An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 476
Brackett series
  سری ِ براکت   
seri-ye Brackett

Fr.: série de Brackette   

A series of lines in the infrared spectrum of atomic hydrogen due to electron jumps between the fourth and higher energy levels (Br α has wavelength 4.052 μm, Br γ 2.166 μm).

Named after the American physicist Frederick Brackett (1896-1980); → series.

Bragg angle
  زاویه‌ی ِ براگ   
zâviye-ye Bragg

Fr.: angle de Bragg   

The grazing angle between an incident beam of X-rays and a given set of crystal planes for which the secondary X-rays from the planes combine to give a single beam.

Bragg's law; → angle.

Bragg's law
  قانون ِ براگ   
qânun-e Bragg

Fr.: loi de Bragg   

A parallel beam of monochromatic X-rays of wavelength λ, incident on a given set of parallel crystal planes at a grazing angle θ will give rise to a reflected beam whenever: n λ = 2d . sinθ, where n is an integer representing the difference in path length, and d is the perpendicular distance between a pair of adjacent planes.

Named after William Lawrence Bragg (1890-1971), British physicist, who, in collaboration with his father, William Henry Bragg (1862-1942), joint Nobel Prize in Physics 1915, pioneered X-ray analysis and spectrometry; → law.

  ۱) لگام، ترمز؛ ۲) لگامیدن، ترمز کردن   
1) legâm, tormoz 2) legâmidan, tormoz kardan

Fr.: 1) frein; 2) freiner   

1) A device for slowing or stopping a vehicle or other moving mechanism by the absorption or transfer of the energy of momentum, usually by means of friction.
2) To slow or stop by means of or as if by means of a brake (

From O.Du. braeke "flax brake," from breken "to break."

Legâm originally "a horse bit," on the model of Fr. frein "horse bit; motor brake;" and Ger. Bremse "horse bit; brake;" tormoz, loan from Russ. тормоз.


Fr.: freinage   

The act or fact of stopping by means of or as if by means of a brake. See: → magnetic braking; → radiative braking; → tidal braking; → braking index.

Verbal noun of → brake.

braking index
  دیشن ِ لگامش   
dišan-e legâmeš

Fr.: indice de freinage   

A parameter indicating the rate at which a → pulsar slows down. Neutron stars are powered by → rotational energy and lose energy by accelerating particle → winds and by emitting → electromagnetic radiation. The → rotation frequency, Ω, thus decreases with time and this slowdown is usually described by the relation Ω. = - kΩn, where k is a positive constant which depends on the → moment of inertia and the → magnetic dipole moment of the → neutron star and n is the braking index. Conventionally, the braking index is derived by differentiation of the above equation, yielding n = ΩΩ.. / Ω.2. In a highly simplified model in which the spin-down torque arises from dipole radiation at the rotation frequency, one expects n = 3 (Johnston, S., Galloway, D., 1999, arXiv:astro-ph/9905058).

braking; → index.

  ۱) شاخه؛ ۲) شاخه زدن   
1) šâxé (#); 2) šâxé zadan (#)

Fr.: 1) branche; 2) se ramifier   

1a) General: A shoot or arm-like limb of a tree; anything like a limb of a tree; any offshoot from a main trunk.
1b) Astro.:asymptotic giant branch; → blue horizontal-branch stars; → red giant branch; → branching; → branching ratio.
1c) Math.: Any of the two halves of a → hyperbola.
1d) Math.: A section of a curve separated by → discontinuity from the rest of the curve.
2a) To put forth branches.
2b) To spread in branches.

M.E., from O.Fr. branche, from L.L. branca "a claw, paw."

1) Šâxé "branch," from Mid.Pers šâk, cf. Mod.Pers. šâx, šax "branch; horn," Skt. sakha- "a branch, a limb," Arm. cax, Lit. šaka, O.S. soxa, PIE *kakhâ "branch."
2) Šâxé zadan with verb zadan "to strike, beat," → outcrop.


Fr.: branchement   

The act of dividing into branches. → branching ratio.

branch; → -ing.

branching ratio
  وابر ِ شاخه‌زد   
vâbar-e šâxé-zad

Fr.: rapport de branchement   

A quantity used to describe a → radionuclide that has more than one → decay mode. For a particular decay mode, the ratio of the number of atoms decaying by that decay mode to the number decaying in total: BRi = ki/(k1 + k2 + ...) = ki/k, where k is → decay constant.

branching; → ratio.

breyn (#)

Fr.: brane   

In theoretical physics, an entity which can have any number of allowed spatial dimensions. It is usually accompanied by a prefix, i.e. p-brane, indicating the number of dimensions. For example, a 0-brane is a zero-dimensional point-like particle, a 1-brane is a → string, a 2-brane is a "membrane," and so forth. Our Universe is a 3-brane.

Brane, short for membrane, from L. membrana "parchment," from membrum "limb, member of the body," → member.

Breyn, loanword from E., as above.

  ۱) شکستن؛ بریدن؛ گسستن؛ ۲) شکست؛ برش؛ بره؛ گسست   
1) šekastan; boridan; gosastan; 2) šekast; boreš, boré; gosast

Fr.: 1) couper, rompre; 2) brisure, coupure   

1) To separate into parts or fragments violently; to become broken.
2) The act or instance of breaking; fracture, rupture; a sudden decline in a continuity.

From break, from M.E. breken, O.E. brecan, from P.Gmc. *brekan (cf. Du. breken, O.H.G. brehhan, Ger. brechen), from PIE base *bhreg- "to break" (see also → fraction).

1) Šekastan, škan- "to break, split;" Mid.Pers. škastan "to break;" Av. scind-, scand "to break, cleave;" Proto-Iranian *skand- "to break, cleave;" PIE sken- "to cut off."
Boridan "to cut off," → cut.
Gosastan "to tear, cut, break," from Mid.Pers. wisistan "to break, split;" Av. saed-, sid- "to split, break," asista- "unsplit, unharmed;" cf. Skt. chid- "to split, break, cut off;" Gk. skhizein "to split;" L. scindere "to split;" Goth. skaidan; O.E. sceadan "to divide, separate;" PIE base *skei- "to cut, split."
2) Šekast; boreš boré; gosast, respective nouns from the verbs.

break luminosity
  تابندگی ِ بره   
tâbandegi-ye boré

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.

break; → luminosity.

break-up velocity
  تندای ِ گسست   
tondâ-ye gosast

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.

break + up; M.E.; O.E. up, uppe, → hyper-; → velocity.

bereš (#)

Fr.: brèche   

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.


Fr.: bréchifier   

To form as → breccia.

From → breccia + → -ate.

  برشیده، برشمند   
berešidé, beršmand

Fr.: bréchifié   

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.

brecciated rock
  سنگ ِ برشیده   
sang-e berešidé

Fr.: roche bréchifiée   

A rock formed by the process of → brecciation.

brecciated; → rock.


Fr.: bréchification   

The formation of → breccia.

Verbal noun of → brecciate.

nasim (#)

Fr.: brise   

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.

Breit-Wheeler process
  فراروند ِ برایت-ویلر   
farâravand-e Breit-Wheeler

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.

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