A photometric study of mutual phenomena of Galilean satellites.

Two mutual occultations and four mutual eclipses of Galilean satellites were observed with a photoelectric photometer mounted on a 60-cm Cassegrain telescope. Formulas are presented for the occulted areas and brightness corresponding to various occultation configurations, and the brightness distribution over the apparent disk of an occulted satellite is calculated. A drop in the combined visual magnitude of two satellites is measured which is much larger than predicted values. It is shown that the occulted satellite J2 has a basically uniform disk with some limb brightening, no atmosphere or a very thin atmospheric layer, and a possible concave area on its surface. Theoretical light curves are calculated and compared with observed curves, and the radius of J2 is obtained by iteration.