I was looking at a very bright moon tonight through light cloud cover and saw a halo of light far bigger than the moon imposed on the clouds. Almost in a conic shape by comparison. I was wondering if early astronomers could use this difference to calculate the distance of the moon given the height of the cloud and the dimensions of earth.
No, because the size of the halo is determined by the properties of ice crystals, the distance to the Moon is irrelevant. So you get a 22° halo with both the Sun & the Moon, even though the Sun's much further away.