Why do we always see the same side of the Moon?
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The Moon always shows us the same face, so it can't be spinning... right? It is: the Moon spins exactly once per trip around Earth (about 27 days), so the same side keeps facing us. Long ago it spun faster, until Earth's gravity worked like a brake and the spin matched the orbit (tidal locking). A slight wobble even lets us see about 59% of the surface over time.
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Transcript
- Sef The Moon always shows us the same face. So it never spins, right?
- Tiggy It does spin. Watch me circle you.
- Tiggy To keep facing you, I turn once every lap.
- Tiggy The Moon does the same. One spin per orbit, about every 27 days.
- Sef What a lucky match!
- Tiggy Not luck. Long ago, it spun faster.
- Tiggy Earth's gravity tugged on it like a brake, until it spun once per lap.
Sources
- NASA Science: Tidal Locking science.nasa.gov
- NASA Science: The Moon's Rotation science.nasa.gov
- Royal Museums Greenwich: Everything you've ever wanted to know about the Moon rmg.co.uk
- ESA Science & Technology: Moon sci.esa.int
- Ohio State News: What's on the far side of the moon? news.osu.edu
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