Let's Get Complicated

Understanding the Chinese Calendar

By PROFESSOR HELMER ASLAKSEN

Department of Mathematics, National University of Singapore

Used with permission by Pureinsight.org

We human beings invented calendars to keep track of time. Most calendars are made of years, months and days. The ancient Chinese wanted something...more interesting. Their calendar invested a basic calendar with layers of meaning. It may, in fact, be the most complicated calendar system in existence and a mystery even to the Chinese people themselves.

The calendar system during the Warring States period (475 – 221 B.C.) was called the“quarter calendar.” A year had 365 and 1/4 days. A month had 29 and 499/940 days. The first complete calendar was established in 104 BC, the 7^th year of the reign of Emperor Han Wu. That calendar had 365 and 385/1539 days in a year and 29 and 43/81 days in a month.

The last calendar before western calendars were accepted into China was “Da Tong” (“big unity”), so called because there is no continuous year number. The beginning of a new emperor's reign started the calendar year to zero. For example, the Da Tong calendar during the reign of Ming Dynasty's Emperor Hong Wu started in his 17^th year (1384 AD). The current Chinese calendar was modified in Qing Dynasty Qian Long’s 7^th Year (1742 AD) and uses 1723 as the start of the calendar.

The ancient Chinese calendar was constantly modified based on astronomical observations. In fact, the history of ancient Chinese astronomy was also a history of researching and improving calendars. This is a characteristic of ancient Chinese astronomy that is quite different from its western counterpart.

Most of us use a solar calendar known as the Gregorian calendar, established in 1582 by Pope Gregory XIII. A lunar calendar is 11 days shorter than a solar calendar. The ancient Chinese did it both ways. They set months according to the lunar cycle and years according to solar year and matched months to seasons by adding a leap month.

The Chinese calendar uses what is known as a sexagenary cycle, a combination of 10 “heavenly stems”, (tiān gān 天干) and 12 “earthly branches” (dì zhī 地支). Below you'll recognize the five elements as well as animals of the Chinese zodiac.

Stems