Why does the moon look so much larger when it's close to the horizon?

Question

Been scratchin' my head about that one for a while . . .

Answer 1

It's called "atmospheric refraction" and it also accounts for the illusion that the Sun is huge at sunset and sunrise.

Basically, if the Moon is straight overhead. it is not passing through very much of the atmosphere before the light reaches your eye. Thus, there is no distortion.

However, when the Moon is low on the horizon, the light must pass through thousands of miles of the atmosphere before it reaches your eyes. It's very similar to water refraction.

Live long and prosper
~\@/~
Mack

Answer 2

It's very wierd why it occurs. It is simply an optical illusion apparently created because when it is high in the sky, you have no reference to other items to judge its size. When you see it right above the horizon, your mind is comparing it to the objects that are right below it.

When reviewing this answer, I came upon this site:

http://facstaff.uww.edu/mccreadd/intro9.htm

Lots of details explaining compething theories about how the mind's peception of the moon is different at horizon and zenith. From my reading of the site, they seem to settle on the effect of visual distant clues (objects near to the horizon) as the most probable cause.

Also, it is interesting that a picture of the two moons, one taken at horizon and one at zenith, will not produce this effect. That proves that the actual size of the moon, its angular subtense of 0.52 degrees, is always the same, regardless of location.

Answer 3

Because it is being compared to objects like trees or tall buildings That create the illusion that it is larger than it is. When it is high above the horizon, we do not have such a comparison and the moon appears its actual size.