bardid bâ gonj-e hyaddmand
Fr.: relevé limité en volume
A survey in which the observed objects are contained in a given volume of space.
von Zeipel paradox
pârâdxš-e von Zeipel
Fr.: paradoxe de von Zeipel
A → rotating star cannot simultaneously achieve → hydrostatic equilibrium and → rigid body rotation. The paradox can be solved if → baroclinic flows (essentially a → differential rotation and a → meridional circulation) are included. For a broader view of the subject see: M. Rieutord, 2006, in Stellar Fluid Dynamics and Numerical Simulations: From the Sun to Neutron Stars, ed. M. Rieutord & B. Dubrulle, EAS Publ., 21, 275, arXiv:astro-ph/0608431.
von Zeipel theorem
farbin-e von Zeipel
Fr.: théorème de von Zeipel
A theorem that establishes a relation between the → radiative flux at some → colatitude on the surface of a → rotating star and the local → effective gravity (which is a function of the → angular velocity and colatitude). For a rotating star in which → centrifugal forces are not negligible, the → equipotentials where gravity, centrifugal force, and pressure are balanced will no longer be spheres. The theorem states that the radiative flux is proportional to the local effective gravity at the considered colatitude, F(θ) ∝ geff (θ)α, where α is the → gravity darkening coefficient. As a consequence, the stellar surface will not be uniformly bright, because there is a much larger flux and a higher → effective temperature at the pole than at the equator (Teff (θ) ∝ geff (θ)β, where β is the → gravity darkening exponent. In → massive stars this latitudinal dependence of the temperature leads to asymmetric → mass loss and also to enhanced average → mass loss rates. Also called → gravity darkening. See also → von Zeipel paradox; → meridional circulation; → baroclinic instability; → Eddington-Sweet time scale.
Named for Edvard Hugo von Zeipel, Swedish astronomer (1873-1959), who published his work in 1924 (MNRAS 84, 665); → theorem.
von Zeipel's law
qanun-e von Zeipel
Fr.: loi de von Zeipel
Same as the → von Zeipel theorem.
A whirling mass of water or air.
From L. vortex, variant of vertex "whirlpool; whirlwind, an eddy of water, wind, or flame;" from stem of vertere "to turn," cognate with Pers. gardidan, as below.
Gerdšâr (on the model of gerdâb "whirlpool" and gerdbâd "whirlwind"), from gard present stem of gardidan "to turn, to change" (Mid.Pers. vartitan "to change, to turn;" Av. varət- "to turn, revolve;" cf. Skt. vrt- "to turn, roll," vartate "it turns round, rolls;" L. vertere "to turn;" O.H.G. werden "to become;" PIE base *wer- "to turn, bend") + šâr, from šâré, → fluid.
Of or pertaining to a → vortex.
Adj. from → vortex.
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.
A speech sound that is produced as a stream of air that is not obstructed or blocked in any way by the vocal organs, but only modulated by the position of the tongue, lips, etc.
A hypothetical small planet proposed in the 19-th century to exist in an orbit between Mercury and the Sun. In order to explain some characteristics of Mercury's orbit, the French astronomer Urbain Jean Joseph Le Verrier (1811-1877) hypothesized the presence of another planet, which he named Vulcan. Those particularities of Mercury's orbit were later explained by Albert Einstein's theory of general relativity.
L. Vulcanus in Roman mythology the blacksmith god of fire and volcanoes, a word of Etruscan origin
1) Characterized by ignorance of or lack of good breeding or taste.
From L. vulgaris, volgaris "of or pertaining to the common people, common, vulgar, low, mean," from vulgus "the common people, multitude, crowd, throng" (cognates: Skt. varga- "a company, group, section," Pers. jarga, as below, Gk. eilein "to press, throng," Welsh gwala "sufficiency, enough").
Jargvâr, from jarg, jarga, jargé "a group of people, a ring of men or beasts;" cf. Lori, Laki jarga "group, throng," jarra "bundle;" Kurd. jerge, cerge "assembly, club;" + -vâr a suffix denoting "suiting, befitting, resembling, in the manner of, possession."
Fr.: fraction d'entiers
Same as → common fraction.
M.E., from L. vulgaris, from vulgus "the common people," + -aris, → -ar.
Fr.: Petit Renard
The Little Fox. A faint constellation in the northern hemisphere, at 20h right ascension, +25° declination, between Cygnus and Aquila. Abbreviation: Vul; Genitive: Vulpeculae.
L. Vulpecua, from vulpes "fox," cognate with Pers. rubâh, as below, + diminutive suffix -cula, variant of → -ule.
Rubâhak "little fox," from rubâh
VY Canis Majoris (VY CMa)
VY Sag-e Bozorg
Fr.: VY Grand Chien
A → red supergiant star which is one of the largest and most intrinsically luminous stars in the sky. It has a radius of about 1,420 solar radii (→ solar radius) and a luminosity of 3 × 105 Lsun (→ solar luminosity). It is about 3,900 → light-years from the Earth. Excluding solar system bodies, VY CMa is the third brightest object in the sky at 10 µm. It has a large optical → reflection nebula, visible through even small telescopes, created by its prodigious mass loss (> 10-4 Msun per year). Its initial mass is estimated to be about 25 Msun and its current mass 17 Msun. Recent observations have shown the presence of submicron → dust grains, with an average radius of ~ 0.5 μm, in the ejecta. These grains are 50 times larger than those found in the diffuse → interstellar medium (P. Scicluna et al., 2015, A&A, 584L, 10S).
Fr.: étoile de type Vz
A class of → O-type stars whose spectra show He II 4686 absorption line much stronger than any other He line especially He II 4541 or He I 4471. Vz stars are thought to be young stars lying close to the → ZAMS (Walborn & Parker 1992, ApJ 399, L87). Alternatively, the Vz characteristics may be related to the wind properties rather than to the youth of the star (Martins et al., 2005, A&A 441, 735).