Radio galaxies and quasars

Observations of radio emission from radio galaxies and quasars are reviewed and possible emission mechanisms are discussed. Consideration is given to the observed structure and energy of the giant radio galaxies, very rapid variations in the flux density and size of compact radio sources, evidence of superluminal expansion in the quasars 3C 273, 3C 279 and 3C 345 and the Seyfert galaxy 3C 120 and the stationary sources NGC 1275 (an active galaxy) and 4C 39.25 (a quasar). The physical interpretation of the apparent superluminal motion observed in some of these sources in terms of the relativistic expansion of the synchrotron source aligned nearly along the line of sight is discussed, and problems with this model are indicated