CICLOPS: Cassini Imaging Central Laboratory for OPerationS
Shadows Big and Small

Shadows Big and Small
PIA 11564

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  Saturn's moon Tethys casts a shadow on the planet's A ring alongside the larger shadow cast by the planet itself in this image taken as Saturn approached its August 2009 equinox.

The night side of the planet is dimly lit here by ringshine. Tethys, located off to the left of this image, is not seen. The moon Janus (179 kilometers, 111 miles across) can be seen orbiting outside the thin F ring at the top of the image. Other bright specks are background stars.

The novel illumination geometry created around the time of Saturn's August 2009 equinox allows 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.

The vertical brightness on the left of the image is lens flare, an artifact resulting from light being scattered within the camera optics. This view looks toward the unilluminated side of the rings from about 34 degrees above the ringplane.

The image was taken in visible light with the Cassini spacecraft wide-angle camera on June 19, 2009. The view was obtained at a distance of approximately 1.8 million kilometers (1.1 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 116 degrees. Image scale is 105 kilometers (65 miles) per pixel.

The Cassini Equinox Mission is a joint United States and European endeavor. 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 was designed, developed and assembled at JPL. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini Equinox Mission visit, and

Credit: NASA/JPL/Space Science Institute
Released: August 24, 2009 (PIA 11564)
Image/Caption Information

Alliance Member Comments
Dragon_of_Luck_Mah_Jonng1971 (Sep 3, 2009 at 5:11 PM):
There seem to be 3 background stars shining through the darkened part of the rings.
Pikaia (Aug 24, 2009 at 3:45 PM):
The notes say "The vertical brightness on the left of the image is lens flare", but I cannot see any obvious lens flare. The lighting can all be explained as light from Saturn reflecting onto the rings, and vice versa. Also, to produce lens flare you would need a bright source of light in or near the field of view, but the Sun is about 90 degrees away. Is this a mistake?
Red_dragon (Aug 24, 2009 at 1:07 PM):
Simply put, amazing. Not only the geometry, but also to see stars through t he rings. And if Tethys' shadow was in the middle of the rings would be even more impressive.

Although this has not much to see with Saturn, I'd be pleased if you asked me about this: we know asteroid belts as appear on sci-fi movies, etc. are innacurately represented and perhaps the closest thing to them would be Saturn's rings or the like.

But what about a protoplanetary disk?. Could it look like as for example the asteroid field of "The Empire Strikes Back"?. Thanks in advance.