Talk:Moon illusion

The moon illusion is currently UNEXPLAINED

THESE REMARKS REFER TO AN OLD (2005) VERSION. It has been extensively revised in 2008.

http://www.google.com/search?hl=en&lr=&client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&q=%22moon+illusion%22+%22is+still+unexplained%22&btnG=Search

We need to rewrite the "cause" to reflect the current body of evidence. I don't have time right now, but people shouldn't be misled by an explanation of an unexplained phenomenon. There is no mention of this being a spectulation or otherwise. This is deceptive.

Above is by User:Jabin1979. Mgm|^(talk) 10:42, Mar 7, 2005 (UTC)

If I can find the time, I'll see if I can do a rewrite on the info to make the status of the info clearer. Mgm|^(talk) 10:39, Mar 7, 2005 (UTC)

• I don't buy the google link at all. The article by Maurice Hershenson is listed in two of the four results. There's a much more scientific, and IMHO, better explanation already listed on this page. If you want to skip the technical aspects, just examine the 'big man/little man' pictures on the last page of the Micropsia site: http://facstaff.uww.edu/mccreadd/appendix2.htm Krupo 14:57, July 24, 2005 (UTC)

Also, change your google search and get 7400 pages that state the opposite: http://www.google.ca/search?num=100&hl=en&client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&q=%22moon+illusion%22+%22explained%22&btnG=Search&meta=

After looking through all those pages, I can't seem to find "the" answer. If we are going to say this illusion is "solved" once and for all, we need A) A citation in a peer reviewed journal (not just what one psycholigist says on his webpage (or even worse, The Straight Dope) or B) an established consensus among a large number of experts found on Google. I do think now that it is closer to being solved than not. Citing any one physicist or psychologist would be bad research however, we really need something more widely accepted. If someone writes that it's "solved" on here, it would be best if you provide a number of strong sources annotating each page to show a consensus.

There definitely isn't a consensus. I can cite The Columbus Dispatch, June 22, B7: Richard Pogge and Gerald Newsom, two Astronomy professors at OSU, have two different explainations. James Todd, a psychology professor in the field of visual perception at OSU, says, "We can explain a lot of illusions, but this one is a particularly tough one." They also quote several other people. Before stating this illusion as "explained," I would insure there is an consensus among experts, maybe several emails?

Non-possiblities

Just to clarify, things such as Diffraction of light also don't answer the question. Diffraction only changes it slightly, while what we see is a much bigger difference. Another possiblity proposed is that the Moon in comparison with smaller objects near the horizon makes it seem larger. 128.6.175.26 16:51, 2 February 2006 (UTC)

What a mess this has become

First there is this: "This explanation is, of course, the apparent distance theory which now is rejected by modern vision researchers who have specifically researched the moon illusion. See below." (and yes, I wrote most of the paragraphs that that follows)

I think there are far better ways of doing this. One...I personally don't agree that the "experts" which rejected that hypothesis are any more credible than those who advocate it. Regardless...you should reorganize the page, and put that section into the appropriate subsection, rather than just saying "this is discredited, see below".

Then further on there is "for the latest research do a web search for "moon illusion." " and repeated "for details see link to "the moon illusion explained." " That sort of thing is exceptionally unprofessional looking in an encyclopedia.

I suggest this page be marked as "not conforming to quality standards" or whatever. What process do we need to go through to do that?

--Robbrown 05:47, 15 April 2006 (UTC)

Field of view theory

I'm surprised this theory isn't mentioned. Everybody who has delved into photography knows about it.

The synopsis and premise is quite simple: When you look at an object on a uniform surface with little background clutter, your eyes make larger motions since your brain is able to process the little amount of information per degree. When you place the same object in a cluttered background (near the horizon you usually have multiple trees, houses, lights, as well as a lot of motion), your eyes don't make that much motion since the brain must process a lot more information per degree, thus your field of view narrows and you focus on objects in the center of the image.

