After talking about days and hours, this is the turn of the month. Like the day, it corresponds to a natural cycle: the revolution of the moon around the Earth. As we know, seen from the Earth, the moon does not seem to rotate around its axis and always shows us the same face. However, if we take as a reference point a star or the sun, a rotation can be seen. An observer located on the sun would see successively all the points on the surface of the moon, therefore would see it rotating around itself. It could also be observed that its period of rotation is the same as its revolution around the Earth. This is why it always shows the same face towards our planet.
