ANALYSIS OF SOLAR ASTROLABE MEASUREMENTS DURING 20 YEARS

Recent observations of the Sun made between 1974 and 1995 at two obser vatories were examined to determine the constant and/or linear terms t o the equinox and equator of the FK5 reference frame, the mean obliqui ty of the ecliptic, the mean longitude of the Sun, the mean eccentrici ty of the Earth's orbit, and the mean longitude of perihelion. The VSO P82 theory was used to reduce the data. The global solution of the wei ghted least-squares adjustment shows that the equinox of the FK5 requi res a correction of +0.'' 072 +/- 0.'' 005 at the mean epoch 1987.24. The FK5 and dynamical equinox agree closely at J2000.0 (-0.'' 040 +/- 0.'' 020), but an anomalous negative secular variation with respect to the dynamical equinox was detected: -0.'' 881 +/- 0.'' 116 century(-1 ). The FK5 equator requires a correction of +0.'' 088 +/- 0.'' 016, an d there is no indication of a time rate of change. The corrections to the mean longitude of the Sun (-0.'' 020 +/- 0.'' 010) and to the mean obliquity of the ecliptic (-0.'' 041 +/- 0.'' 016) do appear to be st atistically significant, although only marginally. The time rates of c hange for these quantities are not significant on the system to which the observations are referred. In spite of the short time span used in this analysis, the strong correlation between constant and linear ter ms was completely eliminated with the complete covering of the orbit b y the data sets of both sites.