Since the founding of the People's Republic of China, there have been four National Day and Mid-Autumn Festival on the same day, namely 1963, 1982, 200 1, 2020 and so on. It only appears once in about 19 years, and the last time was in 200 1 year. This situation is mainly the result of leap month.

According to the Chinese lunar calendar, the big moon has 30 days, the small moon has 29 days, and a year has 12 months ***354 or 355 days, which is about 1 1 day less than a tropical one. Four years later, 1 month was missing. Over time, there will be a strange phenomenon of time sequence and time disorder.

In order to solve this problem, the method of adding "leap month" is adopted. The leap month occurred in June this year, which not only delayed Valentine's Day in China, but also delayed the Mid-Autumn Festival. In addition, the Lunar Mid-Autumn Festival generally occurs between September 7th and June 6th in the solar calendar 10, resulting in the calendar phenomenon that the Mid-Autumn Festival coincides with the National Day.