From a scientific point of view, beginning of autumn marks the turning point of temperature, not the arrival of autumn.

From the meteorological point of view, the average daily temperature is lower than 22℃ for five consecutive days before it can be considered as autumn. Although there is a saying that it is cool in beginning of autumn, it is impossible to enter autumn in beginning of autumn at the same time because of the vast territory and large latitude and altitude span in China.

According to the climate characteristics, many areas are still very hot in early autumn due to the residual heat in midsummer. Therefore, there is a folk saying of "autumn tiger". Generally, it will not cool until the middle and late September. After beginning of autumn, the temperature in most parts of China is still very high, especially in parts of southern China. The weather is still very hot, and it is difficult to dissipate the heat in summer. Autumn is the transitional season when the weather turns from hot to cold, and then from cold to cold.

In ancient China, beginning of autumn was divided into three periods: one was when the cool wind came: people would feel cool when it was windy, and the wind at this time was different from the hot air in summer; Second, the Millennium is born: there will be fog on the ground in the morning; Third-class cicada singing: cicadas that sing in autumn also begin to sing.

Astronomical changes of solar terms in beginning of autumn

In ancient times, the direction of bucket handle determined the alternation of four seasons, and the Big Dipper rotated repeatedly, which was closely related to the change of seasons. Taking the direction pointed by Beidou bucket handle as the standard to judge the season is called sword fighting. When Beidou bucket handle points southwest, it is called the beginning of the autumn solar term.

The current 24 solar terms comes from the fixed gas method which was formulated more than 300 years ago (starting from 1645). Fixed space method is a method to determine solar terms according to the position of the sun on the ecliptic, that is, on the 360-degree circle of the ecliptic (the apparent path of the sun on the celestial sphere for one year), it is divided into 24 equal parts, each 15? First-class books, with spring as the starting point of 0 degrees (but beginning of spring is still used to ranking first), are arranged according to the degrees of the yellow meridian; Every time the sun runs 15 degrees on the ecliptic, it is a solar term, and each solar term has the same degree and different time; Twenty-four solar terms are 24 time points, and when the points fall is the natural result of celestial movement; Does the sun meridian reach 135? It is a solar term in beginning of autumn, which falls on August 79 in the solar calendar. At the beginning of the autumn solar term, the sun moves from Cancer to Leo (longitude 135? )。 At night, you can see the bucket handle of the Big Dipper pointing in the direction of the God of the Earth (southwest). The day of handover to beginning of autumn is usually July of the lunar calendar, and July is also the application time of the moon. In early autumn, the sun is at declination+16? 19', compared with +23 on the day of summer solstice?' 26' is much farther south.