Why does the earth have four seasons?
Four seasons refer to the four seasons that appear alternately in a year, namely, spring, summer, autumn and winter. Astronomically speaking, the division of the four seasons is determined by the orbital position of the earth around the sun. When the earth is in different positions in the orbit of revolution at different times of the year, different places on the earth receive different sunlight and different heat from the sun, which leads to seasonal changes and differences between cold and hot.
The four seasons on the earth are not only periodic changes in temperature, but also periodic changes in the length of day and night and the height of the sun. It affects or determines the movement rhythm of many things in the earth's environment, especially the adaptation of creatures.
divide
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.
First kind
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 second type
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.
The third kind
In order to accurately reflect the actual climate situation in various places, climatology is often used to divide the four seasons, that is, the classification method of modern scholar Zhang Baokun and the average climate temperature are used to divide the four seasons. 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.
The fourth kind
According to climate statistics, since 65438+ 10 is generally the most Leng Yue, it is March, April and May in spring, June, July and August in summer, 9 10 in autumn, 165438+ 10 in winter.
References:
Four seasons Baidu encyclopedia