Odishatv Bureau

Moon is our friendly floating next-door neighbour, the only celestial object other than Earth on which man has set foot. It has been the inspiration for so many poets and lovers that the moon is part of our art, culture, cinema and stories. But why is that we can never see what’s on the other side. We bring you the answer as well as the surprise discovery. Read on. 

Actually, the reason why we can’t see the other side of the moon has to do with the tidal locking with Earth. 

Why can't we see the other side of the moon?
We only see one side of the moon because it rotates around the Earth at the same rate as it rotates around its axis. Because of its rotation, the same side of the moon is always facing Earth as it moves around the planet. This is known as tidal locking, and it means that an object's orbital period coincides with its rotational period. Other parts of the moon were once visible from Earth, but that was millions of years ago when the moon rotated differently. The moon's rotation is due to the gravity of the Earth, and it is the same for moons orbiting other planets in our solar system. The theory that the moon does not rotate is false because if it did, we would see the moon's dark side at various points while it orbits the Earth.

Tidal Locking
The dark side of the Moon is another name for the opposite side of the Moon. It refers to the Moon's hemisphere that faces away from the Earth. In reality, it is no darker than any other part of the Moon's surface because sunlight falls equally on all sides. It is only 'dark' to us because that hemisphere can never be seen from Earth due to a phenomenon called 'Tidal Locking.'

Over the millions of years that the Moon has orbited the Earth, gravitational interactions between the two bodies have subtly altered their orbits and rotational speeds. Since the Earth is much larger than the Moon, the Moon's rotation is slowed until it reaches a point of balance. The time required for the Moon to complete a full rotation around its axis coincides with the time required for the Moon to complete a full orbit around the Earth at this point, causing it to become tidally locked. The same side of the Moon always faces us, and we can never see the far side.

As you can see, there is no reason why this should be limited to our Moon. In fact, most satellites are tidally locked. The situation is even direr for Pluto and its moon Charon. They're both so close in mass that they've become tidally locked to each other. That is, they both show only one face to each other. This is more like two balls attached to a rod that is twisting on its own than a satellite revolving around a dwarf planet.

The Moon's tidal forces, it turns out, are also slowing the Earth's rotation. A single day when the Earth was formed lasted roughly a quarter of our day. Even today, the Moon continues to slow our day by 15 microseconds per year.

Surprise Discovery: First ever landing made on the dark side of the moon
We only got to see the Moon's "other side" for the first time, when a Chinese lunar rover landed on the other side of the moon. The first-ever landing on the moon's dark side, or the side never visible from Earth, is no longer unexplored by humans. In January 2019, a Chinese lunar rover landed on the dark side of the moon and became the world's first spacecraft to touch down on the moon's uncharted side. The successful landing formally launched the world's first expedition to the far side of the planet that never faces Earth, and it fulfilled scientists' long-held desire to closely observe it.

After a successful landing, we finally got their first photo of the far side of the moon along with a tiny’ Earth' by its side, on February 4 thanks to the camera aboard the Chinese DSLWP-B/Longjiang-2 satellite. The stunning image clicked on by the Chinese lunar orbiter showed the giant dark side of the moon with the planet, Earth.  This photo of Earth and the Lunar farside, maybe our best ever, was taken by the Chinese Lunar satellite DSLWP-B (Longjiang-2). This image was the first photo of Earth with the rear side of the moon clicked since 2014 when yet another Chinese spacecraft Chang'e 5T1 had shot the celestial bodies together.