Saturn's wide, but very thin, rings are tilted with respect to its plane of orbit around the Sun. Once every 15 years, the rings are edge-on (perpendicular) to the Sun. During those times, some of Saturn's moons can cast shadows across the rings.
This time-lapse movie shows the icy moons Enceladus, Mimas, Dione, and Tethys orbiting Saturn. Enceladus, seemingly chased by Mimas, is first to speed past the rings and in front of the planet. Both moons cast small shadows on the planet, but only Enceladus casts a shadow on the rings. The orbit of Mimas is inclined so that its shadow misses the rings. Dione is next, and its long shadow also tracks across the ring system. As the three moons move across Saturn's disk, the viewer catches a fleeting view of Tethys as it moves behind the planet on the right.
The 30-second movie is created from Hubble images taken over a 9½-hour span. The images were taken Nov. 17, 1995, with Hubble's Wide Field and Planetary Camera 2. The movie has a standard aspect ratio, but is presented within a widescreen frame - the black bars along the sides are normal.
E. Karkoschka (Arizona), G. Bacon (STScI)
HubbleSite's NewsCenter is the place to find the story behind this video, along with its original news release and all related material.