CICLOPS: Cassini Imaging Central Laboratory for OPerationS
Weaving a Shadow

Part of the shadow of Saturn's moon Mimas appears as if it has been woven through the planet's rings in this unusual series of images from Cassini. Together the sequence of frames comprise an unusual demonstration of the varying particle density across the rings.

In these images, which were combined to create both a mosaic and a movie, the Cassini spacecraft looks toward the unilluminated side of the rings from about 61 degrees above the ringplane. Mimas' shadow, shown in multiple locations simultaneously in the mosaic, lies across the inner B ring, C ring and even the very faint D ring. The inner B ring is in the top left, and the C ring is in the middle of the image. The transparent D ring is faintly visible in the dark area in the lower right. Mimas is not shown.

The densest parts of the B and C rings, seen as bright stripes across Mimas' shadow, do not let much sunlight pass through to the spacecraft's camera. Consequently, one might expect these dense areas to appear dark because they are on the dark side of the rings. But these areas, particularly the inner B ring in the upper left of the image, appear brightly lit, even where Mimas' shadow crosses them. It is likely that illumination from Saturn itself and the subsequent reflection to the cameras keeps them relatively bright. As a result, the moon's shadow appears cut off and diminished in these areas.

Nineteen images, each taken about 2 minutes 24 seconds apart, were combined to create this mosaic and movie. Contiguous images were stitched together to create a mosaic showing the whole swath of the rings across which the moon's shadow passed. One image is missing from the sequence, creating a gap in the movie.

The novel illumination geometry created as the Saturnian system approaches 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 see a similar image showing a different moon's shadow on the unlit side of the rings, see PIA11498. To see movie and mosaic of Mimas' shadow moving across the sunlit side of the rings, see PIA11658.

These images have been processed, and the faint D ring was brightened relative to the other rings. Background stars have been removed.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on April 30, 2009. The view was obtained at a distance of approximately 1.4 million kilometers (870,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 73 degrees. Image scale is 8 kilometers (5 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: June 22, 2009 (PIA 11660)
Image/Caption Information
  Weaving a Shadow
PIA 11660

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Flash 304 KB
MP4 movie 46 KB


Weaving a Shadow
PIA 11660

Avg Rating: 9.40/10

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Alliance Member Comments
jmason (Jun 26, 2009 at 9:01 AM):
mipsandbips: As the caption says, there is one image missing from the sequence. So, one frame in the middle of the movie is missing. I think that little hiccup in the animation is what you may be seeing when you write that the shadow seems to "jump the gap." It still makes for a great view though, doesn't it?
-Joe Mason, CICLOPS Media Relations Coordinator
mipsandbips (Jun 25, 2009 at 7:26 PM):
When viewing the traversal of Mimas' shadow past the gaps in
the rings, what is truly remarkable is the way the shadow traverses
the first gap where it seems to "jump the gap" (center gap in image)
as compared to the traversal of the shadow in the second gap
where it seems to pass more evenly (lower right gap in image).
Red_dragon (Jun 25, 2009 at 7:29 AM):
Thanks for the input, John
bman (Jun 23, 2009 at 11:12 AM):
pretty cool
Dragon_of_Luck_Mah_Jonng1971 (Jun 23, 2009 at 11:12 AM):
That's very interesting. It looks indeed ( somewhat ) like woven.
At my first glance it appeared to me that that bright parts not "accepting" the shadow are a bit higher than the "normal" parts of the rings. But after several further examinations of this picture I found very slight darkenings on roughly three quarters of the bright parts of the ring not "accepting" Mimas' shadow. Thus they're not higher than the other parts. But there may still be out-of-plane components in the rings.
CheshireCat (Jun 23, 2009 at 9:50 AM):
(I should add that when I say that *I* haven't had a chance to analyze these images for possible morphology changes, I meant "I". It's possible someone else in our team has noticed something and I'm not in the loop. I don't want it to sound like I'm the only one who can do this, I'm just using the singular 'cause I can't speak for others right now.)
CheshireCat (Jun 23, 2009 at 9:31 AM):
I haven't had a chance to really analyze these images yet, but I don't *think* that the morphology changes much (if any) over the course of the movie. The density of the ring between us and the moon does change a lot from ring radius to ring radius, so we often see the shadow clipped or striped, but that's an illusion due to the photometry.
That said, if there is significant variation of the shadow with location in the rings, one possible cause is an out-of-plane component to the ring. We're looking at that now. If we find anything, I'm sure we'll announce it. :-)

-- John Weiss, CICLOPS.
Red_dragon (Jun 23, 2009 at 7:07 AM):
Superb. It's curious the way the shadow changes, perhaps due to relief in the rings -so they're not plane-.