Why the moon looks bigger at the horizon

[Buckleymanor]

To your mind, yes, it appears to be larger on the horizon. That is an illusion, however. Here is what a camera sees (time-lapsed photograph):

Is it just me or does the Moon right at the bottom of the picture, the one with the slightly reddish glow and partly obscured look just slightly bigger than the other Moons.

 

[lenfromkits]

1) is the answer I have heard too.

Our perception of the sky - in the absence of visual clues - is that of a low dome, its roof closer to us than its rim. Thus, when we see the Moon above us, we perceive it to be closer than when it is at the horizon. Because we think it's closer yet its disk is the same size, we interpret that as if it is smaller over our heads..

This is in fact the correct answer to the illusion. This is a great topic in psychology. I'm so happy to be able to share some cool psych stuff in a physics forum.

The reason for the moon illusion is very similar to this famous illusion of which line is longer. In the example attached picture, 'A' looks longer than 'B' but they are the same length.

The explanation is the really cool part. Since most of us grew up in a western society where rooms and buildings are all rectangular (ie, not round), we learned very early to recognize these two shapes. 'A' represents the corner of a room when you are looking at it from inside the room. 'B' represents the corner of a building when you are looking at it from outside. Notice that the line in 'A' then is FAR away from you. In fact, the longer the diagonal lines on it, the farther away it would be - if this were a room. If the vertical line in there is the same size for a close corner as for a far away one, the far away one would have to be HUGE (due to perspective).

So the vertical line in 'A' looks like it is far away and large. 'B' shows the opposite. Here the line is the closest point of the building. Being 'big' in this case doesn't mean much.

In the end 'A' looks bigger than 'B' because 'A' looks a lot further away than 'B' does (to the brain). The REALLY interesting point here is that this illusion has no effect on societies in some places of, say, Africa where people did not grow up around rectangle buildings (where they grew up in round houses!)

 

[DaveC426913]

The explanation is the really cool part. Since most of us grew up in a western society where rooms and buildings are all rectangular (ie, not round), we learned very early to recognize these two shapes. 'A' represents the corner of a room when you are looking at it from inside the room. 'B' represents the corner of a building when you are looking at it from outside.

While the "which line is longer" illusion is quite cool, your explanation is nonsense.

Same illusion, cannot be explained by "corners":

 

[JDługosz]

The sky-as-dome explanation is mentioned athttp://www.lhup.edu/~dsimanek/3d/moonillu.htm" , and shown to be wrong.

I thought I had read a detailed explanation on Phil Plait's site, but now I can't find it. Something involving the rotation center of the head being different from the center of the eye, and processing corrections to normal perception can cause certain illusions.

 

[sophiecentaur]

Did you ever notice how slowly Jumbo Jets fly?
Your poor little brain just ca't comprehend how something soooo massive can be up there so it thinks it must be smaller object flying low and slow.

 

[pallidin]

The sky-as-dome explanation is mentioned athttp://www.lhup.edu/~dsimanek/3d/moonillu.htm" , and shown to be wrong.

...Something involving the rotation center of the head being different from the center of the eye, and processing corrections to normal perception can cause certain illusions.

The human eye's are spatially off-set from the center of our head.
Rotation of the human head effects a visual displacement.
OK, understood. Makes sense.
Not sure where you are going with this though.

Wonder if a video cam could further illuminate this displacement phenomenon, and, most importantly, implications.

 

[Mindscrape]

Good lord, folks, the solid angle of the moon (from earth) is
\Delta \Omega=A/r

which gives
5.74*10^-5 steradians at minimum to 7.71*10^-5 steradians at maximum

Atmospheric lensing? Give me a break... How did this topic go on for 10 pages?

The optical illusions listed by some users are pretty cool though. I wish my brain weren't defect. Oh well, at least everyone else's is defect too!

 

[raylphscs]

Is it just me or does the Moon right at the bottom of the picture, the one with the slightly reddish glow and partly obscured look just slightly bigger than the other Moons.

on this picture, the moon never steered away from being horizontal to being vertical. so the picture means noting for argument. the moon in the picture acturally kept as basically horizontal.

 

[DaveC426913]

Me thinks you have utterly missed the point of the conversation.

