ИСТИНА

Attempts of radar detection of Venus were being undertaken from 1958. And the first reliable observations of Venus were made in 1961 by groups in the USA -W.K. Viktor, R. Stevens et al., in the United Kingdom - J.H. Thompson, J.E.B. Ponsonby et al., and in the USSR - V.A. Kotelnikov, V.M. Dubrovin et al. The observations carried out by these groups and other workers in the period from 1961 to 1964 allowed obtaining many new data. The analysis of radar echoes from Venus contributed to determination of the Solar parallax. The observations made it possible to calculate much more precisely the value for the astronomical unit and showed that it was close to 149 598 000 km. Radar astronomy helped to settle the question of Venus' rotation that could not be solved by optic observations for more than 300 years. Venus ground-based radar measurements taken in the 1960-s showed that the period of Venus' rotation was 243 earth days long and the Venusian day was about 59 Earth days. A certain information concerning the position of the Venus pole had been obtained.