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Here are some optical illusions involving the moon:
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1. Lunar craters look like bumps? These can look like craters or bumps, depending on the direction that you think the sunlight is coming from. The picture is from Apollo 8. | |
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1a. Craters look like craters? This is the same picture, rotated 180 degrees. And you may realize that the sunlight is coming from behind us. These can look like bumps too, and once they look like bumps, it is hard to resolve them back into craters. Actually these pictures are both rotated 90 degrees from the original picture, and the sunlight was coming from the side. | |
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2. The full moon looks flat: The moon looks like a disc
instead of a sphere. The effect looks even more dramatic in person than it does
with this photo. The reason for this is that the moon's surface is rough (made
of dust and rocks), which is illuminated right up to the edge of the image, and
is not a smooth surface which the light would glance off and make the edges
look darker. A similar effect is that, for the astronauts on the moon, the moon looked dark when they looked toward the sun, and very bright when they looked away from the sun. Looking toward the sun, they were seeing the shaded side of every speck of dust that was on the ground. |
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| 3. The moon looks huge when it appears near the horizon, and very small when it is high overhead: This is probably because we can compare it with other distant objects in our view when it is near the horizon, and we can only compare it with the sky itself (which is huge) when it is high overhead. | ||
| 4. Another illusion for astronauts: On the moon the horizon looked even closer than one might expect, because there is no air to soften the distant view, or give it a blue color. Distant objects looked very sharp. This happens to some extent on earth. When the air is very clear, or when distant objects are an abnormal color, they may appear closer than at other times. |