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Saturn's moon Prometheus casts a narrow shadow on the rings near the much larger shadow cast by the planet in this Cassini image taken about five months after Saturn's August 2009 equinox.
Prometheus (86 kilometers, 53 miles across) orbits in the Roche Division between the A ring and the thin F ring, and its shadow can be seen on the F ring above the middle of the image. The shadow of the planet covers the upper left of the image. Several background stars are visible.
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 southern, unilluminated side of the rings from about 10 degrees below the ringplane.
The image was taken in visible red light with the Cassini spacecraft narrow-angle camera on Jan. 2, 2010. The view was acquired at a distance of approximately 2.3 million kilometers (1.4 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 102 degrees. Image scale is 13 kilometers (8 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.