Sunlight passing through the Cassini Division between Saturn's A and B rings sweeps across and illuminates the surface of the moon Janus in this movie captured shortly after Saturn's August 2009 equinox.
The novel illumination geometry that accompanied equinox lowered the sun's angle to the ringplane, significantly darkened the rings, caused out-of-plane structures to look anomalously bright and cast shadows across the rings. As this movie shows, the equinox period also allowed the rings to cast shadows on the moons. These scenes were possible only during the few months before and after Saturn's equinox which occurs only once in about 15 Earth years. Before and after equinox, Cassini's cameras spotted not only the predictable shadows of some of Saturn's moons (see PIA11657), but also the shadows of newly revealed vertical structures in the rings themselves (see PIA11665).
This view looks toward the trailing hemisphere of Janus (179 kilometers, 111 miles across). North on Janus is up and rotated 8 degrees to the right.
The movie is a concatenation of 12 still images. The images were taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 27, 2009. The view was acquired at a distance of approximately 268,000 kilometers (167,000 miles) from Janus and at a Sun-Janus-spacecraft, or phase, angle of 25 degrees. Image scale is 2 kilometers (5,271 feet) 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.