September 18, 2009
Rhea joins other Saturnian moons in casting a shadow on the rings in this image taken as the planet approached its August 2009 equinox.
From the middle left to upper right of the image, the moon's long shadow can be seen crossing several rings and features: the A ring, the Encke Gap, the outer A ring, the wide Roche Division and the thin F ring.
The larger shadow of the planet cuts across the rings in the lower right of the image. The night side of the planet is dimly illuminated here by ringshine, the southern hemisphere more so than the north. The excess brightness in the lower left of the image is lens flare, an artifact resulting from light being scattered within the camera optics.
The novel illumination geometry created around the time of Saturn's August 2009 equinox allows 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 Moon Shadow in Motion and Weaving a Shadow.
This view looks toward the unilluminated side of the rings from about 17 degrees above the ringplane.
The image was taken in visible light with the Cassini spacecraft wide-angle camera on July 21, 2009. The view was obtained at a distance of approximately 1.9 million kilometers (1.2 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 127 degrees. Image scale is 110 kilometers (68 miles) per pixel.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. 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 and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.
Credit: NASA/JPL/Space Science Institute