Beginning of autumn is the 13 solar term among the 24 solar terms, which falls from August 7th to 9th in the Gregorian calendar every year. At this time, the bucket handle of the Big Dipper points southwest, and the sun reaches longitude 135. Beginning of autumn is the first solar term and the starting point of autumn.
Autumn begins in the beginning of autumn and ends in beginning of winter, which is the result of celestial movement. Beginning of autumn is the node where Yang gradually closes and Yin gradually grows, and Yang gradually turns into Yin. Autumn means precipitation, humidity, etc. At the turning point of the year, there is a downward or decreasing trend; In nature, everything begins to grow from lush to mature.
"beginning of autumn" is often at noon. The so-called "three-volt fever" can be divided into initial, middle and final three volts, and its date is determined by the date of the solar term and the date of the branch year. According to China's traditional calculation method, the third and fourth Geng days from summer to the future are the first (head) and middle start dates respectively, and the first Geng day after beginning of autumn is the last first day.
Because every Geng day is 10 days apart, the stipulated time of the first day and the last day is 10 days. Because the third Geng day (the first autumn) after the summer solstice solar term appears sooner or later, the number of days in autumn is long or short, which may be 10 or 20 days. According to the three-volt calculation method, "beginning of autumn" is still in the mid-volt period, that is to say, entering the "beginning of autumn" solar term does not mean that the temperature will drop.