English: The Moon illusion - illustration of the apparent distance hypothesis (i.e. a cloud of a certain size at a certain height in the atmosphere subtends a smaller angle if it's lower towards the horizon than if it's more nearly overhead; since the moon subtends basically the same angle whether it's overhead or near the horizon, therefore it's perceived as larger near the horizon.

1: Moon near to horizon 2: Moon higher in sky (appears smaller than 1, actually has the same size) 3: Size that moon should have according to perspective rules.

o: Observer c: Cloud's path

m: Moon's path