This presents an ability to train the brain in overcoming the illusion. Once you stare long enough on the Moon, it should seem to have grown larger (if only for a short moment). Key to successfully doing this lies in being completely relaxed. If you get even a bit startled, you'll almost immediately lose the narrower field of view.

Comparison Photo

an example of comparison photos would really be good. ive been waiting for a 'big' moon for a while to snap a shot of it, but it hasnt happened yet.

although it may be that while the photos did show them to be the same size, that it would seem irrelevant since you can't see it 'big' to compare. Sahuagin 18:26, 29 October 2006 (UTC)

Discovering the Illusion

I'm surprised that what (for me!) is the most compelling demonstration that this is an illusion is not mentioned. Namely, look at the Moon when it is near the horizon through a tube (like a toilet paper tube, or the tube used as a core for paper towels--or even through the space made by your hands and thumb) and suddenly it looks small again!

Also, concerning the explanation: "The problem is, of course, that our neural nets are not trained to see objects more than some 100 meters away." There is perhaps a citation for this "fact"? First, it seems to presuppose that the brain is organized in the form of neural nets; I'm not sure that is accepted (although maybe it is, and I'm just ignorant of it). Second, it seems to imply that someone's neural nets could be trained to "see" objects further away, and if this were done, the illusion would vanish, or at least diminish. (Or more easily tested, if someone had spent their life seeing only nearby things, and were then given glasses allowing them to see things further away, the illusion would be even more compelling than it is for those of us who have had good vision all our lives.) But third, it is not at all apparent what it means to _not_ be able "to see" objects more than some 100 meters away." Obviously we do see objects further away, the Moon being one of them. So what does "see" mean in this context?

Finally, since this is an illusion, I presume that you can't discern any smaller areas on the Moon when it is near the horizon than when it is high--that is, it would be no easier to see the large craters, or "bays" in the maria. I have tried unsuccessfully to tell whether this is true, nor have I ever seen any discussion. It would be illuminating (pardon the pun). —Preceding unsigned comment added by Mcswell (talk • contribs) 01:23, 12 May 2008 (UTC)

Illusion?

I've never noticed the difference between rising and zenith moons before, but I have noticed the varying sizes of the moon many times. (Never thought about how high in the sky the moon was at the times, strangely enough..) And, well, I'm not sure if this is the same thing then, but the differences in size that I have noticed are definitively *not* an illusion, sometimes the difference can be as much as ten times! On some nights, the moon can be so small as to be nearly a tiny dot, but on others it can be larger than a plate. And when it's small, I can't discern any of the craters, but when it's large, they are all very visible. Also, allthough I haven't made a point of noticing the height of the moon, I have noticed that on the few times the moon has been particullary large, it has been consistently large all through the night, likewise when it comes to the small moons. On this page "http://www.netaxs.com/~mhmyers/moon.tn.html#moonillusion" it mentions that "If you place your thumb and index finger a pencil width apart and hold it at arm's length, you will always be able to fit the moon between them no matter where it is." which is simply not true. Sometimes the moon has been as large as my hand when I've tried this. This page, while trying to explain the "illusion" even illustrates it very good with two photos: http://niquette.com/books/sophmag/moonill.htm While, yes, they are the same size on the photos, the topmost photo is the result of a zoom, unless the moon was large to begin with. And the one with the mountains? I rarely see such a large moon, even when it is on the horizon, so.... My question then is, is there a real effect of moon sizes not mentioned in this article, or is what I'm talking about the same thing as the "moon illusion"?

- NightRaven

Just an update, I just came in, and the current moon is thrice as large as usual, and it is in the middle of the sky, nowhere near the horizon. Is this page a hoax?

