* Phases of Venus: He observed that Venus goes through phases, just like the Moon. This is only possible if Venus orbits the Sun, not the Earth. In the geocentric model, Venus would always be seen in a crescent shape.

* Moons of Jupiter: He discovered four moons orbiting Jupiter. This proved that not everything revolved around the Earth, which was a major challenge to the geocentric model.

* Sunspots: He observed sunspots, which demonstrated that the Sun was not perfect and unchanging, as the geocentric model believed.

These observations, along with his telescopic observations of the Milky Way and the surface of the Moon, contributed significantly to the growing acceptance of the heliocentric model.