How the year A.D. was determined

It is a historical calculation based on the year of the birth of the Christian Jesus, which in China was the first year of the reign of Emperor Pingdi of the Western Han Dynasty (Xinyou). In China, this year was the year of Yuan Shi (Xin You) of Emperor Ping of the Western Han Dynasty. Using this year as the basis for calculation, the period before this year is called the year BC, and the period after this year is called the year AD.

Extended information:

The year of Xin You is one of the sixty A Zi of the dry-branch calendar, which roughly corresponds to calendar years such as 1921, 1981, and 2041 --- (a 60-year cycle). In a year, the number of years is divided by 60 and the remainder is 1, or the number of years is reduced by 2, the remainder of 10 is 9, the remainder of 12 is 11, and the number of years from the beginning of spring to the end of the following year is "xinyou nian" (辛酉年).

The Chinese lunar calendar is a dry-branch calendar, and the seasons are used to guide agricultural production. The dry-branch calendar is not divided into seasons, either by traditional customs or by official calendars (for details, see the Universal Perpetual Calendar compiled by the Zijinshan Astronomical Observatory of the Chinese Academy of Sciences). The so-called stem and branch chronology means: the stem and branch are literally equivalent to the trunk of a tree and its branches and leaves.

In ancient China, the sky is the main and the earth is the subordinate, the sky and the stem are connected called the heavenly stem, the earth and the branch are connected called the earthly branch, and together they are called the heavenly stem and the earthly branch, or the stem and branch for short. There are ten heavenly stems, that is, A, B, C, D, E, F, G, C, N, N, D, and twelve earthly branches, in order, is the son, ugly, c, d, e, S, N, W, S, Y, X, H, H, Hai.

The ancients put them in accordance with the a son, b ugly, c c ...... (that is, six turns of the celestial trunk and five turns of the earth's branches, exactly one cycle) of the order without repeating the match up, from the Azi to Dec. Ohio **** sixty pairs, called a Azi. China's ancient people used these sixty pairs of branches to indicate the year, month, day, hour of the serial number, week after week, a continuous cycle, which is the stem and branch chronology.

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