9 ms·

Moon Illusion

129 points by dcminter 4y ago

stevebmark 4y ago
You could probably test out some of the perception in VR by doing things like putting the moon straight overhead but also put the horizon or some buildings in the sky overhead to see if it has the same enlarging effect as at the real horizon
- lostgame 4y ago
  People who think AR/VR is a 'fad', won't last; etc - really miss out on the potential for simulation and work in legitimate scientific and research fields. Screw games, I'm more interested in stuff like VR/AR software that's helping surgeons and mechanics. That's the real future to me.
  - Apocryphon 4y ago
    Such VR applications were foreseen even three decades ago http://www.youtube.com/watch?v=h58lRIVHhGc&t=2m47s http://www.youtube.com/watch?v=h58lRIVHhGc&t=2m47s
blueflow 4y ago
Does this happen to everyone? Because i don't see this effect for the skyline, cloud and monochrome diagram picture in the article (despite the captions), only a tiny bit in the Ebbinghaus diagram.
- tristanj 4y ago
  It depends on how far away the camera is. The further away the camera is, the more visible the effect. The moon illusion effect is quite visible in this photo of the Manhattan skyline, taken from 15 miles away in West Orange, New Jersey. https://cdn.theatlantic.com/thumbor/r3PYEwue-SKDCmd_v7HgzEF2DbE=/1200x763/media/img/photo/2012/05/supermoon-2012/s01_RTR31PUL/original.jpg https://cdn.theatlantic.com/thumbor/r3PYEwue-SKDCmd_v7HgzEF2...
  - shrx 4y ago
    That's not really what the illusion is about, it's just perspective compression.
    - dwringer 4y ago
      AFAIU perspective compression is a key element of the illusion - when the moon gets closer to the horizon/treeline/skyline, our mind creates a sort of vignette with limited FOV for perceiving it, in which the relative size of the moon appears larger (because our focus has become inadvertently and subconsciously narrower).
- cassianoleal 4y ago
  I don't think it can "happen" to someone and not the person next to them, i.e. I don't think each individual observer sees it differently. I have seen what the article calls a harverst moon a few times. Every time everyone I asked from the same city has also seen it. I've seen it on the news, captured by photo and video cameras, so I'm pretty confident it's as optical as using lenses to zoom into things.
  - exitb 4y ago
    Oh, it's definitely just an illusion. You can take a suggestive picture of it, if that's your intention, but in fact if you took a couple pictures with a digital camera, few hours apart, you'd note that the Moon has the exact same pixel width in the pictures, regardless of it position in relation to the horizon. Moreover, the near-horizon pictures would actually show a lower pixel height, due to the atmospheric distortion.
- pengaru 4y ago
  It isn't happening for me at all in the examples. In the same page they clearly state that the full moon's size varies due to its eccentric orbit. We all know the moon is sometimes clearly larger and that's the reason, this illusion stuff strikes me as mostly subtle b.s.
  - thatjoeoverthr 4y ago
    It should vary over the course of the month, but not a few hours. Many people experience the feeling that the moon is bigger when it’s near the horizon. It’s a feeling. You might not personally experience it. That’s OK. But other people report it, so unless they’re lying, the illusion exists empirically.
  - lm28469 4y ago
    > It isn't happening for me at all in the examples. You mean looking at the images on the wiki page ? Yeah it doesn't work for me either, seeing it in real life works every single time on me though
- red369 4y ago
  Just my thoughts on the illusion in case it's helpful. I saw this illusion tonight when I suddenly saw the moon behind the top of a distant tree. I think the suddenness adds to the illusion, and the explanation of the brain's image processing reasoning about the size because it is compared to something distant feels right. It does not feel just a small amount bigger - at least double the usual size. Even as I looked at it, the illusion weakened. It was obscured by trees and building as I walked towards it, and again I saw it rise again over a building a little way off. The illusion repeated, though not as strong. Much later I saw the moon in the sky, and it looked normal size. I do not have the illusion anywhere near as strongly when I look at that skyline photo, although I can sort of see what they are trying to describe. I think many photos of the moon zoom in, greatly increasing the apparent size, and I don't think this is the same as the illusion, although in a way, comparing the moon to a building which is known to be large may contribute to the illusion we perceive when seeing it in real life (not in a photo).
