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.
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).
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.
tâbeš-e siyah-jesm (#)
Fr.: rayonnement de corps noir
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.
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.
Fr.: panne d'électricité, black-out
1) A period of darkness caused by a complete loss of electrical power in a
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."
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.
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.
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."
Fr.: modèle à effet de couverture
Fr.: effet de couverture
Fr.: effet de couverture
Blazar, a combination of BL Lac and quasar.
Fr.: flambée; blaze
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."
Fr.: angle de blaze
The angle between the operating facet of the grooves and the overall plane of a diffraction grating.
→ blaze; → angle.
Fr.: longueur d'onde de blaze
The wavelength in a given diffraction order for which the efficiency curve reaches its maximum.
Fr.: réseau échelette
Turi, noun from tur "a net, a fishing net;" belizi adj. from beliz, → blaze.
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.
Fr.: étoile à effet Blazhko
A star showing the → Blazhko effect.
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."