-NightRaven —Preceding unsigned comment added by 90.149.29.3 (talk) 17:34, 17 February 2008 (UTC)

I think your post is a hoax. You cannot be serious!76.113.105.186 (talk) 05:38, 23 October 2010 (UTC)

This article confuses me

Just thought I'd mention that. It seems to be written like a (bad) academic paper, not an encyclopedia article. What is the illusion? Why does it happen? Did this have an impact on any events in the real world at any time? Mythologies, theories? Why is there enough geometry to make my eyes bleed? --99.236.163.79 (talk) 04:52, 16 March 2008 (UTC)

I agree, this is a very confusing article. It's very much below par compared to most other wikipedia articles. I (tried to) read this article and now know less about the moon illusion than I did before I read it! And I'm an astronomer! -- JSF, --35.8.153.13 (talk) 19:36, 18 April 2008 (UTC)

What on earth has happened to this article?

When I last looked here 18 months ago, this article was much better. It described the illusion and gave a few brief plausible explanations. Now the article is 5 times longer, is full of strange notation and strange explanations, and is far less encyclopedic. Is this a subtle form of vandalism? Occultations (talk) 15:22, 21 March 2008 (UTC)

I totally aggree. It looks more like a conference paper than an encyclopedic entry. I think the article should be restored to what it was then. Tó campos (talk) 18:16, 24 March 2008 (UTC)

Avargasm (talk) 21:51, 5 May 2008 (UTC) I agree with you both. Seems like someone has done a big self research. I am returning the article to the point where it was concise and had meaning and usefulness.

We must remember that web pages are generally not an acceptable source of citations for Wikipedia articles. Contributors: please take this into account: (from: What Wikipedia is not)

please do not use Wikipedia for any of the following:

1. Primary (original) research such as proposing theories and solutions, original ideas, defining terms, coining new words, etcetera. If you have done primary research on a topic, publish your results in other venues such as peer-reviewed journals, other printed forms, or respected online sites, and Wikipedia will report about your work once it becomes part of accepted knowledge.

It's a plausible theory, but when you look at the evidence, the atmosphere is clearly acting as a lens and bending the light. See the photos of the moon through the atmosphere from the space station for proof that the 'Illusion Theories' are completely wrong, although, it was a reasonable explanation before we knew the facts. ~~ concerned scientist —Preceding unsigned comment added by 75.162.34.110 (talk) 12:26, 14 May 2010 (UTC)

Reply to "What has happened?"

NOTE added May 14, 2008. A revision of the long article you refer to was in progress on May 12 , to make it more user friendly. But this revising stopped because someone removed that "long" article and substituted for it an entry that was unsatisfactory.

However, a different user,(see the next entry in talk by 81.157.197.236) now is providing a well-written summary.

Here is a word of friendly advice to others who plan to comment on the moon illusion: First read, for instance, the excellent book, "The Mystery of the Moon Illusion" by Ross and Plug (2002). It will bring you up to date with modern visual science. Since 1985 there has been a radical change in how vision scientists describe and explain classic visual illusions, including the moon illusion. The terms, equations and diagrams of this new approach (paradigm) have appeared only in refereed journals, in two "moon illusion" books (1989, 2002) and in only two or three websites (including "The Moon Illusion Explained.")

This new approach emphasizes that the moon illusion for most people begins as an angular size illusion. This definition is accepted and emphasized in the Ross & Plug (2002) book, etc..

The (now removed) article you referred to was too long because it used seemingly "strange" terms, concepts, equations, and diagrams not yet offered elsewhere in Wikipedia. (Such as, perceived visual angle, perceived linear size, size-distance invariance, perceptual size-distance invariance, angular size contrast, linear size constancy, equidistance tendency, and oculomotor micropsia.)

Likewise, the Wikipedia entries for other classic "size" illusions (such as the Ponzo illusion and Convergence micropsia ) have not yet been revised to also describe them in terms of the new paradigm, and thereby relate them to the moon illusion.

It has been a giant step forward to show that the basic moon illusion (the visual angle illusion) is an example of the well-known relative angular size contrast illusions or else the illusons of oculomotor micropsia. But that merely redescribes it. The main task facing researchers is to explain why those two more basic illusions occur. Various theories currently are being considered. They are complicated and differ widely in the kind of brain activities they propose. These theories are not yet reviewed in Wikipedia.