benhoyt 4y ago
A beautiful, big full moon was visible over Christchurch, New Zealand tonight, and I was just talking about this with the kids. It fascinates me that scientists have sent us up to the moon, but can't figure out exactly why it appears bigger when it's rising.
- adolph 4y ago
  Key word is "appears." Brain function is another frontier of knowledge just like all those encountered in a space program. The Ponzo illusion is one possible explanation of the Moon illusion, with objects appearing "far away" (because they are "on" the horizon) appearing bigger than objects "overhead". However, some have argued that explaining one perception ("appears far away") in terms of another ("appears bigger") is problematic scientifically, and that there are probably complex internal processes behind these illusions. https://en.wikipedia.org/wiki/Ponzo_illusion https://en.wikipedia.org/wiki/Ponzo_illusion
- tejtm 4y ago
  if you are still young and flexible enough .... compare the apparent size of the full moon near the horizon when standing normally and then upside down, by looking between your legs, or standing on your head. It is how proved to myself my eyes can not be trusted really
- mihaic 4y ago
  Maybe objects at low angles are perceived with another computational unit, since they are part of the scenary and we need to extrapolate, and the sky is a big whatever. But really maybe there's no simple explanation other than "that's how the brain works", and we assume there has to be one.
- Gatsky 4y ago
  Just came to say I saw the same full moon of startling clarity in Christchurch.
- doctoboggan 4y ago
  I am also in Christchurch and was wishing my iPhone was able to capture the moon in any amount of detail tonight
pcardoso 4y ago
There is a view of the Taj Mahal from Agra fort where it looks larger when viewed from a particular window. Looks similar to this illusion.
IshKebab 4y ago
I love that the proof of illusion section doesn't even try to prove that there's an illusion.
- deleted 4y ago
  [deleted]
isolli 4y ago
In which I discovered an explanation for an illusion that always surprised me [0]: the fact that a partially illuminated moon does not seem to reliably indicate the direction of the sun. [0] https://en.wikipedia.org/wiki/Terminator_(solar)#Lunar_terminator_illusion https://en.wikipedia.org/wiki/Terminator_(solar)#Lunar_termi...
- Zinu 4y ago
  When you come across this illusion, you can "break" it by getting a piece of string and holding one end over the moon and one over the sun, and you'll more easily see how the moon does after all point at the sun. Lying on the ground can also help.
- tome 4y ago
  I find the description of the phenomenon and its explanation incomprehensible. Can anyone explain more clearly what it means? EDIT: here is a better explanation: https://chrisjones.id.au/MoonIllusion/ https://chrisjones.id.au/MoonIllusion/ OK, the point is that when the moon and the sun appear to be the same height in the sky the sun is actually "above" the moon, because it's further away. Therefore the moon is lit from "above".
  - isolli 4y ago
    This video is also quite interesting: https://www.youtube.com/watch?v=Y2gTSjoEExc https://www.youtube.com/watch?v=Y2gTSjoEExc
  - jayknight 4y ago
    It doesn't have anything to do with distance to the objects. Straight lines in the sky are great circles that may appear curved to us because of our biased view standing on the surface of earth. Light rays traveling from the sun to the moon take a great circle path through the sky, and the path might look to us (if we could see it) like it goes "higher" in the sky than either object, but it's a straight line across the dome of the sky.
    - 4y ago
