CICLOPS: Cassini Imaging Central Laboratory for OPerationS
Shadow and Spokes

Shadow and Spokes
PIA 11634

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  A moon's shadow strikes Saturn's rings near bright spokes on the B ring near the center of this Cassini image taken about one month after the planet's August 2009 equinox.

Mimas, the moon casting the shadow, is not shown. To learn more about the ghostly radial markings called spokes, see PIA11144 and PIA08288. Spokes appear bright when they are viewed at phase, or Sun-Saturn-spacecraft, angles higher than about 45 degrees. The phase angle in this image is 106 degrees.

The novel illumination geometry that accompanies equinox lowers the sun's angle to the ringplane, significantly darkens the rings, and causes out-of-plane structures to look anomalously bright and cast 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. Before and after equinox, Cassini's cameras have spotted not only the predictable shadows of some of Saturn's moons (see PIA11657), but also the shadows of newly revealed vertical structures in the rings themselves (see PIA11665).

This view looks toward the northern, sunlit side of the rings from about 8 degrees above the ringplane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Sept. 9, 2009. The view was obtained at a distance of approximately 2.9 million kilometers (1.8 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 106 degrees. Image scale is 17 kilometers (11 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: November 30, 2009 (PIA 11634)
Image/Caption Information

Alliance Member Comments
stowaway (Nov 30, 2009 at 10:08 AM):
This one gets the award for longest shadow cast on rings by a small moon on 999