full transcript

From the Ted Talk by Andrew Vanden Heuvel: The moon illusion

Unscramble the Blue Letters

Have you ever noticed how the full moon looks bigger when it's near the horizon than when it's high over head? If so, you're not alone. People have wondered about this strange ecefft since ancient times, and surprisingly, we still don't have a great explanation, but that's not for lack of trying. Some of the greatest minds in history - Aristotle, Ptolemy, Da Vinci, Decartes - have all wrestled with this problem and failed to generate an auaetdqe explanation. One of the first iaeds suggested was that the igmae of the moon in the sky really is bggeir near the horizon. Perhaps the Earth's atmosphere acts like a giant lens, magnifying the moon as it rises and sets. But this eipxaanlton doesn't cut it. If anything, the rfoaitcren of the atmosphere would make the moon look slightly smaller. Plus, if you actually mreusae the size of the visible moon at different positions, it doesn't cgnhae at all. But then, why does it still seem bigger when it's rising? This must be some kind of oaticpl illusion. The question is, which one? One explanation is the Ebbinghaus Illusion, where two identical objects look different because of the relative size of the objects they're surrounded by. Here the two cneetr circles are actually the same size. Maybe the moon looks bigger near the horizon because it's next to tiny trees, houses, and towers in the distance. But when the moon is higher up, it's snrrduueod by the vast darkness of the night sky and looks tiny by cpsmoriaon. Another pisstiilboy is the famous Ponzo Illusion. If you've ever tried to draw in perspective, you know that the closer something is to the horizon, the smaller you should draw it. Our brain compensates automatically for this by perceiving objects near the horizon as lgraer than they actually appear. The two yellow lines in this drawing are the same size, but the upper one seems bigger because we interpret it as receding farther into the horizon. So, between Ponzo and egabuhinbs, it seems like we've solved the mystery of the moon illusion, but, unfortunately, there are a few details that complicate things. For one thing, if this was just the Ebbinghaus effect, then we would expect the moon illusion to dpaspaier for pilots flying high above the clouds since there wouldn't be any other smaller objects near the horizon. But in fact, pilots and sailors out on the ocean still cialm to see the moon illusion. On the other hand, if it's just our brain's autocorrecting the size of objects near the horizon, then we'd ecpext the moon isiollun to be visible inside a planetarium, where the whole sky, including the horizon, is displayed on a shipcearl dome overhead. Studies have shown, though, that this is not the case. To make matters wsroe, it seems the moon illusion daspeprais entirely if you just bend over and look at the moon between your legs. Now, this is just getting ridiculous! One of the most promising explanations today is known as Convergence Micropsia. Our brains judge the distance to otjbces and their aenrppat size by the focus of our eyes. When looking at the horizon, your eyes focus far off into the distance so your bairn knows you're looking far away. The moon appears a certain size. Your brain thinks it's far away, which it is, so you naturally conclude the moon must be big. But when looking up at the nghit sky, there's nothing for your eyes to focus on, so they default to their rest fcuos, which is a point just a few meters away. Now your brain thinks the moon is much celosr than it really is, so you naturally conclude the moon's not as big as you thought it was. Rather than epxalin why the moon looks so big near the horizon, Convergence Microspia explains why the moon looks so small when overhead. Still not satisfied? Well, frankly, neither are many scientists, so the dteabe over the moon illusion still rgeas on and may continue as long as we still see it in the night sky.

Open Cloze

Have you ever noticed how the full moon looks bigger when it's near the horizon than when it's high over head? If so, you're not alone. People have wondered about this strange ______ since ancient times, and surprisingly, we still don't have a great explanation, but that's not for lack of trying. Some of the greatest minds in history - Aristotle, Ptolemy, Da Vinci, Decartes - have all wrestled with this problem and failed to generate an ________ explanation. One of the first _____ suggested was that the _____ of the moon in the sky really is ______ near the horizon. Perhaps the Earth's atmosphere acts like a giant lens, magnifying the moon as it rises and sets. But this ___________ doesn't cut it. If anything, the __________ of the atmosphere would make the moon look slightly smaller. Plus, if you actually _______ the size of the visible moon at different positions, it doesn't ______ at all. But then, why does it still seem bigger when it's rising? This must be some kind of _______ illusion. The question is, which one? One explanation is the Ebbinghaus Illusion, where two identical objects look different because of the relative size of the objects they're surrounded by. Here the two ______ circles are actually the same size. Maybe the moon looks bigger near the horizon because it's next to tiny trees, houses, and towers in the distance. But when the moon is higher up, it's __________ by the vast darkness of the night sky and looks tiny by __________. Another ___________ is the famous Ponzo Illusion. If you've ever tried to draw in perspective, you know that the closer something is to the horizon, the smaller you should draw it. Our brain compensates automatically for this by perceiving objects near the horizon as ______ than they actually appear. The two yellow lines in this drawing are the same size, but the upper one seems bigger because we interpret it as receding farther into the horizon. So, between Ponzo and __________, it seems like we've solved the mystery of the moon illusion, but, unfortunately, there are a few details that complicate things. For one thing, if this was just the Ebbinghaus effect, then we would expect the moon illusion to _________ for pilots flying high above the clouds since there wouldn't be any other smaller objects near the horizon. But in fact, pilots and sailors out on the ocean still _____ to see the moon illusion. On the other hand, if it's just our brain's autocorrecting the size of objects near the horizon, then we'd ______ the moon ________ to be visible inside a planetarium, where the whole sky, including the horizon, is displayed on a _________ dome overhead. Studies have shown, though, that this is not the case. To make matters _____, it seems the moon illusion __________ entirely if you just bend over and look at the moon between your legs. Now, this is just getting ridiculous! One of the most promising explanations today is known as Convergence Micropsia. Our brains judge the distance to _______ and their ________ size by the focus of our eyes. When looking at the horizon, your eyes focus far off into the distance so your _____ knows you're looking far away. The moon appears a certain size. Your brain thinks it's far away, which it is, so you naturally conclude the moon must be big. But when looking up at the _____ sky, there's nothing for your eyes to focus on, so they default to their rest _____, which is a point just a few meters away. Now your brain thinks the moon is much ______ than it really is, so you naturally conclude the moon's not as big as you thought it was. Rather than _______ why the moon looks so big near the horizon, Convergence Microspia explains why the moon looks so small when overhead. Still not satisfied? Well, frankly, neither are many scientists, so the ______ over the moon illusion still _____ on and may continue as long as we still see it in the night sky.

