Solar diameter observations at Observatorio Nacional in 1997-1998

In January 197, at the Observatorio Nacional (ON), Rio de Janeiro, Brazil, CCD observations of the solar diameter with a Danjon astrolabe equipped with a variable angle reflecting prism began. This prism is operated manually and enables to observe the Sun many times per day and all year round on the Southern latitude phi = -22 degrees 54'. Thanks to this and owing to a large number of sunny days at Rio de Janeiro, a high density of observations was achieved - 2900 East and 1730 West observations during the first 18 months. Results of the observations are available in electronic form in the SIMBAD database and at the World Wide Web page of the Observatorio Nacional, Solar Radius Data: http://obsn.on.br/radius/.