The four seasons refer to the four seasons that appear alternately in a year, namely, spring, summer, autumn and winter, and each season has 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.
In ancient times, according to bucket handle's direction, the four seasons alternated and the Big Dipper rotated circularly, which was closely related to the change of seasons. At present, the division of seasons is usually determined by the position of the earth in the orbit around the sun. The rotation of the four seasons reflects the changing laws of phenology and climate such as spring, long summer, autumn harvest and winter storage.
South China has abundant precipitation, abundant sunshine, high humidity, small temperature difference between winter and summer, and climate factors such as sunshine and precipitation change obviously with seasons. There is little precipitation in the northern region (mid-latitude region), and there is a great temperature difference between dryness and winter and summer. When the seasons change, the obvious change of climate factors is temperature.
From vernal equinox to summer solstice to autumnal equinox, the northern hemisphere is in summer and the southern hemisphere is in winter. During this period, the northern hemisphere has long days and short nights, while the southern hemisphere has short days and long nights. The north pole is in the extreme day and the south pole is in the extreme night; The height of the sun north of the Tropic of Cancer is always greater than the average, while the height of the sun south of the Tropic of Cancer is less than the average. North of the Tropic of Cancer, the sun rises on the northeast horizon and sets on the northwest horizon. On the vernal equinox, the sun all over the world rises in the east and sets in the west.
From the autumnal equinox to the winter solstice and then to the vernal equinox, the northern hemisphere is in the winter half year and the southern hemisphere is in the summer half year. During this period, the length of day and night, the extreme value of day and night and the height of the sun in the northern and southern hemispheres are contrary to the above situation. North of the Tropic of Cancer, the sun rises from the horizon in the southeast and sets on the horizon in the southwest.