天干地支是中國歷法中用以記錄和命名年歲的方法。十天干為：甲、乙、丙、丁、戊、已、庚、辛、壬、癸;十二地支為：子、丑、寅、卯、辰、巳、午、未、申、酉、戊、亥。古人觀測朔望月，發現月亮圓缺12次大體上是一年的天數，而兩個朔望月約是60天。古人以十天干與十二地支的順序依次相配，記錄不同年份，60年為一個輪回。干支紀年法從古沿用至今。按干支紀年法，2011年便是辛卯年。

【參考譯文】

The Chinese era is the symbol that the Chinese calendar uses for recording and naming years. The ten Heavenly Stems are: jia, yi, bing, ding, wu, ji, geng, xin, ren, gui. The twelve Earthly Branches are: zi.chou, yin, mou, chen, si, wu, wei, shen, you, xu, hai. After observing the lunar month, the ancients found that the moon always wazes and wanes roughly 12 times a year, and two lunar months account for about 60 days, so the order of the ten Heavenly Stems and the order of the twelve Earthly Branches are properly matched in turn. In terms of recording date, 60 years is considered to be a full time cycle. The Chinese era chronology was first invented in ancient times and is still in use now. according to the chronology of the “ten Heavenly Stems,” 2011 is the year of “the seventh of the ten Heavenly Stems” and “ the fifth of the twelve Earthly Branches”.