Solution

  1. worse
  2. ebbinghaus
  3. focus
  4. comparison
  5. rages
  6. closer
  7. spherical
  8. possibility
  9. larger
  10. ideas
  11. brain
  12. change
  13. optical
  14. explain
  15. expect
  16. disappear
  17. adequate
  18. objects
  19. claim
  20. bigger
  21. center
  22. explanation
  23. disappears
  24. image
  25. apparent
  26. surrounded
  27. measure
  28. debate
  29. night
  30. refraction
  31. illusion
  32. effect

Original Text

Have you ever noticed how the full moon looks bigger when it's near the horizon than when it's high over head? If so, you're not alone. People have wondered about this strange effect since ancient times, and surprisingly, we still don't have a great explanation, but that's not for lack of trying. Some of the greatest minds in history - Aristotle, Ptolemy, Da Vinci, Decartes - have all wrestled with this problem and failed to generate an adequate explanation. One of the first ideas suggested was that the image of the moon in the sky really is bigger near the horizon. Perhaps the Earth's atmosphere acts like a giant lens, magnifying the moon as it rises and sets. But this explanation doesn't cut it. If anything, the refraction of the atmosphere would make the moon look slightly smaller. Plus, if you actually measure the size of the visible moon at different positions, it doesn't change at all. But then, why does it still seem bigger when it's rising? This must be some kind of optical illusion. The question is, which one? One explanation is the Ebbinghaus Illusion, where two identical objects look different because of the relative size of the objects they're surrounded by. Here the two center circles are actually the same size. Maybe the moon looks bigger near the horizon because it's next to tiny trees, houses, and towers in the distance. But when the moon is higher up, it's surrounded by the vast darkness of the night sky and looks tiny by comparison. Another possibility is the famous Ponzo Illusion. If you've ever tried to draw in perspective, you know that the closer something is to the horizon, the smaller you should draw it. Our brain compensates automatically for this by perceiving objects near the horizon as larger than they actually appear. The two yellow lines in this drawing are the same size, but the upper one seems bigger because we interpret it as receding farther into the horizon. So, between Ponzo and Ebbinghaus, it seems like we've solved the mystery of the moon illusion, but, unfortunately, there are a few details that complicate things. For one thing, if this was just the Ebbinghaus effect, then we would expect the moon illusion to disappear for pilots flying high above the clouds since there wouldn't be any other smaller objects near the horizon. But in fact, pilots and sailors out on the ocean still claim to see the moon illusion. On the other hand, if it's just our brain's autocorrecting the size of objects near the horizon, then we'd expect the moon illusion to be visible inside a planetarium, where the whole sky, including the horizon, is displayed on a spherical dome overhead. Studies have shown, though, that this is not the case. To make matters worse, it seems the moon illusion disappears entirely if you just bend over and look at the moon between your legs. Now, this is just getting ridiculous! One of the most promising explanations today is known as Convergence Micropsia. Our brains judge the distance to objects and their apparent size by the focus of our eyes. When looking at the horizon, your eyes focus far off into the distance so your brain knows you're looking far away. The moon appears a certain size. Your brain thinks it's far away, which it is, so you naturally conclude the moon must be big. But when looking up at the night sky, there's nothing for your eyes to focus on, so they default to their rest focus, which is a point just a few meters away. Now your brain thinks the moon is much closer than it really is, so you naturally conclude the moon's not as big as you thought it was. Rather than explain why the moon looks so big near the horizon, Convergence Microspia explains why the moon looks so small when overhead. Still not satisfied? Well, frankly, neither are many scientists, so the debate over the moon illusion still rages on and may continue as long as we still see it in the night sky.

Frequently Occurring Word Combinations

ngrams of length 2

collocation frequency
moon illusion 5
night sky 2
brain thinks 2
naturally conclude 2

Important Words

  1. acts
  2. adequate
  3. ancient
  4. apparent
  5. appears
  6. aristotle
  7. atmosphere
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  15. case
  16. center
  17. change
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  19. claim
  20. closer
  21. clouds
  22. comparison
  23. compensates
  24. complicate
  25. conclude
  26. continue
  27. convergence
  28. cut
  29. da
  30. darkness
  31. debate
  32. decartes
  33. default
  34. details
  35. disappear
  36. disappears
  37. displayed
  38. distance
  39. dome
  40. draw
  41. drawing
  42. ebbinghaus
  43. effect
  44. expect
  45. explain
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  47. explanation
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  49. eyes
  50. fact
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  52. famous
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  62. head
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  65. history
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  102. planetarium
  103. point
  104. ponzo
  105. positions
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  110. question
  111. rages
  112. receding
  113. refraction
  114. relative
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