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

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.

Same as → collider.

→ collide; → beam; → accelerator.

A → beam of → photons or → subatomic particles with a narrow → cross section that has little or no spatial spread.

→ collimated; → beam.

The angle between extreme points of the main lobe of an antenna pattern where the sensitivity of the antenna is half the value at the center of the lobe. This is the nominal resolving power of the antenna system.

→ half; → power; → beam; → width.

Same as → main lobe.

→ main; → beam.

A beam of radiant energy in the form of a narrow cone or cylinder.

→ pencil; → beam.