202 1 xiaoman is the knowledge about the date of xiaoman.

2. Xiaoman, one of the 24 solar terms, reflects the climatic characteristics of heavy rainfall. "Twenty-four solar terms" is the product of ancient farming civilization, and farming production is closely related to the rhythm of nature. It is a knowledge system formed by ancient ancestors following the farming season, observing the movement of celestial bodies and understanding the changing laws of seasons, climate and phenology throughout the year. "Twenty-four solar terms" was originally formulated according to the cycle of the Big Dipper, which is closely related to the twenty-four solar terms. In different seasons and at different times, the Big Dipper will point in different directions, which became the basis for ancient people to judge the changes of solar terms. The rotation of the Big Dipper bucket handle points to a solar term, and when bucket handle points to A, it is "small full".

3. The current "twenty-four solar terms" come from the method of determining solar terms according to the position of the sun on the ecliptic more than 300 years ago, that is, on a 360-degree circle "ecliptic" (the sun's apparent path on the celestial sphere for one year), it is divided into 24 equal parts, each 15 is 1 equal part, and the spring is divided into 0 degrees (starting point) The solar terms are divided by the degree of the sun's longitude, and when the sun reaches 60 degrees of the longitude, it is "small full".