This 3D movie was made from a sequence of images taken by NASA's Cassini spacecraft as it crossed the plane of Saturn's main rings. The main rings are nearly as broad from edge to edge as the distance from the Earth to the moon but are only a few tens of meters thick -- like a piece of paper the size of Golden Gate Park. Scientists have struggled for centuries to measure their thickness from Earth, without success. The ring particles are centimeters to meters in size, and their gentle collisions keep the rings so strongly flattened.
Note the dramatic change in the appearance of the rings as the ring plane is crossed. Regions containing many particles are opaque (the B ring), so are bright on the sunlit side and dark on the side facing away from the sun. Regions containing only a few particles (the C ring and Cassini Division) appear bright from both the lit and unlit sides.
Credit: Scott Sandford, Astrophysics Branch, NASA-Ames Research Center