As Venus passes behind the Sun and on the opposite side of the solar system to the slower moving Earth, it displays the light hemisphere to us and therefore no variations in appearance when it comes within range of the C3 camera-

https://www.popastro.com/images/planetary/observations/Venus-July%202010-January%202012.jpg

https://sol24.net/data/html/SOHO/C3/96H/VIDEO/

As Venus passes between the slower moving Earth and central Sun, it shows less and less of its light hemisphere and therefore the appearance diminishes as it approaches Earth at its closest approach-

https://www.youtube.com/watch?v=w2uCtot1aDg

Galileo marvelled at this as Venus is many times larger as it is nearer the Earth than when it is on the opposite side of the solar system even though the planet retains roughly the same brightness. Only now can the diminishing of appearance can be seen.

SALV. "But the telescope plainly shows us its horns to be as bounded
and distinct as those of the moon, and they are seen to belong to a
very large circle, in a ratio almost forty times as great as the same
disc when it is beyond the sun, toward the end of its morning appearances. "

SAGR. " Oh, Nicholas Copernicus, what a pleasure it would have been for
you to see this part of your system confirmed by so clear an experiment [telescope]!"

SALV. " Yes, but how much less would his sublime intellect be celebrated among the learned! "

Galileo, Dialogue Concerning the Two Chief World Systems, 1632

Celebrated among the learned. How I wish that was possible, including the new perspective.

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