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There Is No Dark Side of the Moon, Really

To many folks, the phrase "dark side of the moon" suggests there's a place you could go to on the moon which is perpetually cloaked in darkness. This is incorrect!

Let's ignore lunar eclipses for now. With that exception, sunlight is always falling on some part of the moon. The amount of moon that receives sunlight is roughly one-half, but that doesn't mean that any given part of the moon is always dark or light. It's like saying "half the people on earth are always asleep." That may be so, but it doesn't mean the same people never wake up. The sun's light goes around the moon as the moon spins, just as it does the earth.

As the moon orbits the earth, the illumination from the sun gradually slides in and out of our view. Depending on the positions of the moon and sun, we on earth see the moon as waxing, full, or waning. During a new moon, the moon looks completely dark from earth. But that's just because the light is now falling entirely on the other side.

Another thing that confuses people is that the moon always shows us the same side. That's because its rotation around the earth takes just as long as one complete spin: 27 and 1/3 days. The result is the moon as seen from earth seems not to spin, but it is spinning, just like the earth.

So, "the dark side of the moon" is only "dark" in the sense that we never see it. It gets just as much light as the side we can see.

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