A radar investigation of Venus

Abstract

Radar measurements of Venus carried out by the Millstone radar of the Massachusetts Institute of Technology Lincoln Laboratory from 6 March to 18 May 1961 are reported. Range measurements reduced with the help of Duncombe's elements for the orbits of the earth and Venus lead to a value for the astro- nomical unit of 149 597 850+400 km. Reduced with 6378.388 km for the earth's equatorial radius, this yields for the solar parallax irO = 8'.' +0'.'000024. Small residual systematic errors in the planetary ephemerides are disclosed. Measurements of the signal intensity and range dispersion are compatible with a relatively smooth rocky surface as the reflecting agency. The observed frequency broadening is com- patible with a sidereal rotational period of 225 (+275, -110) days, which suggests that the period of rotation equals the period of revolution.