The Moon always lights up during nights and it is the origin of many myths, but if we observe it during some time we see that it always shows us one face, whatever the period of the year we’re in. But then, why does the Moon only shows us one face?
The Moon always shows us the same landscape. We always see the same craters, seas and polar ice caps. This can lead us to conclude that the Moon doesn’t turn onto its axis and that for that reason it only shows us one face. Why does this happen?
In fact, the Moon turns onto its axis, as any other body in the universe. The answer for why does the Moon only shows us one face is very simple. What happens is that the Moon turns onto its axis and orbits around the Earth in the same time interval: 27 days, 7 hours and 43 minutes. As the Moon takes the same time to turn onto its axis and turn around the Earth, it only shows us one face (or hemisphere), leaving a hemisphere hidden from the Earth view. This face that we can’t see is the hidden face of the Moon.
This phenomenon happens due to the mutual gravitational interaction between the Earth and the Moon, which after millions of years after the formation of the Moon, have ended by synchronizing the two movements.
Sometimes, an 18% of the hidden face of the Moon can be seen from the Earth, but the remaining 82% couldn’t be photographed until 1959 by the Soviet spacecraft Luna 3.