How do Scientists know the Sun is 93 million miles from the Earth? (How do they measure it)
It's a trig problem, the classic right triangle with the Earth, Venus and Sol at the points.
IF you know the distance to Venus (use radar and get it to the foot ... or the mm)
AND you know the angle to the Sun
AND you wait until the angle from us to Venus to the Sun is 90 degrees,
(not as bad as it sounds, Venus will look like a half moon)