Four seasons refer to four seasons that appear alternately in a year, namely spring, summer, autumn and winter, and each season lasts for three months. All the year round is formed because the earth revolves around the sun.
Because of the existence of the ecliptic angle, the direct point of the sun moves back and forth between the north and south latitudes of the earth, which changes every year, resulting in the seasonal changes of the height of the sun at noon, the length of day and night, and the seasonal changes of the solar energy obtained in various places, thus forming the replacement of the four seasons.
The gradual changes of the four seasons are not uniform all over the world. It is summer in the northern hemisphere and winter in the southern hemisphere. The northern hemisphere changes from warm to cold, and the southern hemisphere changes from cold to hot. The length of day and night and the height of the sun change periodically in different seasons.