Signs of seasonal change

The earth is like a top, it keeps spinning around its axis, and every rotation is a day. Rotation produces the phenomenon of alternating day and night. The side facing away from the sun is daytime, and the side facing away from the sun is night. When it's daytime here in China, it's only night in the United States on the other side of the globe; The direction of the earth's rotation is from west to east, so we see the sun, moon and stars rising in the east and gradually setting in the west. The earth not only rotates, but also revolves around the sun. The orbit of the earth's revolution is elliptical, the half-length diameter of the orbit is149,597,870 km, the eccentricity of the orbit is about 0.0 167, the average revolution speed is 29.79 km/s after one year's revolution, and the intersection angle between the orbital plane and the equatorial plane is about 23 27', which shows periodic changes and is the rotation and revolution of the earth. ?

Because the earth's axis of rotation and the orbital plane of revolution are inclined at an angle of about 66 33', during the year when the earth revolves around the sun, sometimes the northern hemisphere of the earth leans towards the sun, and sometimes the southern hemisphere leans towards the sun (left). In short, the direct point of the sun always moves between the tropic of cancer, which leads to the change of the length of day and night and the alternation of the four seasons. ?

In astronomy, the four seasons start from the vernal equinox, the summer solstice, the autumn equinox and the winter solstice, respectively, but the seasons divided in this way can not fully reflect the phenological signs of each season in various places. So our ancestors divided a year into 24 solar terms, and each solar term was divided into three periods. Climate is often divided into four seasons by the average climate temperature (once every five days): winter is the average climate temperature < 10℃; > 22℃ is summer; Average temperature in spring and autumn 10 ~ 22℃.