Saturn Rings Cast in Rare Light
The shadow of Saturn's moon Mimas dips onto the planet's rings and straddles the Cassini Division in this natural color image taken as Saturn approaches its August 2009 equinox.
Credit: NASA/JPL/Space Science Institute

Just once every 15 years, Saturn approaches its equinox ? when the sun passes through the plane of the planet's rings.

NASA's Cassini spacecraft has captured rare scenes of moons eclipsing each other and casting long shadows against the rings during the approach to this equinox.

One year on Saturn is equal to 29.5 Earth years. Twice during that period Saturn aligns with the sun so that the flat plane of the planet's titled rings also intersects the sun. During these equinox alignments, the angle of the sun illuminates the Saturnian system in a unique way and creates rare shadow patterns.

These patterns recently revealed enormous mile-high vertical waves on the edges of a gap in Saturn's outer ring that had never been spotted before.

The exact date of the approaching equinox is Aug. 11. Over the next few months, scientists hope the special views lead to even more new discoveries about Saturn's rings.

"It has been a scientist's delight to watch this almost wafer-thin collection of icy debris, that we have come to know so well, change in character and spring into the third dimension," said Carolyn Porco, leader of the Cassini Imaging Team.

Launched in October 1997, the Cassini spacecraft has been orbiting Saturn since 2004. Among the probe's many discoveries, it revealed three previously unknown moons, Methone, Pallene and Polydeuces, to add to Saturn's tally of 61. Cassini is currently slated to run until next year, but if funding is approved the mission could be extended until 2017.

Correction: This article has been corrected to reflect the correct year Cassini went into orbit around Saturn: 2004.

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