Optical illusions

[NoParty]

Let's have someone (with better Photoshopping or AI skills than I), do a similar one,
but using fraudster Charles Ponzi instead of a car: A Ponzi Ponzo!

 

[John J.]

A Ponzi Ponzo!

(I didn't quote the first part of the sentence, not claiming to have any Photoshopping or AI skills )

 

[Trailblazer]

Yeah, I guess so. I'm not articulating my feelings about the picture very well. It illustrates the Ponzi illusion, but as a facsimile of a real-world scene it isn't believable (although not physically impossible- different scale models of an otherwise visually identical car could be made).

But as @Mendel says, it shows how unreliable estimates of size are when we are dealing with objects at unknown distances. It also (to me at least) clearly shows that the cause of the "Moon illusion" is simply the Ponzo illusion and not any of the other outlandish explanations that have been advanced over the years.

 

[FatPhil]

But as @Mendel says, it shows how unreliable estimates of size are when we are dealing with objects at unknown distances. It also (to me at least) clearly shows that the cause of the "Moon illusion" is simply the Ponzo illusion and not any of the other outlandish explanations that have been advanced over the years.

So you're saying "the object lower in field of view seems smaller relative to a flat surface" is an explanation for an object appearing larger when lower in the field of view and viewed across a nearly flat surface?

 

[Trailblazer]

So you're saying "the object lower in field of view seems smaller relative to a flat surface" is an explanation for an object appearing larger when lower in the field of view and viewed across a nearly flat surface?

No, I was saying "Our brains see objects as being larger when they appear to be at a distance in a 3D scene".
The theory being that if the moon is high up in the sky, it is visually quite unrelated to our mental map of objects on the ground - it's just a "light in the sky". But if it is close to the horizon it becomes part of that 3D scene of known objects - trees, houses, street lights, etc.

Unfortunately for my theory, the illusion doesn't really seem to work in a picture.

 

[jon_eir]

@Trailblazer @FatPhil
Am I missing something or are you guys looking for an explanation of a different real world illusion

Heres the my take again on the story your mind tell you that's leads to the moons apparent apparent larger size at the horizon
On the left the blue circles are clouds over head and closer to you.
On the right the blue circles are clouds at the horizon and fair away from you.
Without reference your mind thinks they are the same size
This leads the orange dot (Moon) on the right to appear bigger in your mind.

In fairness this is only one likely explanation and requires the present of clouds

This likely explains why the illusion above didn't work the above post

Unfortunately for my theory, the illusion doesn't really seem to work in a picture.

Is there a better real world example you could give of the illusion you are looking to explain?

 

[Mendel]

So you're saying "the object lower in field of view seems smaller relative to a flat surface" is an explanation for an object appearing larger when lower in the field of view and viewed across a nearly flat surface?

replace "lower in the field of view" with "closer to the horizon" and replace "smaller" with "larger", please

 

[GM4AJK]

But as @Mendel says, it shows how unreliable estimates of size are when we are dealing with objects at unknown distances

I'd like to add to this that, as I believe we all know, a large majority of Americans love firearms, and if they trained on rifles with scopes attached, they are fully aware of how to use mil-dots. The basics are: if you know the rough size of your target, you can estimate the range to it; conversely, if you are unfamiliar with the target but know the range, you can estimate the target size. However, if you are unfamiliar with the target and you don't know the range, then all bets are off. I can't help but feel confident that many who tell us how far away a UFO is or how big it is are aware of mil-dots yet totally forget the lesson they should have learnt when they weren't looking through a rifle scope.

 

[JMartJr]

Yeah, I guess so. I'm not articulating my feelings about the picture very well. It illustrates the Ponzi illusion, but as a facsimile of a real-world scene it isn't believable (although not physically impossible- different scale models of an otherwise visually identical car could be made).

I would not be surprised if somebody recreated this illusion with cars of different sizes, arranged so that forced perspective makes them all the same size in the picture, so you would have cars that LOOK difeerent sizes, but measured on the pictures they are the same size, but for an extra layer they are in fact not the same size. (If that makes sense...)

There are people for whom forced perspective is an enjoyable hobby, it seems...

 

[John J.]

There are competing theories about the Moon illusion (the perception of the Moon being larger when it's close to the horizon).

From the NASA website, "Why Does the Moon Look Larger at the Horizon? We Asked a NASA Scientist:", 12 February 2015, Emily Furfaro
https://www.nasa.gov/general/why-do...horizon-we-asked-a-nasa-scientist-episode-50/

One popular idea is that this is a variation on the Ponzo illusion. Everything in our experience seems to shrink as it recedes toward the horizon — I mean clouds and planes and cars and ships. But the Moon doesn't do that. So our minds make up a story to reconcile this inconsistency. Somehow the Moon gets bigger when it's at the horizon. That's one popular hypothesis, but there are others. And we're still waiting for the experiment that will convince everyone that we understand this.

