Observation and Analysis of Some Recent Galilean Satellite Phenomena

Five well observed recent mutual phenomena (1 occultation, 4 eclipses) of the Galilean satellites have been analysed and four fitting parameters determined for each event. The times of mid-minima are well determined in all cases (generally to within a second or two), but the separation and velocity parameters depend on the penumbral illumination modelling. For this reason, parameters derived from eclipses are somewhat less well determined than from occultations. Taken together with the dependence on the inherent surface reflection properties of the rearward satellite, the results indicate that Asknes et al.'s (1984) suggestion of order 0.01 arcsec accuracies on positional determinations from mutual phenomena data represents rather a lower limit to the real errors in most cases.