How did Galileo's observation of Venus support the Copernican heliocentric system?

Answer

It displayed a full range of phases

The observation of Venus through successive phases—ranging from crescent to gibbous to full—provided powerful, tangible evidence supporting the Sun-centered model proposed by Copernicus. In a strictly geocentric model, Venus's apparent phase progression, viewed from Earth, would be severely limited; it could never appear fully illuminated or 'full' because it would always remain positioned between the Earth and the Sun from our perspective. However, Galileo's telescopic observations revealed that Venus exhibited all phases, a pattern only geometrically possible if Venus orbited the Sun, placing it sometimes behind the Sun relative to Earth. The inability of the traditional geocentric framework to account for these complete phases made the observational data highly favorable to the heliocentric explanation.

How did Galileo's observation of Venus support the Copernican heliocentric system?

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