And what was observed by the Hubble space telescope just some years ago bears
striking similarity to Galileo’s observation. Such close resemblance must have a very
strong scientific reasoning as its base which was laid down by Galileo in his clear
mention of the Copernican model.
In the Ptolemaic model, Venus lies between the Earth and the Sun and hence it must
always be lit from behind, so one could only see crescent phases whilst its angular size
would not alter greatly.[Angular size is the angle subtended by a huge body with an
observer's eye.] In contrast, in the Copernican model Venus orbits the Sun. When
Venus is nearer to us, it would show crescent phases; while when away from us, it
would show almost full phases. As its distance from us would change significantly, its
angular size would likewise show a large change.
Galileo's drawings showed precisely what the Copernican model predicts: almost full
phases when Venus is on the far side of the Sun and a small angular size coupled with
thin crescent phases, having a significantly larger angular size, when it is closest to the
Earth.
Credit: "Phases-of-Venus" by Nichalp (Wikimedia Commons)
Now, next time when you see Venus, do remember how it actually appears, and do not
forget to appreciate the great intellect of Galileo as well as Copernicus!!!