Cassini spacecraft panorama of Saturn at equinox yields unique view of rings
The Cassini spacecraft snapped this panorama of Saturn—actually a mosaic of dozens of photographs taken over eight hours—just after the ringed planet's equinox, which occurs once every 15 Earth years or so. During equinox, which fell in August, the plane of Saturn's rings align with the sun, making them nearly invisible from Earth but allowing nearby spacecraft a unique view of the rings' structure. (In this image, the illumination of the rings originates mostly from sunlight reflecting off of the planet.)
Among the discoveries from Cassini's unprecedented view: a four-kilometer-high wave in one of the planet's rings (viewable here in a photograph taken before equinox), apparently caused by the unusually close proximity of the ring's edge to Saturn's moon Daphnis. Thanks to the sun's low position relative to the rings, the peak cast a shadow roughly 500 kilometers long across the ring—on Earth, that shadow would darken the entire region between Boston and Philadelphia.