The moon illusion will not be fully "explained" until an agreement is reached on those more basic theories.

tit  ding unsigned comment added by Mccreadd (talk • contribs) 22:08, 22 March 2008 (UTC) 

Pruning too extreme

Fair enough, this article had become overblown and dauntingly complicated, but now it has been decimated to such an extent that lots of valuable information from earlier versions has been lost, and what's left has in some places become so sketchy as to be pretty much useless. As I get around to it, I will be re-adding some text from an earlier version. 81.157.197.236 (talk) 11:07, 13 May 2008 (UTC).

Avargasm (talk) 06:26, 26 May 2008 (UTC) Sorry if the pruning was too extreme, and thank you for re-adding the lost info. The article seems much better now IMHO, without the overwhelming details of this or that theory. I recommend to keep this style, and if a deep technical discussion is needed, I suggest to do it in a separate article for that theory alone.

Is relative size hypothesis a particular case of the apparent distance hipotesis?

The apparent distance hypothesis is the general explanation about "cues" that make us think that objects near the horizon are further away than others. In this scenario, it seems to me that the relative size hypothesis is only a special case of "cues", that is, small objects in moon's immediate visual environment give us a "cue" that the moon is at great distance. This "relative size cues" are even mentioned in the apparent distance hypothesis. Avargasm (talk) 06:39, 26 May 2008 (UTC)

No, it is a serious mistake to think the two theories are the same.

The obvious connection between distance cues and "relative sizes" has been exploited by all "relative size" moon illusion researchers at least since Restle's (1970) article in Science, which made it perfectly clear that the crucial variable is the relative perceived angular size, not the relative perceived linear size.

At least since 1962 the relative perceived angular size theory has been the best known alternative to the apparent distance theory which, as all researchers know, can explain a relative linear size illusion, but cannot logically explain the relative angular size illusion that most people have for the moon.

I echo the earlier request (May 14, by user Mccreadd) that contributors to this "TALK" section get familiar with the extensive published research on the moon illusion before they offer suggestions like that. The book by Ross and Plug (2002) reviews research up to 2001. Reviews of research since 2001 can be found in "The Moon Illusion Explained" (the only website Ross and Plug referred to.) (That website's Section II reviews the relative size theory and specifically mentions "The Distance-Cue Connection.") Ojosepa (talk) 16:59, 7 June 2008 (UTC)

Expand the illusion

IMHO the sun can not randomly have offsetting distance and size differences from the moon, perfectly perhaps there is a larger illusion containing this one

Past cultures on earth have cosmologies that have this at their centers why does ours completely ignore it????? 32.139.49.166 (talk) 11:24, 7 June 2008 (UTC)

"Point of reference" theory

Someone has plonked the following text in an inappropriate place in the article:

"Another theory is called point of reference. When the moon is near the horizon there are usually common objects in the foreground (trees, telephone poles etc.) that give a point of reference. Therefore the moon appears bigger next to an object for which the observer has a reference of size. As the moon travels higher in the sky the observer loses this point of reference for comparison therefore the moon appears to be smaller than when it is close to the horizon."

If this is a separate theory then it need to go in a separate section. Or is it basically the same as the "Relative size hypothesis", and should therefore be merged into that section? If it's not the same then I think the difference between the two ideally needs to be explained better. I'll leave this to someone more knowledgeable than me to sort out! —Preceding unsigned comment added by 86.134.55.109 (talk) 03:20, 6 October 2008 (UTC)

Is the moon the real issue here?

Forgive my naivete or inopportuneness, but I thought I could express a couple of thoughts here.

The perception of the sun behaves in the same way. Last week I was driving on a highway around sunset and I saw a sun that was huge, not just 20% or 100% bigger, but probably 10 times bigger than usual. So the effect in question is really remarkable.

