1. The Spring Equinox is the fourth solar term among the twenty-four solar terms and is an important season for farming. The sun shines directly on the Earth's equator, making day and night almost equal. In ancient times, spring was from the beginning of spring to the beginning of summer, and the vernal equinox was in the middle of the three months of spring. The sun reaches 0 degrees ecliptic longitude, which is celebrated every year from March 19th to 22nd in the Gregorian calendar. "On the vernal equinox, yin and yang are half in phase. Therefore, day and night are even and the cold and heat are equal." It is recorded in the lunar calendar that "Dou Zhi Ren is the vernal equinox, and it travels around the sky. Day and night are equally divided in the northern and southern hemispheres. It is also the middle of spring, so it is called the vernal equinox." From this day on, the direct position of the sun gradually moves northward, and day and night are equally divided in the northern and southern hemispheres. The length also changes accordingly. The days are longer in the Northern Hemisphere and the nights are shorter in the Southern Hemisphere.

2. As soon as the vernal equinox arrives, the rainfall increases significantly, and the average ground temperature in China has stabilized through 10 degrees, which is the spring temperature defined by climatology. After the Spring Equinox, the climate is mild, the rain is abundant, and the sunshine is bright. Overwintering crops in most parts of China enter the spring growth stage, and this is also the sowing period for early rice.

3. Astronomical phenomena: In terms of time period, the vernal equinox refers to the position of the sun between 0° and 15° of celestial longitude, which is approximately between March 20 and April 5. But in practice, it usually refers to the day when the sun is truly at 0° ecliptic longitude: March 20 or March 21.