September 25, 2009
The shadow of the moon Enceladus appears on Saturn just south of the thin shadow of the planet's rings in this image captured shortly after Saturn's August 2009 equinox.
Enceladus (504 kilometers, or 313 miles across) is not shown, but Mimas (396 kilometers, or 246 miles across) is visible outside the rings below the middle of the image.
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 Across Resplendent Rings), but also the shadows of newly revealed vertical structures in the rings themselves (see A Small Find Near Equinox).
This view looks toward the northern, sunlit side of the rings from about 11 degrees above the ringplane. The rings have been brightened relative to the planet to enhance visibility.
The image was taken in visible green light with the Cassini spacecraft wide-angle camera on Aug. 19, 2009. 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 115 degrees. Image scale is 132 kilometers (82 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