Humanity's view of the universe was profoundly changed when in 1610 Galileo turned his telescope to the night sky and Jupiter in particular. He discovered four satellites revolving around the planet.

This was a profound revelation because it was thought that everything revolved around the Earth. This changed that idea.

You can see in this picture, of his very own drawings, how the satellites around Jupiter changed position from night to night.

I took a ten week backpacking adventure in Europe. And I spent a fair amount of time in Italy. But, my point here is that if you are interested in Galileo they have a museum dedicated to his life right in Florence! And I visited! You can learn more and see pictures which include his famous book and the actual telescopes he used. Check it by clicking on the thumbnail.