An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 435 Search : ad
radiation damping
  میرایی ِ تابشی   
mirâyi-e tâbeši

Fr.: amortissement par rayonnement   

Damping of a system which loses energy by → electromagnetic radiation.

radiation; → damping.

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.

radiation era
  دوران ِ تابش   
dowrân-e tâbeš

Fr.: ère du rayonnement   

The epoch in the history of the Universe, lasting from the → Big Bang until about 400,000 years later, when the temperature had dropped to 109 K and the rate of electron-positron → pair annihilation exceeded the rate of their production, leaving radiation the dominant constituent of the Universe. The radiation era was followed by the → matter era.

radiation; → era.

radiation field
  میدان ِ تابش   
meydân-e tâbeš

Fr.: champ de rayonnement   

1) The portion of an → electromagnetic field outside the → induction field where there is a power flow of both → magnetic and → electric components in a well-defined relationship.
2) → interstellar radiation field

radiation; → field.

radiation length
  درازای ِ تابش   
derâzâ-ye tâbeš

Fr.: longueur de rayonnement   

The mean distance traveled by a photon or particle in a given medium before its energy is reduced by a factor e due to its interaction with matter.

radiation; → length.

radiation pattern
  الگو‌ی ِ تابش   
olgu-ye tâbeš

Fr.: diagramme de rayonnement   

Same as → antenna pattern.

radiation; → pattern.

radiation pressure
  فشار ِ تابش   
fešâr-e tâbeš

Fr.: pression de radiation   

The → momentum carried by → photons to a surface exposed to → electromagnetic radiation. Stellar radiation pressure on big and massive objects is insignificant, but it has considerable effects on → gas and → dust particles. Radiation pressure is particularly important for → massive stars. See, for example, → Eddington limit, → radiation-driven wind , and → radiation-driven implosion. The → solar radiation pressure is also at the origin of various physical phenomena, e.g. → gas tails in → comets and → Poynting-Robertson effect.

radiation; → pressure.

radiation sickness
  بیماری ِ تابشی   
bimâri-ye tâbeši

Fr.: mal des rayons   

An illness resulting from excessive exposure to ionizing radiation. The earliest symptoms are nausea, vomiting, and diarrhea, which may be followed by loss of hair, hemorrhage, inflammation of the mouth and throat, and general loss of energy.

radiation; sickness, M.E. siknesse, seknesse; O.E. sēocnesse, from seoc + suffix -ness.

Bimâri "sickness, infirmity, disease," from bimâr "sick, infirm, afflicted;" Mid.Pers. vêmâr "sick, ill;" maybe by corruption of Proto-Iranian *amavayā-bara- "bearing illness;" cf. Av. amavayā- "pain, suffering, affliction;" Skt. ámīvā- "pain, grief, distress" + *bara- "bearing;" cf. Av. bar- "to bear, carry;" Mod.Pers. bar-, bordan "to bear, carry, lead." Alternatively, from *vi-mar-, prefixed *mar- "to die;" cf. Av. mar- "to die;" Mod.Pers. mir-, mordan "to die;" Skt. mar- "to die;" cognate with Gk. emorten "died;" L. morior "to die;" tâbeši related to tâbeš, → radiation.

radiation spectrum
  بیناب ِ تابش   
binâb-e tâbeš

Fr.: spectre de rayonnement   

The components of radiation arranged in order of their wavelengths, frequencies, or quantum energies. For particle radiation they are arranged in order of their kinetic energies.

radiation; → spectrum.

radiation temperature
  دمای ِ تابش   
damâ-ye tâbeš

Fr.: température de rayonnement   

The temperature of a source calculated assuming that it behaves as a → blackbody that radiates with the same intensity at the same frequency. Compared to the → effective temperature, the radiation temperature is measured over a narrow region of the → electromagnetic spectrum.

radiation; → temperature.

radiation transfer
  تراواژ ِ تابش   
tarâvâž-e tâbeš

Fr.: transfert radiatif, ~ de rayonnement   

radiative transfer.

