Joining other moons in heralding the coming of Saturn's August 2009
equinox, the moon Tethys casts its shadow across Saturn's F ring and part
of the A ring.
The penumbra, or outer non-opaque part of Tethys' shadow, has intersected
the A ring. Only around the time of equinox are the shadows of the moons
cast onto Saturn's rings. For an animation of the moon Epimetheus casting
a shadow on the A ring, see PIA11651.
The image on the left was taken in visible light with the Cassini
spacecraft wide-angle camera on March 20, 2009. The image on the right was
taken with the narrow-angle camera at nearly the same time. Tethys itself
is not visible in these images, but the small moon Prometheus (86
kilometers, or 53 miles across) can be seen between the F and A rings in
the top of the wide-angle camera image.
This view looks toward the unilluminated side of the rings from about 37
degrees above the ringplane. The view was obtained at a distance of
approximately 880,000 kilometers (547,000 miles) from Saturn and at a
Sun-Saturn-spacecraft, or phase, angle of 124 degrees. Image scale is 49
kilometers (31 miles) per pixel in the wide-angle image. In the
narrow-angle camera image, the scale is 5 kilometers (3 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.