Why did observing the full phases of Venus support the heliocentric model?

Answer

Showing a full disc meant Venus orbited the Sun, placing it sometimes on the far side of the Sun.

In the Earth-centered model, Venus could only show crescent phases; observing a full disc implied it had to orbit the Sun to be visible on the far side of it from Earth.

Why did observing the full phases of Venus support the heliocentric model?
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