Make a wooden disc and a stick whose length is 108 times the diameter of the disc. Attach the disc to one end of the stick and hold the other end near your eye. Observe that the disc has the same apparent diameter as the moon, eclipsing it. You could do the same with the sun through light clouds or mist, but be careful, obviously. There are indications that some ancient peoples, such as the builders of Stonehenge, were sufficiently interested in astronomical observation that they might have done a measurement like that and noted the result.