An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

To form as → breccia.

From → breccia + → -ate.

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.

→ breccia, → brecciated.

A rock formed by the process of → brecciation.

→ brecciated; → rock.

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.

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.

The → electromagnetic radiation emitted by a → fast moving → charged particle when it passes within the strong → electric field of an → atomic nucleus and is → decelerated.

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."

Legâm-tâbeš, from legâm, → brake, + tâbeš, → radiation.

The → angle of incidence for which the sum of the incident angle and the → angle of refraction is 90°. The value of Brewster's angle for glass is 57° and for water is 53°. Same as → polarizing angle.

→ Brewster's law; → angle.

A → neutral point located 15 to 20° directly below the Sun.

→ Brewster's law; → point

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.

In radio astronomy, the temperature of a source calculated on the assumption that it is a blackbody emitting radiation of the observed intensity at a given wavelength. → antenna temperature.

→ brightness; → temperature.

The inner region of a → quasar or an → active galactic nucleus exhibiting broad → spectral lines which indicate ionized matter moving with speeds in excess of 10,000 km sec^-1, probably due to the presence of an → accretion disk surrounding a → supermassive black hole. Also called Type I AGN. See also → obscuring torus.

→ broad; → line; → region.

The frequency at which an air parcel will oscillate when subjected to an infinitesimal perturbation in a stably stratified atmosphere. For a medium with a continuous density gradient, it is expressed by the formula: N² = -(g/ρ)∂ρ/∂z , where g is the → gravitational acceleration, ρ is density, and z geometric height. The stability condition is N > 0. It is also sometimes referred to as the buoyancy frequency. The higher the value of N the more stable the flow.

Named aster David Brunt (1886-1965), British meteorologist (1927, Q.J.R.Met.Soc. 53, 30) and Vilho Väisälä (1889-1969), Finnish meteorologist (1925, Soc. Sci. Fenn. Commental. Phys. Math. 2 (19), 19); → frequency.

Same as the → Brunt-Vaisala frequency.

→ buoyancy; → frequency.

A piece of glass of roundish shape, possibly made of rock crystals or a globular container filled with water, whose use is attested in ancient civilizations. In his comedy The Clouds, the Greek playwright Aristophanes (448-380 BC) mentions globules of glass that were known as burning spheres. Several Roman writers (Pliny, Seneca, Plutarch) speak of burning glasses. In particular, Seneca specifies that small and indistinct written characters appear larger and clearer when viewed through a globular glass filled with water. See also → magnifying glass.

→ burning; → sphere.

Guy, → globe; suzân "burning," → burning.

A discontinuity in the spectrum of galaxies near the Ca II → H and K lines at about 4000 Å. The Ca break is the most prominent feature in the spectra of elliptical galaxies. Its strength is given by the → calcium break index.

→ calcium; → break.

The strength of the → calcium break, as measured from the fluxes in the intervals 3750-3950 Å and 4050-4250 Å. It is given by the expression Ca-break[%] = 100 · (f_upper - f_lower)/f_upper, where f_upper and f_lower are the mean fluxes measured in the 3750-3950 Å and 4050-4250 Å bands, respectively, in the rest frame (Dressler & Shectman 1987, AJ 94, 899).

→ calcium; → break; → index.

A → claculus based on the properties of the successive values of → variable quantities and their → differences or → increments.

→ calculus, → finite, → difference.

Afmârik, → calculus, degarsânihâ, plural of degarsân, → difference, karânmand, → finite.

The application of → Cauchy's theorem to compute residues and poles, evaluate contour integrals, sum infinite series, and carry out related calculations.

→ calculus; → residue.

An exposure obtained with an instrument mounted on the telescope using an artificial illuminating source in order to calibrate the instrument.

→ calibration; → exposure.

Nurdâd, → exposure; kabizeš, → calibration.