Why we see only one side of the Moon?

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India has recently successfully landed its space vehicle Chandrayan 3 on the moon. While it was the 4th country to achieve the feat, there was something very special in this mission. It became the first to successfully land near the illusive lunar south pole, which we can ever seen from earth.

Did I say humans can never seen the lunar south pole? How is it possible? We all know moon is earth’s natural satellite which also rotates around it’s own axis. So, how come no one has seen the southern hemisphere of moon?

This phenomenon of observing only one side of the moon, referred to as “tidal locking” or “synchronous rotation,” is a result of the intricate relationship between the moon’s rotation and its orbit around the Earth. Here’s an explanation of why we witness only one side of the moon:

Rotation and Orbital Periods: The moon completes one orbit around the Earth in approximately 27.3 days, while it also takes around 27.3 days to make one full rotation on its own axis. This synchronous rotation means that the moon rotates at the same rate it orbits the Earth, consistently presenting one side (the “near side”) to us while keeping the other side (referred to as the “far side” or “dark side”) hidden from Earth’s view.

Influence of Tidal Forces: Tidal forces, primarily generated by the Earth’s gravitational pull on the moon, play a crucial role in achieving this synchronization. Over billions of years, these tidal forces have acted to decelerate the moon’s rotation. This gradual transfer of the moon’s rotational energy to its orbital motion is a key factor in tidal locking.

Formation of Tidal Bulges: As the moon orbits the Earth, the gravitational forces from the Earth lead to the formation of “tidal bulges” on the moon’s surface. These bulges result in uneven gravitational forces across the moon, generating torque that gradually diminishes the moon’s rotational speed.

Establishment of a Stable Configuration: Eventually, the moon’s rotation rate becomes harmonized with its orbital period, establishing a stable configuration where one side consistently faces Earth. This phenomenon is known as “tidal locking” or “captured rotation.”

Libration: While we predominantly observe only one side of the moon, there is a minor rocking or “libration” effect that permits us to glimpse a slight portion of the moon’s eastern and western edges at different times. This is due to minor variations in the moon’s orbital velocity and its slightly elliptical orbit, leading to small fluctuations in its distance from Earth.

In summary, the concept of tidal locking results in the observation of only one side of the moon because the moon’s rotation period has become synchronized with its orbit around the Earth. This phenomenon is not exclusive to the moon; it’s a common outcome for celestial bodies with close orbits around larger celestial bodies due to the gravitational interactions between them.

Swarup Biswas

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