An Etymological Dictionary of Astronomy and Astrophysics
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The ratio of the → effective aperture of a radio telescope to the true aperture.

→ aperture; → efficiency.

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.

Fraction of the original charge which is successfully transferred from one pixel to the next in one CCD cycle.

→ charge; → transfer; → efficiency.

The fraction of → star formation which happens in → bound clusters. It is defined as the ratio between the → cluster formation rate and → star formation rate (Bastian, 2008, MNRAS 390, 759, arxiv/0807.4687).

→ cluster; → formation; → efficiency.

The square of the ratio of the output → signal-to-noise (S/N) to the input S/N.

Detective, adj. of → detect; → quantum; → efficiency.

1) The state or quality of being efficient; competence. Compare → effectiveness.
Of a machine, engine, or device, the ratio of the physical quantity which may be stored, transferred, or transformed to the total input quantity.

L efficientia, from efficient-, → effect, + -ia "-y," an E. suffix of adjectives.

Kârâyi, from kârâ "efficient," from kâr, → work + â present stem of âmadan "to come," from Av. ay- "to go, to come," aēiti "goes," O.Pers. aitiy "goes," Skt. e- "to come near," eti "arrival," Gk. eimi "I go," L. eo "I go," Tokharian AB i-; PIE *ei- "to go, to walk."

The measure of the light intensity diffracted from a grating.

→ grating; → efficiency.

In a detector, the ratio of the number of photoelectrons released to the number of incident photons at a specific wavelength.

→ quantum; → efficiency.

The degree to which stars form in a system, such as a → molecular cloud or a → galaxy. It is given by the ratio of the total mass of stars to the initial gas mass: ε_SFE = M_stars / (M_stars + M_gas).

→ star formation; → efficiency.