Synchronous rotation is when an astronomical body's rotational period matches its orbital period around a partner, causing the same side to always face that partner. The Moon exhibits synchronous rotation with Earth, which is why we only see one hemisphere of the Moon from our planet.
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The Moon's synchronous rotation means it takes about 27.3 days to both rotate on its axis and orbit Earth.
Synchronous rotation results in the near side and far side of the Moon, with humans only able to view the near side without the aid of spacecraft.
This phenomenon occurs due to tidal forces that gradually slowed the Moon's rotation until it became synchronized with its orbit.
Synchronous rotation can occur in other celestial bodies; many moons of other planets also have this characteristic.
The fact that we always see the same face of the Moon has enabled detailed mapping and study of lunar features on its near side.
Review Questions
What is synchronous rotation?
Why do we only see one face of the Moon from Earth?
How long does it take for the Moon to complete one full orbit around Earth while also completing one full rotation?
Related terms
tidal locking: A state where gravitational forces cause a moon or planet to rotate at the same rate as it orbits another body, leading to synchronous rotation.