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

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.

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

→ 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.

→ 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).

→ break; → through.

Tarâšekâft, from tarâ-, → trans-, + šekâft, past stem of šekâftan "to split, break, tear," → fission.

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.

The dividing point in a galaxy's spectrum at wavelengths shorter than the → Lyman limit. Galaxies contain large amounts of → neutral hydrogen which is very effective at absorbing radiation shortward of 912 Å. Hence galaxies are virtually dark at these wavelengths.

→ Lyman; → break.

A star-forming galaxy at → high redshift affected by the → Lyman break. Such a galaxy is detected in the red (R, → photometric band) but not in the blue (U and B bands). At those high redshfits (above 2.5), the → Lyman limit at 912 Å is shifted between the U and B bands.

→ Lyman; → break; → galaxy.

A burst of very bright → ultraviolet or → soft X-ray radiation expected to occur in → core-collapse supernovae at the instant when the → supernova shock breaks out of the stellar surface. During the collapse of the progenitor → massive star, the density in the iron core increases drastically. Once the core material reaches → nuclear density, the core rebounds generating a → shock wave that moves outward through the star. When the shock reaches the outermost layers, it ejects them out into space at → relativistic speeds.

→ shock; breakout "a forceful escape from being confined or restrained," from break, from M.E. breken, O.E. brecan (cf. Du. breken, O.H.G. brehhan, Ger. brechen), from PIE base *bhreg- "to break" (see also → fraction) + → out.

Borunzani "emergence, evasion," from borun, → out, + zani verbal noun of zadan "to strike, beat," from Mid.Pers. zatan, žatan; O.Pers./Av. jan-, gan- "to strike, hit, smite, kill" (jantar- "smiter"); cf. Skt. han- "to strike, beat" (hantar- "smiter, killer"); Gk. theinein "to strike;" L. fendere "to strike, push;" Gmc. *gundjo "war, battle;" PIE *g^when- "to strike, kill."

A physical phenomenon whereby a symmetric system becomes permanently asymmetric. A simple example is a ball lying on top of a hill in equilibrium. The hill-ball system is symmetric about the vertical axis through the top of the hill. Moreover, there is no preferred horizontal direction to the system. However, its state is unstable, since the slightest perturbing force will cause the ball to roll down the hill in some particular direction. The system becomes permanently asymmetric because the ball will not roll uphill by itself. Symmetry breaking is found in several fields of physics, for example in → magnetism (→ ferromagnetism), → thermodynamics (→ crystallization), and → particle physics, where it constitutes the basis of → electroweak interactions. In cosmology, according to the → Big Bang model, the fundamental forces of the Universe split off from one another in a form of spontaneous symmetry braking. If a single, unified force existed with a certain symmetry just after the Big Bang, if that symmetry were somehow broken so that the unified force were fractured, then the result might be several fundamental forces. See also → grand unified theory, → theory of everything, → phase transition.

→ spontaneous; → symmetry; → break.