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

Being, relating to, or denoting statistical methods based on → Bayes' theorem.

Referring to → Bayes' theorem.

An approach to → statistical analysis in which → unknowns to be estimated have a prior → probability distribution which combined with the information from data produces a posterior probability distribution for the target quantities.

→ Bayesian; → inference.

A mathematical framework described by the prior distribution of a random parameter and by the likelihood of the observations. In this framework, all information on the random parameter based on the observations is included in the posterior distribution which can be obtained using → Bayes' theorem (see, e.g., Andrieu et al., 2001, "An Introduction to Monte Carlo Methods for Bayesian Data Analysis," in Nonlinear Dynamics and Statistics, ed. A. I. Mees, Boston: Birkhäuser).

Bayesian; → model.

An approach to model selection in which one bases inference on an average of all possible models instead of a single best model. The BMA is largely used in various branches of knowledge to properly account for model uncertainty in performing predictions.

→ Bayesian; → model; → average.

The episodic occurrence of abrupt → mass loss in → Be stars resulting in → Balmer lines in emission and → infrared excess. The Be phenomenon results from a combination of a long-term secular effect and short-term instabilities, such as pulsation. The secular evolution brings the star close enough to the critical → break-up velocity, so that the additional velocity field due to the instability may allow some mass ejection (Maeder 2011).

→ Be star; → phenomenon.

A hot star of → spectral type B showing → Balmer lines in emission. Be stars are fast rotators (spinning at about 200 km/sec) and have strong → stellar winds with important → mass loss.

B, referring to the spectral type; e for emission lines; → star.

1) A collection of nearly parallel → light  → rays or a concentrated stream of → particles. See also → beam of light.
2) The area of the sky being observed at any one time by a → radio telescope.
3) The size of the → diffraction pattern; synonymous with point spread function.

M.E. beem, from O.E. beam "tree;" akin to O.H.G boum "tree," Ger. Baum.

Tâbé, from tâb; tâbidan "light; to shine" + -é noun suffix.

A parameter indicating the quality of an antenna as a direction measuring device. It is given by the ratio of the total received power contained in the main beam of an antenna to the total power (including the sidelobes); the same as main beam efficiency. See also → beamwidth.

→ beam; → efficiency.

A relatively large bundle of → rays of light. See also → pencil of light.

→ beam; → light.

A narrow unidirectional flow of particles

→ beam; → particle.

A partially reflecting mirror which permits a part of the light beam to pass through and reflects the rest.

→ beam; splitter, from to split, from M.Du. splitten, from P.Gmc. *spl(e)it-, PIE *(s)plei- "to split, splice."

Fâqgar, from fâq "split, breach, division" + tâbé→ beam.

In single dish radio astronomy, any technique which forms the difference of signals received from two (or more) pointings on the sky without physically moving the main reflector of the antenna. By rapidly forming differences between sky positions that do and do not contain astronomical sources, beam switching can minimize the corruption of spectral baselines by non-idealities in the instrumental frequency response, or of continuum observations by atmospheric fluctuations.

→ beam; → switching.

The angle between the two directions in the main beam at which the power response has fallen to half its maximum value. → beam efficiency.

From → beam + → width.

Tâbe-pahnâ, from tâbé, → beam, + pahnâ "width," → broad.

The periodic and alternatively strengthening and weakening of two waves of similar frequencies when they interfere with one another. In particular, the soft and loud sounds created by the interference of two sound waves of similar frequencies.

M.E. beten, from O.E. beaten, from P.Gmc. *bautan; IER *bhau- "to strike."

Zaneš, noun from zan- present tense stem of zadan "to beat, strike" + -š verbal noun suffix. Zadan 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 Cepheid variable in which two or more almost identical periods of variability pass into and out of phase with each other, producing periodic amplitude fluctuations in their light curves. Beat periods are typically about 2 hours.

→ beat; → Cepheid.

One of the frequencies that results from the combination of two waves of slightly different frquencies. A beat frequency is equal to the absolute value of the difference between the two frequencies. An unknown frequency can be determined by beating it with a reference frequency. More specifically, when the two frequencies are superimposed, the phase difference will change with time and wave interference alternate between constructive and destructive. The alterations of intensity brings about a beat frequency.

→ beat; → frequency.

A system for estimating and reporting wind speeds which has 13 standardized categories and associated descriptions. The Beaufort scale ranges from 0 for complete calm to 12 for a cyclone. In this scale, the wind speed (in km/h) equals 3B^1.5, where B is the Beaufort number of the wind. The scale was originally devised for use at sea but has subsequently been modified for use over land.

Named after Admiral Sir Francis Beaufort (1774-1857), who introduced the first version of the system in 1805; → scale.

A combination of qualities that pleases the mind.

M.E. be(a)ute, from O.Fr. beautez, beltet "beauty, seductiveness, beautiful person" from V.L. bellitatem (nominative bellitas) "state of being handsome," from L. bellus "pretty, charming."

Zibâyi, from zibâ "beautiful," related to zib "beauty, elegance, ornament," zibidan "to suit, to adorn."

A large, amphibious rodent of the genus Castor, having sharp incisors, webbed hind feet, and a flattened tail, noted for its ability to dam streams with trees, branches, etc. (Dictionary.com).

M.E. bever, O.E. beofor, befor; cognate with Ger. Biber; Av. bawra-, bawri- "beaver" (Mid.Pers. bawrak "beaver"); Skt. babhrav- "reddish-brown," babhrus- "mangoose," L. fiber "beaver" (Fr. bièvre "River of Beavers"); O.H.G. biorr; Lith. bêbrus; Rus. bobr "beaver."

Bidastar "beaver," of unknown origin.

For the reason that; on account of.

M.E. bi cause "by cause," from O.E. bi "by" (akin to Du. bij, O.H.G. bi, Ger. bei, Goth. bi) + → cause.

Zirâ, variants azirâ, zirâk, azirâk, from Mid.Pers. êt rây cê or ê(t) râd cê "because," literally "this reason why;" from êd "this" (O.Pers. aita; Av. aēta "this;" cf. Skt. etá); rây, → reason; cê "what" (O.Pers/Av. ci- "what, any," collateral stem to ka- "who?, what?;" cf. Skt. ka-; Gk. po-; L. quo-; E. what, who; PIE *qwos/*qwes).