Solar diameter measurements at São Paulo Observatory

In this work we describe solar radius measurements made from 1972 with the São Paulo astrolabe. We find values of 959.52 ± 0.03 arcsec for the visual data and 959.61 ± 0.05 arcsec for the CCD data using a modified data acquisition system. We compare our results with other astrolabe measurements and with SOHO—MDI. Observations of the solar radius show contradictory results when we try to correlate changes in the diameter with the solar cycle. Our series is not correlated with the solar cycle but it shows a period of 13.4 ± 2.2 yr. We have also compared our time series with other long-term measurements of solar radius along solar cycle 21 and analysed our measurements as a function of heliographic latitude. We do not find a significant solar oblateness.