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
siyah-jesm (#)

Fr.: corps noir   

A theoretical object that is simultaneously a perfect → absorber (it does not reflect any radiation) and a perfect → emitter of → radiation in all → wavelengths and whose radiation is governed solely by its → temperature. Blackbody radiation cannot be explained by → classical physics. The study of its characteristics has, therefore, played an important role in the development of → quantum mechanics. A blackbody can be realized in the form of a cavity with highly absorbing internal walls and a small aperture. Any ray entering through the aperture can leave the cavity only after repeated reflection from the walls. When the aperture is sufficiently small, therefore, the cavity will absorb practically all the radiation incident on the aperture, and so the surface of the aperture will be a black body. The light within the cavity will always interact and exchange energy with the material particles of the walls and any other material particles present. This interaction will eventually → thermalize the radiation within the cavity, producing a → blackbody spectrum, represented by a → blackbody curve.
See also → blackbody photosphere; → blackbody radiation; → Planck's blackbody formula; → Planck's radiation law; → Rayleigh-Jeans law; → Stefan-Boltzmann law; → thermalization; → Wien's displacement law.

black; → body.

blackbody curve
  خم ِ سیه‌جسم   
xam-e siyah-jesm

Fr.: courbe de corps noir   

The characteristic way in which the → intensity of → radiation emitted by a → blackbody varies with its → frequency (or → wavelength), as described by → Planck's radiation law. Also referred to as the → Planck curve. The exact form of the curve depends only on the object's → temperature. The wavelength at which the emitted intensity is highest is an indication of the temperature of the radiating object. As the temperature of the blackbody increases, the peak wavelength decreases (→ Wien's displacement law) and the total energy being radiated (the area under the curve) increases rapidly (→ Stefan-Boltzmann law).

blackbody; → curve.

blackbody photosphere
  شیدسپهر ِ سیه‌جسم   
šidsepehr-e siyah-jesm

Fr.: photosphère de corps noir   

The → blackbody surface of the → Universe defined at a → redshift of about z ≥ 2 × 106. This is distinct from the → last scattering surface, in other words the → cosmic microwave background radiation (CMBR), which refers to z = 1100. Prior to the epoch of the blackbody photosphere the distortions from the → Big Bang are exponentially suppressed.

blackbody; → atmosphere.

blackbody radiation
  تابش ِ سیه‌جسم   
tâbeš-e siyah-jesm (#)

Fr.: rayonnement de corps noir   

The radiation emitted by a blackbody at a given → temperature. The → distribution of radiation with → wavelength is given by → Planck's blackbody formula or → Planck's radiation law.

blackbody; → radiation.

blackbody spectrum
  بیناب ِ سیه‌جسم   
binâb-e siyah-jesm (#)

Fr.: spectre de corps noir   

A curve displaying → blackbody radiation intensity versus the wavelength for a given temperature, according to → Planck's blackbody formula. It is an asymmetrical curve with a sharp rise on the short wavelength side and a much more gradually sloping long-wavelength tale. Same as → Planck spectrum.

blackbody; → spectrum.

blackbody temperature
  دما‌ی ِ سیه‌جسم   
damâ-ye siyah-jesm (#)

Fr.: température de corps noir   

The temperature at which a blackbody would emit the same radiation per unit area as that emitted by a given body at a given temperature.

blackbody; → temperature.


Fr.: panne d'électricité, black-out   

1) A period of darkness caused by a complete loss of electrical power in a particular area.
2) The extinguishing of all artificial light enforced as a precaution against air raids.

black; → out.

Xâmušzâr, târikzâr from xâmuš "extinguished," → extinction, târik, → dark, + -zâr suffix denoting profusion and abundance, sometimes with negative nuance, such as in šurezâr "unfertile, salty ground; nitrous earth," xoškzâr "arid land far from water," lajanzâr "field of black mud, marsh," kârzâr "a field of battle; conflict; engagement."

Blandford-Zanjek process
  فراروند ِ بلندفورد-زنجک   
farâravand-e Blandford-Zanjek

Fr.: processus de Blandford-Zanjek   

A mechanism for the extraction of energy from a rotating → Kerr black hole. It relies on the assumption that the material → accreted by a → black hole would probably be → magnetized and increasingly so as the material gets closer to the → event horizon. Since all black holes of current astrophysical interest are probably accreting from magnetized disks, this has led to suggestions that the Blandford-Znajek process plays a vital role in → active galactic nuclei (AGN) and other accreting black hole systems. The power, P, generated is given by: P = (4π/μ0) B2RS2c, where B is the → magnetic field of the → accretion disk, and RS is the → Schwarzschild radius of the black hole. As an example, for a 108 solar mass black hole with a 1 T magnetic field, the power generated is approximately 2.7 × 1038 W. In perspective, the annual energy consumption of the world is estimated around 5 × 1020 J. The example case presented produces more energy in a single second than the entire globe consumes in a year. While this is a bold claim to make, it is only an example case where not all the energy produced is extractable as useable energy. However, at that point, even a system which is less that < 10-15 % efficient would be sufficient to supply enough energy to power the world for a full year. Of course, the system itself is limited in its lifetime due to the extraction of energy by slowing down the rotation of the black hole. Hence, the system can only exist as long as the black hole has angular momentum, continuing to rotate. At some point, the rotation will cease and the energy source will be unusable (D. Nagasawa, PH240, Stanford University, Fall 2011).

