Who first observed the phases of Venus, providing evidence for the heliocentric model?

Galileo Galilei was the first to observe the phases of Venus, which provided critical evidence supporting the heliocentric model of the solar system proposed by Copernicus. Using his telescope, Galileo noted that Venus exhibited a full set of phases similar to those of the Moon. This observation was significant because, under the geocentric model, which placed Earth at the center of the universe, Venus could not show a full range of phases. The phases of Venus could only be adequately explained if Venus orbited the Sun rather than Earth, demonstrating that the heliocentric model was more consistent with observable phenomena.

Galileo's findings were pivotal in the shift toward the acceptance of the heliocentric view, and they contributed to the broader scientific revolution by challenging existing beliefs about the structure of our solar system. His observations essentially laid the groundwork for the eventual dismissal of the geocentric model.