Solar astrometry with Rio Astrolabe and Heliometer

Abstract: Monitoring the micro-variations of the solar diameter helps to better understand local and secular trends of solar activity and Earth climate. The instant measurements with the Reflecting Heliometer of Observatorio Nacional in Rio de Janeiro have minimized optical and thermal distortion, statistically reducing air turbulence effects down to 0.01 arcsec. Contrarily to satellites RHRJ has unlimited lifetime, and it bridges and extends the measures made with drift-scan timings across altitude circles with 0.1 arcsec rms with Astrolabes. The Astrolabe in Rio operated from 1998 to 2009 to measure the solar diameter and the detected variations have statistical significance.