radiation; → transfer.

radiation transfer equation
  هموگش ِ تراواژ ِ تابش   
hamugeš-e tarâvâž-e tâbeš

Fr.: équation de transfert radiatif, ~ de rayonnement   

radiative transfer equation.

radiation; → transfer; → equation.

radiation-dominated Universe
  گیتی ِ تابش‌چیره   
giti-ye tâbeš-ciré

Fr.: Univers dominé par le rayonnement   

An early epoch in the history of the → Universe when the radiation → density parameter was Ωr≈ 1, while other density parameters had negligible contributions. A radiation-dominated Universe is characterized by R/R0 ∝ t1/2, where R is the → cosmic scale factor and t is time. According to the → Big Bang model, the radiation-dominated phase was followed by the → matter-dominated phase.

radiation; → dominate; → Universe.

radiation-driven implosion (RDI)
  فروکفت از راه ِ تابش   
forukaft az râh-e tâbeš

Fr.: implosion induit par rayonnement   

A hydrodynamic process occurring in star forming regions where a neutral cloud (→ clump) is subjected to the intense ultraviolet radiation of a newly-born → massive star. The gas within the layer exposed to the radiation is ionized and forms an → ionization front at the front surface. The increased pressure due to temperature rise at the top layer drives an → isothermal  → shock front into the clump, which compresses the neutral gas ahead of it, below the surface. A density → gradient builds up leading rapidly to the formation of a condensed core. With further concentration of the gas, the hydrogen density in the center of the core increases drastically, reaching 108 cm-3 about 4 x 105 years after the first impact of the ionizing radiation on the clump, according to current models (e.g. Bertoldi 1989, ApJ 346, 735; Miao et al. 2006, MNRAS 369, 143, and references therein). The core can develop further to form a → cometary globule or → collapse under its self-gravity, eventually giving rise to new → low-mass stars (→ triggered star formation). In the process, the whole clump accelerates away from the initial ionizing star. Indeed, the gas evaporated off the side of the clump facing the ionizing star can create a rocket effect accelerating the clump away from the star (with a velocity of up to 5 km s-1), while losing part of its initial mass.

radiation; driven, p.p. of → drive; → implosion.

radiation-driven mass loss
  دسترفت ِ جرم از راه ِ باد ِ تابشی   
dastraft-e jerm az râh-e bâd-e tâbeši

Fr.: perte de masse par vent radiatif   

The → mass loss experienced by a → massive star due to the effect of → radiation-driven wind.

radiation; driven, p.p. of → drive; → mass; → loss.

radiation-driven wind
  باد ِ تابشی، ~ تابش‌زاد   
bâd-e tâbeši, ~ tâbešzâd

Fr.: vent radiatif   

The loss of matter from the → photosphere due to the acceleration imparted to the outer layers of the star by photons created inside the star. The coupling between radiation and matter creates a → radiative acceleration that may exceed the → gravity. This mechanism is particularly important in → massive stars, since the luminosity is high and therefore the number of energetic ultraviolet photons important. Same as → line-driven wind.

radiation; → drive; → wind.

radiationless relaxation
  واهلش ِ بی‌تابش   
vâhaleš-e bitâbeš

Fr.: relaxation sans rayonnement   

A process in which a molecule relaxes without emitting a → photon.

radiation; → -less; → relaxation.

tâbešisi (#)

Fr.: radiatif   

Of or pertaining to radiation.

Adjective of → radiation.

radiative acceleration
  شتاب ِ تابشی   
šetâb-e tâbeši

Fr.: accélération radiative   

The acceleration imparted to matter by → radiation pressure.

radiative; → acceleration.

radiative braking
  لگامش ِ تابشی   
legâmeš-e tâbeši

Fr.: freinage radiatif   

The slowing down of a star's rotation due to radiative momentum transfer caused by emission of electromagnetic radiation.

radiative; → braking.

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