Several examples of `intrinsic-type' superluminal motion in astronomy are taken. A simple signal-delay transformation is devised and shown to be sufficient to explain the superluminal effect as resulting from differential signal delay across an expanding source. The distinction between relativistic motion and relativistic kinematics is made. The key kinematical equation used to describe superluminal motion is an alternative statement of the Doppler effect. Relativistic transformations, which are relevant when intervals in different reference frames are compared, then lead to the relativistic Doppler factor (δ), which is applicable to measurements on a photographic image, for example that of a relativistic quasar jet with superluminal components.

The echo produced when a light 'pulse' from a stellar source (e.g. a nova or supernova) is reflected by circumstellar or interstellar material can appear as a luminous ring expanding at a rate that can be superluminal, i.e. having an apparent motion within the source, transverse to the observer's line of sight, at a speed greater than that of light. 'Light-echo optics' applied to the star RS Puppis and its nebula suggests that when nebular features in peripheral regions of circumstellar-shell images are observed, superluminal effects are not evident; however, such observations can give the stellar distance from the observer. Light-echo optics for an interstellar plane sheet, inclined to the observer's line of sight, can be applied to Nova GK Persei 1901 and SN 1987A, which show superluminal effects. For SN 1987A, an intense thermal x-ray source should be produced in AD 2003, when the advancing supernova ejecta interact with a circumstellar ring, 250 light days in radius: the arc-shaped x-ray image, while not actually a 'radiation echo', should expand at a superluminal rate for about 75 days from the time of its first appearance, and also for the same time before the completion of its 'circuit' around the ring.