An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The electric potential difference expressed in volts.

From → volt.

Of, relating to electricity or electric currents, especially when produced by chemical action, as in a cell. → photovoltaic detector.

Alessandro Volta (1745-1827), Italian physicist, known for his pioneering work in electricity.

The amount of space occupied by a three-dimensional object or region of space, expressed in cubic units.

M.E. volum(e), from O.Fr. volume, from L. volumen (genitive voluminis) "roll (as of a manuscript), coil, wreath," from volvere "to turn around, roll."

Gonj "volume," gonjidan "to be contained or held; to hold;" gonjâyeš "capacity, holding, containing;" Mid.Pers. winj- "to be contained;" Proto-Iranian *uiac-/*uic-; cf. Skt. vyac- "to contain, encompass," vyás- "extent, content, extension;" L. uincire "to bind."

A survey in which the observed objects are contained in a given volume of space.

→ volume; → limited; → survey.

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; → paradox.

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) ∝ g_eff (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 (T_eff (θ) ∝ g_eff (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.

Same as the → von Zeipel theorem.

→ von Zeipel theorem; → law.

Meteo.: A whirling mass of water or air.
A pattern of rotation in which the rotation direction rotates by 360° along any path which surrounds the centre of the vortex.

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.
Meteo.: The rotation of air around a vertical axis.

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

Gerdšârigi, from gerdšâr→ vortex + -igi, → -ity.

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.

M.E., from O.Fr. vouel, from L. vocalis shortening of littera vocalis, literally "vocal letter," from  → vox "voice," cognate with Pers. âvâ, → phone, vâžé, → word.

Xodâvâ, literally "self-voice," as Ger. Selbstlaut, from xod-, → self-, + âvâ, → phone.

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.
2) Spoken by, or being in the language spoken by, the people generally; vernacular (Dictionary.com).

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."

Same as → common fraction.

M.E., from L. vulgaris, from vulgus "the common people," + -aris, → -ar.

→ common; → fraction.

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

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).

V and Y, following the → variable star designation scheme; → Canis Major.

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).

V indicating → main sequence, z for "zero age;" → star.

One of the most massive → star formation regions in the → Galaxy, situated in the constellation → Aquila at the junction point of the → Galactic bar and the → spiral arms. It lies at a distance of about 6 kpc from the Sun and covers a vast area of the → Galactic plane with l = (29° to 32°) and b = (-1° to + 1°). W 43 is a complex of more than 20 → molecular clouds in ¹³CO emission with systemic velocities ranging from 12 km s^-1 to 110 km s^-1. The total → virial mass is estimated to be several 10⁶Msun. Close to its center, W 43-Main is undergoing a remarkably efficient episode of → star formation and qualifies as a mini-starburst Among the 15 dense cores of W 43-Main (0.2 pc FWHM size and 5 × 10⁵ cm^-3 density), three extremely massive, → dense cores are potentially forming → massive stars: W 43-MM1 (M = 3600 Msun), W 43-MM2 (M = 1600 Msun), and W 43-MM3 (M = 1000 Msun). Adjacent to W 43-Main is a → giant H II region, illuminated by a cluster of → Wolf-Rayet and → OB stars, emitting ~ 10⁵¹ → Lyman continuum photons per second and a → far-infrared  → continuum luminosity of ~ 3.5 × 10⁶  Lsun. It is not yet clear what the impact is of this → starburst cluster on the W 43-Main cloud located 2-10 pc away. With its special characteristics, W 43 represents a type of molecular cloud complex which hosts high luminosity embedded clusters. Other well-known examples are W 49 and W 51 (e.g., Nguyen Luong et., 2013, arXiv:1306.0547).

Number 43 in the following catalog: Gart Westerhout, 1958, Bull. Astron. Inst. Netherlands, 14, 215, A survey of the continuous radiation from the galactic system at a frequency of 1390 Mc/s.

A → boson particle that, along with → Z boson, mediates the → weak force in particle interactions. Two kinds of W bosons exist, the W⁺ and its antiparticle W^-. With a mass of 80.4 GeV/c², the W boson is almost 100 times as massive as the → proton.

W for → weak; → boson.

A member of a class of → pulsating stars with a period of 1 to 35 days located in the → instability strip of the → H-R diagram. Also known as type II Cepheid variables, W Virginis stars are typically 1.5 mag fainter than classical Type I Cepheids and have a mass less than that of the Sun. They also exhibit a period-luminosity relation which is distinct, but works in a similar way to the relation for Type I Cepheids. Hence W Virginis stars can also be used to measure Galactic and extragalactic distances.

W, alphabetical letter; → variable star designation; → Virgo; → star.