Why Does the Moon Always Show the Same Side of the Earth? This is the Explanation

Illustration (Magnific)

YOGYAKARTA - Why does the face of the Moon that is seen from Earth always look the same? This can be observed, for example, when the full moon, the dark pattern and the plain that appear on the surface are in the same position. Even when the Moon is crescent or half, the surface that faces the Earth is still the same part.

Does the Moon not rotate so that one side is always facing the Earth? This assumption is clearly wrong because the Moon still rotates like other objects in the Solar System. So why does the Moon always show the same side? Reported from IFL Science, here is the discussion.

Why does the same side of the moon always face us?

The moon still rotates or rotates on its axis. The interesting thing is that the Moon's rotation speed has the same period as the time it takes to orbit the Earth. That's why we always see the same side of the Moon every time.

This condition is called tidal locking or synchronous rotation, which is the state when the rotation period of an object is equal to its orbital period. The moon takes about 29 days to complete one rotation and one orbit around the Earth. Because the two periods are the same, the same side of the Moon will continue to face the Earth.

Imagine an object that is walking around us while spinning at the right speed so that its face is always facing us. From our position, the face never changes even though the object is actually moving and spinning. It's a little like what happens to the Moon when it orbits the Earth.

This condition is the result of the gravitational interaction between the Earth and the Moon. The much larger mass of the Earth exerts a strong influence on the Moon's rotation and slowly pushes its rotation period to be in sync with its orbital period. If the Moon rotates faster than its orbit, the influence will slow down its rotation, while if its rotation is slower, the gravitational influence will speed it up.

So, can we only see one side of the Moon from Earth? Not entirely so. The Moon's orbit is not perfectly circular so its speed varies, becoming faster when closer to Earth and slower when further away. Meanwhile, its spin rate is relatively constant so that over time we can see a little extra on the edge of the Moon.

The change in position allows for several degrees of parts of the normally unseen side to appear along the edge of the Moon. At the same time, a small part of the area we normally see can disappear from the opposite edge. This effect allows us to observe an area of the Moon slightly exceeding half of its surface.

That is the explanation for why the Moon always shows the same side to Earth. So it's not because it doesn't rotate, but because the Moon has the same rotation period as the time it takes to orbit the Earth.

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