Heavenly Stems and Earthly Branches

Heavenly stems and earthly branches (or Tian Gan Di Zhi, commonly abbreviated to Gan Zhi) are the basic units of the ancient Chinese astronomical calendar, which originated from the observation of celestial phenomena. "Gan" literally means stems and "Zhi" means branches. There are ten heavenly stems: Jia, Yi, Bing, Ding, Wu, Ji, Geng, Xin, Ren, and Gui, and twelve earthly branches: Zi, Chou, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu, and Hai. The heavenly stems and earthly branches are combined in a fixed order to form the Gan Zhi chronology, an important means of recording years, months, days, and hours in ancient China. They are still the basic units of the Chinese lunar calendar today. For example, 2022 is the year of Ren Yin with the heavenly stem "Ren" and the earthly branch "Yin", and 2023 is the year of Gui Mao with the heavenly stem "Gui" and the earthly branch "Mao".

In Chinese folk culture, the twelve earthly branches are paired with the twelve zodiac animals (rat, ox, tiger, rabbit, dragon, snake, horse, goat, monkey, rooster, dog, and pig). Each animal corresponds to a lunar year. For example, the year of Ren Yin is the year of the tiger, and the year of Gui Mao is the year of the rabbit. The Gan Zhi chronology is based on a 60-year cycle, known as a "Jia Zi", reflecting the ancient Chinese belief in the cyclical nature of history. It was also widely used in divination, arithmetic, naming, and other fields.

天干地支

天干地支簡稱“干支”，是中國古代天文歷法的基本計數單位，源自中國遠古時代對天象的觀測。“干”原指樹干，“支”原指樹枝。天干有十個，依次為：甲、乙、丙、丁、戊、己、庚、辛、壬、癸；地支有十二個，依次為： 子、丑、寅、卯、辰、巳、午、未、申、酉、戌、亥。十天 干和十二地支按固定的順序相互配合，組成干支紀元法。干 支紀元法是中國古人紀年、月、日、時的重要方法，直到現 在仍是中國農歷紀年的基本單位，例如，2022年是農歷壬 寅年，2023年是農歷癸卯年。

中國民間又將十二地支與十二生肖（鼠、牛、虎、兔、龍、蛇、馬、羊、猴、雞、狗、豬）相配，與農歷年相對應，如壬寅年為虎年，癸卯年為兔年。干支紀年法以六十年為一個周期，稱為一“甲子”。這種紀年法反映了中國古人循環往復、生生不息的歷史觀。此外，天干地支還廣泛應用于術數、計數、命名等領域。