Blandford, R. D., & Znajek, R. L., 1977, MNRAS 179, 433; → process.

patu (#)

Fr.: couverture   

1) A large piece of thick cloth for use as a bed covering, animal covering, etc, enabling a person or animal to retain natural body heat.
2) Any extended covering or layer (
blanketed model, → blanketing, → blanketing effect, → line blanketing, → line-blanketed model, → unblanketed model, → wind blanketing.

From M.E., from O.Fr. blanchet, diminutive of blanc "white; white cloth."

Patu "blanket; a kind of woolen cloth," Kermâni dialect poto "wollen; woolly;" cf. Skt. patta- "cloth, colored or fine cloth."

blanketed model
  مدل ِ پتومند   
model-e patumand

Fr.: modèle à effet de couverture   

line blanketing.


Fr.: effet de couverture   

line blanketing.

blanketing effect
  ا ُسکر ِ پتومندی   
oskar-e patumandi

Fr.: effet de couverture   

line blanketing.


Fr.: blazar   

A term specifying → BL Lac objects or → quasars when the → continuum radiation emitted from the active nucleus is highly polarized and very variable.

Blazar, a combination of BL Lac and quasar.


Fr.: flambée; blaze   

1) General: A bright → burst of fire, a flame; a bright or steady light or glare.
2) Optics: The concentration of a limited region of the spectrum into any → order other than the zero order.

O.E. blæse "a torch, flame," from P.Gmc. *blason, from PIE *bhel- "to shine."

Beliz, from Lori beleyz "flame, blaze," Kordi belise "flame, blaze," Mid.Pers. brâh, Av. braz- "to shine, gleam, flash, radiate," cf. Skt. bhâ- "to shine," bhrajate "shines, glitters," O.H.G. beraht "bright," O.E. beorht "bright;" PIE *bhereg- "to shine."

blaze angle
  زاویه‌ی ِ بلیز   
zâviye-ye beliz

Fr.: angle de blaze   

The angle between the operating facet of the grooves and the overall plane of a diffraction grating.

blaze; → angle.

Angâl, zâviyée, → angle; belizblaze.

blaze wavelength
  موج-طول ِ بلیز   
mowjtul-e beliz

Fr.: longueur d'onde de blaze   

The wavelength in a given diffraction order for which the efficiency curve reaches its maximum.

blaze; → wavelength.

Mowjtulwavelength; belizblaze.

blazed grating
  توری ِ بلیزی   
turi-ye belizi

Fr.: réseau échelette   

A → diffraction grating ruled appropriately so that a large proportion of the diffracted light is concentrated into a few, or even a single → order of interference.

Blazed, adj. of → blaze; → grating.

Turi, noun from tur "a net, a fishing net;" belizi adj. from beliz, → blaze.

Blazhko effect
  اسکر ِ بلاژکو   
oskar-e Blazhko

Fr.: effet Blazhko   

A long term, generally irregular modulation of → light curves of a large subclass of → RR Lyrae stars. Most of the modulations occur on the time scale of some 60 periods, although the range extends from some tens to some hundreds of periods. Since its discovery over a hundred years ago, a number of explanations have been proposed for this effect, but its nature is still a matter of investigation. The explanations include: closely spaced pulsation modes, a modal 1 : 2 resonance, an oblique rotator model, a non-radial modal interaction, convective cycles, and nonlinear resonant mode coupling between the 9th overtone and the fundamental mode (see, e.g., R. Buchler and Z. Kolláth 2011, astro-ph/1101.1502).

Named after Sergei N. Blazhko (1870-1956), a Russian astronomer who discovered the effect for the star EW Dra (1907, Astron. Nachr. 175, 325); → effect.

Blazhko star
  ستاره‌ی ِ بلاژکو   
setâre-ye Blazhko

Fr.: étoile à effet Blazhko   

A star showing the → Blazhko effect.

Blazhko effect; → star.



The capcity of a diffraction grating, in certain configurations, to concentrate a large percentage of the incident light into a specific diffraction order.

Blazing, noun from → blaze.

Belizeš, noun from beliz "blaze."

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