Introduction of vernal equinox in the 24 solar terms

1, the vernal equinox is the fourth of the 24 solar terms and an important season for farming. The sun shines directly on the equator of the earth, and day and night are almost equal. In ancient times, it was spring from beginning of spring to long summer, and the vernal equinox was in the middle of three months in spring. The sun reaches the longitude of the Yellow River at 0 degrees, in March every year in Gregorian calendar 19~22. "The vernal equinox, Yin and Yang. So it's hot and cold day and night. " 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." 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.

2. When the vernal 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. However, after the spring equinox and solar terms, the climate is mild, the rain is abundant and the sun is shining. Winter crops in most parts of China enter the spring growth stage, which is also the sowing time of early rice.

3. Astronomical phenomenon: The vernal equinox refers to the position where the sun is located between 0 degrees and 15 degrees of the yellow longitude in a time period, from March 20th to April 5th. But in fact, it usually refers to the day when the sun is really at 0 degrees of the yellow meridian: March 20 or March 2 1.