The moon Enceladus passes behind the larger moon Tethys, as seen in this pair of Cassini spacecraft images.The image on the left was taken a little more than a minute before the image on the right. These images are part of a "mutual event" sequence in which one moon passes close to or in front of another. Such observations help scientists refine their understanding of the orbits of Saturn's moons.The images were taken in visible light with the Cassini spacecraft narrow-angle camera on Nov. 11, 2009. The view was obtained at a distance of approximately 2.6 million kilometers (1.6 million miles) from Enceladus (504 kilometers, or 313 miles across) and 2.3 million kilometers (1.4 million miles) from Tethys (1,062 kilometers, or 660 miles across).Scales on Tethys and Enceladus in the original images were 14 kilometers (9 miles) per pixel and 16 kilometers (10 miles) per pixel, respectively. The images were contrast enhanced and magnified by a factor of two to enhance the visibility of surface features.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.