Epimetheus' Long Shadow
October 1, 2009
The long shadow of a small moon cuts across Saturn's A ring and thin F ring in this image taken as the planet approached its August 2009 equinox.
The moon Epimetheus (113 kilometers, or 70 miles across) is not pictured here, but the moon's shadow stretches past the Encke Gap of the A ring in the upper right of the image. See Moon Shadow in Motion for an earlier view which showed a shorter shadow from Epimetheus.
The shadow does not appear uniformly dark on all parts of the ring because this view is of the unlit side of the rings and the particle density of the rings varies. See Weaving a Shadow to learn more.
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 28 degrees above the ringplane.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 30, 2009. The view was obtained at a distance of approximately 1.7 million kilometers (1.1 million miles) from Saturn. Image scale is 10 kilometers (6 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