April 5, 1995: This Hubble telescope image of a rich cluster of galaxies called Abell 2218 is a spectacular example of gravitational lensing. The arc-like pattern spread across the picture like a spider web is an illusion caused by the cluster's gravitational field.
This cluster of galaxies is so massive and compact that light rays passing through it are deflected by its enormous gravitational field, much as a camera's lens bends light to form an image. This phenomenon magnifies, brightens, and distorts images of those faraway objects, providing a powerful "zoom lens" for viewing galaxies that are so far away they could not normally be observed with the largest telescopes.
Credit: W.Couch (University of New South Wales), R. Ellis (Cambridge University), and NASA