So why does the Moon look larger on the horizon? We don't really know, but scientists are still trying to figure it out.

Video, 1 min. 19 sec.; the NASA scientist is identified as Science Visualizer Ernie Wright


Source: https://www.youtube.com/watch?v=yuxWyIe8TIc&t=15s


The Ponzo illusion is often mentioned in discussions of the Moon illusion,

Extensive experiments in 1962 by Kaufman and Rock showed that a crucial causative factor in the illusion is a change in the pattern of cues to distance, comparable to the Ponzo illusion. The horizon Moon is perceived to be at the end of a stretch of terrain receding into the distance, accompanied by distant trees, buildings and so forth, all of which indicate that it must be a long way away, while these cues are absent from the zenith moon. Experiments by many other researchers have found the same result; namely, when pictorial cues to a great distance are subtracted from the vista of the large-looking horizon Moon it looks smaller. When pictorial cues to an increased distance are added into the vista of the zenith Moon, it appears larger.

Wikipedia, Moon illusion (in section "Apparent distance hypothesis"), https://en.wikipedia.org/wiki/Moon_illusion

The same Wikipedia article also has a section "Relative size hypothesis", which mentions the Ebbinghaus illusion described by @jon_eir ;

Historically, the best-known alternative to the "apparent distance" theory has been a "relative size" theory. This states that the perceived size of an object depends not only on its retinal size, but also on the size of objects in its immediate visual environment. In the case of the Moon illusion, objects in the vicinity of the horizon Moon (that is, objects on or near the horizon) exhibit a fine detail that makes the Moon appear larger, while the zenith Moon is surrounded by large expanses of empty sky that make it appear smaller.[17]​

The effect is illustrated by the classic Ebbinghaus illusion, where a circle appears larger when surrounded by smaller circles, than it does when surrounded by larger circles.

The article also mentions the "Angle of regard hypothesis",

According to the "angle of regard" hypothesis, the Moon illusion is produced by changes in the position of the eyes in the head accompanying changes in the angle of elevation of the Moon. Though once popular, this explanation no longer has much support.

This is sort of alluded to on the Biology Insights website (after a section describing the probable role of depth cues that doesn't clearly differentiate between Ponzo and Ebbinghaus), "Why Does the Moon Look So Close? The Science Explained", Travis Lund 29 September 2026

A competing camp has argued that the causation runs the other direction: the elevated moon appears smaller first, perhaps because of changes in eye posture or convergence when looking upward...

https://biologyinsights.com/why-does-the-moon-look-so-close-the-science-explained/

Scientific American, "Why Does the Moon Look Bigger Near the Horizon?", Phil Plait, 18 October 2024 (https://www.scientificamerican.com/article/why-does-the-moon-look-bigger-near-the-horizon/) states that two factors are in play:
One is the Ponzo illusion, the other is our internal representation of the dome of the sky / celestial dome:

The Ponzo illusion is the heart of the moon illusion, but there's more to it. If I were to ask you what shape the sky over your head appears to be, you'd probably say it's a hemisphere—a half of a sphere. But we don't actually perceive it that way. If we did, you'd see the zenith, the point directly over your head, as the same distance from you as any point on the horizon. Yet experiment after experiment shows that's not the case: we see the horizon as farther away and the sky as more like a flat-bottomed bowl overhead, with the zenith closer to us.

That's not too surprising, actually. If you're outside on a cloudy day, the clouds over your head really are closer to you; they might be five kilometers above you, but the ones near the horizon can be more than 100 kilometers distant. So we've evolved to think of the sky as flattened that way.

The article doesn't provide links that support the flattened dome perception; a (very) quick search found one item, again on Biology Insights (and by Travis Lund), "Why Does the Local Sky Look Like a Dome?", https://biologyinsights.com/why-does-the-local-sky-look-like-a-dome/
(lots of dubious ads),

...the sky directly above seems closer, while the sky near the horizon appears much further away. Our brain attempts to reconcile these differing distance perceptions by constructing a mental model of the sky as a flattened dome...

Scientific American is a popular science magazine, the lack of thorough references isn't unusual and a contributing writer might be free to put their views without the checks of formal peer review. (I haven't checked but I'd be a bit surprised if we often see clouds near the horizon at 100 km, 62 miles).

We know that the perception of the Moon as being larger closer to the horizon- the Moon illusion- is an illusion, but there doesn't seem to be a broad consensus about the exact mechanism or mechanisms involved.