The 15-year wait is over! At 00:15 Universal Coordinated Time on August 11, the moment of equinox arrived at Saturn, and Cassini was on hand to witness this spectacle of sunlight and shadow. A series of raw, unprocessed images has just beamed back from the spacecraft, and a few are posted here.
Equinox occurs every half-Saturn-year which is equivalent to about 15 Earth years. The illumination geometry that accompanies equinox lowers the sun's angle to the ringplane and causes out-of-plane structures and some moons to cast long shadows across the rings. The ring shadows themselves have become a rapidly narrowing band cast onto the planet.