An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 222
van den Bergh catalogue (vdB)
kâtâlog-e van den Bergh

Fr.: catalogue de van den Bergh   

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

van der Waals equation
  هموگش ِ وان در والس   
hamugeš-e van der Waals

Fr.: équation de van der Waals   

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.

van der Waals force
  نیروی ِ وان در والس   
niru-ye van der Waals

Fr.: force de van der Waals   

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.

vânâdiom (#)

Fr.: vanadium   

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.

  ۱، ۲) پره؛ ۳) بادنما   
1, 2) parré (#); 3) bâdnemâ (#)

Fr.: 1) aile, pale; 2) barbe; 3) girouette   

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.


Fr.: 1, 2) disparaître, se volatiser; 3) s'en aller   

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.

boxâr (#)

Fr.: vapeur   

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.


Fr.: vaporisation, évaporation   

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

Verbal noun of → vaporize.

  ۱) بخاریدن؛ ۲) بخاراندن   
1) boxâridan; 2) boxârândan

Fr.: 1) s'évaporer; 2) évaporer   

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

vapor + → -ize.


Fr.: variabilité   

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

Quality noun from → variable.

variability index
  دیشن ِ ورتندگی   
dišan-e vartandegi

Fr.: indice de variabilité   

A measure of variability of a star (such as Welch-Stetson variability index) which combines the information from two passbands assuming that changes in the star's luminosity occur nearly simultaneously at all optical wavelengths.

variability; → index.


Fr.: variable   

Something that may or does vary. → variable star.
Math.: A symbol, usually a letter, which in a mathematical or logic expression represents any member of a set of possible values or possible objects.

M.E., from O.Fr. variable, from L. variabilis "changeable," from variare "to change," → vary.

Vartandé agent noun from vartidan "to change," → vary.

variable star
  ستاره‌ی ِ ورتنده   
setâre-ye vartandé

Fr.: étoile variable   

A star whose luminosity changes over periods of time; there are many reasons and many types. → cataclysmic variable; → Cepheid; → pulsating star; → nova; → long-period variable; → short-period variable; → Luminous Blue Variable (LBV); etc.

variable; → star.

variable star designation
  نامگزینی ِ ستاره‌ی ِ ورتنده   
nâmgozini-ye setâre-ye vartandé

Fr.: designation des étoiles variables   

A set of conventions used for naming → variable stars. Stars with existing → Bayer designations are not given new designations. Alternatively, the letters R through Z are used followed by the Latin genitive of the name of the hosting constellation. Otherwise, two letters of alphabet are used (334 combinations) with the Latin genitive of the name of the constellation. Finally, the letter V (variable) is used followed by numbers 335, 336, and so on. Some examples are: → P Cygni, → T Tauri, → FU Orionis, → EX Lupi, and → V2052 Oph.

variable; → star; → designation.


Fr.: variance   

A measure of the scatter of the values of a random variable (X) about its mean (μ). Var(X) = E(X -μ)2. The positive square root of the variance is called the → standard deviation.

M.E., from O.Fr. variance, from L. variantia, from variare "to change," → vary.

Vartâyi quality noun from vartâ agent noun from vartidan, → vary.


Fr.: variante   

1) Liable to or displaying variation.
2) Something that differs from a standard or type. For example, a different form of the same word.


  ورتنده‌ی ِ کاتوره   
vartande-ye kâturé

Fr.: variable aléatoire   

A quantity which may take any of the values of a specified set with a specified relative frequency or probability. The variate is therefore often known as a → random variable.

L. variatus, p.p. of variare, → vary, + → -ate.

variable; → random.


Fr.: variation   

1) General: An instance of changing, or something that changes.
2) Astro.: The periodic inequality in the Moon's motion that results from the combined gravitational attraction of the Earth and the Sun. Its period is half the synodic month, that is 14.77 days, and the maximum longitude displacement is 39'29''.9.
See also: → calculus of variations, → annual variation, → secular variation.

M.E., from O.Fr. variation, from L. variationem (nominative variatio) "difference, change," from variatus, p.p. of variare "to change," → vary.

Varteš, verbal noun from vartidan, → vary.


Fr.: variationnel   

Of or describing a → variation.

variation; → -al.

variational principle
  پروز ِ ورتشی   
parvaz-e varteši

Fr.: principe variationnel   

Any of the physical principles that indicate in what way the actual motion of a state of a mechanical system differs from all of its kinematically possible motions or states. Variational principles that express this difference for the motion or state of a system in each given instant of time are called → differential. These principles are equally applicable to both → holonomic and → nonholonomic systems. Variational principles that establish the difference between the actual motion of a system during a finite time interval and all of its kinematically possible motions are said to be → integral. Integral variational principles are valid only for holonomic systems. The main differential variational principles are: the → virtual work principle and → d'Alembert's principle.

variational; → principle.

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