A lunar illusion you'll flip over

By Phil Plait | May 19, 2010 9:26 am

The Lunar Reconnaissance Orbiter has a great blog where they post images from the hi-res camera onboard. I was perusing a recent image, and was a bit befuddled:

LRO_dome_crater

What the heck? Is this a plateau of some kind? Is that a small dome just below the center of it? The whole thing looks pitted around the edge, too, like some sort of erosion has taken place. But that can’t be right!

Happily, being an old hand with optical illusions, I knew exactly what to do. I flipped the image over, and all became clear:

LRO_dome_crater_flipped

Ah, that’s better. Now you can see what’s what: it’s a crater with boulders in it. The small dome is now clearly a tiny meteorite impact crater. What looked like pitting is now obviously rocks and rubble that have slid down the slope of the crater wall.

This is an old illusion. Having evolved on the surface of a planet, we interpret our surroundings assuming sunlight is coming from above. If we see a picture rotated such that the sunlight is coming from below, it plays tricks on our perception. Shadows point the wrong way, making craters look like domes. Flip the picture over, and voila! All is as it should be.

This image is a wonderful example of this illusion (though I’ve never run across a name for it. I suggest "Plait’s Plateau"). You can take lots of lunar pictures and see it if you rotate them. I suggest you check out the LRO archive, because it’s a terrific lesson that what you see is not always what you get (and also because the images are simply too cool). It’s incredibly easy to fool our brains, and if more people realized that then it would be a lot easier for them to be skeptical of what they see, and of claims from other people about what they see!


Related posts:

Terra spots an impact on, um, Terra

Spelunking the lunar landscape

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (54)

  1. Isn’t it funny just how EASY it is to fool our brains?! This is why it’s so important to be a skeptic in what you hear from other people. What they saw is most likely not what was really there. Heck, what you see may not be what is really there as shown by the above pictures. :)

    And ther is a HUGE difference between skepticism and denialism (or cynicism for that matter). Learn it!

  2. Mchl

    Having seen this kind of light tricks before (right on this blog), I knew that what seemed to be a plateau, was probably a a crater… Still after flipping my laptop upside down (cause I didn’t want to scroll down yet) it still looks strangely plateau-like

  3. I guess my brain doesn’t want to play, this morning. Other than the inversion, they both look the same???

  4. I’m still somewhat confused by the shadows. All the shadows of the rocks seem to be going toward the lower left corner in the flipped picture. Yet the top side of the crater is in deep shadow. Is there something off the picture creating that shadow?

    I’m not thinking anything unique, just confused by the shadows.

  5. Weird – the second image looks MUCH more like a plateau to me than the first, and the first looks pretty convincingly like a crater. The illusion seems flipped for me.

  6. Darrin Chandler

    The boulders give it away immediately in this particular image. Not all images have such easy “anchor” cues, though.

  7. Something is wrong with my brain. I saw the crater in the top picture not a plateau and think the lower picture looks like a big dome, not a big crater. (but the when I look at little dome/crater – I do see as a dome in top pic and crater in bottom.)

    I wonder if I am a “lunatic”. Get it?

  8. Sam

    @3 Lunar dyslexia?

  9. I’ll second that, @Sman. Maybe it’s from flipping images like this t-shirt upside-down and right-side up relative to how I first perceive it. Flipping the dome into a divot is the same process.

  10. MoonShark

    Finally, a “dome/plateu” illusion that I fell for! The previous ones just looked like craters. Thanks Phil :) This reminds me a bit of that “optical illusion of the year” winner, which was fun.

    To everybody who saw a crater right away: I guess brains are funny! I’m usually a bit resistant to this. Any cognitive/neuroscience people want to study this effect? I know there’s already some decent progress on how we perceive 3D space. I’ll volunteer my noggin ;)

  11. Dirk F.

    I think the perspective shift comes because we’re getting two pieces of contradictory information.
    1. The rocks in the image are all casting shadows in one direction
    2. The large dark area in the image seems to point in the opposite direction
    I don’t really understand the illumination in this image. Is there something out of the frame that is creating the large shadowed area?

  12. Yeah – I’m with Chrissyo. The first is easily a crater in my mind while the second resembles a big dome.

  13. Marsha Keller

    Well now, that was amazing. I write a life-coaching blog, and I was wondering if it would be alright with you if I use these images for a little piece on perception of self, myself. Sometimes our problems are quite different if we look at them exactly as they are, simply from another perspective.

