  We reconsider the case of the geodesic motion of a massive and massless beam
of test particles in a gravitational wave. In particular, we use a direct
Lagrangian approach which simplifies the calculation. Our findings differ
partly from previously performed calculations The final result can be
interpreted as rings of light seen by the observer. We give a new
interpretation to this picture and show that over large distances the effect,
albeit rare, could in principle be observable.
