The origin of vernal equinox

The origin of the spring equinox solar term is the fourth solar term in the "twenty-four 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. It is recorded in the almanac that "the bucket refers to the vernal equinox, which is about Sunday, and the northern and southern hemispheres are equally divided day and night, which is also the half of spring, hence the name vernal equinox." The vernal equinox usually refers to the moment when the sun's apparent yellow meridian is at 0, around February 15 of the lunar calendar (about March 19 ~22 in the Gregorian calendar). The vernal equinox is a traditional festival in China. On this day, the sun shines directly on the equator of the earth, and the seasons in the northern hemisphere are opposite. The northern hemisphere is the vernal equinox and the southern hemisphere is the autumnal equinox. The vernal equinox was also called "Japan-China", "Day and Night Equinox" and "Midspring Moon" in ancient times. "Li Mingshi Yi" said: "The dividing line, the turn of Huang Chi, the sun stops here, and the day and night are equally divided." Therefore, the significance of the vernal equinox, first, refers to the equal division of day and night, each of which is 12 hours; Second, in ancient times, it was spring from beginning of spring to long summer, and the vernal equinox happened to be in the three months of spring, and spring was equally divided. There are two theories about the origin of the vernal equinox. One is that the period from beginning of spring to Changxia is ancient spring, and the vernal equinox is in the middle of three months of spring, which divides the spring equally. For example, it is recorded in "Twenty-four Solar Terms": "Half-hour in February is half of ninety days, so it is called minutes. Autumn is synonymous. " Dong Zhongshu, who pays attention to the connection between man and nature, said in the first half of Spring and Autumn Annals: "The vernal equinox is half-phase, so it is cold and summer day and night." Day and night are basically equal in a year, and the other day is the autumn equinox. In addition, from this day on, the day is longer than the night. The vernal equinox is also a festival and ritual celebration. Ancient emperors had rituals of offering sacrifices to the sun in spring and the moon in autumn. Book of Rites: "Altar." Ying Da Shu by Confucius: "Also called vernal equinox". In the Qing Dynasty, Pan Rongbi wrote in "Ji Sheng at the Age of Emperor Jingdi": "The vernal equinox and autumn are national gifts, and scholars should not sacrifice them at will.