CICLOPS: Cassini Imaging Central Laboratory for OPerationS
Iapetus' Dark Side

Iapetus' Dark Side
PIA 06521

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  This image shows the dark, leading hemisphere of the mysterious moon Iapetus (1,471 kilometers, 914 miles across). The dark area is the Cassini region, named for Giovanni Cassini, who discovered the moon in 1672.

Cassini noted that he was able to see the moon on one side of its orbit around Saturn, but not on the other side. From this, he correctly deduced that one hemisphere must be dark while the other is much brighter.

The image was taken in visible light with the narrow angle camera on September 24, 2004, from a distance of 7.4 million kilometers (4.6 million miles) from Iapetus and at a Sun-Iapetus-spacecraft, or phase, angle of 51 degrees. The image scale is 45 kilometers (28 miles) per pixel. The image has been magnified by a factor of four to aid visibility.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. 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-Huygens mission, visit and the Cassini imaging team home page,

Credit: NASA/JPL/Space Science Institute
Released: November 16, 2004 (PIA 06521)
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