How to determine the lunar month according to the change of the lunar phase?

(1) From the perspective of our observation from the earth, the moon phase can be roughly divided into four stages, namely, the new moon, the first quarter moon, the full moon and the last quarter moon.

On the 30th or 1 day of each month in the lunar calendar, 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.

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 angle θ between the ecliptic plane and the ecliptic plane, under normal circumstances, the earth can't stop the sunlight, and the bright side of the moon all faces the earth, so people can see a bright moon, which is called the full moon or the moon.

At the new moon, we can't see the moon at all. At the full moon, the moon is the brightest, but in the first quarter and the second quarter, we can only see some light. This change in the "appearance" of the moon reflects the changes in the positions of the sun, the moon and the earth.

(2) In terms of time, the moon phase reflects the progress of the "cycle". It takes 8 days from the new moon to the first quarter moon, 8 days from the first quarter moon to the full moon, 7 days from the full moon to the last quarter moon, 7 days from the last quarter moon to the new moon, and the four stages of new moon-first quarter moon-full moon-last quarter moon form a week.

(3) From the perspective of the cosmic system, the laws of the moon phases reflect the fate of all things in the universe that change and grow again and again. For example, every 19 years, there will be the same moon phase as before 19 years, and it will appear on the same day with the same degree (for example, 1938 1, Capricorn 10,1957 65433)

For another example, there are generally 12- 13 full moons in a year, and there will be no exceptions. For another example, the new moon and the full moon usually appear in pairs.

Extended data:

Lunar phase occurrence

The moon shines by reflecting sunlight, which is different from the relative position of the sun (longitude difference), so it will take on various shapes.

1, new moon: the difference between the sun and the moon is 0. At this time, the moon is located between the earth and the sun, with its dark side facing the earth and appearing almost at the same time as the sun, so it can't be seen on the ground. This is the new moon, the first day of the lunar calendar.

2. First quarter moon: The moon continues to rotate forward. On the eighth day of the seventh lunar month, the longitude difference is 90. The sun went down and the moon was already overhead. It didn't fall until midnight. At this time, just half of the moon illuminated by the sun is displayed in front of you. This is the so-called "first quarter moon".

3. Full Moon: On the 15th and 16th day of the lunar calendar, the moon turns to the other side of the earth with longitude difference 180. At this time, the earth is between the sun and the moon, and the half moon illuminated by the sun is just facing the earth. At this time, we see the full moon, or "looking". Because the moon is just opposite to the sun, the sun sets in the west and the moon rises in the east. When the moon sets, the sun rises in the east, and you can see the bright moon all night.

4. First quarter moon: After the full moon, the moon rises later every day, and the bright part of the moon gets smaller every day. On the 23rd day of the lunar calendar, the longitude of the Yellow Sutra is 270. The full moon is half lost, and then half a moon only appears in the eastern sky in the middle of the night, which is the "lower chord".

Near the end of the month, the moon will rotate between the earth and the sun again, and the waning moon will rise in the east shortly before sunrise. On the first day of next month, it is a new moon, and a new cycle begins.

References:

Baidu encyclopedia-moon phase