Problems related to the 24 solar terms

The traditional method of dividing the four seasons in China takes four solar terms as the starting point of the four seasons, and bisection and two to one as the midpoint. For example, in spring, the starting point is beginning of spring, the solar line is 3 15, the spring is divided into the midpoint, the long summer is the end point, the solar line becomes 45, and the sun runs 90 on the ecliptic. This is a traditional and commonly used method.

The division of the four seasons in astronomical classification (that is, western classification) emphasizes the climatic significance of the four seasons, with the vernal equinox of the sun as the starting point of the four seasons, such as spring as the starting point and summer solstice as the end point. These four seasons are one and a half months later than the traditional four seasons in China.

At the equinox, the length of day and night and the height of the sun around the world are equal to the annual average, which has the typical characteristics of transition from maximum (or minimum) to minimum (or maximum). Therefore, it is very reasonable to regard the vernal equinox as the midpoint of spring and the autumnal equinox as the midpoint of autumn. In summer, the day is the longest and the night is the shortest. On the day of summer solstice, the height of the sun is the highest and the surface gets the most solar energy. Therefore, it is very reasonable to take the summer solstice as the midpoint of summer; Similarly, the winter solstice as the midpoint of winter is also very scientific.

In terms of actual climate, arranging summer solstice and winter solstice as the start dates of summer and winter respectively can better correspond to the actual climate. Therefore, the division of four seasons in the west can better reflect the actual climate significance.

Whether it is the division of four seasons with astronomical significance in China or the division of four seasons with climatic significance in the west, it is an astronomical division method.