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

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 3079 Search : on
wavefront tilt
  گرای ِ پیشان ِ موج   
gerâ-ye pišân-e mowj

Fr.: inclinaison du front d'onde   

The average slope in both the X and Y directions of a → wavefront or phase profile across the pupil of an optical system.

wavefront; → tilt.

waxing moon
  مانگ ِ فزاینده   
mâng-e fazâyandé (#)

Fr.: lune montante   

The circumstance when the phase of the Moon is increasing from → new moon to → full moon.

waxing; → moon.

weak emission-line central star (wel)
  ستاره‌ی ِ مرکزی با خط ِ گسیلی ِ نزار   
setâre-ye markazi bâ xatt-e gosili-ye nezâr

Fr.: étoile centrale à faibles raies d'émission   

A member of a class of cntral stars of planetary nebula, → CSPN, which have weaker and narrower emission lines than → Wolf-Rayet-like CSPNe (Tylenda et al. 1993, A&AS 102, 595).

weak; → emission; → line.

weak gravitational lensing
  لنزش ِ گرانشی ِ نزار   
lenzeš-e gerâneši-ye nezâr

Fr.: effet de lentille gravitationnelle faible   

A gravitational bending of light by structures in the Universe that distorts the images of distant galaxies. The distortion allows the distribution of → dark matter and its evolution with time to be measured, thereby probing the influence of → dark energy on the growth of structures. Weak gravitational lensing is generally difficult to identify in individual images, in contrast to → strong gravitational lensing (see, e.g., Bartelmann & Peter Schneider, 2001, Phys. Rept. 340, 291).

weak; → gravitational; → lensing.

weak interaction
  اندرژیرش ِ نزار، ~ کمزور   
andaržireš-e nezâr, ~ kamzvr

Fr.: interaction faible   

One of the fundamental forces of nature that accounts for some particle interaction, such as → beta decay (→ radioactivity), the decay of free → neutrons, → neutrino interactions, and so forth. It is short-ranged, dominating at distances of 10-16 cm and occurs at a rate slower than that of the → strong interaction by a factor of about 10-13, hence its name. Although the weak interaction also includes interactions in which no neutrinos are emitted, neutrino emission accompanies all weak interactions of interest to astrophysics. Weak interaction plays an important role in the evolution of the stars from birth to death. For example, the → proton-proton reaction is a weak interaction. Also called → weak force or → weak nuclear force.

weak; → interaction.

Weierstrass approximation theorem
  فربین ِ نزدینش ِ وایرشتراس   
farbin-e nazdineš-e Weierstrass

Fr.: théorème d'approximation de Weierstrass   

If a function φ(x) is continuous on a closed interval [a,b], then for every ε > 0 there exists a polynomial P(x) such that |f(x) - P(x)| <ε, for every x in the interval.

After German mathematician Karl Wilhelm Theodor Weierstrass (1815-1897); → approximation; → theorem.

weight concentration
  دبزش ِ وزنی   
dabzeš-e vazni

Fr.: concentration en poids   

of a gas included in the composition of a → gas mixture, the ratio of mass of this gas to the mass of the whole mixture. Same as → weight fraction and → weight-fraction concentration.

weight; → concentration.

weight fraction
  برخه‌ی ِ وزنی   
barxe-ye vazni

Fr.: fraction en poids   

Same as → weight concentration.

weight; → fraction.

weight-fraction concentration
  برخه‌ی ِ وزنی ِ دبزش   
barxe-ye vazni-ye dabzeš

Fr.: concentration en poids   

Same as → weight concentration.

weight; → fraction; → concentration.

western elongation
  درازش ِ باختری   
derâzeš-e bâxtari

Fr.: élongation ouest   

The position of a planet when it is visible in the eastern sky before dawn.

western; → elongation.

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.

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).

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.

Wilkinson Microwave Anisotropy Probe (WMAP)
     
WMAP

Fr.: WMAP   

A space telescope launched by NASA in 2001 which measures the temperature fluctuations in the → cosmic microwave background (CMB) radiation. It creates a full-sky map of the CMB, with a 13 arcminute resolution via multi-frequency observations. WMAP is the first mission to use a → Lagrangian point L2 as its permanent observing station at a distance of 1.5 million km. WMAP completed its prime two years of mission operations in September 2003 and is continuing in 2009 its observations for still several years to come. WMAP's measurements have played a considerable role in establishing the current standard model of cosmology. They are consistent with a Universe that is dominated by → dark energy, with negative pressure or a → cosmological constant. In this model, the age of the Universe is 13.73 ± 0.12 billion years. The current expansion rate of the Universe measured by the Hubble constant, is 70.5 ± 1.3 km·s-1 Mpc-1. The content of the Universe consists of 4.56% ± 0.15% ordinary → baryonic matter, 22.8% ± 1.3% → cold dark matter, and 72.6% ± 1.5% of → dark energy, that accelerates the → expansion of the Universe.

WMAP, short for Wilkinson Microwave Anisotropy Probe, in honor of David Todd Wilkinson (1935-2002), who had been a member of the mission's science team.

Wilson depression
  نشیب ِ ویلسون   
našib-e Wilson

Fr.: dépression de Wilson   

The depression on the → Sun's → photosphere associated with → sunspots and involving the → Wilson effect. The measured depression values vary between about 700 and 2,000 km.

Wilson effect; → depression.

Wilson effect
  اسکر ِ ویلسون   
oskar-e Wilson

Fr.: effet de Wilson   

A phenomenon in which the shape of → sunspots flattens as they approach the → Sun's limb due to the → solar rotation. More specifically, when a sunspot approaches the → solar limbs the width of the → penumbra, relative to the → umbra, on the side facing the center of the Sun seems to become narrower than on the side facing the limb. This phenomenon arises from a projection effect, and is due to a geometrical depression (the → Wilson depression) in the layers of constant → optical depth in sunspots (see, e.g., Sami K. Solanki, 2003, Sunspots: An overview, The Astron. Astrophys. Rev., 11, 153).

First noticed by Alexander Wilson (1714-1786); → effect.

Wilson-Bappu effect
  اسکر ِ ویلسون-باپو   
oskar-e Wilson-Bappu

Fr.: effet de Wilson-Bappu   

The strong correlation between the equivalent width of Ca II → H and K lines of a late-type giant or supergiant star with the absolute visual magnitude of the star.

O. C. Wilson & M. K. Vainu Bappu (1957, ApJ 125, 661); → effect.

wind accretion
  فربال ِ بادی، ~ پت باد   
farbâl-e bâdi, ~ pat bâd

Fr.: accrétion par vent   

A quasi-spherical accretion that is likely to occur in a → high-mass X-ray binary (HMXB) when the optical star of → early spectral class (O-B) does not fill its → Roche lobe, but has a significant → mass loss via → stellar wind. In → close binary systems another accretion regime, → disk accretion, occurs when the optical star overfills its Roche lobe.

wind; → accretion.

window function
  کریای ِ روزنه   
karyâ-ye rowzané

Fr.: fonction fenêtre   

A function whose value is zero outside a given interval. Applications of window functions include signal filtering and spectral analysis. The various types of windw functions include: → rectangular window, cosine window, triangular window, Gaussian window, Hanning window, and so on.

window; → function.

Wollaston prism
  منشور ِ وُلاستون   
manšur-e Wollaston (#)

Fr.: prisme de Wollaston   

An optical device for producing and analyzing polarized light. It divides incoming unpolarized light into two orthogonal, linearly polarized beams. It consists of two prisms of either quartz or calcite cemented together.

After the English scientist William Hyde Wollaston (1766-1828); → prism.

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