eyes aren't playing tricks on you. This image of a massive cluster
of galaxies, called Abell 2218, does show several arc-shaped
patterns, which are duplicate images of galaxies that lie five
to 10 times farther than Abell 2218. How can that happen? The
cluster is so massive that its enormous gravitational field
bends, distorts, and duplicates light rays passing through it.
This phenomenon is called a gravitational lens.