An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 222
violet
  بنفش   
banafš (#)

Fr.: violet   

A color at the opposite end of the visible spectrum from red, an effect of light with a wavelength between 4000 and 4500 Å. → ultraviolet.

M.E., from O.Fr. violete, diminutive of viole "violet," from L. viola, akin to Gk. ion "violet."

Banafš "violet," related to banafšé "violet flower;" Mid.Pers. vanafšak "violet flower."

violet layer
  لایه‌ی ِ بنفش   
lâye-ye banafš

Fr.: couche violette   

A layer of particles in the upper Martian atmosphere that scatter and absorbs electromagnetic radiation at shorter wavelengths, making the atmosphere opaque to blue, violet, and ultraviolet light.

violet; → layer.

Virgo
  دوشیزه   
Dušizé (#)

Fr.: Vierge   

The Maiden. A large constellation of the Zodiac, situated at the celestial equator with 13h right ascension, 2° south declination. The brightest star is the first magnitude → Spica, and there are seven others brighter than fourth magnitude. Because of the presence of a background galaxy cluster, → Virgo cluster, this constellation is especially rich in galaxies. Eleven of the brighter galaxies are listed in the → Messier catalog. Abbreviation: Vir; Genitive: Virginis.

L. virgo "maiden, unwedded girl or woman."

Dušizé "maiden, virgin;" Mid.Pers. dôšizag "maiden, virgin," related to duxtar, duxt "daughter" (O.Pers. *duxçi-; Av. dugədar-, duγdar-; cf. Skt. duhitár-, Gk. thygater; E. daughter; Ger. Tochter; PIE base *dhug(h)əter-); Manichean Mid.Pers. duxš "princess, girl of noble birth;" O.Pers. duxši- (Elamite du-uk-ši-iš) "royal princess" + diminutive suffix -izag, -izé (as in suffixed Fr. demoiselle, from V.L. *dominicella, from domin(a) "lady" + -i- + -cella diminutive suffix).

Virgo A
  دوشیزه A   
Dušizé A

Fr.: Virgo A   

The most powerful radio source in the constellation Virgo, among the thousands of galactic systems comprising the → Virgo Cluster. Optically, it is an elliptical galaxy (M87) with a luminous blue jet about 1500 pc long. It is also an X-ray source (3C 274, Virgo X-1, 2U 1228+12).

Virgo.

Virgo cluster
  خوشه‌ی ِ دوشیزه   
xuše-ye dušizé

Fr.: amas de la Viege   

The largest and nearest galaxy cluster to the Local Group. The Virgo cluster spans 120 square degrees on the sky and contains on the order of 2,000 galaxies. It is located at a distance of about 60 million light-years. It is an irregular cluster with no central concentration. The giant elliptical galaxy M87 is the most massive in the cluster.

Virgo; → cluster.

Virgo interferometer
  اندرزنش‌سنج ویرگو   
andarzaneš-sanj Virgo

Fr.: interféromètre Virgo   

A → Michelson interferometer using → laser beams designed to detect → gravitational waves. It consists of two 3-km-long arms, which house the various machinery required to form a → laser interferometer. The gravitational waves searched for have frequencies between 10 Hz and 10 kHz. Virgo has been designed and built by a collaboration between the French Centre National de la Recherche Scientifique (CNRS) and the Italian Istituto Nazionale di Fisica Nucleare (INFN). It is now operated and improved in Cascina, a small town near Pisa on the site of the European Gravitational Observatory (EGO), by an international collaboration of scientists from France, Italy, the Netherlands, Poland, and Hungary. The initial Virgo detector observed the sky between 2007 and 2011 together with the two interferometers of the → Laser Interferometer Gravitational-Wave Observatory (LIGO), located in the United States. Virgo underwent a major upgrade after a long shutdown period. The "Advanced Virgo" overhaul lasted 5-year and costed 23 million Euros. The upgraded observatory was inaugurated on 20 February 2017 and, notably, detected the → GW170817 event.

Named after the → Virgo cluster of galaxies whose stellar explosions it aims to detect; → interferometer.

Virgo supercluster
  اَبَر-خوشه‌ی ِ دوشیزه   
abar-xuše-ye Dušizé

Fr.: superamas de la Vierge   

The irregular supercluster that contains the Virgo cluster and the Local Group. At least 100 galaxy groups and clusters are located within its diameter of 110 million light-years. It is one of millions of superclusters in the observable Universe.

Virgo; → supercluster.

virial
  ویریال   
viriyâl

Fr.: viriel   

Of or pertaining to the interactive forces between components of a system, such as particles or molecules in a gas or stars in a cluster.
virial equation of state, → virial equilibrium, → virial mass, → virial parameter, → virial radius, → virial temperature, → virial theorem, → virialization.

From L. vires, plural of vis "strength," and by extension "force" or "energy," first used by Rudolf Clausius in the investigation of problems in molecular physics.

