An Etymological Dictionary of Astronomy and Astrophysics

In Dirac’s notation for describing a quantum state, a vector which together with → ket constitutes the dual vector → bracket. A bra is shown by <|, the mirror image of the symbol for a ket vector. The scalar product of a bra vector < B| and a ket vector |A> is written < B|A >, i.e. as a juxtaposition of the symbols for the bra and the ket vectors, that for the bra vector being on the left, and the two vertical lines being contracted to one for brevity.

See also: From bra- the first syllable in → bracket.

In Dirac’s notation, an expression which is a → scalar product of the dual vectors → bra and → ket which describe a quantum state. The bra vector appears on the left of the ket vector.

See also: From M.Fr. braguette “codpiece armor.”

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).

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

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.

See also: → Bragg’s law; → angle.

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.

See also: 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.

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 (Dictionary.com).

Etymology (EN): From O.Du. braeke “flax brake,” from breken “to break.”

Etymology (PE): 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.

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.

See also: Verbal noun of → brake.

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).

See also: → braking; → index.

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.

Etymology (EN): M.E., from O.Fr. branche, from L.L. branca “a claw, paw.”

Etymology (PE): 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.

The act of dividing into branches. → branching ratio.

See also: → branch; → -ing.

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:

BR_i = k_i/(k₁ + k₂ + …) = k_i/k, where k is → decay constant.

See also: → branching; → ratio.

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.

Etymology (EN): Brane, short for membrane, from L. membrana “parchment,” from membrum “limb, member of the body,” → member.

Etymology (PE): Breyn, loanword from E., as above.

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.

Etymology (EN): 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).

Etymology (PE): 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.

A characteristic luminosity around which the → luminosity function of a sample of galaxies changes to a steeper slope or exponentially declines.

See also: → break; → luminosity.

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.

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

1. An act of overcoming or penetrating an obstacle or restriction.
   

   2. A military offensive that penetrates an enemy’s lines of defense.
      

   3. A major achievement or success that permits further progress, as in technology (TheFreeDictionary.com).

Etymology (EN): → break; → through.

Etymology (PE): Tarâšekâft, from tarâ-, → trans-,

• šekâft, past stem of šekâftan “to split, break, tear,” → fission.

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.

Etymology (EN): From It. breccia “broken (rock),” from a Germanic source akin to O.H.G. brecha “a breaking,” ultimately from PIE *bhreg- “to break,” → fraction.

Etymology (PE): Bereš, loan from Fr.

To form as → breccia.

Etymology (EN): 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.

See also: → breccia, → brecciated.

A rock formed by the process of → brecciation.

See also: → brecciated; → rock.

The formation of → breccia.

See also: Verbal noun of → brecciate.

A wind or current of air, especially a light or moderate one (2-14 m/sec).

Etymology (EN): From O.Sp. briza “cold northeast wind;” alternatively from East Frisian brisen “to blow fresh and strong.”

Etymology (PE): 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.

See also: 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.

Etymology (EN): 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.”

Etymology (PE): 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.

See also: → Brewster’s law; → angle.

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

See also: → 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.

See also: 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.
   

2. Any one of a variety of → elctrical networks in which one branch connects two points of equal → potential and so carries no → current when the → circuit is suitably adjusted.
   

3. In → graph theory, a simple → edge whose removal disconnects a → graph.

Etymology (EN): M.E. brigge, O.E. brycge, from P.Gmc. *brugjo (cf. Ger. Brücke), from PIE *bhru- “log, beam.”

Etymology (PE): Pol, Mid.Pers. puhl,, Av. pərətav- “bridge, passage.”

Giving out or reflecting much light, shining.

Etymology (EN): 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.

Etymology (PE): 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.

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.

See also: → bright; → giant.

In contrast to a → dark nebula, a bright cloud of interstellar gas and dust. The term designates both emission nebulae and reflection nebulae.

See also: → bright; → nebula.

The act or process of becoming bright or brighter. → limb brightening, → gravity brightening

See also: Verbal noun of brighten, from → bright.

General:The state or quality of being bright.
Astronomy:The amount of light or other radiation received from a celestial object. It depends on the intrinsic brightness of the object, its distance and the amount of interstellar extinction. → luminosity.

Etymology (EN): → bright + → -ness.

Etymology (PE): Deraxšandegi, from deraxš, present stem of deraxšidan “to shine,” → bright,

• -andé adjective suffix + -gi noun suffix.

A statistical distribution of the brightness of an astronomical extended object.

Etymology (EN): → brightness; → distribution.

Etymology (PE): Vâbâžeš, → distribution; deraxšandegi, → brightness.

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.

See also: → brightness; → temperature.

A mathematical function appearing in the → magnetization equation of a → paramagnetic substance.

See also: → Brillouin zone; → zone.

