An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < vac van var Vel ver ver vio vir vis vol vul > >>

Number of Results: 204

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.

virtual image
  تصویر ِ ویر‌آگین   
tasvir-e virâgin

Fr.: image virtuelle   

Optics: An image formed inside an instrument at the point where diverging rays would cross if they were extended backward into the instrument. Such an image cannot be obtained on a screen placed at its apparent position, since the rays do not pass through that point. → real image.

virtual; → image.

virtual observatory
  نپاهشگاهِ ویر‌آگین   
nepâhešgâh-e virâgin

Fr.: observatoire virtuel   

An international initiative by the astronomical community to allow global electronic access to the available astronomical data archives of space and ground-based observatories. It also aims to enable data analysis techniques through a coordinating entity that provides common standards, wide-network bandwidth, and state-of-the-art analysis tools. The Virtual Observatory is also intended for re-using data for scientific objectives different from the original ones, in order to optimize the science return of astronomical observations. The Virtual Observatory's capabilities are enabled through the use of standard protocols for registering the existence and location of data and for requesting data that satisfies the user's interests. These standards are developed on an international basis through the → IVOA. The cornerstone of the Virtual Observatory is → interoperability.

virtual; → observatory.

virtual particle
  ذرّه‌یِ ویر‌آگین   
zarr-ye virâgin

Fr.: particule virtuelle   

A subatomic particle that, according to the uncertainty principle, comes into being out of energy fluctuations of the "vacuum" and lasts for extremely short periods of time. An electron-positron pair can exist only about 4 x 10-21 seconds. The lifetime increases as the mass and energy involved decreases. Virtual particles are real and have measurable effects, but cannot be directly observed, according to the uncertainty principle. → vacuum polarization.

virtual; → particle

virtual work
  کار ِ ویر‌آگین   
kâr-e virâgin

Fr.: travail virtuel   

In → analytical mechanics, an element of work performed in a → virtual displacement by the → forces acting on all n particles of a → holonomic system with s degrees of freedom (→ degree of freedom).

virtual; → work.

virtual work principle
  پروز ِ کار ِ ویر‌آگین   
parvaz-e kâr-e virâgin

Fr.: principe du travail virtuel   

In → analytical mechanics, a principle whereby it is necessary and sufficient for the equilibrium of any material system with ideal constraints that the sum of the elements of work, performed by the applied forces acting on the system in any virtual displacement, be equal to zero (if all constraints are bilateral) or less than zero (if some of the constraints are unilateral).

virtual; → work; → principle.


Fr.: viscosimètre   

An instrument used to measure the → viscosity of a liquid. Same as viscosimeter.

viscosity; → -meter.


Fr.: viscosimètre   

Same as → viscometer.

viscosity; → -meter.

vošksâni (#)

Fr.: viscosité   

The property of a → fluid that resists the force tending to cause the fluid to flow. Viscosity may be thought of as the internal → friction of two fluid layers which flow parallel to each other at different speeds. The cause of viscosity is the transport of → momentum by the molecules from one layer to the other. Viscosity is given by η = φ.u.λ.ρ, where φ is a coefficient which depends on the nature of the interaction between the molecules, u is the average velocity of thermal motion of the molecules, λ is the → mean free path, and ρ the → density of the fluid. Also called → dynamic viscosity or → absolute viscosity. See also → kinematic viscosity.

Noun from → viscous; → -ity.

vošksân (#)

Fr.: visqueux   

Having the property of → viscosity. See also: → viscous dissipation, → viscous fluid, → viscous force, → nonviscous.

M.E., from M.Fr. viscous, from L. viscosus "sticky," from viscum "anything sticky; mistletoe."

From vošk "a kind of sticky gum" + -sân suffix of similarity, from sân "way, manner."

viscous dissipation
  افتال ِ وشکسان   
eftâl-e vošksân

Fr.: dissipation visqueuse   

A degradation of → mechanical energy that is irreversibly converted to → thermal energy due to → viscous forces in the → fluid. Viscous dissipation occurs in → turbulent flows.

viscous; → dissipation.

viscous fluid
  شاره‌ی ِ وشکسان   
šârre-ye vošksân (#)

Fr.: fluide visqueux   

A fluid whose viscosity is sufficiently large to make the viscous forces a significant part of the total force field in the fluid.

viscous; → fluid.

viscous force
  نیروی ِ وشکسان   
niru-ye vošksân

Fr.: force visqueuse   

The force per unit volume or per unit mass arising from the action of tangential stresses in a moving → viscous fluid.

viscous; → force.

  دیاری، پدیداری   
diyâri, padidâri (#)

Fr.: visibilité   

General: The state or fact of being visible.
1) Optics: If the intensity in an interference fringe pattern has the maximum and minimum values Imax and Imin, the visibility is defined by the relation ν = (Imax - Imin) / (Imax + Imin), where 0 ≤ ν ≤ 1. In terms of the intensities of the two interfering waves: ν = 2(I1 . I2)1/2/(I1 + I2).
2) Meteo.: A measure of transparency of the atmosphere. The maximum horizontal distance at which objects can be identified. → turbidity.

visible + → -ity.

visibility function
  کریای ِ دیاری، ~ پدیداری   
karyâ-ye diyâri, ~ padidâri

Fr.: fonction de visibilité   

The Fourier transform of a source's brightness distribution, weighted by the characteristics of the interferometer's antennas.

visibility; → function.

visibility plane
  هامن ِ دیاری، ~ پدیداری   
hâmon-e diyâri, ~ padidâri

Fr.: plan de visibilité   

In interferometry, the projection of a baseline onto the plane normal to the source direction defining a vector in (u,v) space, measured in wavelength units.

visibility; → plane.

  دیار، پدیدار، پیدا   
diyâr (#), padidâr (#), peydâ (#)

Fr.: visible   

Capable of being seen by, or perceptible to, the human eye.

M.E., from O.Fr. visible, from L. visibilis "that may be seen," from visus, p.p. of videre "to see;" cognate with Pers. bin, present stem of didan "to see" (Mid.Pers. wyn-; O.Pers. vain- "to see;" Av. vaēn- "to see;" cf. Skt. veda "I know;" Gk. oida "I know," idein "to see;" PIE base *weid- "to know, to see").

Diyâr "visible" in several dialects, e.g. štiyâni, Malâyeri, Širâzi, Tabari, related to didan "to see;" Mid.Pers. ditan "to see, regard, catch sight of, contemplate, experience;" O.Pers. dī- "to see;" Av. dā(y)- "to see," didāti "sees;" cf. Skt. dhī- "to perceive, think, ponder; thought, reflection, meditation," dādhye; Gk. dedorka "have seen."
Padidâr (→ phenomenon) and peydâ are both also related to dā(y)- (with prefixes).

visible horizon
  افق ِ پدیدار، ~ دیار   
ofoq-e padidâr, ~ diyâr

Fr.: horizon apparent   

That line where Earth and sky appear to meet, and the projection of this line upon the celestial sphere. Also known as the apparent horizon.

visible; → horizon.

visible light
  نور ِ دیار، ~ دیدنی   
nur-e diyâr, ~ didani

Fr.: lumière visible   

The portion of the → electromagnetic radiation that can be seen by the human → eye. The → wavelengths extend from about 400 nm (violet) to 750 nm (red). The wavelengths of various colors of the visible spectrum are as follows: → violet: 390-455 nm; → blue: 455-492 nm; → green: 492-577; → yellow: 577-597; → orange: 597-622; → red: 622-780 nm.

visible; → light.

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