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Twice-lit Janus

Nov. 19, 2009
Janus, Saturn's small moon named after the two-faced god, here displays two illuminated hemispheres taken by NASA's Cassini spacecraft.

Janus, Saturn's small moon named after the two-faced god, here displays two illuminated hemispheres.

Janus (179 kilometers, or 111 miles across) orbits beyond the thin F ring in the top left of the image. The moon is lit by sunlight on the left and light reflected off Saturn on the right.

This image, taken a little more than a week after Saturn's August 2009 equinox, also shows vertical structures in the F ring casting faint shadows near the middle right of the image. 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 PIA11657), but also the shadows of newly revealed vertical structures in the rings themselves (see PIA11665).

This view looks toward the northern, sunlit side of the rings from about 10 degrees above the ringplane.

The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on Aug. 20, 2009. The view was acquired at a distance of approximately 2.3 million kilometers (1.4 million miles) from Saturn. Image scale is 13 kilometers (8 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.

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