The principle of yin and yang in Zhouyi expounds the natural phenomenon of geographical division between day and night.

According to "Iraq? According to the records in the copula, Fu looked up and down, and then drew the hexagrams "Dead Son" and "Classic Method" on the river map and Luo Shu, which recorded that "the Yellow Emperor had four sides" and "four reached from it". Yu Shu? Yao Dian is one of the "four intermediate stars"

According to legend, Emperor Yao ordered people to be divided into five roads, and was responsible for observing the astronomical phenomena such as the appearance of the sun at four o'clock, day and night and its length for many years. So there are "star birds in the sun" (referring to the average day and night of the vernal equinox) and "eternal sparks" (the summer solstice is long and the night is short)

Records of "no stars at night" (the autumnal equinox is average day and night) and "short days and high stars" (long days from winter to day and night). Among them, "bird", "fire", "virtual" and "ang" are the names of the stars, which are medium-sized stars in the fourth of the twenty-eight nights. Four-star appearance mark

The dichotomy and dichotomy are established. The concept of yin and yang is based on this long-term observation and summary of the periodic changes of four-time rhythm. On the summer solstice, the days are long, the nights are short and the sun is very high. The anode must produce yin, so it is called "summer and yin"

Born. "On the solstice in winter, the days are short, the nights are long and it is very cloudy. Yin will give birth to Yang, so it is called "Winter Yang". The vernal equinox and the autumnal equinox are equal day and night, but yin and yang are in balance, so they are called "half-phase of yin and yang". This is the so-called Yi Zhuan.

The basis of "observing yin and yang and establishing divination"

"Guanzi" said: "Spring, summer, autumn and winter, Yin and Yang are connected; When the length, the use of Yin and Yang also; Day and night are easy, and yin and yang are also transformed. "