Re: Why does the moon appear larger when it is closer to the horizon?

Spencer,

You are right, the moon only appears to be larger nearer the horizon, it is an optical illusion. If you ask most people how large an object you would have to hold up at arm's length to just cover the full moon,they are surprised to find out that the answer is the width of the nail on your little finger! Try covering the moon with your little finger when the moon is on the horizon and when it is high in the sky - you'll find that it's exactly the same.

Exactly why the illusion occurs is more difficult to answer and related to psychology rather than astronomy. It probably has something to do with the moon near the horizon being viewed together with familiar nearby objects and the brain interprets the moon as being larger and nearer whereas high in the sky it is in spendid isolation. An illustration of the point can be found in this Web link from Sky and Telescope magazine. If you explore Sky and Telescope's web site and related ones you'll find much fascinating material about astronomy.