Galileo was really confused about the geocentric system. He was strongly convinced that sun is in the center of our planetary system, so he was looking for undoubtedly evidences. Then he got the idea to target his telescope to Venus. According to the geocentric system (Ptolemy’s Model) it would not be possible to view all Venus in all phases, but only as a meniscus. But, when he pointed his telescope at Venus he saw all phases from full phase to new Venus. This was an ultimate evidence of the heliocentric system. Furthermore, Galileo turned his telescope to Jupiter revealing for the very first time the moons of Jupiter. These were the first observed planets orbiting around another planet and not around Earth. Imagine now being the assistant of Galileo recording all his observations and claiming explanations. This is now your role. Become Galileo’s assistant!