August 17, 2009
Saturn's moon Janus casts a shadow on the F and A rings while the moon Prometheus, seen on the left of the image, creates a streamer-channel in the thin F ring.
The gravity of potato-shaped Prometheus (86 kilometers,or 53 miles across) periodically creates streamer-channels in the F ring. See Opening a Channel and Busy Moon to learn more. To watch a movie of this process, see Soft Collision.
Janus, the moon casting the shadow, is not shown in this image taken as Saturn approaches its August 2009 equinox. Six background stars are visible. They appear elongated by the camera's long exposure time.
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 28 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on June 20, 2009. The view was acquired at a distance of approximately 1.7 million kilometers (1.1 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 123 degrees. Image scale is 10 kilometers (6 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