CICLOPS: Cassini Imaging Central Laboratory for OPerationS

Along the F Ring
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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, 53 miles across) periodically creates streamer-channels in the F ring. See PIA10461 and PIA10593 to learn more. To watch a movie of this process, see PIA08397.

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 PIA11651 and PIA11660.

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 Equinox Mission is a joint United States and European endeavor. 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 was designed, developed and assembled at JPL. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini Equinox Mission visit, and

Credit: NASA/JPL/Space Science Institute
Released: August 17, 2009 (PIA 11559)
Image/Caption Information
  Along the F Ring
PIA 11559

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