The fact that China just retrieved rocks from the dark side of the moon confuses me. Does the moon rotate in the same manner as Earth does so we never see the “dark” side of the moon?
In: Planetary Science
If the moon didn’t rotate, we’d see all of it over the course of a month. It does rotate, but it takes exactly as long to rotate as it does to orbit the earth. You can demonstrate this by putting an “Earth” on a table and taking a (preferably round) “Moon” and moving it around the “Earth” such that the same side always faces it. You’ll see that you had to turn the “Moon” all the way around once to accomplish this.
This happens because the earth and the moon pull on each other with gravity. It’s a *tidal force* that tugs on each body and slows down their rotation (it would happen to the earth too if we gave it enough time). The moon used to rotate faster, but tidal forces slowed it down until it achieved *synchronous rotation.*
This took a couple hundred million years after the moon was formed, which was well before any creature on Earth had evolved eyes…trillions of life-forms have looked at the moon, but none of them saw the other side of it until the middle of the twentieth century.
Synchronous rotation is **common** and all round moons in our solar system are tidally locked to their host planet. Pluto and its moon Charon are tidally locked to each other, and both Mercury and Venus show different forms of synchronicity to the Sun.
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