How many shapes does the moon have?

1. On the first day of the lunar month, the moon lies between the sun and the earth. People on earth only see the moon deviating from the dark side of the sun, so they can't see the moon on earth, which is called a new moon or a new moon.

2. From the second day of the lunar calendar to the sixth day of the lunar calendar, the moon moves eastward around the earth, leaving the moon between the earth and the sun and leaning to one side, that is, the moon is located in the east of the sun. The moon faces west when it is illuminated by the sun for half a month. On the earth, we can see that part of it is sickle-shaped, and its convex surface faces the western sun. This is the so-called waning moon.

3. From the seventh day to the eleventh day of the seventh lunar month, as the moon continues to move eastward around the earth, the relative positions of the sun, the earth and the moon are at right angles, that is, the connection between the moon and the earth is 90 degrees. Observers on the earth just see that the moon is bright in the western half, and the bright side faces west. This is a semicircle called the first quarter moon.

During the period from December to 14th of the lunar calendar, observers on the earth saw that more than half of the western part of the moon was illuminated by the sun, and the phase of the moon became convex. In the southeast sky, the moon faces the west.

On the 15th to 17th day of the first lunar month, the moon moves to the outside of the earth, that is, the sun and the moon are located on both sides of the earth. Because there is an included angle θ between the ecliptic plane and the ecliptic plane (the average value of θ is 5 09'), under normal circumstances, the earth can't block the sunlight, and the bright side of the moon all faces the earth, so people can see a bright moon, called the full moon or the moon, which is located in the southern sky.

6. From the 18th to 21st lunar month, the moon phase becomes convex and the moon faces east.

7. From the 22nd to 24th of the lunar calendar, the relative positions of the sun, the earth and the moon become right angles again, and the moon is 90 degrees west of the connecting line between the sun and the earth. At this time, the eastern half of the moon is semi-circular and bright, and the moon faces east, which is called the last quarter moon.

8. From the 25th to the end of each month in the lunar calendar, the moon phase becomes a waning moon, with its bright face facing east.

Extended data:

The moon revolves around the earth, so the relative positions of the sun, the earth and the moon change regularly within a month. Because the moon itself is not luminous and opaque, the visible part of the moon is the part that reflects sunlight. Only the part of the moon that is directly illuminated by the sun can reflect sunlight. We see the part of the moon that is directly illuminated by the sun from different angles, which is the source of the moon phase.

The moon phase is not caused by the earth covering the sun (this is an eclipse), but because we can only see the part of the moon illuminated by the sun, and its shadow part is the dark side of the moon itself.