  14. Coffeekraken

    I’m with Chrissyo, too. I was confused more by the words with the post (since they were the opposite of what I was seeing), LOL

  15. John Grigni

    It looks actually like a flat spot (settled dust?) in the bottom of a larger crater – that would explain the dark area at the bottom of the original image

  16. Eric

    I think the illusion has indeed befuddled the BA…the photos are clearly posted in reverse.

  17. Silverlock

    I think that you have to look at the bigger picture – a bigger portion of the picture, that is – to see the first picture as a dome and the second as a crater. Are you only considering the area in the middle of both images (kind of shaped like a painter’s palette) instead of the surrounding terrain?

    To me, in the top picture the central area looks like a depression in the top of a hill and in the bottom it looks like a dome in the bottom of a large crater. The dark area in the upper right of the bottom picture is caused by the wall of the large crater.

  18. Aleksandar

    May be bacuse im left handed, so some of my “wiring” is opposite, or just a “thing”. I see first picture correctly and the second one wrong.

  19. Oddly enough I could tell it was a crater in the first photo. When you flipped it, it looked more like a plateau! I’m backwards! It just takes some adjusting to either one if you’re used to the other. I’m used to looking at photos of the Moon, etc and thinking “what the heck is the orientation here??” :)

    I’ll note that I’m left handed as well. Might be on to something? ;)

  20. Chanelle

    Both look like plateaus to me. I’ve been able to do this crater/plateau thing on other photos before. In fact, I can usually adjust my eyes to flip back and forth between crater and plateau on a single image, but this one, I just see plateau.

    After staring at them for a while, I could get the original to sort of turn into a volcanic crater (crater in the middle with steeply sloping sides outside, but I can’t get anything remotely craterlike from the flipped image.

  21. Paul from VA

    I see the illusion in the correct order, as did my officemate. (also, @Aleksandar, I am also left handed, so I don’t think that’s the reason you see it in reverse)

    I’ve also sometimes experienced this illusion when looking at the moon through a telescope where it happens on all of the craters simultaneously. If I blink enough I can switch between the domes and craters at will. It makes my brain hurt….

  22. Renee Marie Jones

    Hmmm. Looks exactly the same to be both ways.

  23. I couldn’t really figure out either of the pictures, but after some prompting I can now see the top picture, but not the bottom, the way it really is. Looking down into a crater with a flat bottom with the sun “behind” me.

  24. I think that because of decades of staring at pixels in Photoshop, I see images different than most. I saw the same thing in the first pix as I did in the second. Craters and rocks.

  25. mike burkhart

    This is just one of many illusions on the moon I’ve read about (in past comments I mention the bridge over the Mare Crisum seen by an amature astronomer in the 50s) . I have read about tranist luner phenomea (tlp for short) but I have never seen it myslef.this inculdes red spots seen around craters ,clouds of gas seen on the luner surface, and flashes of light (once thought to be meteors crashing into the surface).Some think this is some kind of geologacal activy going on on the moon.

  26. XPT

    I perceived the first picture correctly as well… I mean they both looked like a crater with scattered boulders. Maybe I’m just expecting too see craters on the moon :)

  27. RogerPenna

    sorry, but it made NO DIFFERENCE to me when the picture was rotated. It looked like a crater with boulders in both pictures.

    I dont think the angle of the shadows plays any tricks. After all, its not like if we dont see shadows coming in our direction, while on Earth! For that, you only need to have the sun ahead of you!

  28. Eidolon

    I experienced exactly this illusion two nights back. Looking around the crater Rosenberger suddenly, there were domes a plenty and craters became plateaus. By moving the scope northwards a bit to larger craters, the illusion disappeared. My hypothesis is that the nearly flat crater floor allowed the inversion where more detailed walled craters set things to right. I found the illusion to be very durable and located only right along the terminator.

  29. NAW

    This is really great to show how our different minds can see an image as either “right” or “wrong”. It may really show how the fools out there keep holding onto their misconceptions of what they see.

    And I am really sad for those of you that can’t see the image in the “wrong” way. Optical illusions are one of the fun parts of life. But an odd questions to those of yall’ that can’t see the illusion, can you see the hidden things in those magic pictures things. I have never been able to trick my mind into seeing them.

