A shadow creates a sharp edge to a ring arc. Credit: NASA/JPL/Space Science Institute

I always find these shots where the rings are cut off by a shadow interesting.   If you watch enough ISS crossings you can see a similar thing happen, the ISS will just wink out before it gets to the horizon, it’s weird to see because it is not expected.

Anyways here is the caption to explain the image from the Cassini site:

The bright arc within Saturn’s G ring is shown truncated by the shadow of the planet at the bottom of this image.

Although it can’t be seen here, the tiny moonlet Aegaeon (formerly known as S/2008 S 1) orbits within the bright arc. See Tiny Moonlet Within G Ring Arc; to learn more. This view looks toward the northern, sunlit side of the rings from about 4 degrees above the ringplane. Many background stars are visible elongated by the motion of the spacecraft during the image’s exposure.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Oct. 9, 2009. The view was obtained at a distance of approximately 2.1 million kilometers (1.3 million miles) from Saturn. Image scale is 12 kilometers (7 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.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .