Just as the night side of Earth is illuminated by moonlight, Saturn’s night side is lit by light reflected by its rings—“ringshine”. Unlike moonlight, which illuminates the Earth more or less uniformly, ringshine varies with the latitude on Saturn, with the equator (in which plane the rings orbit) receiving little light from the edge-on rings. Since the rings are composed mostly of water ice, they reflect more light than Earth’s dark Moon (although sunlight is, of course, dimmer at Saturn due to its distance from the Sun).
This photo from the Cassini Saturn orbiter is in the near infrared, but ringshine is apparent in visible light as well. Here is another Cassini photo, overexposed on portions illuminated by the Sun, which shows ringshine on a larger portion of the dark side. Note that regions of the disc adjacent to the portion of the rings in Saturn’s shadow receive less ringshine.
