Apparent variations of the sun's radius observed at the Cote d'Azur observatory (Solar astrolabe at Calern site, 1975-1998)

The results here discussed were produced by a program of visual observation s carried out at the Calern Observatory from 1975 to 1998. The sun radius d ata collected display some variability, in particular an oscillation of 0.2 '' amplitude and 11.8 years period which seems anticorrelated with the suns pot cycle. These apparent variations might also be put together with other structural solar parameters: frequency shifts of low-degree p-modes or neut rino flux. Moreover the series shows a deviation from the mean diameter as a function of heliographic latitude. The origin of these apparent variation s is currently unclear and will be better understood by ground measurements over a long period of time (e.g. the DORAYSOL Instrument and Program at Ca lern) and by the results expected from the future PICARD mission of the Fre nch Space Agency CNES. (C) 1999 Academie des sciences/Editions scientifique s et medicales Elsevier SAS.