The ancients divided the sky above the equator into twelve equal parts, and Jupiter (also called the old star) walked through one equal part every year, and it took twelve years to complete a cycle. According to Jupiter's position in the sky every year, it is divided into "ugly, ugly, ugly, ugly, ugly, ugly, ugly, ugly, ugly, ugly, ugly, ugly, ugly, ugly, ugly, ugly, ugly.
After the Han Dynasty, the chronology of the branches and branches replaced the chronology of the stars, but the branches and branches recorded "years" instead of "years", so they were called "ugly years" or "ugly years".
The year of Xin Chou is the first Jia of the lunar calendar.
For example, 190 1, 196 1, 202 1 (60-year cycle) is the so-called calendar year of the lunar calendar, that is, literally speaking, branches are equivalent to trunks and branches. In ancient China, the sky was dominant and the earth was subordinate. The connection between heaven and stem is called heavenly stem, and the connection between earth and stem is called earthly branch. Together, it is called heavenly stems and earthly branches, or "dry branch" for short.
There are ten heavenly stems, namely A, B, C, D, E, Ji, G, Xin, Ren and Gui, and twelve earthly branches, namely Zi, Ugly, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu and Hai. The ancients put them together in the order of Jiazi, Ugly B and Bingyin (that is, the sky turns six times and the earth turns five times, which is just a cycle). Sixty pairs from Jiazi to Guihai are called Jiazi.
Reference to the above content: Baidu Encyclopedia-Xin Chou Nian