Abstract

The much larger appearance of the moon near horizon than the perceived size of the moon at zenith has motivated many scientists to develop theories that aim at explaining this puzzling phenomenon. Considering that the size of retinal images of the moon in these positions are very similar, the explanation of difference in their apparent sizes has relied on perceptual cues of distance embedded in the retinal image of their respective contexts. Although this account of the moon illusion is quite popular, it does not explain all aspects of this phenomenon. The theoretical formulation of the moon illusion based on other factors such as size contrast later may have had some advantages but has also created some new problems. Although the moon is perceived in a three-dimensional (3D) environment, the present analysis proposes that an explanation of the moon illusion based on two-dimensional (2D) cues can remove some of the unnecessary problems. The empty space and size contrast that have already been considered in explaining classic geometric-optical illusions play a parallel role in explaining the moon illusion. In other words, the role of open space in interaction with the image of the moon and different objects near horizon, all reflected on the retina, are considered as the main explaining factors. The advantages of this approach will be discussed and some of the facts pertaining to the moon illusion will be explained within this theoretical framework.