Shepherd’s Shadow

The shepherding moon Pandora, near the bottom of the image, casts a shadow on Saturn's thin F ring as the planet nears its August 2009 equinox.

Pandora (81 kilometers, or 50 miles across) orbits outside the F ring and, with the inner shepherd moon Prometheus (not seen in this image), helps to keep the narrow lanes of the F ring in check.

The novel illumination geometry that accompanies equinox lowers the sun's angle to the ringplane and causes out-of-plane structures to cast long shadows across 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
Moon Shadow in Motion and Weaving a Shadow.

This view looks toward the unilluminated side of the rings from about 15 degrees above the ringplane. The image was taken in green light with the Cassini spacecraft wide-angle camera on June 25, 2009. The view was acquired at a distance of approximately 575,000 kilometers (357,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 25 degrees. Image scale is 31 kilometers (19 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 .

Credit: NASA/JPL/Space Science Institute