Scattering of electromagnetic waves in solids and liquids when, as a result of the scattering process, an acoustic → phonon is emitted or absorbed. Brillouin scattering is analogous to → Raman scattering.

See also: → Brillouin zone; → scattering.

Crystallography: One of the several regions which, in reciprocal space, represent the solution of the wave equations for the propagation of → phonons or electrons in solids. The first Brillouin zone is the Wigner-Seitz cell of the reciprocal lattice. It is a polyhedron obtained by connecting a lattice point to its first neighbors and drawing the planes perpendicular to these connecting lines and passing through their midpoints. The second Brillouin zone is obtained by a similar construction but the second-nearest neighbours.

See also: After Léon Brillouin (1889-1969) French physicist; → zone.

1. Water saturated or strongly impregnated with salt.
   

2. Any saline solution.

Etymology (EN): M.E. from O.E. bryne “brine,” origin unknown; cognate with Du. brijn.

Etymology (PE): Aždem, from Gilaki and Tâti aždem “very salty water” used for preserving fish.

An international collaboration between Austria, Canada, and Poland, currently comprising five nano-satellites to investigate stellar structure and evolution of the brightest stars in the sky and their interaction with the local environment. BRITE is also used to study micropulsation, wind phenomena, and other forms of stellar variability. These nano-satellites aim to monitor stars brighter than V ~ 5 mag using two color pass-bands, over various observing campaigns. Each nano-satellite hosts a 3 cm telescope, providing a wide field of view (24° x 20°) to simultaneously observe up to a few dozen stars (Weiss et al. 2014).

See also: BRITE, short for → BRIght Target Explorer; → bright; → target; → explorer.

A → substance that has a low → elastic limit. For example → glass, which breaks if its low elastic limit is exceeded.

Etymology (EN): M.E. britel, from brit-, akin to O.E. brytan “to crush, break to pieces,”

• -el adj. suffix.

Etymology (PE): Tord “brittle, fragile;” ultimately from Proto-Ir. *tard- “to split, pierce;” related to tâlidan (Dehxodâ) “to spoliate, plunder,” eftâlidan “to tear, break,” → dissipate; cf. Shughni tidarδ- “to tear, pluck,” zidarδ- “to tear, break;”
Skt. tard- “to split, to pierce.”

Wide in extent from side to side.

Etymology (EN): M.E. bro(o)d, from O.E. brad; cf. O.N. breiðr, Du. breed, Ger. breit, Goth. brouþs.

Etymology (PE): Pahn “wide, broad,” from Mid.Pers. pah(a)n; Av. paθana- “broad, wide, spacious;” PIE root *pete- “to spread;” cf. L. patere “to be open,”
Gk. petannynai “to spread out,” petalon “a leaf.”

Photometric measurements carried out through filters
with a band-width (about one-tenth the central wavelength) in the range 30-100 nm. Typical examples are Johnson photometry, Krons-Cousins RI photometry, and the six-color system.

See also: → broad; → band; → photometry.

A radio galaxy that shows broad optical emission lines. → broad-line region.

See also: → broad; → line; → radio galaxy.

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.

See also: → broad; → line; → region.

To make or become broad or broader.

Etymology (EN): → borad.

Etymology (PE): Pahnidan, from pahn, → broad, + -idan infinitive suffix.

The act of making something wider. → instrumental broadening; → line broadening.

Etymology (EN): Broadening, from → broad + → -ing noun froming suffix.

Etymology (PE): Pahneš, from pahn (→ broad, present tense stem of pahnidan “to broaden” + -idan infinitive suffix) + eš verbal-noun suffix.

Same as the → Coathanger and Collinder 399.

See also: Named after the American amateur astronomer D. F. Brocchi who created a map of the cluster in the 1920s for calibrating photometers; → cluster.

A system of connected line → segments joined end to end.

See also: Past participle of → break; → line.

The only liquid non-metallic chemical element; symbol Br. → Atomic number 35; → atomic weight 79.904; → melting point -7.2°C; → boiling point 58.78°C; → specific gravity of liquid 3.12 at 20°C; → valence -1, +1, +3, +5, or +7.

A member of the halogen group of elements. Volatilizes readily at room temperature to a red vapor with strong disagreeable odor and very irritating effect on the eyes and throat. Occurs in combination with various metals, as potassium, sodium and magnesium bromides, which are found in mineral waters, in river and sea-water, and occasionally in marine plants and animals. Its compounds are widely used in photography and medicine. Discovered by Antoine-Jerome Balard (1802-1876) in 1826. Its two stable → isotopes are ⁷⁹Br (50.69%) and ⁸¹Br (49.31%).

Etymology (EN): From Fr. brome, from Gk. bromos for “stench, bad odor,” coined by its discoverer.

Etymology (PE): Brom, loan from Fr., as above.

