Final answer:
Galileo Galilei confirmed the Copernican theory of a heliocentric system through his telescope observations, especially discovering Jupiter's moons and observing the phases of Venus, which contradicted the geocentric view.
Step-by-step explanation:
Galileo Galilei's support for the Copernican theory that planets, including Earth, orbit the Sun was based on his significant astronomical discoveries. With the use of the telescope, a technology newly invented at the time, Galileo made observations that clearly supported the heliocentric model. One of the most groundbreaking discoveries made by Galileo was the observation of Jupiter's moons, which showed that there could be centers of motion that are not Earth-centric. This observation was crucial because it demonstrated that not everything revolves around the Earth, thus challenging the prevalent geocentric view supported by the Church.
Additionally, Galileo observed the phases of Venus, similar to the moon's phases, providing conclusive evidence that Venus orbits the Sun. These phases were inconsistent with the geocentric model that placed Earth at the center of the universe, as advocated by Aristotle and Ptolemy, and upheld by the Roman Catholic Church at that time. Despite his evidence-based claims, Galileo faced severe opposition from the Church, which led to him being condemned to house arrest. Nevertheless, his findings were instrumental in the eventual acceptance of the Copernican heliocentric model.