CICLOPS: Cassini Imaging Central Laboratory for OPerationS
Reciprocating Rings

Reciprocating Rings
PIA 11488

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  A quartet of Saturn's moons is seen here with the planet's F and A rings, but something special is happening to the moon in the middle of this Cassini image.

As Saturn approaches its August 2009 equinox, the planet's moons have been casting shadows onto the rings (see PIA11651). Now the rings take a turn casting a shadow on a moon. Tethys is just to the left of the center of the image, and the northern part of the moon is darkened by a shadow cast by Saturn's A ring.

From left to right, the moons shown are Mimas (396 kilometers, 246 miles across), Tethys (1062 kilometers, 660 miles across), Rhea (1528 kilometers, 949 miles across), and Pandora (81 kilometers, 50 miles across). Pandora is a tiny speck inside the rings.

This view looks toward the unilluminated side of the rings from about 1 degrees above the ringplane. The rings and Pandora have been brightened relative to the other moons to enhance visibility. The image was taken in green light with the Cassini spacecraft wide-angle camera on April 11, 2009. The view was acquired at a distance of approximately 1.4 million kilometers (870,000 miles) from Tethys and at a Sun-Tethys-spacecraft, or phase, angle of 21 degrees. Image scale on Tethys is about 82 kilometers pixels 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: May 8, 2009 (PIA 11488)
Image/Caption Information

Alliance Member Comments
Dragon_of_Luck_Mah_Jonng1971 (May 24, 2009 at 1:27 PM):
( No details visible on the 4 moons and no sun on Tethys' north polar area. )
( On 'Shadow Cap' Mimas is looking unusual with the penumbra and umbra of the rings darkening its north polar area. )
Red_dragon (May 12, 2009 at 8:39 AM):
Actually, a few months ago CICLOPS released an image in which Mimas appeared being eclipsed by Saturn's rings:
Dragon_of_Luck_Mah_Jonng1971 (May 9, 2009 at 8:12 PM):
I think this is the first time ever a spacecraft has taken an image of a gas giant's ring shadow falling on one of its major moons. ( Of course it's an unmanned one. ) Thus it's an important image.
mipsandbips (May 9, 2009 at 2:42 PM):
Wonder what shadows lurk for Enceladus and Dione?
Red_dragon (May 9, 2009 at 4:59 AM):
Really interesting image as usual on you. By the way, have you thought to make a movie of the rings eclipsing a moon similar to this one: ?. No doubt it would be a sight to see.