How to explain the relationship between the twenty-four solar terms and the movement of the sun in theory?

During the Three Kingdoms period, the relationship between solar terms and the movement of the sun was further mastered. Mathematician Zhao's "Weekly Parallel Calculation Classics" introduced "seven levels and six diagrams", which theoretically explained the relationship between the 24 solar terms and the sun's movement.

During the Jin Dynasty, "wooden birds related to the wind" and wind direction measuring instruments prevailed. Li Jiang, a philosopher in the Eastern Jin Dynasty, pointed out that floating clouds close to the ground can reduce the inter-satellite sight distance and make the colors of the stars turn red in the morning and evening when they rise. Zhou Chu, a celebrity in Jin Dynasty, put forward the concept of plum rain in Local Records.