In general, the moon on the night of Mid-Autumn Festival is not the roundest in a year, and it is usually 15 and 16.

Fifteen moons and sixteen circles are an astronomical phenomenon. The reason is that the lunar standard is that the first day of the lunar calendar must fall on the moon. Under normal circumstances, in the early morning of the first day, it should be the fifteenth night of the lunar calendar. So the new moon appeared late on the first day, and Wang appeared on the sixteenth lunar month. Sometimes even on the seventeenth day of the lunar calendar.

The most perfect and brightest moment of the moon is when looking. On the first day of the lunar calendar, the moon runs between the earth and the sun, and the illuminated hemisphere of the moon faces away from the earth, so we can't see the moon, which is called "new moon" or "new moon". On the fifteenth and sixteenth day of the lunar calendar, the bright side of the moon faces the earth, so we see a round moon, which is called "full moon" or "full moon".

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Related reasons

According to the lunar calendar, the new moon is on the first day of every month. But on the first day of the first lunar month, the new moon may appear in the morning or at night, and each new moon has its own length and short. In this way, the perfect moment of "seeing" the moon can occur in the early morning of 15, and at the latest in the morning of 17. ?

As we all know, the lunar calendar is based on the law that the moon moves around the earth, so it corresponds to the moon more accurately. But the lunar calendar is a mixture of the advantages of the lunar calendar and the solar calendar, and it is inevitable that there will be errors.

When people regard the first day of the first lunar month as the "new moon", "hope" depends on the movement of the moon. It usually appears on the fifteenth and sixteenth day of the lunar calendar. The fundamental reason why the full moon is late is that the speed of the moon's revolution around the earth is not constant.