Saturn's rings cast a shadow on the moon Janus in this image made possible
only around the time of the planet's August 2009 equinox.
Some of the planet's moons cast shadows onto the rings at equinox, but in
this image, it's the rings casting shadows on a moon. The shadow obscures
part of Janus (179 kilometers, or 111 miles across) in the image. The
planet's thin F ring can be seen in the upper left of the image.
See PIA11488 to see the rings casting a shadow on the moon Tethys.
This image was taken shortly after the planet's equinox. 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
17 degrees above the ringplane.
The image was taken in visible light with the Cassini spacecraft
narrow-angle camera on Aug. 14, 2009. The view was acquired at a distance
of approximately 1.4 million kilometers (870,000 miles) from Janus and at
a Sun-Janus-spacecraft, or phase, angle of 90 degrees. Image scale is 8
kilometers (5 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.