Rings At Opposition

 

When Cassini gazes down at Saturn's rings with the Sun directly behind the

spacecraft, an unusual phenomenon called the "opposition effect" can be

seen. The effect is visible here as a bright region, near right, toward

the inner edge of the A ring.

 

 

The precise nature of the effect at Saturn is still under scrutiny by

imaging scientists. However the effect in Saturn's rings can be witnessed

from Earth, when the viewing conditions are right. It can also be seen in

photographs of the lunar surface taken by the Apollo astronauts.

 

 

To understand the effect, imagine an observer standing on a dry, sandy

beach. When the Sun is directly behind the observer, the shadows cast by

the grains in the field of view in front of the observer will fall

directly behind the grains and will not be visible. When the Sun is at

any other angle relative to the observer, the shadows cast by the grains

will be visible to the observer. These shadows in the field of view make

the scene a bit darker. This effect would cause a centrally bright spot

to appear on the sandy surface in the first case, but not in the second.

 

 

For Cassini, the opposition effect is seen when the angle between the Sun,

the rings and the spacecraft is extremely close to zero. For the sequence

of images during which this view was obtained, Cassini maintained this

viewing angle and the bright spot appeared to move across the rings with

the spacecraft's motion.

 

 

The moon Janus (181 kilometers, or 113 miles, across) is seen here at

lower left.

 

 

The image was taken in visible light with the Cassini spacecraft

wide-angle camera on June 7, 2005, at a distance of approximately

738,000 kilometers (458,000 miles) from Saturn. The image scale is 40

kilometers (25 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 team is based at the Space Science

Institute, Boulder, Colo.

 

 

For more information about the Cassini-Huygens mission visit saturn.jpl.nasa.gov.

For additional images visit the Cassini imaging team homepage ciclops.org.

 

 

credit: NASA/JPL/Space Science Institute

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