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

Logic: Of an argument, whether or not the conclusion follows logically from the premises and the allowable syllogisms of the logical system being used.

Quality noun from → valid.

A system of canyons located just south of the Martian equator. The system is about 4000 km long. The central individual troughs, generally 50 to 100 km wide, merge into a depression as much as 600 km wide. In places the canyon floor reaches a depth of 10 km, 6 to 7 times deeper than the Grand Canyon on Earth.

L. Valles Marineris "Mariner's Valleys," named after the Mars orbiter Mariner 9, which discovered the Martian canyon in 1971-72. → valley.

A long, narrow region of low land between ranges of mountains, hills, or other high areas, often having a river or stream running along the bottom.

M.E. valeie, valey, from O.Fr. valee "valley," from V.L. *vallata, from L. vallis "valley," of unknown origin.

Darré "valley," from Mid.Pers. dar, darrak "ravine, cleft;" cf. Skt. pradará- "cleft."

Math.: Magnitude; quantity; a numerical quantity assigned to a mathematical symbol.

M.E., from O.Fr. value "worth, value," noun use of feminine p.p. of valoir "be worth," from L. valere "be strong, be well, be of value."

Arzeš, verbal noun of arzidan "to be worth," arzân "worthy; of small value, cheap," arj "esteem, honour, price, worth;" Mid.Pers. arz "value, worth," arzidan "be worth," arzân "valuable;" Av. arəjaiti "is worth," arəja- "valuable," arəg- "to be worth;" cf. Skt. arh- "to be worth, to earn," árhant- "worthy person;" Gk. alphanein "to bring in as profit," alphein "to ear, obtain;" Lith. algà "salary, pay;" PIE base *alg^wh- "to earn; price, value."

Any device that halts or regulates the flow of a fluid through a passage, pipe, etc.

From L. valvae "leaves of a door."

Daricé, leterally "small door, window," → stop. Supâp, loan from Fr. soupape, from O.Fr. sourpape, probably from souspape "a blow under chin," from sous "under," from L. subtus, → sub-, + *pape "jaw," from paper, from L. pap(p)are "to eat."

A mechanism proposed by Eddington to explain → stellar pulsations. Same as the → kappa mechanism. In this analogy the stellar layer acts like a heat engine with radiation taking the role of stream. The expanding and contracting layer acts as the piston, and the opacity of the layer behaves as the valve mechanism (Eddington, 1917, The pulsation theory of → Cepheid variables, The Observatory 40, 290).

→ valve; → mechanism.

The ring-shaped regions of charged particles surrounding the Earth from 1 to 6 Earth radii into space. The charged particles are trapped in by the Earth's magnetic field. The inner belt is between 1.2 and 4.5 Earth radii and contains high-energy electrons and protons which originate mainly from interactions between cosmic rays and the upper atmosphere. The outer belt, located between 4.5 and 6.0 Earth radii, contains lower-energy charged particles mainly coming from the solar wind.

Named after James Van Allen (1914-2006), who discovered the belts in 1958 based on measurements made by Explorer 1, the USA's first successful artificial satellite; → belt.

In → Young's experiment of → interference with double apertures, if a monochromatic source is a considerable distance from the → aperture plane and aperture separation is small, → fringe visibility from an extended source is proportional to the → Fourier transform of the source's spatial distribution. The transform variable is the angular separation of the aperture-plane sampling points divided by the wavelength. The van Cittert-Zernike Theorem is at the heart of → aperture synthesis.

Developed independently by Dutch physicists Pieter Hendrick van Cittert (1889-1959) in 1934 and Frits Zernike (1888-1966) in 1939; → theorem.

