Why does the Moon appear to be larger when it is on the horizon than when its higher in the sky?

mumby21

If I remember correctly it's because the moon is viewed on the horizon through the earth's atmosphere, which acts as a magnifier and when viewed directly overhead the atmosphere is thinner diminishing the magnifying effect. Apr 30 05, 7:47 AM

odin_sas

While I see the logic of mumby21's answer, it also has to do with the fact that when the moon is higher up there is nothing with which to compare it - closer to the horizon you can see it in relation to buildings and trees and you have a better idea of how much sky it actually covers. Apr 30 05, 8:32 AM

kaylofgorons

If you photograph the moon, it won't even look nearly that big. This site says that if you see a photograph of the moon being huge it is probably a composite. The size of the moon is an illusion of sorts. Let me know if there's an error in the site, or at least let them know. http://www.grand-illusions.com/moon.htm Apr 30 05, 1:19 PM

kaylofgorons

If the link doesn't work for anyone, here's the basic info from it: "How does this illusion come about? Since the moon always subtends an angle of 0.5 degrees, the image on the retina must always be the same. Clearly the problem is one of interpretation. One simple experiment shows this to be so. A full moon just above the horizon will not appear so large to the human eye if a piece of paper is held up to that eye with a hole in it, so that only the moon can be seen through the hole and not the horizon. If the other eye is open at the same time, viewing both the moon and the horizon, the two eyes will each see different sized moons!" Apr 30 05, 1:21 PM

gmackematix

See #24799 Apr 30 05, 7:43 PM

kaylofgorons

Gmack, I just tried entering that number three times and got no question. Is my computer being fussy again, or is there a glitch in the archives? Apr 30 05, 9:02 PM

gmackematix

Not at all Kay. The glitch is in my head! You might like to try #24977 instead. Apr 30 05, 10:57 PM

peasypod

Yes, all to do with that 'reference point' of course. Having nothing to compare it to when it is way up hovering over your head in the middle of nothing, yet against a mountain out-line the figure plays tricks on your eyes. As for the #24977, wonder what DB is up to these days?, and quite odd what happens when you click on Nude Dude..... Apr 30 05, 11:36 PM

UT-7	The Moon does appear larger on the horizon, but it is because of the way we perceive the sky. May 01 05, 7:26 AM

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