Chinese Calendars

Evidence from the Shang oracle bone inscriptions shows that at least by the 14th century BC the Shang Chinese had established the solar year at 365 1/4 days and lunation at 29 1/2 days. In the calendar that the Shang used, the seasons of the year and the phases of the Moon were all supposedly accounted for. One of the two methods that they used to make this calendar was to add an extra month of 29 or 30 days, which they termed the 13th month, to the end of a regular 12-month year.

There is also evidence that suggests that the Chinese developed the Metonic cycle (see above Complex cycles)--i.e., 19 years with a total of 235 months--a century ahead of Meton's first calculation (no later than the Spring and Autumn period, 770-476 BC). During this cycle of 19 years there were seven intercalations of months. The other method, which was abandoned soon after the Shang started to adopt it, was to insert an extra month between any two months of a regular year. Possibly, a lack of astronomical and arithmetical knowledge allowed them to do this.

By the 3rd century BC, the first method of intercalation was gradually falling into disfavour, while the establishment of the meteorological cycle, the erh-shih-ssu chieh-ch'i (Pinyin ershisi jieqi), during this period officially revised the second method. This meteorological cycle contained 24 points, each beginning one of the periods named consecutively the Spring Begins, the Rain Water, the Excited Insects, the Vernal Equinox, the Clear and Bright, the Grain Rains, the Summer Begins, the Grain Fills, the Grain in Ear, the Summer Solstice, the Slight Heat, the Great Heat, the Autumn Begins, the Limit of Heat, the White Dew, the Autumn Equinox, the Cold Dew, the Hoar Frost Descends, the Winter Begins, the Little Snow, the Heavy Snow, the Winter Solstice, the Little Cold, and the Severe Cold.

The establishment of this cycle required a fair amount of astronomical understanding of the Earth as a celestial body, and without elaborate equipment it is impossible to collect the necessary information. Modern scholars acknowledge the superiority of pre-Sung Chinese astronomy (at least until about the 13th century AD) over that of other, contemporary nations.

The 24 points within the meteorological cycle coincide with points 15 apart on the ecliptic (the plane of the Earth's yearly journey around the Sun or, if it is thought that the Sun turns around the Earth, the apparent journey of the Sun against the stars). It takes about 15.2 days for the Sun to travel from one of these points to another (because the ecliptic is a complete circle of 360), and the Sun needs 365 1/4 days to finish its journey in this cycle.

Supposedly, each of the 12 months of the year contains two points, but, because a lunar month has only 29 1/2 days and the two points share about 30.4 days, there is always the chance that a lunar month will fail to contain both points, though the distance between any two given points is only 15. If such an occasion occurs, the intercalation of an extra month takes place. For instance, one may find a year with two "Julys" or with two "Augusts" in the Chinese calendar. In fact, the exact length of the month in the Chinese calendar is either 30 days or 29 days--a phenomenon which reflects its lunar origin. Also, the meteorological cycle means essentially a solar year. The Chinese thus consider their calendar as yin-yang li, or a "lunar-solar calendar."

Although the yin-yang li has been continuously employed by the Chinese, foreign calendars were introduced to the Chinese, the Hindu calendar, for instance, during the T'ang (Tang) dynasty (618-907), and were once used concurrently with the native calendar. This situation also held true for the Muslim calendar, which was introduced during the Y�an dynasty (1206-1368). The Gregorian calendar was taken to China by Jesuit missionaries in 1582, the very year that it was first used by Europeans. Not until 1912, after the general public adopted the Gregorian calendar, did the yin-yang li lose its primary importance.

One of the most distinguished characteristics of the Chinese calendar is its time-honoured day-count system. By combining the 10 celestial stems, kan (gan), and the 12 terrestrial branches, chih (zhi), into 60 units, the Shang Chinese counted the days with kan-chih (gan-zhi) combinations cyclically. For more than 3,000 years, no one has ever tried to discard the kan-chihday-count system. Out of this method there developed the idea of hs�n, (xun), 10 days, which some scholars would render into English as "week." The kan-chihcombinations probably were adopted for year count by Han emperors during the 2nd century AD.

The yin-yang li may have been preceded by a pure lunar calendar because there is one occurrence of the "14th month" and one occurrence of the "15th month" in the Shang oracle bone inscriptions. Unless there was a drastic change in the computation, it is quite inconceivable that an extra 90 days should have been added to a regular year. Julius Caesar had made 45 BC into a year of 445 days for the sake of the adoption of the Julian calendar in the next year.

