CICLOPS: Cassini Imaging Central Laboratory for OPerationS
Against a Hail of Stars

Tethys appears here, against a background of star trails, in a view acquired as the icy moon exited Saturn's shadow.

Tethys is illuminated in this view by two main sources: reflected "ringshine" and refracted sunlight passing through the edge of Saturn's atmosphere. An observer viewing Saturn from the moon's surface would see the planet's southern hemisphere aglow with dimly reflected sunlight bouncing off the rings, called ringshine. They would also witness the beginning of an orbital sunrise. Cassini shared a similar perspective when it acquired the images for PIA08329 (the principal difference being that Tethys is nearly in the ringplane and Cassini was 15 degrees above the ringplane when it acquired the images for the color mosaic.)

A long exposure time was required in order to image Tethys while it was in shadow, resulting in the stars' point-like images being smeared into streaks.

The view looks toward the northern hemisphere of Tethys (1,062 kilometers, 660 miles across) from 36 degrees above the moon's equator.

The image was taken in visible light with the Cassini spacecraft wide-angle camera on June 30, 2008. The view was acquired at a distance of approximately 263,000 kilometers (163,000 miles) from Tethys and at a Sun-Tethys-spacecraft, or phase, angle of 52 degrees. Image scale is 16 kilometers (10 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: August 8, 2008 (PIA 10443)
Image/Caption Information
  Against a Hail of Stars
PIA 10443

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Alliance Member Comments
Mercury_3488 (Aug 10, 2008 at 7:53 AM):
I agree completely, bruno.thiery,

I've researched what the background sky was, forming a backdrop for Tethys.

This image was obtained back in June on the final day of the Primary Mission of the Cassini Spacecraft, which has now been extended to Wednesday 30th June 2010.

Tethys is seen here, in the shadow of Saturn, but dimly lit by reflected sunlight from Saturn's rings & other moon. Dione is off the frame to the bottom left & I wonder if Dione is responsible for most of the weakillumination of Tethys?

The stars in the background ar within the far north of the constellation of Bootes close to the stars Merez / Rho Bootis & Upsilon Bootis. The red giant star Arcturus / Alpha Bootis is way out of the frame to the lower right.

I really hope we get to see a lot more of these sort of obervations.

Andrew Brown.
bruno.thiery (Aug 10, 2008 at 4:06 AM):
These are nice too, these pictures with a background of stars.
They provide a different, wider perspective.