  30. Andrew S.

    Phil, I’m always fascinated to see you post these, because they never work on me. I see a crater no matter which way you point it.

    I’M EVOLUTIONARILY DEFUNCT!

  31. jcm

    ” It’s incredibly easy to fool our brains, and if more people realized that then it would be a lot easier for them to be skeptical of what they see, and of claims from other people about what they see!”

    Reminds me of creationists (ID) trying to bamboozle the public with their shortsightedness.

  32. The same idea is used with submit buttons like the one just below the box I’m typing in; that one that says “Submit Comment”…at least in Windows XP. One state of the button is simply the other rotated 180 degrees (with the text being stationary or sometimes moved right and down 1-2 pixels.

  33. Rob G.

    My brain must be broken. Both images look like a crater with boulders in it.

  34. Pieter Kok

    They both look like craters to me.

  35. js

    The first one looks like a completely normal lunar crater to me, while the second one looks more like the illusion you described.

  36. Sarah

    I don’t know why most people have the perception Phil explained… it has to do with interpretation of shadow in a relief image assuming the illumination is from the “top” left or right. Given this bias ( ceiling lights? Bas Reliefs? ) it makes sense.

    I can get either interpretation if I tell myself where the light is coming from.

    Interpretation of 3d from shading is an elusive thing. My very favorite illusion is the one that makes paintings eyes “follow you” … or, more dramatically:

    http://www.grand-illusions.com/opticalillusions/dragon_illusion/

  37. There must be a third object out of frame. Using the first image as reference, there’s clearly a shadow being cast from the bottom-right to the top-left, which puts the bottom-right side of the crater in shadow.

    That fact, totally messed me up. I’m calling shenanigans!

  38. It’s always the other way around for me. For example, I saw the bottom of a crater on the above image. and the top of a plateau on the bottom image.

  39. Hmm – other way around for me, too. Must be because I’m in the Southern Hemisphere :D

  40. Dunc

    There must be a third object out of frame. Using the first image as reference, there’s clearly a shadow being cast from the bottom-right to the top-left, which puts the bottom-right side of the crater in shadow.

    That’s the crater wall – you’re only seeing the crater floor here, you can’t see the rim.

  41. natselrox
  42. Jim A.

    Amusingly, to avoid this confusion on the shadows on shaded relief maps are placed such that the light is shown as comming from the NorthWest: something IMPOSSIBLE for any location North of the Tropics.

  43. Dusty

    Here’s the confusion… As one (only one) other person above has figured out, the image is just of the floor of a much larger crater. The peripheral of the image is all interior crater walls, which the rocks came down from. The floor of the crater is slightly domed, creating the gradient fron light to dark in the center of the image. Imagine a cross-section looking like a “W” mostly flattened in the center.

  44. As soon as you flipped it, that fixed both images for me. Now I have to work to see the illusion…

  45. Tardigrade

    I saw it correctly the first time. Weird.

  46. Thomas

    I see both images as craters but from different perspectives.

    I mean If I stand looking at a hole in the ground then move a half circle around it still look like a hole no matter in what direction the shadows lie :X

    So I don’t really understand the “we interpret our surroundings assuming sunlight is coming from above”. Atleast this illusion don’t work for me since shadows in both direction would break logic.

    If we are talking about wireframe objects I can see these kind of illusions since there are no shadows the break logic.

  47. Heidi

    If you lie looking at a ceiling that is moderately textured, with a window to one side, this illusion happens repeatedly. The little rises and bumps turn into indentations, and then back again.

  48. Teshi

    I see a plateau with a small crater in it both ways :(.

  49. Phil E. Drifter

    Probably caused, well, there’s no atmosphere on the moon so it can’t be caused by wind… hmm very perplexing, indeed… can’t really imagine it was ‘scraped’ off by another meteor, which would have been huge to produce just a relatively flat ‘scrape.’ hmm…

  50. TomB

    I see a crater both ways. I had to squint and try quite hard to see the top image as a plateau…

  51. Jan

    Immediately I saw it as Phil, but being familiar with this lunar illusion I sometimes see the same image as dome, other times as a crater.
    The second image is consistently a crater for me.
    Fun illusion indeed

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