Click on the image for the movie
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-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 mission for NASA's Science Mission Directorate, Washington, D.C. The
Cassini orbiter and its two onboard cameras were designed, developed and
assembled at JPL. The imaging operations center is based at the Space
Science Institute in Boulder, Colo.
For more information about the Cassini-Huygens mission visit
http://saturn.jpl.nasa.gov/. The Cassini imaging team
homepage is at http://ciclops.org.