The phase velocity, ray velocity, and group velocity surfaces for a magneto-ionic medium

The phase velocity surface for waves propagating in a uniform cold plasma is sometimes misinterpreted as having the shape of a wave-front. A summary is presented of the correct interpretations of the phase velocity, ray velocity, and group velocity surfaces. A full set of computer generated plots of such surfaces is presented. These are intended as an aid to visualization of wave propagation in such a medium. (author)