The Ten Heavenly Stems and Twelve Earthly Branches
In the Chinese farming calendar, years are not counted by numbers, but by a method of combining the “stems and branches” (gan zhi, 干支). This method has been in use in China for over two thousand years. It is a major invention in the ancient Chinese calendar system.
Tiān gān 天干, or Heavenly Stems, are represented by ten characters: jiǎ 甲, yǐ 乙, bǐng 丙, dīng 丁, wù 戊, jǐ 己, gēng 庚, xīn 辛, rèn 壬, guí 癸, and in that order.
Dì zhī 地支, or Earthly Branches, are represented by twelve characters: zǐ 子, chǒu 丑, yín 寅, mǎo 卯, chén 辰, sǐ 巳, wǔ 午, wèi 未, shēn 申, yóu 酉, xù 戌, and haì 亥, and in that order.
The year is designated by the Stems and Branches System, combining one of the ten characters representing the Heavenly Stems with one of the twelve characters representing the Earthly Branches. This makes possible sixty combinations or pairs, known as a cycle of 60 years, jiazi 甲子or a huajia 花甲. According to this system, the first year of a sixty-year cycle (jiazi) is the combination of the first character of the Heaven Stems with the first character of the Earthly Branches, i.e., Jiazi 甲子, the second year yichou 乙丑, and the third year bingyin 丙寅, and so on and so forth. Thus, historical events in modern Chinese history are often signified or designated in this way. For instance, the Sino-Japanese War of 1894 is the War of Jiawu 甲午战争; the Reform Movement of 1898 is known in modern Chinese history as Reform Movement of Wuxu 戊戌变法; and the Republic Revolution of 1911 is called the Xinhai Revolution 辛亥革命.