Presumably, the Shang king could have done the same for similar reasons. From the above discussion on the intercalation of months, it is clear that within the yin-yang li the details of the lunar calendar are more important than those of the solar calendar. In a solar calendar the 24 meteorological points would recur on the same days every year. Moreover, if a solar calendar were adopted first, then the problem of intercalation would be more related to the intercalation of days rather than intercalation of months.

Many traditional Chinese scholars tried to synchronize the discrepancy between the lunation and the solar year. Some even developed their own ways of computation embodying accounts of eclipses and of other astronomical phenomena. These writings constitute the bulk of the traditional almanacs. In the estimation of modern scholars, at least 102 kinds of almanacs were known, and some were used regularly. The validity or the popularity of each of these almanacs depends heavily on the author's proficiency in handling planetary cycles. In the past these authors competed with one another for the position of calendar master in the Imperial court, even though mistakes in their almanacs could bring them punishment, including death. (Ch.L.)

Assyrians and the Hittites

Babylonian Calendar

The ancient Babylonians used a calendar with alternating 29- and 30-day months. This system required the addition of an extra month three times every eight years, and as a further adjustment the king would periodically order the insertion of an additional extra month into the calendar.

The Babylonians, who lived in what is now Iraq, added an extra month to their years at irregular intervals. Their calendar, composed of alternate 29-day and 30-day months, kept roughly in step with the lunar year. To balance the calendar with the solar year, the early Babylonians calculated that they needed to add an extra month three times every eight years. But this system still did not accurately make up for the accumulated differences between the solar year and the lunar year. Whenever the king felt that the calendar had slipped too far out of step with the seasons, he ordered another extra month. However, the Babylonian calendar was quite confused until the 300's B.C., when the Babylonians began to use a more reliable system.

In Mesopotamia the solar year was divided into two seasons, the "summer," which included the barley harvest in the second half of May or in the beginning of June, and the "winter," which roughly corresponded to today's fall-winter. Three seasons (Assyria) and four seasons (Anatolia) were counted in northerly countries, but in Mesopotamia the bipartition of the year seemed natural. As late as c. 1800 BC the prognoses for the welfare of the city of Mari, on the middle Euphrates, were taken for six months.

The months began at the first visibility of the New Moon, and in the 8th century BC court astronomers still reported this important observation to the Assyrian kings. The names of the months differed from city to city, and within the same Sumerian city of Babylonia a month could have several names, derived from festivals, from tasks (e.g., sheepshearing) usually performed in the given month, and so on, according to local needs.

On the other hand, as early as the 27th century BC, the Sumerians had used artificial time units in referring to the tenure of some high official--e.g., on N-day of the turn of office of PN, governor. The Sumerian administration also needed a time unit comprising the whole agricultural cycle; for example, from the delivery of new barley and the settling of pertinent accounts to the next crop. This financial year began about two months after barley cutting. For other purposes, a year began before or with the harvest. This fluctuating and discontinuous year was not precise enough for the meticulous accounting of Sumerian scribes, who by 2400 BC already used the schematic year of 30 12 = 360 days.

At about the same time, the idea of a royal year took precise shape, beginning probably at the time of barley harvest, when the king celebrated the new (agricultural) year by offering first fruits to gods in expectation of their blessings for the year.

When, in the course of this year, some royal exploit (conquest, temple building, and so on) demonstrated that the fates had been fixed favourably by the celestial powers, the year was named accordingly; for example, as the year in which "the temple of Ningirsu was built." Until the naming, a year was described as that "following the year named (after such and such event)." The use of the date formulas was supplanted in Babylonia by the counting of regnal years in the 17th century BC.

The use of lunar reckoning began to prevail in the 21st century BC. The lunar year probably owed its success to economic progress. A barley loan could be measured out to the lender at the next year's threshing floor. The wider use of silver as the standard of value demanded more flexible payment terms. A man hiring a servant in the lunar month of Kislimu for a year knew that the engagement would end at the return of the same month, without counting days or periods of office between two dates.

