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# The size of the Moon

RTFishall | 22:03 Sat 04th Aug 2007 | Science
Why does the Moon look so much larger when it is near the horizon?

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Size is a relationship between two or more objects and without a reference loses relevance. When we see the Moon�s apparent size in relationship to distant objects on the horizon they are usually dwarfed in comparison to what �must be� and is a very large object. Provided with visual clues as to the Moon�s distance we can infer how big the Moon actually is.

The illusion that the Moon is larger near the horizon often disappears when looking at the Moon through a tube or hole that renders those visual cues invisible.

More Moon Illusion @ howstuffworks.com
Question Author
I wonder if one sees the same effect from the surface of the Moon when looking at the Earth
Try looking at the oversized moon upside down. This 'cures' the problem and the moon appear normal sized. Ergo, it is an optical illusion.
CT, Last time I saw someone bending over to look at the Moon upside down there was more than one Moon hovering above the horizon . . . and I'm certain at least one of them was no illusion.
Aside from the fact that the Earth is nearly four times as big as the Moon, viewing the Earth from the Moon the same illusion should apply. However the comparative size would be difficult to observe from the lunar surface since the Earth does not change its position much relative to a given location on the Moon's surface. The same side of the Moon always faces the Earth because the Moon�s rotation is in tidal lock with the Earth so the Earth does not rise or set but remains in a relatively fixed position in the Moon�s �sky�.

Just how pronounced this illusion would be seen from a vehicle orbiting above the Moon�s surface is a question for which very few people have been in a position to potentially have the answer. I wonder if occupants of the International Space Station have witnessed such an illusion?

Squashed Moon
Question Author
I've just noticed that it's not just the Moon that looks larger when its nearer the horizon, so do the Constellations. Orion looks much bigger when it is rising.

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