Stellar occultations of planetary rings: from Palomar to Cassini

Chance observations of stars as they pass behind planets have provided some of our most valuable data on the structure of planetary ring systems, beginning with the discovery of the uranian rings with the Kuiper Airborne Observatory in 1977. As a graduate student at Caltech in the 70s, I became involved first in studies of the dynamically-curious uranian rings at Mount Palomar and later in unraveling the story of the even more baffling ring arcs of Neptune. I will review some of the highlights of this early work, which led to my current involvement in the Cassini mission at Saturn, observing stellar occultations with the VIMS (Visual and Infrared Mapping Spectrometer) instrument. Over 150 such occultations have been observed over the past 12 years, leading to the discovery and/or characterization of such novel features as self-gravity wakes, numerous density and bending waves, eccentric and inclined ringlets, `normal modes’ on gap edges and instances of `viscous overstability’ in denser regions of the rings. Our ring observations have also provided insights into the internal structure of Saturn itself.