An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

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Number of Results: 13048 Search : far
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.

Wide Angle Search for Planets (WASP)
   WASP: جستجوی ِ سیاره با زاویه‌ی ِ گشاده   
WASP: josteju-ye sayâré bâ zâviye-ye gošâdé

Fr.: WASP: recherche à angle large de planètes   

An international collaboration, more accurately named SuperWASP, led by the United Kingdom, that aims at detecting → extrasolar planets by means of the → transit method. SuperWASP consists of two robotic observatories that operate continuously all year around, providing coverage of the sky in both hemispheres. The first, SuperWASP-North, is located on the island of La Palma. The second, SuperWASP-South, is located at the site of the South African Astronomical Observatory (SAAO). The observatories each consist of eight wide-angle cameras that simultaneously monitor the sky for → planetary transit events. Using the array of cameras makes it possible to monitor millions of stars simultaneously at an → apparent visual magnitude from about 7 to 13.

wide; → angle; → search; → planet.

wide binary
  درین ِ گشاده   
dorin-e gošâdé

Fr.: binaire écarté   

A binary system with semi-major axis as large as 10,000 → astronomical units.

wide; → binary.

wide field
  بزرگ-میدان   
bozog-meydân

Fr.: grand champ   

A telescope → field of view which covers a relatively large → angular area on the sky.

wide; → field.

Wide-field Infrared Survey Explorer (WISE)
  پویشگر برا‌ی ِ بردید ِ بزرگ-میدان در فروسرخ   
puyešgar barâye bardid-e bozorg-meydân dar forusorx

Fr.: Explorateur pour l'étude grand champ dans l'infrarouge   

A → NASA infrared astronomical → space telescope launched in December 2009 to carry out an → all-sky survey from 3 to 22 → microns. With its 40-cm → telescope telescope and → infrared cameras, WISE aimed at a wide variety of studies ranging from the evolution of → protoplanetary disks to the history of → star formation in normal galaxies. In early October 2010, after completing its prime science mission, the spacecraft ran out of → coolant that keeps its instrumentation cold. However, two of its four infrared cameras remained operational. Hence, NASA extended the NEOWISE portion of the WISE mission by four months, with the primary purpose of hunting for more → asteroids and → comets, and to finish one complete scan of the main → asteroid belt. In August 2013, the WISE telescope's mission was extended for more three years to search for asteroids that could collide with Earth.

wide field; → infrared; → survey; → explorer.

width
  پهنا   
pahnâ (#)

Fr.: largeur   

An extent from side to side; breadth; wideness. → bandwidth; → beamwidth; → equivalent width; → slitwidth.

From wide, M.E., O.E. wid (cf. Du. wijd, O.H.G. wit, Ger. weit) + -th a suffix forming nouns of quality or condition, M.E. -th(e); O.E. -thu, -th.

Pahnâ, from pahn "wide, broad," from Mid.Pers. pah(a)n; Av. paθana- "broad, wide, spacious."

Wiedemann-Franz law
  قانون ِ ویدمن-فرانتس   
qânun-e Wiedemann-Franz

Fr.: loi Wiedemann-Franz   

For all metals the ratio of the → thermal conductivity, κ, to the → electrical conductivity, σ, is directly proportional to the absolute temperature: K/σ = (1/3)(πk/e)2T, where k is → Boltzmann's constant and e the electron's charge.

Named after the German physicists Gustav Heinrich Wiedemann (1826-1899) and Rudolph Franz (1826-1902); → law.

Wien's displacement law
  قانون ِ جا-به-جایی ِ وین   
qânun-e jâ-be-jâyi-ye Wien (#)

Fr.: loi du déplacement de Wien   

The wavelength corresponding to the maximum emissive power of a black body is inversely proportional to the absolute temperature of the body: λmax.T = 0.29 cm-deg. Wien's law explains why objects of different temperature emit spectra that peak at different wavelengths. Hotter objects emit most of their radiation at shorter wavelengths; hence they will appear to be bluer. Wien's law was an early attempt to describe the → blackbody radiation. The law closely approximated the true shape of the blackbody spectrum at short wavelengths, but ultimately failed because it relied solely on classical physics. It was superseded by → Planck's radiation law, which correctly describes the blackbody spectrum at all wavelengths.

After the German physicist Wilhelm Wien (1864-1928), who found the law in 1896. He was awarded the 1911 Nobel Prize in physics; → displacement; → law.

Wiener-Khinchin theorem
  فربین ِ وینر-خینچین   
farbin-e Wiener-Khinchin

Fr.: théorème de Wiener-Khintchine   

A theorem used in signal processing whereby the → spectral density of a random signal is the → Fourier transform of the corresponding → autocorrelation function. In other words, the autocorrelation function and the spectral density function constitute a → Fourier transform pair. The Wiener-Khinchin theorem allows one to estimate the spectral density function from the Fourier transform of the autocorrelation function, which is easier to handle. The theorem has an important application particularly in radio astronomy. The two following → Fourier integrals are called the Wiener-Khinchin relations: K(τ) = ∫ J(f)e-iωτdf and J(f) = ∫ K(τ)eiωτ (both summed over -∞ to +∞), where K(τ) is the autocorrelation function and J(f) is the spectral density.

Named after Norbert Wiener (1894-1964), American mathematician, who first published this theorem in 1930, and Aleksandr Khinchin (1894-1959), Russian mathematician, who did so independently in 1934; → theorem.

wild
  توسن   
towsan (#)

Fr.: sauvage   

Living in a state of nature; not tamed or domesticated (Dictionary.com).

M.E., from O.E. wilde; cognate with Du., O.H.G. wildi, Ger. wild, Sw. vild.

Towsan "wild," cf. Av. disav- "a kind of night predator animal."

wildlife
  زیست ِ توسن، توسن-زیست   
zist-e towsan, towsan-zist

Fr.: vie sauvage   

Animals and plants living in their natural habitat.

wild; → life.

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