A METHOD TO DEFINE A REFERENCE SYSTEM FOR THE REDUCTION OF ASTROMETRIC POSITIONS OF NATURAL SATELLITES

A new method to define a reference system in observations of natural s atellites taken with large focal distance telescopes is presented. Onl y the motion of the planet is used and therefore additional plates wit h large fields are not necessary. The error analysis of both the class ical and the new method are performed showing their equivalence. The m ethod is especially effective in the reduction of CCD frames. It is ap plied to 91 CCD frames and 173 photographic plates of the Uranian sate llites. The results of the classical and the new method are compared f or 55 photographic plates.