At the city of Mari in about 1800 BC, the allocations were already reckoned on the basis of 29- and 30-day lunar months. In the 18th century BC, the Babylonian Empire standardized the year by adopting the lunar calendar of the Sumerian sacred city of Nippur. The power and the cultural prestige of Babylon assured the success of the lunar year, which began on Nisanu 1, in the spring. When, in the 17th century BC, the dating by regnal years became usual, the period between the accession day and the next Nisanu 1 was described as "the beginning of the kingship of PN," and the regnal years were counted from this Nisanu 1.

It was necessary for the lunar year of about 354 days to be brought into line with the solar (agricultural) year of approximately 365 days. This was accomplished by the use of an intercalated month. Thus, in the 21st century BC, a special name for the intercalated month iti dirig appears in the sources. The intercalation was operated haphazardly, according to real or imagined needs, and each Sumerian city inserted months at will; e.g., 11 months in 18 years or two months in the same year.

Later, the empires centralized the intercalation, and as late as 541 BC it was proclaimed by royal fiat. Improvements in astronomical knowledge eventually made possible the regularization of intercalation; and, under the Persian kings (c. 380 BC), Babylonian calendar calculators succeeded in computing an almost perfect equivalence in a lunisolar cycle of 19 years and 235 months with intercalations in the years 3, 6, 8, 11, 14, 17, and 19 of the cycle. The new year's day (Nisanu 1) now oscillated around the spring equinox within a period of 27 days.

The Babylonian month names were Nisanu, Ayaru, Simanu, Du'uzu, Abu, Ululu, Tashritu, Arakhsamna, Kislimu, Tebetu, Shabatu, Adaru. The month Adaru II was intercalated six times within the 19-year cycle but never in the year that was 17th of the cycle, when Ululu II was inserted. Thus, the Babylonian calendar until the end preserved a vestige of the original bipartition of the natural year into two seasons, just as the Babylonian months to the end remained truly lunar and began when the New Moon was first visible in the evening. The day began at sunset. Sundials and water clocks served to count hours.

The influence of the Babylonian calendar was seen in many continued customs and usages of its neighbor and vassal states long after the Babylonian Empire had been succeeded by others. In particular, the Jewish calendar in use at relatively late dates employed similar systems of intercalation of months, month names, and other details (see below The Jewish calendar). The Jewish adoption of Babylonian calendar customs dates from the period of the Babylonian Exile in the 6th century BC.

Assyrians and the Hittites

The Assyrians and the Hittites. Of the calendars of other peoples of the ancient Near East, very little is known. Thus, though the names of all or of some months are known, their order is not. The months were probably everywhere lunar, but evidence for intercalation is often lacking; for instance, in Assyria. For accounting, the Assyrians also used a kind of week, of five days, as it seems, identified by the name of an eponymous official.

Thus, a loan could be made and interest calculated for a number of weeks in advance and independently of the vagaries of the civil year. In the city of Ashur, the years bore the name of the official elected for the year; his eponym was known as the limmu. As late as about 1070 BC, his installation date was not fixed in the calendar. From about 1100 BC, however, Babylonian month names began to supplant Assyrian names, and, when Assyria became a world power, it used the Babylonian lunisolar calendar.

The calendar of the Hittite Empire is known even less well. As in Babylonia, the first Hittite month was that of first fruits, and, on its beginning, the gods determined the fates.


At about the time of the conquest of Babylonia in 539 BC, Persian kings made the Babylonian cyclic calendar standard throughout the Persian Empire, from the Indus to the Nile. Aramaic documents from Persian Egypt, for instance, bear Babylonian dates besides the Egyptian.

Similarly, the royal years were reckoned in Babylonian style, from Nisanu 1. It is probable, however, that at the court itself the counting of regnal years began with the accession day.

The Seleucids and, afterward, the Parthian rulers of Iran maintained the Babylonian calendar. The fiscal administration in northern Iran, from the 1st century BC, at least, used Zoroastrian month and day names in documents in Pahlavi (the Iranian language of Sasanian Persia).

The origin and history of the Zoroastrian calendar year of 12 months of 30 days, plus five days (that is, 365 days), remain unknown.

It became official under the Sasanian dynasty, from about AD 226 until the Arab conquest in 621.

The Arabs introduced the Muslim lunar year, but the Persians continued to use the Sasanian solar year, which in 1079 was made equal to the Julian year by the introduction of the leap year.

The Zoroastrian Calendar