Surely you have ever noticed it, but you did not get an answer: Have you noticed that you always see the same face of the Moon? Do you know why it happens like this and in this way? And it is that the visible side of our satellite is very different from the one that we cannot observe from Earth. Different theories have emerged over time, but the most recent is the one that makes all the sense.
The horizon of the Moon and the reason for its ‘only face’
Something important to answer that why has to do, in part, with what is the gravitational attraction of the Moon on the Earth. This, in turn, is the cause of the tides that we observe in our oceans.
When the Moon formed about 4.5 billion years ago , it was spinning around its axis faster than it is now (and much closer). The Earth rose and set over the lunar horizon, and the Moon experienced tidal forces induced by Earth’s gravity.
Something that is evidenced by his only perceptible face. However, this gives rise to a phenomenon ; It is what is known as gravitational coupling, and the one that gives us the response of that visible face of the Moon and the reason that explains what happens with the one that is not seen.
The Gravitational Coupling Phenomenon
Most of the planets in the Solar System have satellites. For example, Mars has two moons, Jupiter 79 and Neptune 14. Some are icy, some are rocky, some are geologically active, but there are also some with little or no activity. But what about the Moon and what does it have to do with it?
The question has an easy answer: the Moon behaves like a good dance partner that continually looks at its companion: it always offers the same face towards the Earth. The reason for the ‘single’ view of this face is because the Moon takes exactly the same time to rotate on its axis as it does to orbit around the Earth.
This translates into a time of just over 27 days, and that is why we always see the same lunar hemisphere. It is a phenomenon called gravitational coupling. Or what is the same: its rotation and translation movement are synchronized and that is why we always see the same face.
We can put it into practice ourselves without needing to travel to space, far from it: just take a stick with two papers of two colors and rotate the stick around you in the same time it rotates on itself. So, if from the beginning you could see the yellow paper, the rest of the time you will see only the yellow paper. This is what happens with what is the fifth largest satellite in the Solar System.
What about the dark side of the Moon
But there is more; what’s with that face we can’t see? Since 1959 and thanks to a Soviet space probe, photographs of it could be seen. Today we have high-resolution images of the far side from all sides, where it can be seen that it has more craters: this is because it is more exposed to outer space.
As such, the visible side is made up of 40% seas, large tracts of land that come from a volcanic flow. However, on the hidden side there is only 8%. This is today a mystery that resides precisely in trying to know why the crusts are so different between both sides.
According to the investigations of the Chinese probe of Change 4 in 2019, the coupling could have influenced: “When the Earth and the Moon formed they were practically incandescent. The satellite, being smaller, cooled quickly but our planet continued to emit heat . At that time, the orbit must already have been coupled and that heat was what prevented a thicker crust from forming on the visible side, ”he explained.