A catalog of → reflection nebulae containing 158 objects. The catalog gives information for all BD and CD stars north of δ = -33 deg which are surrounded by reflection nebulosity visible on both the blue and red prints of the → Palomar Observatory Sky Survey .

van den Bergh, S., 1966, AJ, 71, 990; → catalog

An → equation of state that satisfactorily describes the behavior of → real gass over a wide range of temperatures and pressures. It is derived from considerations based on kinetic theory, taking into account to a first approximation the size of a molecule and the cohesive forces between molecules: (P + a / V²) (V - b) = RT, where P, V, and T are pressure, volume, and temperature and R the gas constant. a and b are characteristic constants for a given substance. For a = b = 0, the van der Waals equation reduces to the characteristic equation of an → ideal gas. See also → Dieterici equation.

Named after Dutch physicist Johannes Diderik van der Waals (1837-1923), Nobel Prize in Physics 1910; → equation.

A weak attractive force between neutral atoms and molecules arising from polarization induced in each particle by the presence of other particles. All molecules contain electrically charged particles, and even though the molecule as a whole is electrically neutral there do exist between molecules van der Waals attractive forces of electric origin.

Named after Dutch physicist Johannes Diderik van der Waals (1837-1923), Nobel Prize in Physics 1910; → force.

A soft, ductile, silver-grey metal; symbol V. → Atomic number 23; → atomic weight 50.9415; → melting point about 1,890°C; → boiling point 3,380°C; → specific gravity about 6 at 20°C; and → valence +2,+3, +4, or +5. → It is used in various alloys to increase its shock resistance.

Named 1830 by Swedish chemist Nils Gabriel Sefström (1787-1845), from Old Norse Vanadis, epithet of the goddess Freya, + → -ium.

1) A blade attached radially to a central axis, as in a windmill, propeller, revolving fin, or the like. → spider vane.
2) → wind vane.
3) The flat part of a bird's → feather.

M.E., from O.E. fana "flag;" cognate with Ger. Fahne "flag," Gothic fana "piece of cloth."

Parré, from parr, → feather.

1) To disappear from sight, especially quickly; become invisible.
2) To disappear by ceasing to exist; come to an end.
3) Math.: To become zero or to tend to zero.

M.E., from O.Fr. esvanir "disappear; cause to disappear," from L. evanescere "disappear, pass away, die out," from → ex- "out" + vanescere "to vanish," from vanus "empty," cognate with O.E. wanian "to lessen," wan "deficient;" O.N. vanta "to lack;" L. vacare "to be empty," vastus "empty, waste;" see below for Iranian cognates.

Venidan, from Kurd. ven "missing; away; absent," cf. Pers. vang "empty, empty-handed, poor;" related to Av. ūna- "deficient, empty," ū- "to be incomplete;" akin to Skt. vā- "to disappear, diminish," ūná- "deficient;" L. vanus "empty," as above.

1) To → conquer or subdue by superior force, as in battle.
2) To defeat in any contest or conflict; be victorious over (Dictionary.com).

O.Fr. venquis-, extended stem of veintre "to defeat," from L. vincere "to overcome, conquer."

Vânidan, from Mid.Pers. vânidan "to vanquish, to conquer;" cf. Av. van- "to vanquish, to defeat;" Skt. van- "to win, conquer;" O.E. winnan, E. win, PIE *uen- "to win, conquer."

The gaseous form of substances that are normally in liquid or solid form.

M.E. vapour, L. vapor "exhalation, steam, heat," of unknown origin.

Boxâr, loan from Ar. buxâr.

The equilibrium pressure of a vapor above its condensed phases (liquid or solid). In other words, the pressure of the vapor resulting from evaporation of a liquid (or solid) above a sample of the liquid (or solid) in a closed container. The vapor pressure varies with the temperature. As the temperature increases its the vapor pressure also increases, and conversely. The temperature at which the vapor pressure is equal to the atmospheric pressure is called the → boiling point. For example, at 20 °C, water would boil at a pressure of about 0.023 atm, or about a fortieth of atmospheric pressure.

→ vapor; → pressure.

The act of vaporizing. The state of being vaporized.
The rapid change of water into steam.

Verbal noun of → vaporize.

1) To become converted into vapor.
2) To cause to change into a vapor.

→ vapor + → -ize.

The quality, state, or degree of being variable or changeable.

Quality noun from → variable.