Saturn's moon Prometheus casts a long shadow across the A ring in the middle-right side of this Cassini spacecraft image taken shortly before the planet's August 2009 equinox.
Prometheus (86 kilometers, or 53 miles across) orbits in the Roche Division between the thin F ring and the A ring. The novel illumination geometry created around the time of Saturn's August 2009 equinox allows out-of-plane structures and moons orbiting in or near the plane of Saturn's equatorial rings to cast shadows onto 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. To learn more about this special time and to see movies of moons' shadows moving across the rings, see PIA11651 and PIA11660.
This view looks toward the northern, unilluminated side of the rings from about 31 degrees above the ringplane. Many stars are visible. The rings and stars have been brightened by a factor six relative to Prometheus to enhance visibility.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 29, 2009. The view was acquired at a distance of approximately 1.4 million kilometers (870,000 miles) from Prometheus and at a Sun-Prometheus-spacecraft, or phase, angle of 93 degrees. Image scale is 9 kilometers (6 miles) per pixel.
Photo credit: NASA/JPL/Space Science Institute
Note: The photo also shows several streamer channels and gravitational perturbations in the F-Ring. For more on this topic, see Fleeing the Scene and Fan Structures in Saturn's F-Ring.
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