天干地支是中国历法中用以记录和命名年岁的方法。十天干为：甲、乙、丙、丁、戊、已、庚、辛、壬、癸;十二地支为：子、丑、寅、卯、辰、巳、午、未、申、酉、戊、亥。古人观测朔望月，发现月亮圆缺12次大体上是一年的天数，而两个朔望月约是60天。古人以十天干与十二地支的顺序依次相配，记录不同年份，60年为一个轮回。干支纪年法从古沿用至今。按干支纪年法，2011年便是辛卯年。
【参考译文】
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”.