* The Phases of Venus: Galileo observed that Venus goes through phases, just like the Moon. This was a major blow to the prevailing geocentric model of the universe, which held that all celestial bodies revolved around Earth. The phases of Venus could only be explained if Venus orbited the Sun, as Copernicus had proposed.
* The Moons of Jupiter: Galileo discovered four moons orbiting Jupiter. This discovery was significant because it demonstrated that not everything revolved around Earth. It showed that other celestial bodies could have their own moons, further supporting the heliocentric model.
These two discoveries, along with his observations of sunspots and the Milky Way, helped solidify the heliocentric model and revolutionized our understanding of the universe.
