An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < -it ang bis cit cre dim ele flu gra ima iso lum men nec opt per pri rad rel sim spe the uti vis > >>

Number of Results: 471 Search : ity
  دیاری، پدیداری   
diyâri, padidâri (#)

Fr.: visibilité   

1) General: The state or fact of being visible. → crescent Moon visibility, → Venus visibility.
2) Optics: → fringe visibility. See also: → visibility function, → visibility plane.
3) Meteo.: A measure of transparency of the atmosphere. The maximum horizontal distance at which objects can be identified. → turbidity.

visible + → -ity.

visibility function
  کریای ِ دیاری، ~ پدیداری   
karyâ-ye diyâri, ~ padidâri

Fr.: fonction de visibilité   

The → Fourier transform of a source's → brightness distribution, weighted by the characteristics of the → interferometer's antennas.

visibility; → function.

visibility plane
  هامن ِ دیاری، ~ پدیداری   
hâmon-e diyâri, ~ padidâri

Fr.: plan de visibilité   

In → interferometry, the projection of a → baseline onto the plane normal to the source direction defining a vector in (u,v) space, measured in wavelength units.

visibility; → plane.

visual acuity
  تیزنایی ِ دید   
tiznâyi-ye did

Fr.: acuité visuelle   

Same as → acuity of vision.

visual; → acuity.

volcanic explosivity index (VEI)
  دیشن ِ اسکفتندگی ِ آتشفشانی   
dišan-e oskaftandegi-ye âtašfešâni

Fr.: indice d'explosivité volcanique   

A logarithmic scale, ranging from 1 to 8, used to measure the intensity of volcano eruptions. The VEI is based on several factors: the degree of fragmentation of the volcanic products released by the eruption, the amounts of sulfur-rich gases that form stratospheric aerosols, the volume of the eruptions, their duration, and the height is reached. The largest eruptions (8) produce an amount of bulk volume of ejected → tephra of ~ 1,000 km3.

volcanic; → explosivity; → index.


Fr.: vorticité   

In fluid mechanics, a measure of the rate of rotational spin in a fluid. Mathematically, vorticity is a vector field defined as the curl of the velocity field: ω = ∇ x v.
Meteo.: The rotation of air around a vertical axis.

From L. vortic-, from → vortex + → -ity.

Gerdšârigi, from gerdšârvortex + -igi, → -ity.

wave-particle duality
  دوگانگی ِ موج-ذره   
dogânegi-ye mowj-zarré

Fr.: dualité onde-particule   

The principle admitted in → quantum mechanics that all particles have a wave-like nature and that waves have a particle aspect. The wave-particle duality is of fundamental importance in obtaining a realistic picture of the → elementary particles.
See also: → particle nature, → wave nature, → de Broglie hypothesis, → Davisson-Germer experiment.

wave; → particle; → duality.

weight of a tensor density
  وزن ِ چگالی ِ تانسور   
vazn-e cagâli-ye tânsor

Fr.: poids d'une densité de tenseur   

A constant the value of which is characteristic for any given → tensor density.

weight; → tensor; → density.

wind luminosity
  تابندگی ِ باد   
tâbandegi-ye bâd

Fr.: luminosité de vent   

The final kinetic energy of the → stellar wind expressed by: (1/2)Mdot.v2 = (1/2)(v/c)L For an O6 star, L ~ 3 x 105Lsun and v ~ 2000 km s-1, which give a wind luminosity of ~ 1 x 1037 erg s-1, about 1% of the → stellar luminosity. See also → photon tiring limit.

wind; → luminosity.

wind velocity
  تندای ِ باد   
tondâ-ye bâd

Fr.: vitesse de vent   

The speed at which the → stellar wind is forced away from the star. Wind velocities of → hot stars are directly measured from → P Cygni profiles, which indicate velocities from several hundred to several thousand km s-1. See also → escape velocity, → terminal velocity, → velocity law, → radiation-driven wind, → CAK model.

wind; → velocity.

zero-velocity surface
  رویه‌ی ِ تندای ِ صفر   
ruye-ye tondâ-ye sefr

Fr.: surface de vitesse nulle   

In the → restricted three-body problem, a surface which limits the region of space in which a small body can move. In the expression for the → Jacobi integral, the left side value is always positive or nul; hence the particle motion is confined to the region where U ≤ CJ. The surface that limits this region, defined by U = CJ, is called the zero-velocity surface.

zero; → velocity; → surface.

<< < -it ang bis cit cre dim ele flu gra ima iso lum men nec opt per pri rad rel sim spe the uti vis > >>