Cassini Division
The Cassini Division is a 4,800 km (3,000 mi) wide region between the A Ring and B Ring. It was discovered in 1675 by Giovanni Cassini at the Paris Observatory using a refracting telescope that had a 2.5 inch objective lens with a 20 foot long focal length and a 90x magnification. From Earth it appears as a thin black gap in the rings. However, Voyager discovered that the gap is itself populated by ring material bearing much similarity to the C Ring. The division may appear bright in views of the unlit side of the rings, since the relatively low density of material allows more light to be transmitted through the thickness of the rings (see second image in gallery).
The inner edge of the Cassini Division is governed by a strong orbital resonance. Ring particles at this location orbit twice for every orbit of the moon Mimas. The resonance causes Mimas' pulls on these ring particles to accumulate, destabilizing their orbits and leading to a sharp cutoff in ring density. Many of the other gaps between ringlets within the Cassini Division, however, are unexplained.
Read more about this topic: Rings Of Saturn
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