Why is a year divided into four seasons: spring, summer, autumn and winter? Is it divided into 24 solar terms?

(1), the four seasons are divided according to the length of day and night and the change of sun height. The division of the four seasons is based on the apparent position of the sun on the ecliptic and bounded by the bisector, the second solstice or the fourth day. However, the dividing points used by eastern and western countries to divide the four seasons are not exactly the same.

(2) The first classification: China's traditional method of dividing the four seasons takes the four solar terms as the starting point of the four seasons and bisects and bisects 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.

(3) The second classification: the astronomical classification (that is, the western classification) emphasizes the climatic significance of the four seasons, with the vernal equinox to 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.

(4) Discussion: ` 1 Spring and Autumn, the length of day and night and the height of the sun around the world are equal to the annual average, with 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.

However, from the actual climate, the summer solstice is not the hottest time, and the winter solstice is not the coldest time, so the extreme temperature should be delayed by 1 ~ 2 months respectively. There is a saying in China that "heat is in dogs" and cold is in Sanjiu. Therefore, taking 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. This is because dichotomy, dichotomy and quartering all have exact meanings in astronomy. They all divide the year into four roughly equal seasons, each lasting for three months, and the sun runs 90 degrees on the ecliptic. None of them can reflect the actual situation of the local climate. The seasons divided in this way are the four seasons in astronomy.

The astronomical season is hemispherically unified. In the hemisphere, every season has a unified starting and ending time. In the hemisphere, there are four seasons everywhere, and each season is of equal length.

(5) The third classification: In order to accurately reflect the actual climate situation in various places, climatological methods are often used to divide the four seasons, that is, the classification of modern scholar Zhang Baokun and the climatic average temperature method. It is also stipulated that the period when the average temperature is greater than or equal to 22℃ is summer, the period when it is less than or equal to 10℃ is winter, and the period between 10℃ and 22℃ is spring or autumn. According to this standard, the seasons in mid-latitude areas are consistent with the climate, while the temperature changes in low-latitude areas and near the polar regions are not obvious. At the same time, in mid-latitude areas, the length of each season is different. This is the four seasons. For example, Beijing has 55 days in spring, 0/03 days in summer, 50 days in autumn and 0/57 days in winter. This method can be combined with the specific climate and agriculture in various places, so it is widely used.

(6) The fourth category: climate statistics, because 1 month is the most Leng Yue, so spring is March, April and May, summer is June, July and August, autumn is 9 10, 165438+ 10, and winter is 650.

(7) Astronomical seasons are of theoretical significance and climatic seasons are of practical value. Astronomical seasons are the basis for dividing climatic seasons. The astronomical season is hemispherically unified. It is summer in the northern hemisphere and winter in the southern hemisphere; The climate of the four seasons is unified in some areas (mid-latitude areas). The division of astronomical seasons depends on the change of astronomical phenomena, and the division of climatic seasons depends on the change of temperature. No matter where in any hemisphere, there are astronomical seasons of equal length; In the same place, the time of four climatic seasons is not necessarily equal. This is the main difference between astronomical season and climate season.