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The interest on the solar diameter variations has been primary since thescientific revolution for different reasons: first the elliptical orbits foundby Kepler in 1609 was confirmed in the case of the Earth, and after theintrinsic solar variability was inspected to explain the climate changes. TheCCD Solar Astrolabe of the Observat\'orio Nacional in Rio de Janeiro made dailymeasurements of the solar semi-diameter from 1998 to 2009, covering most of thecycle 23, and they are here presented with the aim to evidence the observedvariations. Some instrumental effects parametrizations have been used toeliminate the biases appeared in morning/afternoon data reduction. Thecoherence of the measurements and the influence of atmospheric effects arepresented, to discuss the reliability of the observed variations of the solardiameter. Their amplitude is compatible with other ground-based and satellitedata recently published.

The solar diameter series of the CCD Solar Astrolabe of the Observat\'orio Nacional in Rio de Janeiro measured during cycle 23