Moon Illusion

[jamesb]

Since the moon has been in the off topic scene lately, I thought I would share this bit of info.

Im sure yall have seen the moon rise when its full and it looks really HUGE, then a few hours later it looks much smaller, then again when it sets it looks huge again. Many call this the "moon illusion" so we will just stick with that for now. (you can Google "moon illusion" to read more on it if you are pretty board).

the "moon illusion" has been argued for a long time as to what the cause is and why it looks much larger at the horizon than directly overhead. As far as I know a definite answer has not been decided on. But there are several good theories and each make their valid points as to why this happens. Im not smart enough to decide which is correct.

one problem with the moon illusion is when photographing the full moon just after it rises, and then again after its been up several hours, it is the same size on film (or your digital photo).  This is one of the things that is in debate as to why this is.

here are 2 shots I took back in June 2006 and I stacked one over top of another to show that the camera captures basically the same size object.

both shots were using the Canon 20D, and the sigma 50-500 @ 500mm. one shot was when the moon was fully above the horizon but still very close to it. the second shot was several hours later when the moon was well above the horizon.

now when I took these shots the moon on the horizon it did look much larger than it did higher in the sky.





James

[Casa Grande]

the "moon illusion" has been argued for a long time as to what the cause is and why it looks much larger at the horizon than directly overhead. As far as I know a definite answer has not been decided on. But there are several good theories and each make their valid points as to why this happens. Im not smart enough to decide which is correct.

James

i always thought it had something to do with the lighting angling off the atmosphere like in a pool of water.  neat experiment.

[Bobcat]

That really is puzzling. I'm going to have to look into this one.

[tjavery]

That's pretty interesting!

[jeffblaylock]

I've done a similar experiment and found the same results. I believe the eye perceives the moon (or sun) as being larger near the horizon because it interprets its size relative to the foreground objects on the horizon. Once it's up in the sky, the brain has nothing to compare it to, so it looks smaller up there all by itself. Just my theory, totally not borne out by any scientific facts ....

[Bobcat]

I think this pretty much explains the illusion(the Ponzo Effect that is):
http://www.unmuseum.org/exmoon.htm

[Bobcat]

Check this out: http://antwrp.gsfc.nasa.gov/apod/ap070103.html