Viriyâl, loan from E., as above.

virial equation of state
  هموگش ِ حالت ِ ویریال   
hamugeš-e hâlat-e viriyal

Fr.: équation d'état du viriel   

In thermodynamics, a generalized → equation of state obtained when the → compression factor Z is expanded in terms of a power series, e.g.: Z = 1 + B(T) / Vm + C(T) / Vm2 + ...

virial; → equation of state.

virial equilibrium
  ترازمندی ِ ویریال   
tarâzmandi-ye viriyâl

Fr.: équilibre du viriel   

The condition of a physical system which obeys the → virial theorem.

virial; → equilibrium.

virial mass
  جرم ِ ویریال   
jerm-e viriyâl

Fr.: masse du viriel   

The mass of a cluster of stars or galaxies in statistical equilibrium derived by using the → virial theorem.

virial; → mass.

virial parameter
  پارامون ِ ویریال   
pârâmun-e viriyâl

Fr.: paramètre du viriel   

A dimensionless parameter that measures the ratio of thermal plus kinetic energies to gravitational energy of a physical system, such as a molecular cloud. The virial parameter is expressed as: αvir = 5σ2R / GM, where R and M are the radius and mass of the cloud respectively, σ is the one-dimensional → velocity dispersion inside the cloud, and G the → gravitational constant. It indicates whether a cloud could be bound or not. For molecular clouds that are confined by their surface pressure and for which self-gravity is unimportant, αvir is much larger than unity, whereas αvir is ~ 1 when the gravitational energy of a clump becomes comparable to its kinetic energy. See, e.g., Bertoldi & McKee, 1992 (ApJ 395, 140). See also → virial theorem.

virial; → parameter.

virial radius
  شعاع ویریال   
šo'â'-e viriyâl

Fr.: rayon du viriel   

The radius centered on a galaxy containing matter at 200 times the → critical density of the Universe.

virial; → radius.

virial temperature
  دمای ِ ویریال   
damâ-ye viriyâl

Fr.: température du viriel   

The mean temperature at which a gravitationally → bound system would satisfy the → virial theorem. For a system of mass M and radius R with constant density, the gravitational energy per unit mass is W = GM/R. The kinetic energy per unit mass is E = (3/2)kTvir, where k is → Boltzmann's constant and μ the mean molecular weight. According to the virial theorem, E = W/2, which leads to the virial temperature Tvir = (1/3)(GM/kR).

virial; → temperature.

virial theorem
  فربین ِ ویریال   
farbin-e viriyâl

Fr.: théorème du viriel   

A general equation applicable to a gravitationally → bound system of equal mass objects (stars, galaxies, etc.), which is stable against → dynamical disruption. It states that in such a system the average → gravitational potential energy (Wvir) is twice the average → kinetic energy (Kvir) of the system: Wvir = -2Kvir. This general proposition, first derived by Rudolf Clausius (1822-1888), has important applications in a variety of fields ranging from statistical mechanics to astrophysics. See also → virialization, → virial equilibrium, → virialized.

virial; → theorem.

virialization
  ویریالش   
viriayleš

Fr.: virialisation   

The process whereby a system of gravitationally interacting particles attains stability. The comparable mass components interact with each other, but the whole system does not expand or collapse. Virialization occurs when the → potential energy is twice the negative → kinetic energy: - Wvir = 2 Kvir (→ virial theorem). In the case of a → galaxy cluster, when the cluster is virialized the merging process and the collapse of matter have finished and the formation process of the galaxy cluster is considered to be done. A cluster has formed by → hierarchical clustering. Virialized clusters, in other words finished clusters, can be found by looking at their radius and density. A cluster is virialized when it satisfies the condition: Rvir ~ Rmax/2, where Rvir is the radius when the cluster is virialized and Rmax is the radius when the collapse starts. From this condition it follows that the object is 8 times denser at virialization than when the collapse started.

Verbal noun of → virialize.

virialize
  ویریالیدن   
viriyâlidan

Fr.: virialiser   

To undergo → virialization.

virial; → -ize.

virialized
  ویریالیده   
viriyâlidé

Fr.: virialisé   

That has undergone → virialization.

Past participle of → virialize.

virtual
  ویر‌آگین   
virâgin

Fr.: virtuel   

1) General: Having the efficacy without the material part; unreal but capable of being considered as real for some purpose.
2) Computers: Simulated by a computer (for reasons of experiment or convenience) of an entity that lacks some elements of total reality.

M.E., from M.L. virtualis, from L. virtus "manliness, excellence, potency, efficacy," from vir "man, human, husband, soldier," cf. Mid.Pers. vīr, wīr "man, hero;" Av. vīra- "man, human;" Skt. vīrá- "man, hero;" Lith. vyras "man, husband;" O.Ir. fer "man;" Goth. wair "man;" O.E. wer "man." In Roman philosophy, virtue became associated with virility and strength of character.

Virâgin from vir "intellect, mind, memory," variants bar, bir (Mid.Pers. vir, varm, vârom "mental faculty, memory, mind;" Av. vārəma, vārəm "according to one's wishes," from var- "to choose") + -âgin a suffix denoting "consisting of, similarity, possession."

virtual displacement
  جابجایی ِ ویر‌آگین   
jâbejâyi-ye virâgin

Fr.: déplacement virtuel   

In → analytical mechanics, any infinitesimal change in the configuration of a material system, consistent with any constraints acting on the system at a given instant. If the constraints are stationary (→ scleronomous), then the actual displacement of the system, in an infinitesimal length of time dt, coincides with one of its virtual displacements. In the case of time-dependent (→ rheonomous) constraints, the actual displacement of the system does not coincide with any of the virtual ones, since the conditions imposed by the constraints vary during the time dt.

virtual; → displacement.

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