An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 471 Search : ity
radial velocity method
  روش ِ تندای ِ شعاعی   
raveš-e tondâ-ye šo'â'i

Fr.: méthode de vitesses radiales   

The technique based on the analysis of the → radial velocity curve, used to detect the presence of an invisible secondary around a host star. This method holds the majority of exoplanet discoveries.

radial velocity; → method.

radiant intensity
  درتنویی ِ تابشی   
dartanuyi-ye tâbeši

Fr.: intensité de rayonnement   

A measure of the amount of radiation emitted from a point expressed as the radiant flux per unit solid angle leaving this source.

radiant; → intensity.

radiation density constant
  پایای ِ چگالی ِ تابش   
pâypa-ye cagâli-ye tâbeš

Fr.: constante de rayonnement   

The constant related to the total energy radiated by a → blackbody and defined as: a = 4σ/c, where σ is the → Stefan-Boltzmann constant and c the → speed of light. Its value is a = 7.5657 x 10-15 erg cm-3 K-4. Same as → radiation constant.

radiation; → density; → constant.

radio flux density
  چگالی ِ شار ِ رادیویی   
cagâli-ye šârr-e râdioyi

Fr.: densité de flux radio   

The flux of → radio waves that falls on a → detector per → unit → surface area of the detector per unit → bandwidth of the radiation per unit → time. The unit is → jansky.

radio; → flux; → density.

  پرتو-ژیرایی، پرتو-ژیرندگی   
partow-žirâyi, partow-žirandegi

Fr.: radioactivité   

The spontaneous disintegration of certain atomic nuclei, which is accompanied by the emission of either α- or β- particles and/or a γ rays.

radio; → activity.

Rayleigh-Taylor instability
  ناپایداری ِ ریلی-تیلر   
nâpâydâri-ye Rayleigh-Taylor

Fr.: instabilité Rayleigh-Taylor   

A type of hydrodynamical instability between two fluids of different densities, which occurs when the heavy fluid lies above the lighter fluid in a gravitational field. More generally a material interface is said to be Rayleigh-Taylor unstable whenever the fluid acceleration has an opposite direction to the density gradient.

rayleigh; → Taylor number; → instability.


Fr.: réactivité   

1) General: The quality or condition of being reactive.
2) Physics: A measure of the deviation from the condition at which a → nuclear reactor is critical.
3) Chem.: The relative → capacity of an → atom, → molecule, or → redical to undergo a → chemical reaction with another atom, molecule, or → compound.

From → reactive + → -ity.


Fr.: réalité   

1) The state or quality of being real. A real thing or fact.
2) Philo.: The totality of what is, as opposed to what merely seems to be.

real + → -ity.

recession velocity
  تندای ِ دورشدن   
tondâ-ye dur šodan

Fr.: vitesse d'éloignement   

The velocity with which an object moves away from another object or a reference point.

recession; → velocity.

reciprocity theorem
  فربین ِ دوسویگی   
farbin-e dosuyegi

Fr.: théorème de réciprocité   

1) General: Any theorem that expresses various reciprocal relations for the behavior of some physical systems, in which input and output can be interchanged without altering the response of the system to a given excitation.
2) In classical electromagnetism, the theorem stating that the current in a detector divided by the voltage at the source remains constant when source and detector are interchanged, as long as the frequency and all the impedances are left unchanged.

Reciprocity, from L. reciproc(us) "returning the same way, alternating" + → -ity; → theorem.

Farbin, → theorem; dosuyegi, quality noun of dosuyé nuanced term of dosu "two-sided," from do, → two, + su "direction, side," from Mid.Pers. sôk "direction, side."


Fr.: réflectivité   

Same as → reflectance; → reflection factor.

From → reflective + → -ity.

  واکوتیدنیگی، واکوتش‌پذیری   
vâkutidanigi, vâkutešpaziri

Fr.: réfutabilité   

The quality of being → refutable.

refutable; → -ity.

relative density
  چگالی ِ بازانی   
cagâli-ye bâzâni

Fr.: densité relative   

The ratio of the density of a substance to the density of a given reference material. For a solid or liquid, it is the density (at 20°C) relative to the maximum density of water (at 4°C). For a gas is its density divided by the density of hydrogen (or sometimes dry air) at the same temperature and pressure. Also called → specific density.

relative; → density.

relative humidity
  نم ِ بازانی   
nam-e bâzâni

Fr.: humidité relative   

The amount of moisture in the air compared to what the air can "hold" at that temperature. It is given by the ratio of the partial pressure of water vapor in the mixture to the saturated vapor pressure of water at a specific temperature.

relative; → humidity.

relative permeability
  تراوایی ِ بازانی   
tarâvâyi-ye bâzâni

Fr.: perméabilité relative   

magnetic permeability.

relative; → permeability.

relative velocity
  تندای ِ بازانی   
tondâ-ye bâzâni

Fr.: vitesse relative   

For two objects A and B, the velocity which B, supposing itself at rest, assigns to A.

relative; → velocity.

relativistic velocity
  تندای ِ بازانیگی‌مند   
tondâ-ye bâzânigimand

Fr.: vitesse relativiste   

The velocity of a body when it is a significant fraction of the → speed of light.

relativistic; → velocity.


Fr.: relativité   

General: The state or fact of being relative.
Physics: 1) Short for the → Galilean relativity.
2) Short for the → relativity theory of Einstein.

Relativity, from → relative + → -ity.

relativity of simultaneity
  بازانیگی ِ همزمانی   
bâzânigi-ye hamzamâni

Fr.: relatitivité de simultanéité   

A basic concept of → special relativity whereby → events that are simultaneous in one → reference frame are not simultaneous in another reference frame moving with respect to the first.

relativity; → simultaneity.

relativity principle
  پروز ِ بازانیگی   
parvaz-e bâzânigi

Fr.: principe de relativité   

The requirement employed by Einstein in his relativity theories, that the equations describing the laws of physics are the same in all frames of reference. This statement and that of the constancy of the speed of light constitute the founding principles of special relativity.

Relativity; → principle.

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