(this page is mostly a placeholder at the moment; for an exhaustive (and exhausting) explanation of the moon illusion, visit Donald Simanek's discussion; for a summary of my personal views, which will be turned into a more thorough discussion as this page is revised and completed, see the next couple of paragraphs)

     To many people, the Moon appears much larger when rising or setting than when it is higher in the sky. This effect is particularly pronounced when the horizon appears far away. In reality, the Moon's image is actually SMALLER when it is on the horizon, than when it is higher in the sky; as a result, this phenomenon is an illusion. No explanation of the Moon Illusion has general acceptance, but this page (when revised and completed) will hew to the following theory:
     Things seen at large distances appear smaller than nearby things (that tiny lion sitting over there is probably just as big, but further away than that huge one, hungrily eyeing us). Almost everyone is aware of this "perspective" effect; but not as many are aware that our brain automatically corrects for the effect, to a certain extent -- that is, things that are further away look smaller than nearby things, but not as small to our brain as on our retinas. For reasons to be discussed below, which are more or less obvious without discussion, the horizon appears further away than the sky appears high, so when the Moon is on the horizon it appears further away, and our brain "adjusts" the image sent to it by our eyes, to tell us that it is really larger than what we see.
     I favor this theory because (1) when we look at distant mountains, they appear larger than in snapshots taken at the same place and (2) on planetarium domes, showing the Moon and Sun at their correct size makes them look much smaller than they do in the sky. In the planetarium, we can tell that the images are much closer to us than in the sky, and even though they are the right size on our retina, they look far too small to our brains. (At LBCC, we have to show the Moon and Sun four times their correct size to approximate their appearance in the sky.) This seems to be corroborated by the fact that constellations also look smaller on the planetarium dome than in the real sky, even though their angular size is actually the same.

The Flattened Appearance of the Sky
To be written when time permits. Leads into...

The Moon Illusion
To be written when time permits. A more thorough explanation, with diagrams and photographs, of the summary above.