September 1, 2009
The shadow of the moon Epimetheus crosses Saturn's rings in this image taken as the planet approached its August 2009 equinox.
The moon Epimetheus (113 kilometers, or 70 miles across), a co-orbital companion to the moon Janus, is not pictured here, but its shadow starts near the middle of the B ring and stretches to the Maxwell Gap in the C ring.
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 Moon Shadow in Motion and Weaving a Shadow.
This view looks toward the unilluminated side of the rings from about 23 degrees above the ringplane. The rings have been brightened relative to the planet to enhance visibility. The excess brightness in the middle of the image is lens flare, an artifact resulting from light being scattered within the camera optics.
The image was taken in visible light with the Cassini spacecraft wide-angle camera on July 11, 2009. The view was obtained at a distance of approximately 470,000 kilometers (292,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 25 degrees. Image scale is 25 kilometers (16 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.
Credit: NASA/JPL/Space Science Institute