A Brief Introduction to the Ancient Chinese Calendar

Mankind established calendars to keep track of time. The elements of calendars
are years, months and days. The ancient Chinese calendar may be the most complicated
calendar system. It remains a mystery even to a lot of Chinese people.

There are three types of calendar systems: solar, lunar and solar-lunar calendars. A solar calendar uses the time it takes for the Earth to make one revolution around the Sun as a year. The current solar calendar is the Gregorian calendar, established in year 1582, when Pope Gregory XIII reformed Julius Caesar¡¯s calendar. A lunar calendar uses the time that it takes the Moon make one circle around the Earth as a month. A lunar year is about 11 days shorter than a solar year.

The ancient Chinese calendar is a solar-lunar calendar. Months are set according to the cycle of the Moon. Years are set according to solar year. In order to match months to seasons, a leap month is inserted. Chinese usually refer to the ancient Chinese calendar as ¡°the lunar calendar.¡± It is also called ¡°the agriculture calendar.¡±

The Sexagesimal Cyclei

An important aspect of the Chinese calendar is the sexagenary cycle. This is a combination of the 10 ¡°heavenly stems¡±, ti¨¡n g¨¡n (Ìì¸É), and the 12 ¡°earthly branches¡±, d¨¬ zh¨© (µØÖ§).

Stems	Ìì¸É	tian gan	Element	Branches	µØÖ§	d¨¬ zh¨©	Animal
1 ¼× ji¨£ Wood 1 ×Ó z¨« Rat
2 ÒÒ y¨« Wood 2 ³ó ch¨¯u Ox
3 ±û b¨«ng Fire 3 Òú y¨ªn Tiger
4 ¶¡ d¨©ng Fire 4 î m¨£o Rabbit
5 Îì w¨´ Earth 5 ³½ ch¨¦n Dragon
6 ¼º j¨« Earth 6 ËÈ s¨¬ Snake
7 ¸ý g¨¥ng Metal 7 Îç w¨³ Horse
8 ÐÁ x¨©n Metal 8 δ w¨¨i Goat
9 ÈÉ r¨¦n Water 9 Éê sh¨¥n Monkey
10 ¹ï gu¨« Water 10 ÓÏ y¨¯u Chicken
11 Ðç x¨± Dog
12 º¥ h¨¤i Pig

To explain how this cycle works, let us denote both the stems and the branches by their numbers. We denote 1 by (1,1) or (¼×, ×Ó), 2 by (2,2) or (ÒÒ, ³ó) and so on up to (10,10) or (¹ï, ÓÏ). But now we have run out of stems, so we denote 11 by (1, 11) or (¼×, Ðç) and 12 by (2, 12) or (ÒÒ, º¥). Now we have run out of branches, too, so 13 becomes (3, 1) or (±û, ×Ó). We continue in this way through 6 cycles of stems and 5 cycles of branches up to 60, which is (10, 12) or (¹ï, º¥). The next number is then (1,1) or (¼×, ×Ó), which starts a new sexagesimal cycle.

A Brief Historyii

The calendar system during the Warring States (475 ¨C 221 B.C.) period was called the¡°quarter calendar.¡± A year had 365 and a quarter days. A month had 29 and 499/940 days. It was a collection of astronomical research results. The first complete calendar in China was established in the Emperor Han Wu¡¯s 7th year, namely 104 B.C. There were 365 and 385/1539 days in a year and 29 and 43/81 days in a month. Before the western calendar spread into China, the Da Tong (meaning ¡°big unity¡±) calendar was the last common calendar. In the Chinese calendar, there is no continuous year number. When a new emperor reigned, the year number went to zero. The Da Tong calendar used the Ming Dynasty Emperor Hong Wu¡¯s 17th year (1384) as the start of the calendar.

The current Chinese calendar was the one modified in Qing Dynasty Qian Long¡¯s 7th Year (1742). It uses 1723 as the start of the calendar.

The ancient Chinese calendar was constantly modified based on astronomical observations. Thus, in ancient China the calendar was interwoven with astronomy. 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.

i This article is from http://www.math.nus.edu.sg/aslaksen/calendar/chinese.shtml#sex
by Professor Helmer Aslaksen at Department of Mathematics, National University
of Singapore
ii This article is translated and edited from http://juns.uhome.net/big5/ast-date/date/B2.htm

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