Tethys sits within Saturn's shadow, but not in complete darkness. While in eclipse the moon is illuminated by feeble ringshine reflected from the planet's night side and by sunlight scattered through the rings.
This is a similar observation to PIA10443. Such images provide confirmation of the spacecraft's precise pointing for Cassini's Composite Infrared Spectrometer (CIRS), which measures Tethys' surface temperature as it responds to the sudden darkness of an eclipse.
Lit terrain seen here is on the Saturn-facing side of Tethys (1,062 kilometers, 660 miles across). North is up and rotated 12 degrees to the right.
A long exposure time was required in order to image Tethys while it was in shadow, resulting in the background stars' point-like images being smeared into streaks. Additionally, the image was taken using a compression scheme that reduces the image file size on the spacecraft's data recorder, resulting in the moon's pixelated appearance.
The image was taken in visible light with the Cassini spacecraft wide-angle camera on Sept. 25, 2008. The view was obtained at a distance of approximately 113,000 kilometers (70,000 miles) from Tethys. Image scale is 7 kilometers (4 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.