Crescent at Equinox
Crescent at Equinox
April 30, 2010
The Cassini spacecraft looks down and pictures Saturn wrapped in a pencil-thin shadow of the rings just days after the planet's August 2009 equinox.
The moon Epimetheus is not shown here, but it is casting a tiny shadow on the planet above the rings. The moon Enceladus (504 kilometers, or 313 miles across) is faintly visible in the far top right of the image.
The novel illumination geometry that accompanies equinox lowers the sun's angle to the ringplane, significantly darkens the rings, and causes out-of-plane structures to look anomalously bright and cast shadows across the rings. These scenes are 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 have spotted not only the predictable shadows of some of Saturn's moons (see Across Resplendent Rings), but also the shadows of newly revealed vertical structures in the rings themselves (see A Small Find Near Equinox).
This view looks toward the northern, sunlit side of the rings from about 13 degrees above the ringplane. The rings have been brightened by a factor of 10 relative to the planet.
The image was taken with the Cassini spacecraft wide-angle camera on Aug. 17, 2009 using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nanometers. The view was obtained at a distance of approximately 2.2 million kilometers (1.4 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 109 degrees. Image scale is 125 kilometers (78 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.
Credit: NASA/JPL/Space Science Institute