andyjohnson0 4y ago
The real paradox is that we think that we see the world as how it is, like a camera does, when in fact what we "see" is reconstruction based on surprisingly imperfect visual perception and equally imperfect recollection of prior experiences.
- the_af 4y ago
  A camera doesn't "see" the world "how it is".
  - lostgame 4y ago
    Depending the sensor or array of sensors, cameras arguably see more of the world 'how it is' than humans are capable of. Night Vision, Heat Maps, LIDAR, and Telescopic lenses can capture more of the world 'as it is' than humans could ever hope to achieve. It's why we developed them! :)
    - the_af 4y ago
      Hard disagree. Cameras and their sensors are just different from the human eye. This doesn't make them capture reality "how it is", they just have different capabilities and they make different trade-offs. They are certainly different, but not necessarily "more real". Cameras don't capture "reality". An insightful link on this topic, shared previously here on HN, which is very illuminating: "Photography is not objective" [1] [1] https://aaronhertzmann.com/2022/03/17/photography-is-not-objective.html https://aaronhertzmann.com/2022/03/17/photography-is-not-obj...
- capableweb 4y ago
  > reconstruction based on surprisingly imperfect visual perception Unlike a camera? ;) > equally imperfect recollection of prior experiences I guess we (humans) put our understanding of the world into the mechanics of the camera, so somehow I see the mechanics of a camera like a summary of human "recollection of prior experiences" regarding visual imperfection.
  - 4y ago
FooHentai 4y ago
>Conversely, if the more distant object did subtend the same angle as the nearer object then it is normally perceived to be twice as big. herein lies I think the real cause of this illusion - It's the way our brain perceives size in things that are considered to be at a disconnected distance from each other, and things that are seen to be 'connected' being perceived as being the same distance. As soon as the moon comes close enough to the horizon to be perceived as 'connected' in our minds, the perception of it's size is shifted dramatically. This same effect occurs with tall islands - If you're standing on the shore and look towards the island, it appears one size. If you move inshore and lose sight of the water, viewing the island over rooftops and such, it appears much more massive.
- hnuser847 4y ago
  I live two blocks away from Lake Michigan and I’ve noticed the same effect with sailboats on the horizon. When I’m walking towards the beach and can only see a small sliver of water, sailboats on the water look absolutely massive, but as I get closer and see them in full context, they seem to shrink.
  - FooHentai 4y ago
    Yep, I witnessed the effect when living out near Kapiti island, which is pretty big, quite tall, and very close to the mainland. The effect some evenings was drastic, especially when you had the moon and island on the horizon. It reminded me of the cover for the film Synchedoche, New York. That sense of the scales all being very wrong.
shireboy 4y ago
It really is puzzling- when I’ve seen this, I’d swear I could make out more detail on the surface of the moon than when it’s higher. I’ve measured with a ruler and know that it’s the same size, but there is definitely something affecting perception. Maybe higher contrast when it’s lower, in addition to having the horizon to measure against?
akolbe 4y ago
- 0des 4y ago
  Somehow I arrived at your soapbox instead of the comments of this article. Wow this is awkward, excuse me, Ill just be on my way.
  - deleted 4y ago
    [deleted]
jibbit 4y ago
In the uk there will be a perfect example of this at around 10:30 this evening
- sph 4y ago
  What's special about this evening?
  - jibbit 4y ago
    Peak full moon coinciding with moon at closest point in its orbit to earth coinciding with perfectly clear skies
    - onionisafruit 4y ago
      Does the "moon at closest point in its orbit to earth" mean that the moon will actually take up a little more sky than usual tonight?
      - SamBam 4y ago
        It's not a huge effect, but it's about 14% larger when it's closest compared to when it's furthest away.

