Explanation:
Method of Aristarchus. wait patiently until the moon is half full literally exactly. Then the Earth, the Moon, and the Sun form a right triangle with moon being at right angle Now we need to measure the angle between the Moon and the Sun, and with the distance of the Moon (previously found by triangulation) obtain the length of the Sun as the distance of the Moon distanced by the angle cosine. The ambiguities in that "precisely" make this a weak method. Once the correct value is nearly 400 times, Aristarchus himself got the Sun 30 times as far away as the Moon.