The moon Prometheus casts a shadow on Saturn's F ring near a streamer-channel it has created on the ring. The image was taken as the planet approached its August 2009 equinox.

Prometheus (86 kilometers, or 53 miles across) and Atlas (30 kilometers, or 19 miles across) both orbit in the Roche Division between the A ring and the thin F ring. Atlas is the smaller moon to the lower left of Prometheus in the image. Other small, bright specks are background stars.

The gravity of potato-shaped Prometheus periodically creates streamer-channels in the F ring. To learn more and to watch a movie of this process, see PIA08397.

The novel illumination geometry created around the time of Saturn's August 2009 equinox allows moons orbiting in or near the plane of Saturn's equatorial rings to cast shadows onto the rings. These scenes are possible only during the few months before and after Saturn's equinox, which occurs only once in about 15 Earth years. To learn more about this special time and to see movies of moons' shadows moving across the rings, see PIA11651 and PIA11660.

This view looks toward the unilluminated side of the rings from about 47 degrees above the ringplane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on June 30, 2009. The view was acquired at a distance of approximately 1.9 million kilometers (1.2 million miles) from Atlas and at a Sun-Atlas-spacecraft, or phase, angle of 88 degrees. Image scale is 11 kilometers (7 miles) per pixel.

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.