  The Kastor-Traschen metric is a time-dependent solution of the
Einstein-Maxwell equations with positive cosmological constant $\Lambda$ which
can be used to describe an arbitrary number of charged dynamical black holes.
In this paper, we consider the null geodesic structure of this solution, in
particular, focusing on the projection to the space of orbits of the timelike
conformal retraction. It is found that these projected light rays arise as
integral curves of a system of third order ordinary differential equations.
This system is not uniquely defined, however, and we use the inherent freedom
to construct a new system whose integral curves coincide with the projection of
distinguished null curves of Kastor-Traschen arising from a magnetic flow. We
discuss our results in the one-centre case and demonstrate a link to conformal
circles in the limit $\Lambda \rightarrow 0$. We also show how to construct
analytic expressions for the projected null geodesics of this metric by
exploiting a well-known diffeomorphism between the K-T metric and extremal
Reissner-Nordstrom deSitter. We make some remarks about the two-centre solution
and demonstrate a link with the one-centre case.
