00:00Why do we only ever see one side of the moon?
00:03It is weird.
00:04The moon completes one rotation around its own axis
00:07in the same amount of time that it takes to orbit the Earth.
00:09The two are perfectly in sync.
00:11But it wasn't always that way.
00:13When the moon formed, likely from a collision with Earth,
00:15the hot, molten, messy object was changing shape,
00:18pulled by Earth's gravity.
00:19And as it settled into its orbit,
00:21Earth's gravity pulled on its lower edge,
00:23making it an oval shape.
00:25And over time, this constant tug on the moon's bulge
00:28caused its rotation to slow,
00:30and eventually to match Earth's.
00:33This is tidal locking,
00:34an effect that's actually really common
00:36and found in most large moons in our solar system.
00:38Because of it,
00:39humanity didn't see the back of our own moon until 1959.
00:43And turns out, it looks completely different.
00:46If you want to know why, subscribe.
