The reason for stopping for 20 days.

The following are the reasons for the formation of supine for 20 days:

Midnight is one of the traditional twenty-four solar terms in China, which usually occurs between the third day and the twenty-second day of the seventh lunar month, that is, from July 23rd to August in the solar calendar 1 1. This time is considered to be the hottest time of the year. In many areas, the weather is extremely hot and humid, which easily leads to physical discomfort symptoms such as heatstroke and fatigue.

Near the Tropic of Cancer: During the mid-day period, the sun is 90 degrees above the Tropic of Cancer. This means that the direct point of the sun is located in the northern hemisphere, with the largest direct angle and the widest irradiation area, which makes most areas suffer from strong sunshine and high temperature.

Climatic conditions of high temperature and humidity: During the Mid-Autumn Festival, especially in southern China, the air humidity is relatively high under the influence of the south wind in summer. High temperature and humid climatic conditions hinder the human body to dissipate heat, and the somatosensory temperature is high, which is prone to heatstroke, fatigue and other discomfort.

Alternation of climatic phenomena: During midsummer, most areas will be affected by climatic phenomena such as typhoons and rainstorms. These weather conditions will aggravate the humidity and instability in tropical areas and further increase the humidity and temperature of the air. It is precisely because of such climatic conditions that Zhongfu became a symbol of the heat in the China lunar calendar. During midsummer, people usually take some measures to prevent heatstroke and cool down, such as avoiding long-term activities in the scorching sun, replenishing water in time, and keeping indoor ventilation.

The reason for the mid-20-day period is also related to the earth's orbit and climate change.

Earth's orbital position: Mid-Autumn Festival is exactly the specific position of the earth in orbit. The earth's orbit around the sun is elliptical, and the earth's orbit is tilted, which makes the hemisphere tilt to the sun in summer, and the sunlight irradiation area is larger, and the direct angle of the sun is higher, which leads to an increase in summer temperature.

Temperature storage effect: midsummer is the middle of summer, and the high temperature weather around this period has formed a continuous high temperature process. This leads to the accumulation of heat in the surface, atmosphere and water under the influence of the early high temperature, which leads to the persistence of the late high temperature.