Why does the full moon look so much larger when it is close to the horizon?

Question

When a full moon is close to the horizon it looks much larger than later on when it is high up in the sky.

Answer 1

It is a well known optical illusion. If you measure the diameter with a telescope or by taking a photo, it is the same, but because it is near the objects on the horizon your brain perceives it as larger.

Answer 2

Our perception of the "dome" of the sky is flatter than it really is. We visually assume that the sky overhead is not very far away, maybe a few miles, because we have no overhead distance cues. But the horizon has visual clues that show some scale. We can compare nearby trees to more distant hills and mountains. The moon behind the mountains looks enormous by comparison because we know what it takes to make something behind them look that big. But overhead, the moon is "small" because there is nothing mediating the distance between us and it. Clouds don't count because there is no way to gauge their relative size. If you were to completely block out the horizon and any foreground objects, the moon would look the same size in either direction.

Answer 3

yeah, it's an optical illusion.

But it is NOT the same size on the horizon as it is high in the sky. Draw a picture, with you on the earth (the outer limb, if you please) and with the moon on a tangent and directly over your head. The moon is one earth radius CLOSER at the zenith than on the horizon. One earth radius (about 6420 km) is about 1/60th of the distance to the moon, so the moon will appear very slightly larger when high in the sky. Get a reallllllly good tape measure for that!!

Answer 4

It is an optical illusion. People see things near the horizon as larger than they really are, but you can destroy the illusion by looking at it upside down. You can stand on your head or look between your legs or lay down or lean over and look behind you, whatever you find the least embarrassing way to view the horizon upside down. Try it. Everything looks smaller, even trees and mountains and buildings. Everything!

Answer 5

rscanner is absolutely right. It's not actually larger nor does the atmosphere magnify the moon. It just looks larger but if you measure it, it's the same. It's an optical illusion due to its closeness to the horizon.

Answer 6

The atmosphere acts to distort the size of the moon, much like looking at an object through a glass of water.

Answer 7

maybe cuz it is closer? or maybe cuz you can compare it to the trees or something

Answer 8

Yes, did you see it this morning? it was huge.