129 points by dcminter 4y ago

You could probably test out some of the perception in VR by doing things like putting the moon straight overhead but also put the horizon or some buildings in the sky overhead to see if it has the same enlarging effect as at the real horizon

lostgame 4y ago
People who think AR/VR is a 'fad', won't last; etc - really miss out on the potential for simulation and work in legitimate scientific and research fields. Screw games, I'm more interested in stuff like VR/AR software that's helping surgeons and mechanics. That's the real future to me.
- Apocryphon 4y ago
  Such VR applications were foreseen even three decades ago http://www.youtube.com/watch?v=h58lRIVHhGc&t=2m47s http://www.youtube.com/watch?v=h58lRIVHhGc&t=2m47s

blueflow 4y ago

Does this happen to everyone? Because i don't see this effect for the skyline, cloud and monochrome diagram picture in the article (despite the captions), only a tiny bit in the Ebbinghaus diagram.

tristanj 4y ago
It depends on how far away the camera is. The further away the camera is, the more visible the effect. The moon illusion effect is quite visible in this photo of the Manhattan skyline, taken from 15 miles away in West Orange, New Jersey. https://cdn.theatlantic.com/thumbor/r3PYEwue-SKDCmd_v7HgzEF2DbE=/1200x763/media/img/photo/2012/05/supermoon-2012/s01_RTR31PUL/original.jpg https://cdn.theatlantic.com/thumbor/r3PYEwue-SKDCmd_v7HgzEF2...
- shrx 4y ago
  That's not really what the illusion is about, it's just perspective compression.
  - dwringer 4y ago
    AFAIU perspective compression is a key element of the illusion - when the moon gets closer to the horizon/treeline/skyline, our mind creates a sort of vignette with limited FOV for perceiving it, in which the relative size of the moon appears larger (because our focus has become inadvertently and subconsciously narrower).
cassianoleal 4y ago
I don't think it can "happen" to someone and not the person next to them, i.e. I don't think each individual observer sees it differently. I have seen what the article calls a harverst moon a few times. Every time everyone I asked from the same city has also seen it. I've seen it on the news, captured by photo and video cameras, so I'm pretty confident it's as optical as using lenses to zoom into things.
- exitb 4y ago
  Oh, it's definitely just an illusion. You can take a suggestive picture of it, if that's your intention, but in fact if you took a couple pictures with a digital camera, few hours apart, you'd note that the Moon has the exact same pixel width in the pictures, regardless of it position in relation to the horizon. Moreover, the near-horizon pictures would actually show a lower pixel height, due to the atmospheric distortion.
pengaru 4y ago
It isn't happening for me at all in the examples. In the same page they clearly state that the full moon's size varies due to its eccentric orbit. We all know the moon is sometimes clearly larger and that's the reason, this illusion stuff strikes me as mostly subtle b.s.
- thatjoeoverthr 4y ago
  It should vary over the course of the month, but not a few hours. Many people experience the feeling that the moon is bigger when it’s near the horizon. It’s a feeling. You might not personally experience it. That’s OK. But other people report it, so unless they’re lying, the illusion exists empirically.
- lm28469 4y ago
  > It isn't happening for me at all in the examples. You mean looking at the images on the wiki page ? Yeah it doesn't work for me either, seeing it in real life works every single time on me though
red369 4y ago
Just my thoughts on the illusion in case it's helpful. I saw this illusion tonight when I suddenly saw the moon behind the top of a distant tree. I think the suddenness adds to the illusion, and the explanation of the brain's image processing reasoning about the size because it is compared to something distant feels right. It does not feel just a small amount bigger - at least double the usual size. Even as I looked at it, the illusion weakened. It was obscured by trees and building as I walked towards it, and again I saw it rise again over a building a little way off. The illusion repeated, though not as strong. Much later I saw the moon in the sky, and it looked normal size. I do not have the illusion anywhere near as strongly when I look at that skyline photo, although I can sort of see what they are trying to describe. I think many photos of the moon zoom in, greatly increasing the apparent size, and I don't think this is the same as the illusion, although in a way, comparing the moon to a building which is known to be large may contribute to the illusion we perceive when seeing it in real life (not in a photo).

benhoyt 4y ago

A beautiful, big full moon was visible over Christchurch, New Zealand tonight, and I was just talking about this with the kids. It fascinates me that scientists have sent us up to the moon, but can't figure out exactly why it appears bigger when it's rising.

adolph 4y ago
Key word is "appears." Brain function is another frontier of knowledge just like all those encountered in a space program. The Ponzo illusion is one possible explanation of the Moon illusion, with objects appearing "far away" (because they are "on" the horizon) appearing bigger than objects "overhead". However, some have argued that explaining one perception ("appears far away") in terms of another ("appears bigger") is problematic scientifically, and that there are probably complex internal processes behind these illusions. https://en.wikipedia.org/wiki/Ponzo_illusion https://en.wikipedia.org/wiki/Ponzo_illusion
tejtm 4y ago
if you are still young and flexible enough .... compare the apparent size of the full moon near the horizon when standing normally and then upside down, by looking between your legs, or standing on your head. It is how proved to myself my eyes can not be trusted really
mihaic 4y ago
Maybe objects at low angles are perceived with another computational unit, since they are part of the scenary and we need to extrapolate, and the sky is a big whatever. But really maybe there's no simple explanation other than "that's how the brain works", and we assume there has to be one.
Gatsky 4y ago
Just came to say I saw the same full moon of startling clarity in Christchurch.
doctoboggan 4y ago
I am also in Christchurch and was wishing my iPhone was able to capture the moon in any amount of detail tonight

pcardoso 4y ago

There is a view of the Taj Mahal from Agra fort where it looks larger when viewed from a particular window. Looks similar to this illusion.

IshKebab 4y ago

I love that the proof of illusion section doesn't even try to prove that there's an illusion.

deleted 4y ago
[deleted]

isolli 4y ago

In which I discovered an explanation for an illusion that always surprised me [0]: the fact that a partially illuminated moon does not seem to reliably indicate the direction of the sun. [0] https://en.wikipedia.org/wiki/Terminator_(solar)#Lunar_terminator_illusion https://en.wikipedia.org/wiki/Terminator_(solar)#Lunar_termi...

