An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 1965 Search : ion

Fr.: unification   

1) The process of unifying or uniting; union.
2) The state or condition of being unified (

Verbal noun of → unify.

uniform circular motion
  جنبش ِ دایره‌ای ِ یکدیس، ~ ~ یکنواخت   
jonbeš-e dâyereyi-ye yekdis, ~ ~ yeknavâxt

Fr.: mouvement circulaire uniforme   

The motion of an object around a fixed point at a constant angular speed, and at constant radius.

uniform; → circular; → motion.

uniform motion
  جنبش ِ یکدیس، ~ ِ یکنواخت   
jonbeš-e yekdis, ~ yeknavâxt

Fr.: mouvement uniforme   

Motion at a constant → velocity. The state of rest is a special case of uniform motion. → accelerated motion; → inertial motion.

uniform; motion.


Fr.: union   

General: The act of uniting two or more things.
A number of persons, organizations, states, etc., joined or associated together for some common purpose, e.g. → International Astronomical Union (IAU).
Math.: A set containing all the elements of two or more sets being combined. It is represented by ∪.

M.E. from O.Fr. union from L.L. unionem (nominative unio) "oneness, unity," from unus, → one, cognate with Pers. yek, as below.

Yekâyeš, from yek, → one, + -ây- epenthetic vowel, + -eš verbal noun suffix, → -tion.

unitary transformation
  ترادیس ِ یکایی، ~ یکانی   
tarâdis-e yekâyi, ~ yekâni

Fr.: transformation unitaire   

A transformation whose reciprocal is equal to its Hermitian conjugate.

unitary; → transformation.

upper culmination
  بالست ِ زبرین   
bâlest-e zabarin

Fr.: culmination supérieure   

Same as → superior culmination.

upper; → culmination.

uranium conversion
  هاگرد ِ اورانیوم   
hâgard-e urâniom

Fr.: convesrion de l'uranium   

A chemical process converting the → yellowcake to → uranium hexafluoride. The uranium hexafluoride is heated to become a gas and loaded into cylinders. When it cools, it condenses into a solid.

uranium; → conversion.


Fr.: utilisation   

The act or process of utilizing.

Verbal noun of → utilize.

vacuum polarization
  قطبش ِ خلاء   
qotbeš-e xala'

Fr.: polarisation du vide   

A quantum field theory a process in which an electromagnetic field gives rise to virtual electron-positron pairs that in turn exert electromagnetic fields of their own, in a manner similar to classical dielectric polarization.

vacuum; → polarization.

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.


Fr.: vaporisation, évaporation   

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

Verbal noun of → vaporize.

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.: 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.

vector function
  کریای ِ برداری   
karyâ-ye bordâri

Fr.: fonction vectorielle   

A function whose value at each point is n-dimensional, as compared to a scalar function, whose value is one-dimensional.

vector; → function.

vector perturbation
  پرتورش ِ برداری   
partureš-e bordâri

Fr.: perturbation vectorielle   

The perturbation in the → primordial Universe plasma caused by → vorticity. These perturbations cause → Doppler shifts that result in → quadrupole anisotropy.

vector; → perturbation.


Fr.: végétation   

1) All the plants or plant life of a place.
2) (Botany) Plant life as a whole, especially the plant life of a particular region.
3) The act or process of vegetating.

Verbal noun from → vegetate.

velocity dispersion
  پاشش ِ تندا   
pâšeš-e tondâ

Fr.: dispersion de vitesses   

The → standard deviation of a velocity → distribution. It indicates how objects of the sample move relative to one another. Objects with similar velocities have a small velocity dispersion, whereas objects with very different velocities have a large velocity dispersion.

velocity; → dispersion.

velocity-distance relation
  باز‌آنش ِ تندا-دورا   
bâzâneš-e tondâ-durâ

Fr.: relation vitesse-distance   

The linear relation wherein all galaxies are moving away from one another, with velocities that are greater with increasing distance of the galaxy. Same as → Hubble's law.

velocity; → distance; → relation.

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