"Vernal Equinox" means "half", which means that one part is divided into two parts, the day and night are evenly divided, and the heat and cold are balanced. In addition, the vernal equinox also means to divide the spring equally. Traditionally, the spring is from the beginning of spring to the beginning of summer, and the vernal equinox is in the middle of three months of spring. Therefore, the vernal equinox in ancient times was also known as the "mid day", the "day and night equinox" and the "mid spring moon". On the day of the spring equinox, the sun shines directly at the earth's equator, and the days and nights are equal. According to Wu Cheng's book Yue Order 72 Hou Ji Jie explains: "In the middle of February, half is divided. This is half of the ninetieth day, so it is called" division ". ”In addition, the Spring and Autumn Dews said: "The vernal equinox is half Yin and half Yang, so the cold and heat are equal day and night 。 ”Lunar calendar: "Douzhiren is the vernal equinox, which runs around the sky. The day and night of the northern and southern hemispheres are equally divided (except for the poles), and it is also half of spring, It is called the vernal equinox. ”
