CICLOPS: Cassini Imaging Central Laboratory for OPerationS
Moon Shadow in Motion

The beauty and spectacle of celestial motion is captured in this short movie of a moon shadow darting across Saturn's rings.

Over the span of about an hour, Cassini's camera tracked the shadow of the small moon Epimetheus, orbiting beyond the rings, as it moved across Saturn's A ring in this movie made up of 21 images.

One of the happy results of Saturn's 29-year revolution around the sun is the changing elevation of the sun seen from the planet, and the changing elevation of the shadows of the rings and moons that the sun's apparent motion brings.

As Saturn approaches equinox, the angle at which the ringplane is inclined away from the sun will continue to decrease until August 2009, when equinox will bring about an alignment of the plane containing the rings with the rays of the sun. Only around the time of equinox is a moon's shadow cast on the rings rather than the planet. Between now and equinox in August, the shadows cast by the moons on the rings will grow longer with time.

Cassini scientists planned a series of observations to chronicle these sights, knowing that the resulting images could hold valuable information about vertical displacements in the rings and the orbital inclinations of the shadow-casting moons. These planned images of course hold another reward: the simple but spectacular depiction of the path of sunlight across the solar system.

The movie images were taken in visible light with NASA's Cassini spacecraft narrow-angle camera on Jan. 16, 2009. This view looks toward the sunlit side of the rings from about 53 degrees below the ringplane. The view was acquired at a distance of approximately 945,000 kilometers (587,000 miles) from Saturn and at a sun-Saturn-spacecraft, or phase, angle of 68 degrees. Image scale is 5 kilometers (3 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: April 2, 2009 (PIA 11651)
Image/Caption Information
  Moon Shadow in Motion
PIA 11651

Avg Rating: 9.28/10

Flash 2.9 MB
MP4 movie 1.3 MB

Alliance Member Comments
CheshireCat (Mar 24, 2009 at 4:10 PM):
We might see the penumbra of Titan on the rings, although without running the numbers, I'm thinking probably not.

As for other moons... stay tuned. :-)
Red_dragon (Mar 24, 2009 at 3:49 PM):
Thanks again. It's a pity; I hope we'll see at least the ones of any other Saturn's largest moons.
Anyway, isn't even the possibility of seeing a partial transit of the shadow?. Sure even that would be quite dramatic
CheshireCat (Mar 24, 2009 at 1:23 PM):
Red_dragon: I don't believe we'll be seeing Titan's shadow on the rings this equinox. Titan is on the wrong side of the planet on the day of equinox and by the time it makes it back around, the Sun will already be too high again.
Red_dragon (Mar 24, 2009 at 8:51 AM):
One of the most dramatic and stunning movies you're ever released. Can't wait to see Titan's shadow doing that.
rochelimit (Mar 24, 2009 at 4:25 AM):
Can't wait for the next moons
Mungo (Mar 23, 2009 at 6:22 PM):
Stunning and beautiful movie! Especially the larger version. Capturing a small moon casting a needle shaped shadow from halfway across solar system. Very impressive bit of camera work. Congratulations to the team!