He discovered that Jupiter has at least four moons. The moons orbiting Jupiter proved that everything in space didnt revolve around the earth. This contradicted church doctrine at that time.
He noticed that the planets Mercury and Venus pass through phases just like the Moon. The only way they could do that is if they circled the Sun, and not the Earth.
In addition to these discoveries, Galileo also discovered that everything falls at the same speed. If you jumped off a bridge at the same time as an elephant you would both hit the water at the exact same time. Galileo did not throw an elephant off a bridge, instead, he dropped two round balls off the Leaning Tower of Pisa. One was very heavy, and one was light. Both hit the ground at the same time.
If we didn’t have these discoveries about space and gravity and telescopes then a lot of people wouldn’t know about gravity. With the gravity discovery everyone knows why they fall but without it they would be confused why they fall. The telescope discovery has made it possible for us to see stuff in space that we couldn’t before. Without the space discoveries then we wouldn’t know what the center of space is. We would have thought that Earth was but it’s the sun.
Anon, Anon A. "Astronomy Timeline." Windows to the Universe. Anon, 22 June 2010. Web. 02 May 2012. <http://www.windows2universe.org/the_universe/uts/timeline.html>. Schwarzberg, Amanda. "Galileos Discoveries and How They Have Influenced Our Lives."Helium. Helium, 20 Nov. 2007. Web. 02 May 2012. <http://www.helium.com/items/708440-galileos-discoveries-and- how-they-have-influenced-our-lives>. Anon, Anon A. "Astronomy and Space for Kids." Astronomy For Kids. Anon, 8 June 2002. Web. 02 May 2012. http://www.kidsastronomy.com/academy/lesson110_assignment2_4.htm Anon, Anon A. "Was Earth a Migratory Planet?" Discovery News. Anon, 9 Nov. 2009. Web. 02 May 2012. <http://news.discovery.com/space/was-earth-a-migratory-planet-120418.html>.