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

Prefix meaning "to, toward, addition to, near," from L. ad "to, toward." It is modified to ac- or af- or ag- or al- etc. according to the following consonant.

Cognate with E. at, from O.E. æt "near, by, at"; compare with O.N., Goth. at, O.Fris. et, O.H.G. az, Skt. adhi "near," PIE *ad- "to, near, at".

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.

→ broad; → band; → photometry.

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

→ 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.

→ broad; → line; → region.

A member of the class of radio galaxies (→ radio galaxy) that have a strong radio emission coming from a bright "head" and a more diffuse emission from a "tail." They are often found in clusters.

→ head; → tail; → galaxy.