"Socialism with human face" was the main slogan of a popular movement demanding more freedom and a relaxation of strict communist political control in Czechoslovakia in 1968. It was known as the Prague Spring. Alexander Dubcek was elected as a top Communist leader and he supported reforms. However, the Soviet Union´s and the socialist camp´s reaction was rejection. 200,000 Soviet and 400,000 other troops from "brotherly" socialist countries entered Czechoslovakia and suffocated the Prague Spring. Dubcek was removed from power and arrested. Soviet tanks occupying the streets of Prague are representative images of that historical moment.
Explanation: Czechoslovakia adopted Russian version of Communism (so-called Bolshevism) in 1948. But after some time, Czechs and Slovaks did find out that they do not agree (especially because of the changes within Eastern block and some changes in the west but also because of new generation) with it and attempted to practice Communism in their own way ("Socialism with human face") but Soviet leadership did not like it and viewed this attempt as a "counter-revolutionary".
The Ptolemaic model of the universe was heliocentric. the Copernican system included uniform circular motion. his years of careful observations of the planets.
