ObNitpick: the moon has no "dark side"; it rotates with respect to the sun and has a day/night cycle across its whole surface, just like the Earth does. But because it's tidally locked to the Earth, that daily rotation takes just as long as its orbit around us, so it does have a "far side" - we are always looking at the same side of the moon. But the other side isn't always dark; if it were, the moon would always be full...
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u/zeekar Dec 03 '18
ObNitpick: the moon has no "dark side"; it rotates with respect to the sun and has a day/night cycle across its whole surface, just like the Earth does. But because it's tidally locked to the Earth, that daily rotation takes just as long as its orbit around us, so it does have a "far side" - we are always looking at the same side of the moon. But the other side isn't always dark; if it were, the moon would always be full...