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Science Coronavirus Coverage U. Travel A road trip in Burgundy reveals far more than fine wine. Travel My Hometown In L. Travel The last artists crafting a Thai royal treasure. Does the Moon increase in size on some nights? The simple answer to this question is, no. While the Moon does come closer to our planet during its The apparent change in our only natural satellite's size when it is near the horizon is an optical illusion. Scientists call it the Moon illusion. Supermoon—When's the next one?
You can easily confirm that there is no change in the Moon's size when it is on the horizon versus when it is high up in the sky by doing a very simple experiment. Take your camera and take a picture of the Moon when it is at the horizon. Wait a few hours. Now, using the same settings, take another picture of the Moon. Compare the sizes of the Moon in the two pictures. You'll find that they are the same.
I believe the moon illusion results from what happens when the mechanism operates in an unusual situation. In normal perception, when rigid objects move in depth distance , the angular size of the light image stimulating our eyes grows or shrinks.
The brain automatically translates this changing stimulation back into the perception of rigid objects whose position in depth is changing. Because the moon is changing its apparent position in depth while the light stimulus remains constant, the brain's size-distance mechanism changes its perceived size and makes the moon appear very large.
Sign up for our email newsletter. Already a subscriber? Sign in. When we observe the Moon near the horizon, it often looks HUGE — whether it's peeking over the shoulder of a distant mountain, rising out of the sea, hovering behind a cityscape, or looming over a thicket of trees.
But here's the thing: it's all in your head. The Moon's seeming bigness is an actual illusion, rather than an effect of our atmosphere or some other physics. You can prove it for yourself in a variety of ways. Hold up your outstretched index finger next to the Moon. You'll find that your fingernail and the Moon are about the same size. Or try looking at the Moon through a paper tube, or bend over and look backward between your legs. When you view it like this, the Moon will be nowhere near as big as it had seemed.
Another ironclad way to size-check the Moon is to take a photo when it's near the horizon, and another when it's high in the sky. If you keep your camera zoom settings the same, you'll find that the Moon is the same width, side to side, in both photos. It may actually appear a little bit squashed in the vertical direction when it's near the horizon. This is the result of the atmosphere acting like a weak lens.
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