Figure 1

Figure 1: Illustration of the exact lens map. p O is the chosen observation event, T is the chosen source surface. T is a hypersurface ruled by timelike curves (worldlines of light sources) which are labeled by the points of a 2-dimensional manifold Q. The lens map is defined on the observer’s celestial sphere SO, given by Equation (1View Equation), and takes values in Q. For each w (- SO, one follows the lightlike geodesic with this initial direction until it meets T and then projects to Q. For illustrating the exact lens map, it is an instructive exercise to intersect the light cones of Figures 12, 24, 25, and 29 with various source surfaces T.