1. How does the moon's diameter compare with the distance between Earth and the Moon Tape a small coin, such as a dime to a window and view it with one eye so that it just blocks out the full Moon. This occurs when your eye is about 110 coin diameters away. Then the ratio of coin diameter/ coin distance is about 1/110. Geometrical reasoning of similar triangles shows this is also the ratio of Moon diameter/Moon distance. So the distance to the Moon is 110 times the Moon's diameter. The early Greeks knew this. Aristarchus's measurement of the Moon's diameter was all that was needed to calculate the Earth - Moon distance. So the early Greeks knew both the size of the Moon and its distance from Earth. 2. moon diameter is 1 and the moon distance is 110 1/110 3. I understand that looking at the moon it is a total of 1 moon diameter and the distance is 110 moons away. but I don't understand at the same time where and how this is theasable. How would you correctly get that measurement and why. I know this man Aritarchus didn't have 110 moons so I am assuming he used geometry but how did he decide on the angle, or what ever. I don't know if I am making sense.