Circles, Curves, and a Line

In this image, Cassini the spacecraft's cameras captured one of Cassini the astronomer's moons - Tethys - and the rings, edge-on. As the light strikes the rings from below, great sweeping shadows are cast on the planet's surface, revealing the complex structure of the rings which, in the picture, look like a straight line. Tethys, one of the larger moons (witness the early date of its discovery - 1684), orbits inside the E Ring (which is created by Enceladus's cryovolcanic activity) but outside the F Ring.

See the Cassini-Huygens page for details.