I believe that what gets enlarged in our visual perception is not the moon (or the sun) itself, but any object that happens to occupy that same spot of our visual field that the moon is occupying. It could be a group of trees that overlap with the moon. As a simple example, suppose that at a particular moment the moon is exactly enclosed between two distant tall trees, one to the left and one to the right of the moon, and looks huge. I believe that we would perceive the distance between those two trees as being the same (and seriously enlarged!) even if the moon were not there. This means that we are not magnifying *the moon* in our perception, we are magnifying just everything that is contained within a certain portion of our visual field (a wide and long vertical strip of space running parallel to the horizon).

In other words, sometimes our whole perception of space is distorted, making far objects appear to us angularly larger than they are. Now, we must also infer that when there is continuity of perspective cues from where we are to where those trees are, *the whole space* between us and the horizon (not only the space near the horizon) is also (continuously) distorted in our perception. In other words, our perception of space based on perspective cues can produce suprisingly wrong results at times. Sometimes the perceived angular size of distant objects will be wrong (perhaps with a smaller error for closer objects and larger error for farther objects). I suppose our perception system first builds a model of space (and things contained therein) from all the available perspective cues (some of which may be ambiguous), and then possibly "adjusts" the perceived angular size of the objects that lie in certain parts of the space to make them fit in that model. Again, it's not just the angular size of the *moon* that gets adjusted, it's the angular sizes of *everything* that lies within a certain vertical strip of space running parallel to the horizon, and probably also of everything else that we are seeing, to an extent varying with the real distance of each object. I suppose the cause lies in a misinterpretation of ambiguous perspective cues by the visual system, which ends up underestimating or overestimating the distance of some objects. The error and the adjustment will depend on the actual distance of each object as well as on the misleading perspective cues. When the moon or sun is up in the sky, there will be no chance of the visual system being misled by ambiguous perspective cues.

The interesting conclusion is that the poor moon has nothing to do with this effect, which exists independent of its presence or position in the sky. Rather, the moon acts as a sort of reference measure, providing us with a way to perceive (perhaps even measure) the effect of the distortion in our perceived space due to the automatic resolution of ambiguous perspective clues by our visual system.

Moreover, the effect probably happens much more often than we believe, but we only notice it when the moon or the sun happens to be within the "stretched" portion of the visual space. If there are only trees and buildings in there, we probably won't notice anything strange.

—Preceding unsigned comment added by 216.86.58.66 (talk) 20:24, 25 February 2009 (UTC)

Alessandro —Preceding unsigned comment added by 216.86.58.66 (talk) 20:08, 25 February 2009 (UTC)

Angle of regard hypothesis

The Angle of regard hypothesis is easily disproved with computer graphics. Since the section has no references - I've removed it. SteveBaker (talk) 23:20, 26 November 2009 (UTC)

Bizarre Rationalization

The moon not only looks bigger at the horizon, it also looks squashed! And it always looks squashed whether you are seeing it in the desert with nothing around, or in the city with buildings. That means only one thing: Lens Effect from the atmosphere. To see more proof of the lens effect of our atmosphere, check out image #7 at: http://www.boston.com/bigpicture/2009/06/recent_scenes_from_the_iss.html That is not an illusion, the lens effect is bending light. Now that's science! —Preceding unsigned comment added by 75.162.34.110 (talk) 12:19, 14 May 2010 (UTC)

Here's another image of the moon: http://twitpic.com/1bz3nm Clearly this is the lens effect, it has nothing to do with 'illusions'. —Preceding unsigned comment added by 75.162.50.219 (talk) 21:00, 15 May 2010 (UTC)

If you are in the vacuum of space and you look through the entire atmosphere at such an incredibly shallow angle, I grant that you will get some atmospheric distortion. However, down here on the surface of the earth, that effect is utterly negligable. But I beg that you don't take my word for it. The illusion is trivially demonstrated - take a UK penny or a US cent or other small coin - and hold it up at arm's length next to the moon at zenith. Then do the same experiment when the moon is on the horizon. You will then be completely and 100% convinced that atmospheric lensing has little part in the illusion. I've done this experiment with my kid and with other doubters a dozen or more times - it is completely and 100% conclusive. Another way I've demonstrated this is with computer graphics (something I do for a living). If you draw any small disk on a plain blue or black background - then draw the same disk behind a reasonably realistic scene of the horizon, the disk that's behind the ground clutter looks much larger than the one drawn on a plain background. And in that case, you can actually do a screen capture of the two images and overlay them one on top of the other to be 100% convinced that the effect is just an illusion.

