Galileo's Observations of the Solar System

Galileo came after Copernicus and added to the evidence in favour of the Copernican model of the solar system. He was the first astronomer to make and use a telescope,

He observed

  • There were mountains and craters on the moon,

  • The planet Venus had phases like the moon and appeared to change in size. The first implied that Venus orbited the Sun closer than the Earth, and the second that it did not orbit the Earth in a circle, since if it did it would always be the same size to us.

  • The planet Jupiter appeared to have four objects orbiting it, representing a mini solar system all itself, implying counter to the model of Ptolemy, that not everything orbited the Earth.

  • The Sun had dark spots or blemishes, counter the the view that the Sun was perfect.

  • The dark spots appeared to move across the Sun's surface, implying that the Sun rotated.

When he tried to publish his ideas, he was tried by inquisition and forced to renounce his observations and ideas. He is supposed to have muttered, 'still it moves', under his breath during his trial, referring to the motion of the Earth around the Sun.