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 [2], Earth [3] and Mars [4]. It happens when sunlit objects (such as the icy particles that make up Saturn's rings) hide their own shadows [5]. A process called coherent backscattering [6] may also contribute to the extra luminosity.
Link: Spaceweather.com [7]
Links
[1] //soundofheart.org/galacticfreepress/content/saturns-rings-surge-brightness
[2] http://www.atoptics.co.uk/atoptics/oppos1.htm
[3] http://www.atoptics.co.uk/atoptics/oppeim.htm
[4] http://www.atoptics.co.uk/atoptics/oppmars.htm
[5] http://www.atoptics.co.uk/atoptics/oppos2.htm
[6] http://www.sciencemag.org/cgi/content/abstract/260/5107/509
[7] http://spaceweather.com/
[8] //soundofheart.org/galacticfreepress/tags/saturn
[9] //soundofheart.org/galacticfreepress/category/type-post/galactic-free-press