Moon Optical Illusion

I can’t believe we still haven’t discussed one of the most common optical illusions that we see almost each day. I’m talking about Moon Optical Illusion. The short intro would go something like this: The Moon illusion is an optical illusion in which the Moon appears larger near the horizon than it does while higher up in the sky. This illusion also occurs with the sun and star constellations. It has been known since ancient times, and recorded by numerous different cultures. There have been numerous tries to figure out why this phenomenon occurs (check Wikipedia), and the closest one in my belief would be “Relative Sizes” explanation – something we explained in the Ebbinghaus article and the Ponzo Collection. What do you think about it? What is your explanation? Have you noticed this illusion as well?

71 Replies to “Moon Optical Illusion”

  1. Possible first comment again, whooo!! I dont really get the illusion- i understand it in writing but in the picture the moons jut look like the same size…

  2. It appears larger because your eye has something to compare the moon too rather then when its high in the sky but it is still the same size no matter where it is in the sky

  3. It happens cuz our eye has something to compare the moon too like a building unlike when its high in the sky but its always the same size no matter where it is in the sky

  4. thats pretty sick. i always saw that, but never really thought about. i guess that it is closer to our line of vision, if not us, when it is on the horizon

    (FIRST POST!!!!!)

  5. Great illusion! I really like this common experience that the moon appears to be bigger at the horizon than higher up the ski. However I never had an idea why, but the relative sizes explanation makes sense. The picture clearly shows how the illusion works. Only when we can compare the size of the moon with other objects at the horizon, the moon seems to be bigger. Not higher up the ski, where there is nothing with which we can compare the moon with. Why is it the closest explanation for you. Isn’t it generally confirmed? It seems logical to me. Thanks for giving me the explanation for this illusion.

  6. Because objects generally get smaller as they go into the horizon, the brain assumes that objects on the horizon are further away and must be smaller. But as the moon is the same size wherever it is in the sky, it doesnt decrease in size as it gets to the horizon and the brain thinks this must be because it is getting bigger.

  7. Last full moon someone a freind commented about how it looked big, and we ending up talking about the illusion and how cool it was, and then we read that the moon was actually the closest it has been in ages so it wasn’t just this illusion :P

    But yeah I thought this had been posted here before…? I guess not.

  8. This is pretty cool. I am impressed that this illusion has actually occurred on our planet for a long time and that it can be translated into a 2D illusion. I gotsta check out these other relative size illusions.

  9. When we see things near the horizon, they shrink in size. Our brain tries to put everything in perspective, so we expect distant objects to get smaller.

    But since the moon is so far away, it’s distance doesn’t change much between us and the horizon.

    In other words the distance between us and the moon and the horizon and the moon is, in a cosmic sense, pretty much the same.

    Our brain doesn’t realize this and assumes that moon much be very large being so far away. Up high in the sky, there are no objects to act as [false] references so it appears smaller.

    It’s the same when you’re driving and everything moves, but distant objects remain stagnant giving the illusion that they’re following you.

  10. Yay!!! First comment! :)

    My explanation for this is that the earth is just closer to the moon at a specific time each day.

  11. The moon appears larger because the distance from your eye to the moon is greatest when the moon is on the horizon. It appears “normal” when it is directly above. The atmosphere acts as a magnifier. That magnification is greatest when the the moon is low and the amount of atmosphere we look though is the greatest.

    The refractive and reflexive properties of the atmosphere help explain the phenomena or illusion that the sky is blue when in fact it is mostly black!

  12. I believe the moon looks bigger while it’s close to the horizon because we are looking at it through a thicker layer of our atmosphere which acts like a magnifying glass. When the moon (or sun, for that matter) is high in the sky we see it through a much thinner layer of atmosphere and it isn’t magnified as much. Any scientists out there to corroborate this?

  13. It’s a great illusion, but it’s just perspective, hence the train tracks.
    In the distance it looks bigger because the closest things to relate it to are small (in the distance), but when it’s closer or higher in the sky, the only things to relate it to are bigger (closer to you)
    Relativity, right?

  14. In my opinion, it is another example of perspective modification… :) Many examples of this illusion (although most don’t talk about the moon) :)
    First post? May be a first for me…

  15. Hi,I’m _____ and I also saw a illusion with the train tracks.WoooHoooooo FIRST COMMENT IF SO IN YOUR FACES MOTHR LOVERS!!!

  16. It’s perspective, of course. When the moon is high in the sky, there is nothing around it to compare its relative size to, so it looks rather small out there in the big black darkness.

    But when it’s near the horizon, we compare the horizon with the size of the moon, and it looks bigger. Also, it reflects more light onto our eyes when near the horizon, so we get the illusion of seeing “more” of it.

    Nice illlusion, btw. =

  17. The moon looks larger when it is lower on the horizon because you are looking thru a longer section of atmosphere which acts as a magnifier.

  18. This is the granddaddy of optical illusions. I have marvelled at it since I was a kid and love the arguments with people when they think the moon actually is bigger on the horizon. No illusion site would be complete without it. ;-)

  19. well, relative size would be a very good explanation.

