Never-before-seen images from Saturn kick off celebrations at Royal Observatory Greenwich in London

This bounty of sights, that includes time-lapse sequences in which Saturnian moons eclipse each other and cast long shadows onto the planet's famous rings, represents only some of the fruits expected for the extended "Equinox Mission" for Cassini, the robotic explorer that has been orbiting Saturn since July 1, 2004.

Saturn's spin axis is tilted relative to its motion around the sun, and its year is equal to 29.5 Earth years. Equinox, the twice-yearly period when the sun passes through the plane containing the planet's rings, will happen for the first time in almost 15 Earth years on Aug. 11, 2009. The novel illumination geometry created by the approaching equinox lowers the sun's angle to the ring plane and causes some of Saturn's moons, as well as out-of-plane structures in the rings, to cast long shadows across the rings, creating vistas never before seen by any Saturn-bound spacecraft. In fact, only recently, Cassini's high-resolution camera spotted for the first time, on the edges of a gap in Saturn's outer ring, enormous mile-high vertical waves whose presence was unknown until betrayed by the waves' shadows.

Speaking of the recent images of the rings acquired as Saturn marches towards its mid-August equinox, Carolyn Porco, leader of the Cassini Imaging Team, said:

"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. Five years into this mission and we find there are still new tales to be told." Porco is also the Director of the Cassini Imaging Central Laboratory for Operations in Boulder, Colorado.

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. The novel illumination geometry created as the Saturnian system approaches equinox allows moons orbiting in or near the plane of Saturn's equatorial rings to cast shadows onto 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. This view looks toward the sunlit side of the rings from about 52 degrees below the ringplane. Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were obtained with the Cassini spacecraft wide-angle camera on April 8, 2009 at a distance of approximately 1.1 million kilometers (684,000 miles) from Saturn. Image scale is 64 kilometers (40 miles) per pixel. Credit: NASA/JPL/Space Science Institute

Time-lapse sequences:

• A Shadow's Traverse - Mimas' shadow traverses the sunlit side of Saturn's rings in this movie and mosaic showcasing the unusual sights seen at Saturn as the planet approaches its August 2009 equinox.
• Weaving a Shadow - Part of the shadow of Saturn's moon Mimas appears as if it has been woven through the planet's rings in this unusual series of images from Cassini.
• Shadow from the Dark Side - The shadow of Saturn's moon Tethys seems to disappear as it crosses the planet's rings, demonstrating variations in the density of particles across the rings.
• Eclipsing Mimas - As the moon Enceladus eclipses its neighbor Mimas, Cassini records a scene possible only around the time of Saturn's approaching equinox.

The release of the new images coincides with the opening of a week-long celebration of the Cassini mission and all that it has discovered in the last 5 years. A unique exhibition of the mission's images revealing the beauty of Saturn, its rings and moons, opens at the Royal Observatory, Greenwich today. "Visions of Saturn" features striking pictures of hurricane-force storms in Saturn's turbulent atmosphere, the delicate tracery of the ring system and a weird and wonderful array of satellites, including Enceladus -- the whitest place in the solar system -- and a planet-sized moon where liquid methane rains form orange clouds.

Designed by Christopher Wren, the Observatory is home of Greenwich Mean Time and the Prime Meridian and one of the most important historic scientific sites in the world. Since its founding in 1675, Greenwich has been at the centre of the measurement of time and space. Visitors can stand in both eastern and western hemispheres simultaneously by placing their feet either side of the Prime Meridian line. Today the galleries describe the achievements of early astronomers, explain the history of the search for longitude at sea and tell the story of precision timekeeping.

Source: CICLOPS/Space Science Institute
	More on • Cassini • Saturn • Mimas • Tethys • Enceladus