DOSSIER / Why do we always see the same side of the Moon? Coincidence or scientific explanation?


As you may have noticed, the Moon always keeps the same face facing the Earth.

Its rate of rotation is in fact synchronized with its rate of revolution around the Earth (the time required to perform an orbit).

In other words, the Moon turns on itself exactly once every time it circles the Earth.

In the same way that the mass of the Moon generates the tides in the oceans of the Earth (the gravitational pull of the Moon distorts the oceans in its direction), the gravitational force of the Earth on the Moon has distorted the latter for 5 years. billion years in a slightly elongated shape, (like an egg or an exaggerated rugby ball). The gravitational forces of the Earth exert a torque which makes the point of the rugby ball orient towards it.

It is very unlikely that the Moon synchronized by chance, it would indeed be a surprising "coincidence". It is believed that the Moon's state of synchronous rotation arose billions of years ago, when the Moon was much closer to the Earth, and therefore the tidal forces were much stronger than they are today.

Earth's gravity maintained this rotating state even though other gravitational interactions caused the Moon to move outward to its current orbital radius.

The Moon continues to move away from Earth by 3,78 cm per year.


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