Why does the moon shine and darken?

First of all, what we see about the moon is called the change of the moon phase, which is also called profit and loss.

Secondly, why did this happen? Because on the first day of the lunar calendar, the moon just runs between the earth and the sun, and the dark side of the moon is facing the earth, so the moon can't be seen on the earth, which is called "new moon" or "new moon"; On the seventh day (or the eighth day), you can see half the moon, which is dark in the east and bright in the west, called the "first quarter moon"; On the fifteenth (or sixteenth) day, the moon moves to the back of the earth, so you can see the round moon hanging high in the sky, which is called "full moon" or "full moon"; Around the 22nd, the western half of the moon is dark and the eastern half is bright, which is called the "last quarter moon". The moon takes the first quarter, the full moon and the last quarter of the new moon as a cycle, and the time between them is a lunar month.

Therefore, the change of the moon's profit and loss is determined by the position between the sun, the earth and the moon. The main reason for their mutual position change is that the moon revolves around the earth (the period is about 27.3 days), and at the same time, because the earth revolves around the sun (this is a secondary reason), the period of the moon phase change is more than 27.3 days, about 29.5 days.

Look at the picture, understand?