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Fraser
2007-Jun-28, 04:49 PM
Have you ever marveled at how large the full Moon looks when it's just peeking up over the horizon? It looks so much larger than when it's high in the sky. ...

Read the full blog entry (http://www.universetoday.com/2007/06/28/explaining-the-moon-illusion/)

mathman
2007-Jun-29, 12:27 AM
One factor that I have observed personally is my position. Specifically, when lying on my back (on the ground) things (clouds, moon) look bigger than when I am standing up and look up. I have not analyzed it in any way, but I state it as an empirical fact.

Doctor Know
2007-Jun-29, 12:58 AM
Hmm. I always thought it was because when you are seeing the moon on the horizon it's in relation to other objects. Streetlamps, rooftops, trees. Once it's high up and isolated from terrestial objects it appeared diminshed.

Pronzo Illusion...I'll have to remember that one. :)

GrahamC
2007-Jun-29, 07:48 AM
I think Mathman has an interesting observation here. There is no way that parallax from 2 eyes 70mm apart will enable the brain to distinguish 2 miles from 100 miles but if there were a built-in assumption that objects at low elevation (with respect to the normal vertical axis of the body) are further away than those at high elevation then the illusion becomes explicable - and the test is to lay down. Unless vertical is defined by gravity and the inner ear.
It's pouring with rain at the moment, but I shall try it.

regards
GrahamC

Tharsis
2007-Jun-29, 01:17 PM
I've heard and read this explanation of apparent moon size before, I believe it to be true - but I still struggle with it. How can the brain interpret things being bigger when they're farther away? Shouldn't it be the opposite as in perspective drawing?

Nick4
2007-Jul-01, 06:25 AM
The way i thought of it was that when the moon was close to the horizon the curve in the earths atmosphere distortes the light in the of the moon and makes it look bigger.

Tucson_Tim
2007-Jul-01, 06:28 AM
The way i thought of it was that when the moon was close to the horizon the curve in the earths atmosphere distortes the light in the of the moon and makes it look bigger.

This is what I always thought. I've seen some HUGE full moons when first rising - at least they LOOKED huge.

hhEb09'1
2007-Jul-01, 06:36 AM
This is what I always thought. I've seen some HUGE full moons when first rising - at least they LOOKED huge.That's easily disproved by photographs--I think the BA mentions it in his book.