Thanks to the Chang'e 4 probe launched by China on December 8, it has managed to land on what is known as the "hidden side" of the only terrestrial satellite. This name was given to him by pure ignorance, because it is in a space that we will never be able to see from the Earth. But why? Science explains it: it is due to the synchronous rotation, the effect caused by the slowness of its rotation. Or in other words, it takes as long to rotate on its own axis as to complete an orbit to our planet. Hence, the opposite side is never visible. And, even more, this qualification of "dark side" that has been used in astronomy, science or culture also leads to confusion: both satellite sites receive the same amount of sunlight.