Long Shadow, Short Shadow
September 4, 2009
The shadow of the moon Janus dwarfs the shadow of Daphnis on Saturn's A ring in this image taken as the planet approached its August 2009 equinox.
Daphnis (8 kilometers, or 5 miles across) orbits in the A ring's Keeler Gap and, along with the moon's attending edge waves, can be seen casting a short shadow in the top left quadrant of the image. Equinox has exposed shadows cast by these edge waves, or vertical structures of ring material created by Daphnis' gravity (see Wave Shadows in Motion).
Janus (179 kilometers, or 111 miles across) is not pictured here, but the moon's shadow stretches across the A ring from the center of the image to near the Encke Gap on the left of the image. The Cassini Division appears bright on the right of the image.
The novel illumination geometry created around the time of Saturn's August 2009 equinox allows out-of-plane structures and 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 27 degrees above the ringplane.
The image was taken in visible light with the Cassini spacecraft wide-angle camera on July 11, 2009. The view was obtained at a distance of approximately 491,000 kilometers (305,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 26 degrees. Image scale is 26 kilometers (16 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