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Speaker 1: Welcome to Brainstuff from haustuffworks dot com where smart happens.

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Speaker 1: This podcast is brought to you by Audible dot com,

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Speaker 1: slash brain Stuff. That's Audible podcast dot com slash brain Stuff. Hi,

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Speaker 1: ammercial brain With today's question, why does the moon look

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Speaker 1: so much bigger when it's near the horizon. This question

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Speaker 1: has been pondered for hundreds, if not thousands of years.

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Speaker 1: Most scientists today agree that the reason the moon looks

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Speaker 1: bigger is purely in our minds. Our mind interprets the

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Speaker 1: things we see in interesting ways. For example, if you

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Speaker 1: look at any door frame, you can see that it's rectangular,

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Speaker 1: But if you were to sketch the actual outline of

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Speaker 1: the door frame from the angle that you're looking at it,

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Speaker 1: most likely you would sketch a trapezoid. Your mind adjust

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Speaker 1: the door so that you perceive it as a rectangle

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Speaker 1: from whatever angle you look at it. That theory is

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Speaker 1: called shape constancy. There's also something called size constancy. You've

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Speaker 1: probably seen optical illusions that take advantage of this effect.

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Speaker 1: These illusions feature two images that are identical in size,

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Speaker 1: but one looks much bigger than the other because is

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Speaker 1: the way the picture is drawn. This happens because your

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Speaker 1: mind sees queues that cause it to see one image

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Speaker 1: as farther away than the other image, So your minded

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Speaker 1: just the size of the first image to make up

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Speaker 1: for the increased distance. Size constancy is happening all the time.

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Speaker 1: If you look down the street and see a sports

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Speaker 1: car about fifty feet away and behind it, about a

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Speaker 1: hundred feet away a big suv, you know that the

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Speaker 1: suv is bigger, even though it produces a smaller image

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Speaker 1: on your retina. One theory about the moon illusion says

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Speaker 1: that when the moon is near the horizon, we perceive

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Speaker 1: it to be further away from us than when it's

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Speaker 1: high up in the sky. But since the moon is

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Speaker 1: actually the same size in both cases, our minds make

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Speaker 1: it look bigger when it's near the horizon to compensate

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Speaker 1: for the increased distance. One way you can trick your

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Speaker 1: mind out of the moon illusion is to bend over

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Speaker 1: at the waist and look at the moon upside down

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Speaker 1: through your legs. And alternate of explanation holds that the

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Speaker 1: moon illusion is caused by the way our eyes focus

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Speaker 1: on distant and close objects. When we focus on the

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Speaker 1: horizon moon, we focus on the moon at a great distance.

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Speaker 1: The overhead moon lacks visual cues that tell us how

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Speaker 1: far away it is, so we focus on the overhead

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Speaker 1: moon as if it's a short distance away. So for now,

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Speaker 1: the right answer is that there's no right answer. But

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Speaker 1: the one thing people agree on is that the moon

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Speaker 1: does not physically change its size or its distance from

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Speaker 1: the Earth as it moves across the sky. It's perceived

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Speaker 1: size is all in our heads. This podcast is brought

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Speaker 1: of audiobooks, with more than eight thou downloadable titles across

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Speaker 1: Audible podcast dot com slash brain stuff. That Audible well

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