A class of → alloys in which → copper and → tin are the dominant elements. The name
is extended by usage to include many other copper-rich alloys containing → phosphorus, → manganese, → aluminium, or → silicon.

Etymology (EN): From Fr. bronze, from It. bronzo, from M.L. bronzium, of unknown origin, maybe from Iranian, cf. Mid.Pers. brinj “bronze, brass;” Mod.Pers. berenj “brass.”

Etymology (PE): Boronz, loan from Fr., as above. Mefraq, from Ar.

A period of time between the → Stone Age and the → Iron Age when bronze was used widely to make tools, weapons, and other implements. The Bronze Age starts at different areas of the world at different times. The earliest use of bronze for making farm tools and weapons are found in Near and Middle East and date back to about 3700 BC. The Bronze Age starts about 2300 BC in Europe.

See also: → bronze; → age.

Son of the same parents as another person.

Etymology (EN): M.E.; O.E. brothor; cognate with Du. broeder, Ger. Bruder, Goth. brothar, Skt. bhrātr, Gk. phrater, L. frater, Pers. barâdar, as below, Rus. brat; PIE *bhrater.

Etymology (PE): Barâdar, from Mid.Pers. brât(ar) “brother;” O.Pers. brata-; Av. brātar- “brother;” cognate with E. brother, as above.

A dusky color between red and black.

Etymology (EN): M.E. broun, from O.E. brun “dark,” cf. Du. bruin, Ger. braun; PIE base *bher- “shining, brown,”
related to *bheros “dark animal” (cf. beaver, bear).

Etymology (PE): Qahvei-yi, color of qahvé “coffee.”

A star-like object whose mass is too small to sustain
→ hydrogen fusion in its interior and become a star. Brown dwarfs are → substellar objects and occupy an intermediate regime between those of stars and giant planets.
With a mass less than 0.08 times that of the Sun (about 80 → Jupiter masses), nuclear reactions in the core of brown dwarfs are limited to the transformation of → deuterium into ³He. The reason is that the cores of these objects are supported against → gravitational collapse by electron → degeneracy pressure (at early spectral types) and → Coulomb pressure (at later spectral types). Brown dwarfs, as ever cooling objects, will have late M dwarf spectral types within a few Myrs of their formation and gradually evolve as L, T and Y dwarfs → brown dwarf cooling. As late-M and early-L dwarfs, they overlap in temperature with the cool end of the stellar → main sequence (→ M dwarf, → L dwarf, → T dwarf,
→ Y dwarf). In contrast to the OBAFGKM sequence, the M-L-T-Y sequence is an evolutionary one.
These objects were first postulated by Kumar (1963, ApJ 137, 1121 & 1126) and Hayashi & Nakano (1963, Prog. Theor.Phys. 30, 460).

See also: The term brown dwarf was first used by Jill Tarter in her 1975 PhD thesis; → brown; → dwarf.

The process whereby a → brown dwarf cools over time after the → deuterium burning phase, which lasts a few 10⁷ years. The → effective temperature and luminosity decrease depending on the mass, age, and → metallicity. Even though massive brown dwarfs may start out with star-like luminosity (≥ 10^-3→ solar luminosities), they progressively fade with age to the point where, after 0.5 Gyr all → substellar objects are less luminous than the dimmest, lowest mass stars. More explicitly, brown dwarfs may start as star-like objects hotter than 2200 K, with → M dwarf spectral types, and, as they get older, pass through the later and cooler L, T, and Y spectral types (→ L dwarf, → T dwarf, → Y dwarf).

See also: → brown; → dwarf; → cooling.

The observational result indicating a deficit in the frequency of → brown dwarf companions to Sun-like stars,
either relative to the frequency of less massive planetary companions or relative to the frequency of more massive stellar companions.
However, this desert exists mainly for low-separation brown dwarfs detected using orbital velocity surveys. No brown dwarf desert is noticed at wide separations (J. E. Gizis et al. 2001, ApJ 551, L163).

See also: → brown; → dwarf; → desert.

The continuous random motion of solid microscopic particles immersed in a fluid, which is due to bombardment by the atoms and molecules of the medium. It is named after the botanist Robert Brown, who in 1827 first noticed that pollen seeds suspended in water moved in an irregular motion. While there were suspicions that the motion was caused by the collision of atoms against the particles, the first quantitative explanation of the phenomenon, based on the kinetic theory of gases, was forwarded by A. Einstein in 1905. When Einstein’s paper appeared, the notion of atoms and molecules was still a subject of heated scientific debate. Ernst Mach and the physical chemist Wilhelm Ostwald were among those who chose to deny their existence.

Etymology (EN): Named after Robert Brown (1773-1858), a Scottish botanist, who first in 1827 noticed the erratic motion of pollen grains suspended in water. → motion.

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.

See also: 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.