  The propagation of a wave in a medium is generally affected when the medium
is moving with respect to the observer. Because plasma equilibria often involve
plasma flows, for instance in astrophysics or in magnetic confinement nuclear
fusion devices, understanding the effect of motion on plasma waves is
important. Meanwhile, the presence of a background magnetic field in a plasma
makes it anisotropic. To address this problem, we derive here ray tracing
equations for the trajectory of rays propagating in a moving anisotropic
medium. The proposed approach is to use an effective dispersion relation for
the moving medium as seen from the laboratory, obtained by performing a Lorentz
transformation of the dispersion relation known for the medium at rest. This
formalism is illustrated by considering the standard ordinary and extraordinary
modes in a magnetized plasma at rest. Although we work here at lowest order in
the geometrical optics approximation, this method is a first step towards
higher order expansions, as required for instance to capture polarization
effects.
