The most distinguishing feature of the sixth planet from the Sun is the spectacular ring system in the equatorial plane of Saturn. This image was taken as Voyager 1 made its closest approach to Saturn and was moving away from the planet at a 30° angle from the plane of the rings. The image clearly shows the ring system surrounding a gaseous planet 9.5 times the diameter of Earth. The dark band within the rings is named the Cassini division, after the astronomer who first described it. The location of the Cassini division corresponds to the distance at which a ring particle would orbit Saturn twice in the same time that the moon Mimas orbited once; such an orbital “resonance” causes ring particles to be gravitationally forced away from the resonance location, hence clearing out that portion of the ring system. This perspective, of crescent Saturn casting its shadow on the rings, cannot be seen from Earth.
Voyager 1 image (Press Release P-23254).