Credit: Cassini Imaging Team,ISS,JPL,ESA,NASA
Explanation: How would Saturn look if its ring plane pointed right at the Sun? Before August 2009, nobody knew. Every 15 years, as seen from Earth,Saturn's ringspoint toward the Earth andappear to disappear. The disappearing rings are no longer a mystery -- Saturn's rings are known to beso thin and theEarth is so near the Sunthat when the rings point toward the Sun, they also pointnearly edge-on at the Earth. Fortunately, in thisthird millennium, humanity is advanced enough to have a spacecraft that can see the ringsduring equinoxfrom the side. In August 2009, that Saturn-orbiting spacecraft,Cassini, was able to snap a series of unprecedented pictures ofSaturn's rings during equinox. A digital composite of 75 such images isshown above. The rings appear unusually dark, and a very thin ring shadow line can be made out on Saturn's cloud-tops. Objects sticking out of the ring plane arebrightly illuminated and castlong shadows. Inspection of these images is helping humanity to understand the specificsizes of Saturn's ring particles and thegeneral dynamicsof orbital motion. This week, Earth undergoes an equinox.
