Fr.: luminosité de coupure
A characteristic luminosity around which the → luminosity function of a sample of galaxies changes to a steeper slope or exponentially declines.
Fr.: vitesse de rupture
The velocity of a → rotating star at which the → centrifugal force equals the → gravitational force. Also known as → critical velocity. The simplest expression of the break-up velocity for an OB star, ignoring the → Eddington luminosity, is given by the relation: v = (GM / R)1/2, where M and R are the mass and radius of the star respectively, and G the → gravitational constant. A more realistic expression takes into account not only the → radiation pressure, but also the non-uniformity of the brightness over the stellar surface, as indicated by → von Zeipel theorem. With these conditions, the break-up velocity has a more complicated formula, corresponding to the velocity reached when somewhere on the star the → total gravity becomes zero.
A rock composed of angular fragments (over two millimeter diameter) of older rocks melded together with a matrix of smaller particles or a mineral cement.
From It. breccia "broken (rock)," from a Germanic source akin to O.H.G. brecha "a breaking," ultimately from PIE *bhreg- "to break," → fraction.
Bereš, loan from Fr.
To form as → breccia.
Characterized by, converted into, or resembling a breccia; especially of a rock structure marked by an accumulation of angular fragments, or of an ore texture showing mineral fragments without notable rounding.
Fr.: roche bréchifiée
A rock formed by the process of → brecciation.
The formation of → breccia.
Verbal noun of → brecciate.
A wind or current of air, especially a light or moderate one (2-14 m/sec).
From O.Sp. briza "cold northeast wind;" alternatively from East Frisian brisen "to blow fresh and strong."
Nasim "gentle breeze," from Ar.
Fr.: processus Breit-Wheeler
The production of an → electron-positron pair in the → collision of two → gamma ray → photons (γγ → e+e-). It is the → inverse process of → Dirac annihilation (e+e-→ γγ). The Breit-Wheeler process is the simplest way by which pure → light can be potentially transformed into → matter. However, as of 2014, this process has never been observed in practice because of the difficulty in preparing colliding → gamma ray beams.
Breit, G. & Wheeler, J. A. 1934, Collision of two light quanta. Phys. Rev. 46, 1087; → process.
Fr.: rayonnement de freinage, bremsstrahlung
Bremsstrahlung, from Ger. Bremse "brake" + Strahlung "radiation," from strahlen "to radiate," from Strahl "ray," from O.H.G. strala "arrow, stripe;" PIE *ster- "to spread."
zâviye-ye Brewster (#)
Fr.: angle de Brewster
Fr.: point de Brewster
A → neutral point located 15 to 20° directly below the Sun.
Fr.: loi de Brewster
The amount of the polarization of light reflected from a surface is a maximum when the reflected ray is at right angles to the refracted ray. See also → polarizing angle.
Named after Sir David Brewster (1781-1868), Scottish physicist; → law.
1) An apparent structure of → gas or
→ stars linking one → galaxy
to another, such as → Magellanic Bridge.
M.E. brigge, O.E. brycge, from P.Gmc. *brugjo (cf. Ger. Brücke), from PIE *bhru- "log, beam."
Pol, Mid.Pers. puhl,, Av. pərətav- "bridge, passage."
Giving out or reflecting much light, shining.
O.E. bryht, from beorht "bright, splendid," from P.Gmc. *berkhiaz, from PIE base *bhereg- "to gleam, white" (cf. Av. brāz- "to shine, gleam, flash, radiate," Skt. bhrajate "shines, glitters," Mod.Pers. balk, warq, barx, barq "flash, flame, light," barâz "beauty, grace, elegance," barâzidan "to render good, beautiful," Lith. breksta "to dawn," Welsh berth "bright, beautiful," L. flagrare "to blaze"). → electricity.
Deraxšân and rowšan both from M.P. rôc, O.Pers. raucah-, Av. raocah- "light, luminous; daylight;" cf. Skt roka- "brightness, light", cognate with Gk. leukos "white, clear", L. lux "light" (also lumen, luna), PIE *leuk- "light, brightness". The Mod.Pers. words ruz "day," foruq "light", and afruxtan "to light, kindle" also belong to this family, as well as the E. light, Ger. Licht, and Fr. lumière.
Fr.: géante lumineuse
An → evolved star which is more → luminous than normal → giant stars (→ luminosity class III) and between ordinary giants and → supergiants (class I). It is denoted by the symbol II. Examples are → Canopus and → Adhara.
miq-e rowšan, ~ deraxšân
Fr.: nébuleuse brillante
In contrast to a → dark nebula, a bright cloud of interstellar gas and dust. The term designates both emission nebulae and reflection nebulae.
Verbal noun of brighten, from → bright.
General:The state or quality of being bright.
Deraxšandegi, from deraxš, present stem of deraxšidan "to shine," → bright, + -andé adjective suffix + -gi noun suffix.
Fr.: distribution de brillance
A statistical distribution of the brightness of an astronomical extended object.