A Shepherd's Watch
Like a shepherd guarding his sheep, Prometheus keeps a lonely watch over the F ring.
Gravitational interactions between the ring and its shepherd moons, Prometheus (53 miles, or 86 kilometers across) and Pandora (not shown here), keep the F ring narrowly confined. The five small, bright dots in this image (one of them seen through the A ring, which is on the right) are stars.
This view looks toward the unilluminated side of the rings from about 52 degrees below the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 15, 2013.
The view was obtained at a distance of approximately 810,000 miles (1.3 million kilometers) from Prometheus and at a Sun-Prometheus-spacecraft, or phase, angle of 110 degrees. Image scale is 5 miles (8 kilometers) per pixel.
Credit: NASA/JPL-Caltech/Space Science Institute
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