    See for yourself: the moon in the front is laying next to the track, but the moon in the back would cover both tracks and very far beyond them… That is what your mind tells you (or me).

    The tracks gives you a perspective, and thus a reference to sizes.
    Without them, yes, both moons are equal in size.

    Keep up the good work!


  20. It’s an amazing thing, this Moon illusion. I once heard that the horizon moon appears smaller when you’re standing on your hands.

  21. This is especially true at Easter (when I think the Moon is closest to the Earth…I may be wrong on this.) The moon looks huge at this time – it is an amazing illusion.

  22. I think it’s more the apparent distance explanation; because for example, when the moon rises over sea, it still looks bigger. But on sea there is no size reference.

  23. thats awesome i did wonder why the moon was bigger at the horizon but i thought it was justr closer to the earth lol XD but thats awesome

  24. A while ago (I think I was still in college) I got into an argument with my grandpa about the moon. I had just been told about it’s size not changing, and after making sure it was so, I told him about the illusion. He kept telling me I was wrong; that it was closer when it was rising. Had I not measured for myself, I would have agreed. to this day, on full moons, I give it the thumb test. It still makes me smile

  25. Yes, it is quite apparent. The rising moon (especially when full) as it catches hues from our polluted atmosphere, always seems larger than reality. Then, when so far away… appears small and almost insignificant.

  26. Why do people care if they are the first comment?!? Half the time they aren’t! I don’t get it. It’s about the optical illusion, not a race to be the first to comment…

  27. The different size of the object in a distance is an optical illusion due to the thickness of the atmosphere. The lower you get to earth, the thicker the amount of atmosphere. Frank J Leon
    Astrophysics and PHD of Quality Illusionary subjects 1973

  28. Everyone who is commenting about the denser atmosphere is correct. It isn’t an optical illusion as much as the angle on the horizon has a denser atmosphere than looking straight up at the moon. That’s also why the moon on the horizon is not only larger, but a bit discolored as well.

  29. Did you guys notice that it SEEMS to be the ones who always go for the “first comment” are usually dumber than a box of rocks???

  30. Why do people value first post so much? And have you noticed how many people put in first enthusiastically when they aren’t? Oh well.

    I think when the moon is in the sky, you compare it to everything around it, and the large sky like a sea and the moon an island, it looks small. But when you see it on the horizon, the horizon helps you to look at the edges and how far they go out.

  31. I have experimented myself with this one. Consider the moon to be an aeroplane – when it is close to the horison, it is further away than when the aeroplane is passing above your head. Therefore the aeroplane looks much bigger when it gets closer. Of course.

    When it comes to the moon, you by instinct think of it in the same way: The moon is close to the horison. Thereby it should be on a greater distance than when it is passing your head. But since the moon of course follows its path on the same distance above our ground your mind conclude that the moon has to be larger in the first case (it HAS to be bigger to appear to have the same size to your eye)than when it is higher up in the sky.

    Try it for yourselves: Make a black dot, big as a coin, on a white paper. Stare on it for about one minute. Move your eyes to a white area on the paper. You now should have a copy of the “moon” as a shadow in your vision. Now to the cool part: Move the paper closer to your face, and watch the size of the moon diminish! Look at a wall at greater distance, and see the moon being enormous!! This is a really cool illusion! This is possible because your brain automaticly is interpreting the picture to be projected on the surface and at the same distance as the surface.

  32. The moon seems larger especially on a harvest moon because of the moisture in our atmosphere. aka looking at a pool vaccuum broom handle in a pool. moisture or water if you will distorts and enlarges images like looking through a magnifing glass. The curvurature of the earth and our atmosphers make the moon look bigger.if the curverature of the earth was opposite it look look smaller. check out

  33. keith….. hahahahahah really?! moisture? bahahahaha

    its seems larger do to whats around it. you can compare the size to the things around it. you see the railroad tracks and the moon, rather than a moon in a huge open sky. your yes take in more when the moon is closer to earth, to us the objects around it make it look large, rather than it in the sky.

  34. Well obviously there’s the moon at the end of the tracks and a bouncy ball disguised as a moon next to it.

    Sneaky bouncy ball.

  35. its the same moon existing in different time and space at the same time .. its year 4 stuff this is …….. i swear i had this in my year 3 final exam

  36. both moons in this pic are the same size, but the one on the left looks larger ,because the railway track is getting smaller.

  37. The illusion you speak of in relation to a moon of the same size at the horizon to one in the sky playing an illusionary trick on the mind’s eye, yes this is true. In the case of a moon seemingly larger in the night sky to another night where the moon appears smaller in the sky is explained when you equate the elliptical (oval or egg shaped) orbit the moon travels around the Earth, which means the moon is actually closer to the Earth one night as opposed to another night giving it the appearance of a larger moon.

  38. Well anyone who has taken an art class knows that light for some reason bends around a sphere to some extent if you look at it from that perspective which means when the moon is close to the horizon it is bended to some extent making it seem larger as light bends around the spherical shape of our planet earth so as compared to the shrinking size of our view as we look further into the horizon you see with distance things look smaller which in comparison makes other objects appear larger when up above us it looks smaller because there are really nothing to compare

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