Is the moon on the fifteenth day of this year seventeen round?

Yes, one cycle of the moon's waxing and waning is called a "synozygous moon", and the average cycle it experiences is 29.53 days. The day when the moon is the fullest in this month is called "lunar moon", also called "full moon".

According to the lunar calendar, the day of the new moon is the first day of each month. But on the first day of the lunar month, the new moon may occur in the early morning, in the morning, in the afternoon, or in the evening, and each synodic month itself has its own length and shortcomings. In this way, the "looking" when the moon is at its fullest can occur at the earliest on the night of the fourteenth day of the lunar calendar, and at the latest on the morning of the seventeenth day of the lunar calendar.

However, since the new moon must be on the first day of each month of the lunar calendar, it will take another 14 days, 18 hours and 22 minutes after the new moon to reach the moon. Therefore, the "wang" at the roundest moment of the moon must appear on the 15th day of the lunar calendar. Most of them occur on the 16th day of the lunar calendar.

Extended information

The best days to observe the moon with a telescope are from the seventh to the thirteenth and the nineteenth to the twenty-third of the lunar calendar. On the roundest day, the shape of the lunar mountains is not clearly visible. Because of the gravitational force, the moon orbits the earth at times faster and sometimes slower. It is faster when it is near, and slows down when it is far away.

Since the "pace" of the moon's rotation can be fast or slow, the "looking" time of each month is also different, and it is possible on the 14th, 15th, 16th and 17th of the lunar calendar. Among them, the majority are fifteen and sixteen.