According to the classic book "Yao Dian" written in the Spring and Autumn Period, Emperor Yao once organized a group of astronomical officials to observe the stars in the east, south, west and north to compile calendars and forecasts. season.
In "Xia Xiaozheng", which was written no later than the Spring and Autumn Period, it describes the astrology, weather, phenology of the month, as well as the agricultural and other activities that should be engaged in in the order of 12 months.
The basic outline of the Xia Dynasty calendar is that the year is divided into 12 months. Except for February, November, and December, each month is marked by the twilight, twilight, midday, and midday of certain constellations. Seeing each other in the morning and falling in the evening represent festivals.
Although this cannot be regarded as a scientific calendar, it can be called a combination of phenological calendar and astronomical calendar. Or, to be more precise, it has some experience in observing and timing.
"Shangshu·Yao Dian" also records the method of the ancients using significant stars to appear in the south sky at dusk to predict the seasons. This is the famous "Sizhong Middle Star". That is to understand the four seasons, accurately divide the solar terms of the year, and apply them to social production. It can be seen that by the end of the Shang Dynasty and the beginning of the Zhou Dynasty at the latest, people were quite confident in using astrology to predict the seasons.
In terms of counting the days of the stems and branches, the Xia Dynasty already had the method of counting the days with the heavenly stems, that is, using the 10 heavenly stems A, B, B, D, Wu, Ji, Geng, Xin, Ren, and Gui to keep track of the day over and over again.
On the basis of the Xia Dynasty’s Heavenly Stems calendar, the Shang Dynasty developed the stem-branch calendar, that is, the 10 heavenly stems such as A, B, C, and D are paired with the 12 earthly branches such as Zi, Chou, Yin, and Mao in order to form Jiazi. 60 stems and branches, including , Yichou, Bingyin, and Dingmao, can be used in a 60-day cycle.
By the end of the Spring and Autumn Period and the Warring States Period, the return year had been determined to be 365 days, and a method of setting seven leap months in 19 years had been discovered. On the basis of these achievements, the historic scientific calendar "Four Points Calendar" was born. From the Warring States Period to the early Han Dynasty, the four-part calendar was generally implemented.