Why do solar terms change in a year?

Continuing the book of Han Sacrifice is called "Twenty-four Qi". Some scholars found that its order changed in the Han Dynasty. Wang Yinglin, a scholar in the Song Dynasty, pointed out in Volume V of Yi Li: "In the first month of the early Han Dynasty, rain was February Festival." "After the beginning, the name was changed to the same name, with rain as the first month and fright as the February Festival, which has not changed so far." Press "Three Calendars" again: Grain Rain March Festival, Tomb-Sweeping Day. "Shi Xun" and "Tong Guayan" were written in Grain Rain before the Ming Dynasty, which is the same as this calendar. "

Now the sequence of "rain-shock" and "Qingming-Grain Rain" used to be "shock-rain" and "Grain Rain-Qingming". This is related to the warmer climate at that time than today. Jin Luxiang, a scholar in Song and Yuan Dynasties, once assumed that the temperature in Zhou, Qin and Han Dynasties might be higher than that in Song and Yuan Dynasties. According to the analysis of Volume XXIII of the Nazi Party's Order to Gather the Moon edited by Qin Jiamo, "Jin people who are suspicious of Kyrgyzstan have strong yang and wake up early." "Initiator" means "quiet person". The third volume of Yang Guang Miscellaneous Notes by A Qing and Liu Xianting compares the climates of different places with the flowering period, thus inferring the differences between ancient and modern climates. He said: "This calendar also contains seventy-two phases, and this month is the climate of the Central Plains during the Seven Kingdoms period", but "the original of this day is no longer in line with the month". "Strong sun" leads to the understanding that "shock" precedes "rain", which was mentioned by Zhu Kezhen when he investigated the climate change in historical period (Preliminary Study on Climate Change in China in the Last Five Thousand Years, Journal of Archaeology 1972,No. 1 period).