A pair of Saturn's moons accompany the planet and its rings in this image taken shortly after the planet's August 2009 equinox.
Dione (1123 kilometers, 698 miles across) is in top left of the image. Tethys (1062 kilometers, 660 miles across) is on left, below Dione in the image. The vertically thin rings cast a narrow shadow on the planet around the time of equinox. This view looks toward the northern sunlit side of the rings from about 12 degrees above the ringplane. The rings have been brightened relative to the planet to increase visibility.
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).
The image was taken in visible light with the Cassini spacecraft wide-angle camera on Aug. 18, 2009. The view was obtained at a distance of approximately 2.2 million kilometers (1.4 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 114 degrees. Image scale is 131 kilometers (81 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 http://ciclops.org, http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.
Credit: NASA/JPL/Space Science Institute
Released: October 2, 2009 (PIA 11593)
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PIA 11593
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