September 21, 2009
The Cassini spacecraft snags a close-up view of the shadow cast onto Saturn's A ring by the moon Epimetheus as the planet approached its August 2009 equinox.
Epimetheus (113 kilometers, or 70 miles across) is not pictured here. See Moon Shadow in Motion for an earlier, wide-angle-camera view which showed a short shadow from Epimetheus.
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, unilluminated side of the rings from about 19 degrees above the ringplane.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 11, 2009. The view was obtained at a distance of approximately 447,000 kilometers (278,000 miles) from Saturn. Image scale is 2 kilometers (1 mile) 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