Every year from March 19 to 22, one day is the vernal equinox among the 24 solar terms. "The vernal equinox, Yin and Yang. So it's hot and cold day and night. " A word "fen" tells the boundary between day and night, cold and heat. At this time, the longitude of the sun is 0 degrees and the position of the sun is above the equator. According to the lunar calendar, "it refers to the vernal equinox, which is about Sunday. The northern and southern hemispheres are equally divided day and night, which is also half of spring, so it is called the vernal equinox."

The vernal equinox is the midpoint of 90 days in spring, and the northern and southern hemispheres are equal in day and night. From this day on, the direct position of the sun gradually moved northward, and the length of day and night in the northern and southern hemispheres also changed. The northern hemisphere has long days and short nights, but the southern hemisphere is just the opposite. As soon as the spring equinox arrives, the rainfall increases obviously, and the national average ground temperature has stabilized at 10 degrees, which is the spring temperature defined by climatology. After the spring equinox and solar terms, the climate is mild, with plenty of rain and sunny days. Winter crops in most parts of China enter the spring growth stage, which is also the sowing time of early rice. Agricultural proverbs in different places have different opinions on the vernal equinox: there is a saying in Shandong that "the vernal equinox plants trees, the sun shines, and nothing happens"; Hubei has a "rainy spring equinox, everyone is busy, planting melons and beans before transplanting"; There is a saying in Guangdong that "the vernal equinox comes first, and rice competes for money".

Ouyang Xiu once had a wonderful description of the vernal equinox: "At half past the vernal equinox in Nanyuan, the wind and the smell of Ma Si are like peas and willows, and butterflies are flying." Whether in the north or the south, the vernal equinox and solar terms are good times for spring, and orchids are in full bloom in Taiwan Province Province, China.

Because the vernal equinox and solar terms divide day and night equally, people should pay attention to maintaining the balance of yin and yang in health care. Stalin said: "Relatively static objects and the possibility of temporary balance are the fundamental conditions for material differentiation and therefore life". In order to obtain the "basic conditions of life" of this "temporary balance state", maintaining the balance of yin and yang in the human body has become an important rule of health preservation. This rule is very important in spirit, diet, daily life, self-care and medication. How to use the law of yin-yang balance in health care, coordinate various functions of the body, achieve a balanced state inside and outside the body, and keep the organic whole of the human body relatively calm and balanced is the foundation of health care.