If a telescope shows Venus to be a thin crescent, where is Venus relative to the Earth and Sun?

Answer 1

The side of Venus that is illuminated is always the side facing directly towards the Sun. (It's not always the same particular section of Venus' surface.) The phase of Venus that we see depends on how much of the side that is facing the sun is also facing us. If Venus is just a thin crescent, then Venus is almost directly between Earth and the Sun. It is a very small angle displaced from the line connecting us to the Sun, and it is on the same side of the Sun as we are.

If Venus were directly between the Earth and Sun, we'd be looking directly at the side of Venus that is completely unilluminated, and we'd see nothing. If Venus were exactly on the opposite side of the Sun from the Earth, we'd see Venus' surface fully illuminated, except that the Sun itself would overwhelm our ability to actually see Venus in the sky. We see Venus very well and almost full, shortly before and shortly after the opposing conjunction.