I this video Red Orphan tries to calculate how far the Sun is away from the Earth. She selects two points on the Earth that are 60 degrees apart and finds what time of day on the Equinox that the Sun is sixty degrees above the horizon and states this is an equilateral triangle assuming a flat Earth and this gives the distance to the Sun. She also points out if the world is round this would not work out. This is actually the distance to Sun was not determined.

In 250 B.C Aristarchus figured that when there was a half moon the Earth-Moon-Sun angle would 90 degrees so when the moon is that position he measured the Moon-Earth-Sun angle and found to be 87 degrees. He figured the Sun was 19 times as far as the Moon, he was off because the angle was 89 degrees 51 minutes which gives the distance as 400 times away. The distance of 93 million miles or 150 million kms was determined in the 1960’s when a radar pulse was sent from Arecibo and bounced off of Venus. The ratio of distances between the Earth and Sun (1 AU) and the distance between Venus and Sun of 0.72 AU. Once they got the distance between the Earth and Venus it was some simple calculations to find the distance.