1. On the 30th or 1 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. This moon phase rises and sets with the sun, that is, it rises in the morning and sets at dusk, and it can only be detected during the solar eclipse.
2. After the new moon, the moon rotates eastward around the earth, leaving the middle 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. In the waning moon, the moon rises after sunrise and sets after sunset. It is in the sky with the sun, in the bright sky, so we can't see the moon phase. The waning moon can only be seen in the western sky after sunset.
3. On the seventh and eighth day of each 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. The first quarter moon rises around noon. At dusk, it appears in the southern sky, falls below the horizon from the west at midnight, and is visible in the first half of the night.
4. On the 1 1 day and 12 day of each lunar month, observers on the earth see that more than half of the western part of the moon is illuminated by the sun, and the moon phase becomes a convex moon. The convex moon rises after noon, in the southeast sky at dusk, the moon faces west, then continues to the west, and sets from the western horizon before dawn, and can be seen most of the night.
On the fifteenth and sixteenth 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 is all facing the earth, so people can see a bright moon, which is called the full moon or the moon. When the sun sets at night, the full moon rises from the eastern horizon, lies in the southern sky at midnight and sets on the western horizon in the morning. You can see the moon all night.
6. In a few days, on the 18th and 19th of the lunar calendar, the moon will meet and turn into a convex moon, with the moon facing east. At this time, the moon rises after dusk, sets before noon and is visible in the middle of the night.
7. On the 22nd and 23rd day 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, we see that the eastern half of the moon is semi-circular and bright, and the moon faces east, which is called the last quarter moon. It rises from the eastern horizon at midnight, hangs high at dawn, sunrise and noon, sets in the southern sky, sets from the western horizon at noon and is visible at midnight.
8. In a few days, on the 25th and 26th of each month of the lunar calendar, the moon phase will become a waning moon again, with the bright side facing east. At this time, the moon rises after midnight, sets before dusk and is visible before dawn.
Then the moon continued to move eastward between the sun and the earth, and the moon phase became new. It can be seen that the change of the moon phase is: new moon → waning moon → first quarter moon → convex moon → full moon → convex moon → second quarter moon → waning moon. The moon revolves around the earth once, and the time interval from the new moon to the next new moon, that is, the period when the phase of the moon changes, is called the first moon.
Extended data
Moon phase change song:
The new moon on the first day is invisible only because it is trapped in the sun and the earth.
On the eighth day of the seventh lunar month, the half moon faces west.
When the full moon comes out on the 15th and 16th, the earth shoulders the sun and the moon.
Twenty-two, three and the last quarter of the moon, the moon faces east until midnight.
Formula: Go west, go east.
It means: the first quarter moon appears in the first half of the lunar calendar, with the convex surface (right side) facing west and located in the western half of the sky; The last quarter moon appears in the second half of the lunar calendar, with the convex surface (left side) facing east and located in the eastern half of the sky.
Baidu Encyclopedia-Moon Phase Change