Realistic modelling of radiation transfer in and from variable accretion
disks around black holes requires the solution of the problem: find the
constants of motion and equation of motion of a light-like geodesic connecting
two arbitrary points in space. Here we give the complete solution of this
problem in the Schwarzschild space-time.Comment: 14 pages, 10 figures, type C orbits added, analytic solutions for
time of flight of photons for all 3 types of orbits adde