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

Sounds made when speaking or singing.

M.E., from O.Fr. voiz, from L. vox "voice, sound, utterance, cry, call, speech, sentence, word," related to vocare "to call;" akin to Pers. âvâz "voice," as below.

Âvâz "voice, sound, song," related to âvâ "voice, sound, song" (both prefixed forms), bâng "voice, sound, clamour" (Mid.Pers. vâng), vâžé "word," variants vâj-, vâk-, vâ-, vâz-, vât-; Av. vacah- "word," vaocanghê "to decalre" (by means of speech), from vac- "to speak, say;" cf. Skt. vakti "speaks, says," vacas- "word;" Gk. epos "word;" L. vox "voice;" PIE base *wek- "to speak."

1) An empty space; a gap or opening; emptiness. → vacuum.
2) A large region of cosmic space without galaxies. The first of these voids to be discovered lies in the direction of → Bootes and is some 300 million → light-years across. It is estimated that voids take up about 98% of the volume of the Universe, with clusters of galaxies concentrated in the thin walls that surround them.

M.E. voide, from O.Fr. voide "empty, vast, wide, hollow," from L. vocivus "unoccupied, vacant," related to vacuus "empty," → vacuum.

Tohi "empty" (variants in dialects Tabari tisâ, Saraxsi, Lâsgardi, Sangesari tusâ, Aftari tussâ); Mid.Pers. tuhig; Av. taoš- "to become empty," pres. tusa-, caus. taošaya-, tusən "they lose their posture;" cf. Skt. tuccha-, tucchya- "empty;" L. tesqua, tesca "deserted place;" Rus. tošcij "hollow;" PIE base *teus- "to empty."

Double refraction occurring when a strong → magnetic field is applied to a vapor through which light is passing perpendicular to the field.

Named after Woldemar Voigt (1850-1919), a German physicist (1908, Magneto- und Elektro-optik, B. G. Teubner, Leipzig); → effect.

A spectral profile in which a → spectral line is broadened by two types of mechanisms, one of which alone would produce a & rarr; Gaussian profile (usually, as a result of the → Doppler broadening), and the other would produce a → Lorentzian profile.

After Woldemar Voigt (1850-1919), a German physicist; → profile.

The Flying Fish. A constellation in the southern hemisphere at 7h 40m right ascension, -70° declination. Originally called Piscis Volans, and invented by Johann Bayer (Uranometria, published in 1603). Abbreviation: Vol; Genitive: Volantis.

L. Volans "flying," from volare "to fly."

Mâhi-ye Parandé, from mâhi "fish" (Mid.Pers. mâhik; Av. masya-; cf. Skt. matsya-; Pali maccha-) + parandé "flying, flier," from paridan "to fly" (Mid./Mod.Pers. par(r) "feather, wing," Av. parəna- "feather, wing;" cp. Skt. parna "feather," E. fern; PIE *porno- "feather").

A substance that vaporizes at relatively low temperatures (e.g. H₂O, CO₂, CO, CH₄, NH₃, and so forth). The opposite of volatile is → refractory.

M.E., from M.Fr. volatile, from L. volatilis "fleeting, transitory, flying," from p.p. stem of volare "to fly," of unknown origin.

Parrâ "flying," from paridan "to fly in the air," → Volans.

In → planetary science, any of a group of → chemical elements and → chemical compounds with relatively low → boiling points that are associated with a planet's or moon's → crust and/or → atmosphere. For example, H, He, C, N, O are underabundant (relative to the solar → photospheric values) in all types of → meteorites, including the C1 → carbonaceous chondrites. Any heating of the meteorite parent body subsequent to its formation would tend to drive the volatile elements out of the rock, whence it sublimated into → interplanetary medium.

→ volatile; → element.

Of or relating to a volcano. Characterized by volcanoes.

→ volcano; → -ic.

The explosive ejection of superheated matter from a → volcano.

→ volcanic; → eruption.

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.

→ vent.

→ volcanic; → vent.

An opening in the Earth's → crust from which → lava, → ash, and hot → gases flow or are → ejected during an → eruption.

From It. vulcano, from L. Vulcanus, → Vulcan.

Âtašfešân, literally "fire disperser, dispersing fire," from âtaš, → fire, + fešân contraction of afšân, from afšândan "to spread, scatter," Mid.Pers. afšân "to spread, to scatter;" ultimately from Proto-Ir. *apašan-, from root *šan- "to shake" (Cheung 2007).

The SI unit of potential difference, defined as the difference of potentials across the ends of a conductor in which a power 1 watt is liberated when a current of 1 ampere flows through it.

In honor of the Italian scientist Alessandro Volta (1745-1827), known for his pioneering work in electricity and the invention of the first battery.

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.