Gravitational lensing. Coloured visible light image of gravitational arcs in the galaxy cluster Abell 2218. The thin arc-like features seen scattered around the frame are made by light from very distant sources, some 5-10 times further away than Abell 2218. The cluster is so massive that light rays from background galaxies passing through it are deflected and magnified by the cluster's gravity, similar to the way an optical lens bends light to form an image. The study of these arcs will provide a direct glimpse of the evolution of early galaxies. The image was taken by the Hubble Space Telescope.