Zinu 4y ago
When you come across this illusion, you can "break" it by getting a piece of string and holding one end over the moon and one over the sun, and you'll more easily see how the moon does after all point at the sun. Lying on the ground can also help.
tome 4y ago
I find the description of the phenomenon and its explanation incomprehensible. Can anyone explain more clearly what it means? EDIT: here is a better explanation: https://chrisjones.id.au/MoonIllusion/ https://chrisjones.id.au/MoonIllusion/ OK, the point is that when the moon and the sun appear to be the same height in the sky the sun is actually "above" the moon, because it's further away. Therefore the moon is lit from "above".
- isolli 4y ago
  This video is also quite interesting: https://www.youtube.com/watch?v=Y2gTSjoEExc https://www.youtube.com/watch?v=Y2gTSjoEExc
- jayknight 4y ago
  It doesn't have anything to do with distance to the objects. Straight lines in the sky are great circles that may appear curved to us because of our biased view standing on the surface of earth. Light rays traveling from the sun to the moon take a great circle path through the sky, and the path might look to us (if we could see it) like it goes "higher" in the sky than either object, but it's a straight line across the dome of the sky.
  - 4y ago

andyjohnson0 4y ago

The real paradox is that we think that we see the world as how it is, like a camera does, when in fact what we "see" is reconstruction based on surprisingly imperfect visual perception and equally imperfect recollection of prior experiences.

the_af 4y ago
A camera doesn't "see" the world "how it is".
- lostgame 4y ago
  Depending the sensor or array of sensors, cameras arguably see more of the world 'how it is' than humans are capable of. Night Vision, Heat Maps, LIDAR, and Telescopic lenses can capture more of the world 'as it is' than humans could ever hope to achieve. It's why we developed them! :)
  - the_af 4y ago
    Hard disagree. Cameras and their sensors are just different from the human eye. This doesn't make them capture reality "how it is", they just have different capabilities and they make different trade-offs. They are certainly different, but not necessarily "more real". Cameras don't capture "reality". An insightful link on this topic, shared previously here on HN, which is very illuminating: "Photography is not objective" [1] [1] https://aaronhertzmann.com/2022/03/17/photography-is-not-objective.html https://aaronhertzmann.com/2022/03/17/photography-is-not-obj...
capableweb 4y ago
> reconstruction based on surprisingly imperfect visual perception Unlike a camera? ;) > equally imperfect recollection of prior experiences I guess we (humans) put our understanding of the world into the mechanics of the camera, so somehow I see the mechanics of a camera like a summary of human "recollection of prior experiences" regarding visual imperfection.
- 4y ago

FooHentai 4y ago

>Conversely, if the more distant object did subtend the same angle as the nearer object then it is normally perceived to be twice as big. herein lies I think the real cause of this illusion - It's the way our brain perceives size in things that are considered to be at a disconnected distance from each other, and things that are seen to be 'connected' being perceived as being the same distance. As soon as the moon comes close enough to the horizon to be perceived as 'connected' in our minds, the perception of it's size is shifted dramatically. This same effect occurs with tall islands - If you're standing on the shore and look towards the island, it appears one size. If you move inshore and lose sight of the water, viewing the island over rooftops and such, it appears much more massive.

hnuser847 4y ago
I live two blocks away from Lake Michigan and I’ve noticed the same effect with sailboats on the horizon. When I’m walking towards the beach and can only see a small sliver of water, sailboats on the water look absolutely massive, but as I get closer and see them in full context, they seem to shrink.
- FooHentai 4y ago
  Yep, I witnessed the effect when living out near Kapiti island, which is pretty big, quite tall, and very close to the mainland. The effect some evenings was drastic, especially when you had the moon and island on the horizon. It reminded me of the cover for the film Synchedoche, New York. That sense of the scales all being very wrong.

shireboy 4y ago

It really is puzzling- when I’ve seen this, I’d swear I could make out more detail on the surface of the moon than when it’s higher. I’ve measured with a ruler and know that it’s the same size, but there is definitely something affecting perception. Maybe higher contrast when it’s lower, in addition to having the horizon to measure against?

akolbe 4y ago

0des 4y ago
Somehow I arrived at your soapbox instead of the comments of this article. Wow this is awkward, excuse me, Ill just be on my way.
- deleted 4y ago
  [deleted]

jibbit 4y ago

In the uk there will be a perfect example of this at around 10:30 this evening

sph 4y ago
What's special about this evening?
- jibbit 4y ago
  Peak full moon coinciding with moon at closest point in its orbit to earth coinciding with perfectly clear skies
  - onionisafruit 4y ago
    Does the "moon at closest point in its orbit to earth" mean that the moon will actually take up a little more sky than usual tonight?
    - SamBam 4y ago
      It's not a huge effect, but it's about 14% larger when it's closest compared to when it's furthest away.