This raw image, taken by the Cassini spacecraft on December 26, 2009 (on a certain space blogger’s birthday, by the way) shows an amazing view of Prometheus, one of Saturn’s many shepherd moons.
This is the closest yet that Cassini has come to the 96-mile-long oblong moon. Details of its cratered surface are visible, as is the shadow it casts into the material it pulls from the inner edge of the F ring (part of which can be seen at upper left.) This action is a defining characteristic of the little moon as its tumbling orbit causes it to dip in and out of the bright, icy ring, disturbing the material and pulling out long streamers with its passing.
During the springtime on Saturn, Prometheus’ shadow is often cast directly into the F ring with dramatic effect.
Cassini was approximately 36,000 miles from Prometheus when this image was taken. I rotated the original 90º and adjusted levels slightly to emphasize the moon’s shadow a bit, but otherwise this is the raw image straight from the spacecraft as posted on the CICLOPS site.
Image: NASA/JPL/Space Science Institute