The ring moon Prometheus continues its work shaping the delicate F ring as Dione looks on. It is easy to see how Prometheus has an irregular, oblong shape, while Dione is quite round.

The rings are partly cut off by Saturn's shadow at right.

Prometheus is 102 kilometers (63 miles) wide; Dione is 1,123 kilometers (700 miles) wide.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 20, 2005, at a distance of approximately 2.5 million kilometers (1.6 million miles) from Dione and 2.2 million kilometers (1.4 million miles) from Prometheus. The image scale is 15 kilometers (9 miles) per pixel on Dione and 13 kilometers (8 miles) per pixel on Prometheus.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at http://ciclops.org.