CICLOPS: Cassini Imaging Central Laboratory for OPerationS
Shadow Before Equinox

Saturn's moon Prometheus casts a long shadow across the A ring in the lower right of this Cassini image taken shortly before the planet's August 2009 equinox.

Prometheus (86 kilometers, 53 miles across) orbits in the Roche Division between the thin F ring and the A ring. The novel illumination geometry created around the time of Saturn's August 2009 equinox allows out-of-plane structures and 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 PIA11651 and PIA11660.

This view looks toward the northern, unilluminated side of the rings from about 31 degrees above the ringplane. Many stars are visible. The rings and stars have been brightened by a factor six relative to Prometheus to enhance visibility.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 29, 2009. The view was acquired at a distance of approximately 1.4 million kilometers (870,000 miles) from Prometheus and at a Sun-Prometheus-spacecraft, or phase, angle of 93 degrees. Image scale is 9 kilometers (5 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 20, 2010 (PIA 12703)
Image/Caption Information
  Shadow Before Equinox
PIA 12703

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Alliance Member Comments
iwanttogotothere (Aug 21, 2010 at 4:01 AM):
Imagine the view, if you were standing on the moon. Actually, I can't even imagine that view!
stowaway (Aug 20, 2010 at 7:17 AM):
Who's been keeping this one from us?