天干、地支、八卦和六十四卦 Heavenly Stems, Earthly Branches, 8 Trigrams and 64 Hexagrams When looking up individual characters in modern dictionaries, I often come across descriptions such as "one of the ten Heavenly Stems", "nth Earthly Branch", "one of the Eight Trigrams", etc.


Is it something relevant for modern Chinese?
Do people generally know that 甲 is the first heavenly stem, 丑 is the second earthly branch, and so on?
Are they used in modern expressions?


Edit: I can see that 天干, 地支 and 八卦 are still important and serious learners should know about them. One more question: how about the 64 hexagrams (易經六十四卦)? Are they also used for counting or enumeration, or in some fixed expressions?
Brief answer.

Yes. Some modern Chinese words are developed from these conceptions.


坤 in 八卦 represents the earth, female, Yin.

From these meanings, words like 乾坤 (the world. lit. Heaven and earth), 坤角 ( female characters in Beijing Opera, but not necessarily played by a woman) developed.

甲 is the first element in heavenly stems, and 子 is the first element in earthly branches. The heavenly stems and earthly branches were popular to record the year in ancient times.

we have a word 甲子 which means 60 years, because the cycling length of  combinations of heavenly stems and earthly branches is LCM(12, 10) =60.

Yes, all most Chinese know these characters, however, some (at least some people I know ) can not remember the order exactly. It would take them few seconds to think of, for example, what the next element after 未? Today, in Chinese calendar, we still use this system to record the year. For example, this year is the year of 丙申 ( 申 indicates it's the monkey year).

Yes. You can see them in some idioms (成语) .



寅吃卯粮 To consume resources prepared  for or available in the future. Not planned well. Not prepared well. Lit. In the year of tiger, consume food prepared for the year of rabbit.
you can also see them in list bullets in articles. In English, you use a, b, c, d …, while in Chinese, you use 甲乙丙丁
in organic chemistry, 甲乙丙丁 … are used to express the number of carbon atoms in the nomenclature of substance. We have 甲烷 CH4, 乙烷 C2H6, 丙烷 C3H8…