Published online by Cambridge University Press: 14 August 2015
An intervening galaxy acting as a gravitational lens produces usually from a compact radio source two or four enlarged “crescent” shaped virtual images, which have the same surface brightness as the object, but look brighter, due to the lens caused enlargement of the object area in the image. Velocities between elements of a source being vector quantities, will also be seen enlarged, occasionally to superluminal velocities (Fig.1). It is as simple as that. (Barnothy and Barnothy 1971; Barnothy 1976.)