August 28, 2009
The shadow of the moon Janus crosses the Encke Gap as it strikes the plane of Saturn's rings in this image taken as the planet approached its August 2009 equinox.
Janus (179 kilometers, or 111 miles across) is not shown here, but the moon's shadow appears on the A ring. Prometheus (86 kilometers, or 53 miles across) can be seen near the bottom of the image as it orbits in the Roche Division between the A ring and the thin F 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 sunlit side of the rings from about 41 degrees below the ringplane.
The image was taken in visible red light with the Cassini spacecraft wide-angle camera on June 9, 2009. The view was obtained at a distance of approximately 575,000 kilometers (357,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 76 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.
Credit: NASA/JPL/Space Science Institute