<P> Spectroscopic observations in the 1900s gave the first clues about the Venusian rotation . Vesto Slipher tried to measure the Doppler shift of light from Venus, but found he could not detect any rotation . He surmised the planet must have a much longer rotation period than had previously been thought . Later work in the 1950s showed the rotation was retrograde . Radar observations of Venus were first carried out in the 1960s, and provided the first measurements of the rotation period, which were close to the modern value . </P> <P> Radar observations in the 1970s revealed details of the Venusian surface for the first time . Pulses of radio waves were beamed at the planet using the 300 m (980 ft) radio telescope at Arecibo Observatory, and the echoes revealed two highly reflective regions, designated the Alpha and Beta regions . The observations also revealed a bright region attributed to mountains, which was called Maxwell Montes . These three features are now the only ones on Venus that do not have female names . </P> <P> The first robotic space probe mission to Venus, and the first to any planet, began with the Soviet Venera program in 1961 . The United States' exploration of Venus had its first success with the Mariner 2 mission on 14 December 1962, becoming the world's first successful interplanetary mission, passing 34,833 km (21,644 mi) above the surface of Venus, and gathering data on the planet's atmosphere . </P> <P> On 18 October 1967, the Soviet Venera 4 successfully entered the atmosphere and deployed science experiments . Venera 4 showed the surface temperature was hotter than Mariner 2 had calculated, at almost 500 ° C, determined that the atmosphere is 95% carbon dioxide (CO), and discovered that Venus's atmosphere was considerably denser than Venera 4's designers had anticipated . The joint Venera 4--Mariner 5 data were analysed by a combined Soviet--American science team in a series of colloquia over the following year, in an early example of space cooperation . </P>

Does venus rise in the east or west