July 6, 2022
The Moon is the only natural satellite of the Earth. Its proper name is sometimes used, par excellence and with a lowercase initial ("a moon"), as a synonym for satellite also for celestial bodies that orbit other planets. It orbits at an average distance of about 384400 km from the Earth, close enough to be observable with the naked eye, so that on its surface it is possible to distinguish dark spots and light spots. The former, called seas, are almost flat regions covered by basalt rocks and dark-colored debris. The clear lunar regions, called highlands or plateaus, are several kilometers high above the seas and have reliefs that are even 8000-9000 meters high. Being in synchronous rotation it always turns the same face towards the Earth and its hidden side remained unknown until the period of space exploration. During its orbital motion, the different aspect caused by the orientation with respect to the Sun generates clearly visible phases which have influenced man's behavior since ancient times. Impersonated by the Greeks as the goddess Selene, she was long ago regarded as influential on crops, famines and fertility. She conditions the life on Earth of many living species, regulating their reproductive cycle and hunting periods; she acts on the tides and on the stability of the earth's rotation axis. The Moon is thought to have formed 4.5 billion years ago, not long after the birth of the Earth. There are several theories regarding its formation; the most accredited is that it formed from the aggregation of debris left in orbit after the collision between the Earth and an object the size of Mars called Theia. Its astronomical symbol ☾ is a stylized representation of one of its phases (between the last quarter and the new moon seen from the northern hemisphere, or between the new moon and the first quarter seen from the southern hemisphere). The visible face of the Moon is characterized by the presence of about 300,000 impact craters (counting those with a diameter of at least 1 km). The largest lunar crater is the South Pole-Aitken basin, which has a diameter of about 2500 km, is 13 km deep and occupies the southern part of the hidden face.