Spaceweather.com - 4/29/13
"The rings are very bright due to the Seeliger Effect," says Go. Also known as the "opposition effect," the Seeliger effect has been observed on the Moon, Earth and Mars. It happens when sunlit objects (such as the icy particles that make up Saturn's rings) hide their own shadows. A process called coherent backscattering may also contribute to the extra luminosity.
Link: Spaceweather.com
