf; → DC white dwarf; → DO white dwarf; → DZ white dwarf; → DQ white dwarf. For a review see Kepler and Brdaley (1995, Baltic Astron. 4, 166).

The term white dwarf was coined by the Dutch-American astronomer Willem Luyten (1899-1994) in 1922, from → white + → dwarf.

white dwarf cooling track
  راه ِ سردش ِ سفیدکوتوله   
râh-e sardeš-e sefid kutulé

Fr.: trajet de refroidissement de naine blanche   

In the → Hertzsprung-Russell diagram, the evolutionary track followed by a → low-mass or an → intermediate-mass star when it can no longer produce thermonuclear energy. The track starts at the end of the → horizontal branch to lead the star to a → white dwarf phase.

white; → dwarf; → cooling; → track.

white dwarf crystallization
  بلورش ِ سفیدکوتوله   
bolureš-e sefid kutulé

Fr.: cristallisation de naine blanche   

The most important phenomenon occurring during → white dwarf evolution, which results from its cooling. Crystallization is a → phase transition whereby → latent heat is released. At the cooler end of a white dwarf's life (→ cooling time), the → thermal energy of nuclei, which are positively charged ions, becomes small and the effects of electrostatic interaction on the motion of ions become important. The ions repel each other and their distribution will be such that the → Coulomb energy per ion is a minimum. This will cause the ions to form crystal-like lattice structures. As the star cystallizes it releases latent heat, providing an additional energy source that slows the cooling process compared to the → Mestel theory. Once the bulk of the white dwarf is crystalline, heat can travel through the star more easily and the white dwarf cools faster.

white; → dwarf; → crystallization.

white hole
  سوراخ ِ سفید، سفید‌چال   
surâx-e sefid, sefid-câl

Fr.: trou blanc   

A hypothetical opposite of the → black hole, from which particles and light pour out. However, there is a basic problem with white holes. Contrarily to black holes, no physical processes justify their existence. The appearance of a white hole is not due to any cause, it is acausal.

white; → hole.

white night
  شب ِ سفید   
šab-e sefid (#)

Fr.: nuit blanche   

The circumstance pertaining to polar latitudes in which when the Sun sets its center does not go beyond 6° below the horizon and the → twilight lasts all the night.

white; → night.

white noise
  نوفه‌ی ِ سفید   
nufe-ye sefid

Fr.: bruit blanc   

A random signal that has a relatively wide continuous range of frequencies of uniform intensity.

white; → noise.

why
  چرا   
cerâ (#)

Fr.: pourquoi   

For what cause or reason? On what account? wherefore; on account of which.

M.E., from O.E. hwi, hwy instrumental case of hwæt "who."

Cerâ, from Mid.Pers. ce rây "why; how," from "what" (→ because) + rây, → reason.

wide
  بزرگ، گشاد، گشاده   
bozrog (#), gošâd (#), gošâdé (#)

Fr.: grand, ouvert   

Having considerable or great extent from side to side; broad. → wide binary, → wide field.

From M.E., from O.E. wid; akin to Du. wijd, Ger. weit, Old Norse vithr.

Bozorg, → large.
Gošâd, gošâdé "opened; ample, broad," from gošudan "to open up, to loose," → resolve.

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