| Three mirrors arranged
perpendicularly to each other form an interesting type of reflector.
Light rays that enter the corner exit parallel and opposite to their
original direction. When visitors look into this set of mirrors,
they see themselves with their dominant eye centered at the vertex
of the three mirrors. A set of these reflectors in the form of prisms
was left on the moon by the Apollo astronauts, allowing scientists
to determine the distance to the moon to an accuracy of 6 inches.