Galileo Galilei was the first scientist to perform experiments in order to test his ideas. He was also the first astronomer to systematically observe the skies with a telescope. Galileo made four key observations that challenged the widely accepted philosophical beliefs on which the geocentric model was based, thus providing support for the heliocentric model. From the following list of observations, which are the key observations made by Galileo that challenged widespread philosophical beliefs about the solar system? a) Jupiter has orbiting moons.
b) The Sun has sunspots and rotates on its axis.
c) The Moon has mountains, valleys, and craters.
d) Venus goes through a full set of phases.