Although the People's Republic of China uses the Gregorian calendar for civil purposes, a special Chinese calendar is used for determining festivals. Various Chinese communities around the world also use this calendar.
The beginnings of the Chinese calendar can be traced back to the 14th century BC. Legend has it that the Emperor Huangdi invented the calendar in 2637 BC.
The Chinese calendar is based on exact astronomical observations of the longitude of the sun and the phases of the moon. This means that principles of modern science have had an impact on the Chinese calendar.
I can recommend visiting Helmer Aslaksen's web site for more information about the Chinese calendar (see ).
The Chinese calendar - like the Hebrew - is a combined solar/lunar calendar in that it strives to have its years coincide with the tropical year and its months coincide with the synodic months. It is not surprising that a few similarities exist between the Chinese and the Hebrew calendar:
When determining what a Chinese year looks like, one must make a number of astronomical calculations:
First, determine the dates for the new moons. Here, a new moon is the completely ``black'' moon (that is, when the moon is in conjunction with the sun), not the first visible crescent used in the Islamic and Hebrew calendars. The date of a new moon is the first day of a new month.
Secondly, determine the dates when the sun's longitude is a multiple of 30 degrees. (The sun's longitude is 0 at Vernal Equinox, 90 at Summer Solstice, 180 at Autumnal Equinox, and 270 at Winter Solstice.) These dates are called the Principal Terms and are used to determine the number of each month:
Principal Term 1 occurs when the sun's longitude is 330 degrees.
Principal Term 2 occurs when the sun's longitude is 0 degrees.
Principal Term 3 occurs when the sun's longitude is 30 degrees.
etc.
Principal Term 11 occurs when the sun's longitude is 270 degrees.
Principal Term 12 occurs when the sun's longitude is 300 degrees.
Each month carries the number of the Principal Term that occurs in that month.
In rare cases, a month may contain two Principal Terms; in this case the months numbers may have to be shifted. Principal Term 11 (Winter Solstice) must always fall in the 11th month.
All the astronomical calculations are carried out for the meridian 120 degrees east of Greenwich. This roughly corresponds to the east coast of China.
Some variations in these rules are seen in various Chinese communities.
Leap years have 13 months. To determine if a year is a leap year, calculate the number of new moons between the 11th month in one year (i.e, the month containing the Winter Solstice) and the 11th month in the following year. If there are 13 months from the start of the 11th month in the first year to the start of the 11th month in the second year, a leap month must be inserted.
In leap years, at least one month does not contain a Principal Term. The first such month is the leap month. It carries the same number as the previous month, with the additional note that it is the leap month.
Unlike most other calendars, the Chinese calendar does not count years in an infinite sequence. Instead years have names that are repeated every 60 years.
(Historically, years used to be counted since the accession of an emperor, but this was abolished after the 1911 revolution.)
Within each 60-year cycle, each year is assigned name consisting of two components:
The first component is a Celestial Stem:
| 1. | jia | 6. | ji |
| 2. | yi | 7. | geng |
| 3. | bing | 8. | xin |
| 4. | ding | 9. | ren |
| 5. | wu | 10. | gui |
These words have no English equivalent.
The second component is a Terrestrial Branch:
| 1. | zi (rat) | 7. | wu (horse) |
| 2. | chou (ox) | 8. | wei (sheep) |
| 3. | yin (tiger) | 9. | shen (monkey) |
| 4. | mao (hare, rabbit) | 10. | you (rooster) |
| 5. | chen (dragon) | 11. | xu (dog) |
| 6. | si (snake) | 12. | hai (pig) |
The names of the corresponding animals in the zodiac cycle of 12 animals are given in parentheses.
Each of the two components is used sequentially. Thus, the 1st year of the 60-year cycle becomes jia-zi, the 2nd year is yi-chou, the 3rd year is bing-yin, etc. When we reach the end of a component, we start from the beginning: The 10th year is gui-you, the 11th year is jia-xu (restarting the Celestial Stem), the 12th year is yi-hai, and the 13th year is bing-zi (restarting the Terrestrial Branch). Finally, the 60th year becomes gui-hai.
This way of naming years within a 60-year cycle goes back approximately 2000 years. A similar naming of days and months has fallen into disuse, but the date name is still listed in calendars.
It is customary to number the 60-year cycles since 2637 BC, when the calendar was supposedly invented. In that year the first 60-year cycle started.
The current 60-year cycle started on 2 Feb 1984. That date bears the name bing-yin in the 60-day cycle, and the first month of that first year bears the name gui-chou in the 60-month cycle.
This means that the year geng-chen, the 17th year in the 78th cycle, started on 5 Feb 2000.