Good lord, folks, the solid angle of the moon (from earth) is
\Delta \Omega=A/r

which gives
5.74*10^-5 steradians at minimum to 7.71*10^-5 steradians at maximum

Great, you showed a formula that describes the Moon's angle. OK, we start with this a premise, you listing the formula adds nothing.

Atmospheric lensing? Give me a break...

Ironclad logic there.

How did this topic go on for 10 pages?

Well, because contributors were doing more than simply skimming to the end and then performing a drive-by judgement.

 

[raylphscs]

Your picture doesn't show your purported atmospheric effect. It cannot for the simple reason that your purported effect doesn't exist. The atmosphere does not act as a lens that magnifies the size of the Moon.

Aside: The word is lens, not lenz. Most browsers have spell checkers and highlight misspelled words. Mine, for example, shows "lenz" with a red underscore. That means that "lenz" is not a word.

Back on topic: Using the well-known equation 1 picture = 1000 words, here is a several thousand word essay on this topic:

Source: http://antwrp.gsfc.nasa.gov/apod/ap020130.html

Source: http://spaceweather.com/submissions/large_image_popup.php?image_name=Chris-Picking-moon_rising_composite_1213915516.jpg
[PLAIN]http://spaceweather.com/submissions/pics/c/Chris-Picking-moon_rising_composite_1213915516_med.jpg

Source: http://greenmanblog.com/archives/P87.html
http://greenmanblog.com/uploads/FullMoons.jpg

Source: http://epod.usra.edu/blog/2007/06/rising-moon-illusion.html
[PLAIN]http://epod.typepad.com/.a/6a0105371bb32c970b011571a50254970b-600wi[/QUOTE]

on this picture, the moon never steered away from being horizontal to being vertical. so the picture means noting for argument. the moon in the picture acturally kept as basically horizontal.

 

[DaveC426913]

on this picture, the moon never steered away from being horizontal to being vertical. so the picture means noting for argument. the moon in the picture acturally kept as basically horizontal.

1] You said this already in post 158.
2] I have no idea which you mean by 'this picture'. Why not just display and reference one picture?
3] I have no idea what you are trying to say about 'horizontal versus vertical'.

 

[raylphscs]

Our perception of the sky - in the absence of visual clues - is that of a low dome, its roof closer to us than its rim. Thus, when we see the Moon above us, we perceive it to be closer than when it is at the horizon. Because we think it's closer yet its disk is the same size, we interpret that as if it is smaller over our heads..

This is in fact the correct answer to the illusion. This is a great topic in psychology. I'm so happy to be able to share some cool psych stuff in a physics forum.

the sky is a low dome is not an illusion, it is the fact. because the visible part of the atomosphere is exactly the low dome in reference to the point we are standing.please see the picture in post#13

please the analogy picture

[

the sky is a low dome is not an illusion, it is the fact. because the visible part of the atomosphere is exactly the low dome in reference to the point we are standing.please see the picture in post#13

 

[DaveC426913]

the sky is a low dome is not an illusion, it is the fact. because the visible part of the atomosphere is exactly the low dome in reference to the point we are standing.please see the picture in post#13

the sky is a low dome is not an illusion, it is the fact. because the visible part of the atomosphere is exactly the low dome in reference to the point we are standing.please see the picture in post#13

raylphscs, you are not helping your cause by repeating yourself. You've just posted the same comment twice in the same post, and that is a repeat of an earlier thread.

While I acknowledge that English is not your first language, this problem has nothing to do with language, this has to do with you organizing your thoughts before posting (a language-independent task), and providing enough detail for the context of what you are trying to say in a single post, instead of continually adding more posts to try to patch up botched posts.

I'm going to request the thread be cleaned up, removing your fractured posts so that you have a chance to make a single clear concise post that gets your point across. This will help you as well as the rest of us.

 

[Redbelly98]

Thread locked pending moderation.

EDIT: Thread will remained locked.

There is really no reasonable basis for this to be a nine-page thread apart from sheer stubbornness.

... we are just a bunch of guys arguing why a hammer falls faster than a feather with some guy who insists that gravity is different.

Good analogy.