Visual and CCD astrolabe observations of the solar radius

Here we discuss and compare two sets of solar semidiameter measurements mad e with Danjon astrolabes during the period 1997-1999. One is based on 10 52 2 CCD observations made at Rio de Janeiro, Brazil; the other one is based o n 956 visual observations made at Santiago, Chile. Linear fits applied to b oth data sets give a standard deviation of +/- 0."365 and +/-0."360 for eac h daily mean value of the solar radius for Rio de Janeiro and Santiago resp ectively. During the period of this analysis, the apparent solar radius had an annual variation of -0."060 +/-0."013 according to the CCD observations of Rio de Janeiro and of +0."213 +/-0."018 according to the visual observa tions of Santiago. We show here that this discrepancy could be due to syste matic effects, probably of instrumental origin, that produce significant in ternal inconsistencies in the results of Rio de Janeiro. The drift of the a pparent solar radius observed with the astrolabe of Santiago during 1997-19 99 is consistent with former results obtained with this instrument since 19 90. These results show that the apparent semidiameter of the Sun varies in phase with solar activity (Noel 1997, 2001).