What are “ascending” and “descending” ring plane crossings?
Cassini is usually on one side or another of Saturn’s ring plane, because the orbit is usually tilted with respect to the ring plane. Twice each orbit, Cassini crosses the ring plane, once going from south to north (“ascending”) and once from north to south “descending”). Because it is currently summer in Saturn’s southern hemisphere, when Cassini is on the south side of the rings, they are illuminated by the Sun. When Cassini is on the north side of the rings, the rings are backlit. When Cassini goes through a ring plane crossing, the rings are seen edge-on. Cassini often observes the fainter E, F, and G rings during ring plane crossings.
