Phases of Venus
phases of venus:http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/galileo.htm

In the Ptolemaic system (left), Venus always lies between the sun and the earth and it would always show a crescent phase. The Copernican system (right) predicts a full range of phases for Venus as it passes from between the sun and the earth to being on the opposite side of the sun from the earth.
Excerpted from: Galileo