In contrast to the Jovian moons, what type of proof did the phases of Venus offer?

Answer

A geometric constraint

The phases of Venus offered a geometric constraint, proving mathematically what must happen regarding Earth's orbit around the Sun, whereas the moons offered a physical demonstration that other centers of motion existed.

In contrast to the Jovian moons, what type of proof did the phases of Venus offer?
GalileoobservationMooncelestial bodyProof