The solar diameter series of the CCD Solar Astrolabe of the Observatório Nacional in Rio de Janeiro measured during cycle 23

Abstract: The interest on the solar diameter variations has been primary since the scientific revolution for different reasons: first the elliptical orbits found by Kepler in 1609 was confirmed in the case of the Earth, and after the intrinsic solar variability was inspected to explain the climate changes. The CCD Solar Astrolabe of the Observat\'orio Nacional in Rio de Janeiro made daily measurements of the solar semi-diameter from 1998 to 2009, covering most of the cycle 23, and they are here presented with the aim to evidence the observed variations. Some instrumental effects parametrizations have been used to eliminate the biases appeared in morning/afternoon data reduction. The coherence of the measurements and the influence of atmospheric effects are presented, to discuss the reliability of the observed variations of the solar diameter. Their amplitude is compatible with other ground-based and satellite data recently published.