Affecting Two Rings
Date: 30 Jul 2009
The effects of the small moon Prometheus loom large on two of Saturn's rings in this image taken a short time before Saturn's August 2009 equinox.
A long, thin shadow cast by the moon stretches across the A ring on the right. The gravity of potato-shaped Prometheus (86 km, or 53 miles across) periodically creates streamer-channels in the F ring, and the moon's handiwork can seen be on the left of the image. To learn more and to watch a movie of this process, see PIA08397.
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).
Prometheus is overexposed in this image. Bright specks in the image are background stars.
This view looks toward the northern, unilluminated side of the rings from about 28 degrees above the ringplane.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on 30 July 2009. The view was acquired at a distance of approximately 1.8 million km (1.1 million miles) from Saturn and at a sun-Saturn-spacecraft, or phase, angle of 97 degrees. Image scale is 10 km (6 miles) per pixel.
Last Update: 26 Mar 2013 (AMB)