Azimuthal brightness variations in Saturn's rings.

Azimuthal variations in brightness in the rings of Saturn have been studied on recent photographs. A ring- brightness model has been developed which is used in conjunction with a two-dimensional numerical smearing process to investigate the effects of seeing and instrumental smearing on the data. The results of this investiga- tion show that the two ansae of the rings are of equal brightness. Furthermore, the observed surface brightness of ring B, decreasing from the ansae towards the minor axis of the ring ellipse, can be fully accounted for as a result of smearing processes on an initial intensity distribution which is independent of azimuthal angle. In contrast, ring A shows a roughly sinusoidal variation in brightness with minima in the quadrants following geocentric conjunctions and maxima in the others. The smearing is approximately removed from ring A to yield the intrinsic surface brightness of the ring.