So you are completely and utterly WRONG...and the simplest possible experiments demonstrate that.

SteveBaker (talk) 04:02, 17 May 2010 (UTC)

Oculomotor micropsia/macropsia theory

I removed this section - it has no references and definitely cannot be true because the effect is easily reproduced on a computer graphics system when the distance (and therefore focussing effect) is the same for all objects. But in any case, the eye focuses pretty much identically for all distances beyond about 20 meters...so this couldn't be true. SteveBaker (talk) 05:08, 5 June 2010 (UTC)

This is actually discussed in one of the external links [1] ([2]). I've only skimmed thorough, but it sounds like it's more complicated then our article had explained, but the theory hasn't been dismissed. Notably there appear to be some stimulated images and it seems to me from my brief skim that the theory doesn't actually collapse because the effect can be reproduced in a computer graphics sytem. Of course it's possible multiple phenomena may account for the illusion. (I'm not sure how easy it is to prove/disprove that the stimulate illusion is completely the same as the real world phenomena.) Nil Einne (talk) 06:59, 26 September 2010 (UTC)

Let me explain in a little more detail.

This hypothesis says that when the eye focusses to a different distance than the object is truly at, our estimation of the angle that it subtends changes. This Oculomotor Micropsia theory is absolutely true - and well understood. What's wrong is the assumption that it can be applied to the Moon Illusion.

The implication being made is that if you're focussing on objects that are just a few miles away at the horizon, your perception of the moon (which is a quarter million miles away) would be incorrect - but when the moon is high above the horizon, you are focussing at the true distance of the moon and the error goes away. This seems entirely plausible at first sight - which is why the guy who wrote the web page you linked to has been taken in by it. But the last step in the chain of reasoning is incorrect:

1. The fact that we see the illusion on computer screens blows it away because in that case we're focussing at a constant distance between eye and screen - no matter whether the simulated moon is on the simulated horizon or not. If this explanation were true - then the illusion would certainly not occur on a computer screen - yet it most definitely does.
2. The theory works because the lens in your eye changes shape when focussing at different distances (which it does - to a point). But that change in shape only happens when focussing down below about 20 meters. Beyond 20 meters...and certainly out at the horizon, your lens is already stretched out as far as the muscles can possibly stretch it. Hence there is no change in the shape of the lens when focussing at five miles or at a quarter million miles -the horizon versus the distant moon. This again, completely busts this argument.

It is totally, utterly, impossible for this theory to explain the illusion. SteveBaker (talk) 20:11, 26 September 2010 (UTC)

Ptolemy ?

The section headlined "Possible explanations" refers to a rejection of Ptolemy's theory. But there is no real explanation of what this theory was (just says "refraction theory"). Aristotle was mentioned in the previous section -- did someone confuse the two ? Or were Ptolemy and his theory accidentally deleted ?76.113.105.186 (talk) 05:35, 23 October 2010 (UTC)

Strange Illusion - Related?

I was watching the last full moon, and observed a strange illusion. I was looking at from a grove of trees as it rose above the horizon. After a minute or so, I noticed that in my vision, the moon started to rock back and forth. The movement became rapid, and made it seem as if an area around the moon were magnified. Hard to explain, but it was a very strange illusion that apparently the observer next to me could not see. Was this an optical illusion resulting from a problem with my eyesight? Very confusing. --24.14.134.193 (talk) 16:05, 10 December 2010 (UTC)