This time-lapse movie shows the icy moons Mimas, Enceladus, Dione, and Tethys rounding Saturn when the planet's rings were tilted nearly edge-on toward the Sun. This edge-on alignment occurs once every 15 years.
The rings' shadow appears as a thin, almost invisible line across the planet. Since Saturn's moons orbit mostly in the same plane as the rings, their shadows can be seen skirting the planet's surface just above the rings.
The moons appear to be moving along an invisible race track as they speed along their orbital paths. Their speeds are based on their respective distances from Saturn. The faster moons are closest to the planet. Mimas and Enceladus appear first. Mimas is chasing after Enceladus as the pair race across Saturn. 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 the next moon to make its appearance. 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.
Publication: March 20, 2007