Why is the Mid-Autumn Festival the fifteenth day of the moon and the sixteenth round day?

In the Mid-Autumn Festival, "the moon is sixteen round on the fifteenth day", and the roundest moment occurs at 5:05 a.m. on October 2 (the sixteenth day of the eighth lunar month). This year, the Mid-Autumn Festival and the National Day "happily coincide", appearing on October 1st at the same time. This year the "look" moment in the eighth month of the lunar calendar occurs at 5:05 a.m. on October 2, so the Mid-Autumn Festival month is "the fifteenth day of the moon and the sixteenth round".

Although the full moon of the Mid-Autumn Festival is on the sixteenth day, the moon on the fifteenth day looks very close to a perfect circle with the naked eye. It is as round and full as a jade mirror or a white jade plate, and is crystal clear and pleasing to the eye. As long as the weather is fine, the evening of October 1st is destined to be a wonderful night with "good flowers and a full moon".

The sixteenth moon on the fifteenth day is an astronomical phenomenon:

The reason is that the standard of the lunar calendar is that the new moon must fall on the first day of the lunar month. Normally, if New Year falls in the early morning of the first day of the lunar month, then Wang should be in the night of the 15th day of the lunar month. Therefore, when Shuo appears later on the first day of the lunar month, Wang appears on the sixteenth day of the lunar month. Sometimes even seventeen.

The moon is at its fullest and brightest when it is "looking". On every first day of the lunar calendar, the moon moves between the earth and the sun. The illuminated hemisphere of the moon is facing away from the earth. We cannot see the moon. It is called the "new moon", also called "new moon"; on the 15th and 16th day of the lunar calendar, , the bright side of the moon is all facing the earth, so we see the round moon, which is called the "full moon", also called "looking".