How many days are there full moons in a month?

Looking at the moon generally refers to the full 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 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 faces the earth, so people can see a bright moon, which is called full moon or moon.

On the fifteenth and sixteenth day of the lunar calendar, the moon turns to the other side of the earth, that is, position 5 in the figure, and the longitude difference is 180. At this time, the earth is located between the sun and the moon, and the half moon illuminated by the sun is just facing the earth. At this time, the full moon we see is still "looking at the moon."

Extended data

Moon phase change: The order of the moon phase change is: new moon-waning moon-first quarter moon-full moon? -Deficient convex-first quarter moon-waning moon-new moon, and so on. The phase change of the moon is periodic, with a period of about one month.

Reason:

No matter the earth or the moon, the side facing the sun is always bright, and the side facing away from the sun is dark. When observing the moon, we look from the earth, that is, we should imagine that we are standing on the earth and looking at the moon.

We can only see the half of the moon facing us (because even if this part faces us, it is dark because it faces away from the sun, or we are in the daytime at this time), and we can't see the side facing away from the earth.

In the first day of junior high school, the moon is roughly between the earth and the sun, but the side facing the earth is the side facing away from the sun, so we can't see the moon, while the side facing the moon is in the daytime, even if there is a moon, we can't see it. So we can't see the moon on the first day of every month.

On the fourth day of the third grade, when we look at the moon from the earth, only a small part of the half moon facing the earth is illuminated by the sun, so we can only see a small part of the moon, that is, the crescent-shaped Emei moon. ? Because we can't see the moon during the day, the place where we can see the moon on the earth at this time is around sunset.

And the moon we see should be the right half of the moon. Because we are located in the north of the Tropic of Cancer, the moon is basically located in the south of us (because the intersection angle between yellow and white is relatively small, we can think that the orbit of the moon and the orbit of the sun are not much different in myopia). When we face the south, the west is on the right. So at this time, the moon in the west is bright.

On the eighth day, when we look at the moon from the earth, we can see that the part of the moon facing us is half bright and half dark.

During the Tenth Five-Year Plan period, we saw the moon from the earth. We can see the moon on the earth that can be illuminated by the sun, so we see the full moon.

The causes of the moon phases after the Tenth Five-Year Plan are similar to those before, but the differences are as follows: First, before the Tenth Five-Year Plan, that is, in the first half of the month, the right side of the moon shines, and after the Tenth Five-Year Plan, the left side of the moon shines. The other is that before the Tenth Five-Year Plan, the moon was mainly seen in the first half of the night, but generally not in the second half of the night. After the Tenth Five-Year Plan, the moon was mainly seen in the second half of the night, until after sunrise, because of the strong sunshine, the moon slowly disappeared.

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