Who turned out the lights on Saturn's rings?
Well nobody, recently Saturn entered its equinox, meaning the Sun is directly above the equator. As the rings are in the same plane as the equator, they receieve much less light showing only an edge on profile towards the Sun.
This happens every 14.8 years as it travels around the Sun but this is the first time we've had a spacecraft in orbit to capture it. The above image is composed of 75 different exposures, and has had the rings brightened to make them more visible.
For the full size, ideal for wallpapers hit the Cassini imaging website.