Saturn seen at equinox - Saturn during Equinox - Saturn seen by the Cassini probe...

Saturn seen at equinox - Saturn during Equinox - Saturn seen by the Cassini probe on August 12, 2009, 1.25 days after the exact date of Saturn equinox. The images that make up this mosaic were obtained at a distance of 847,000 km from the planet. Several satellites are visible in this image: Janus (lower left), Epimethee (lower middle), Pandora (on the right of the image, outside the rings) and Atlas (on the right, inside the F ring). Seen from our planet, the view of Saturn's rings during equinox is extremely foreshortened and limited. But in orbit around Saturn, Cassini spacecraft had no such problems. From 20 degrees above the ring plane, Cassini's wide angle camera shot 75 exposures in succession for this mosaic showing Saturn, its rings, and a few of its moons a day and a half after exact Saturn equinox, when the sun's disk was exactly overhead at the planet's equator. The novel illumination geometry that accompanies equinox lowers the sun's angle to the ring plane, significantly darkens the rings, and causes out - of - plane structures to look anomalously bright and to 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. Also at equinox, the shadows of the planet's expansive rings are compressed into a single, narrow band cast onto the planet as seen in this mosaic. The images comprising the mosaic, taken over about eight hours, were extensively processed before being joined together. At this time so close to equinox, illumination of the rings by sunlight reflected off the planet vastly dominates any meager sunlight falling on the rings. Hence, the half of the rings on the left illuminated by planetshine is, before processing, much brighter than the half of the rings on the right. On the right, it is only the vertically extended parts of the rings that catch any substantial sunlight. With no enhancement, the rings woul