Chinese Lunar Calendar

The Chinese calendar is based on exact astronomical observations of the longitude of the sun and the phases of the moon. This means that the principles of modern science have had an impact on the Chinese calendar.

The Chinese Lunar New Year is the longest chronological record in history, dating from 2600BC, when the Emperor Huangti (the Yellow Emperor) introduced the first cycle of thezodiac. Like the Western calendar, theChinese Lunar Calendaris a yearly one, with the start of the lunar year being based on the cycles of the moon. Therefore, because of this cyclical dating, the beginning of the year can fall anywhere between late January and the middle of February. This year it falls on February 12. A complete cycle takes 60 years and is made up of five cycles of 12 years each.

The Chinese Lunar Calendar names each of the twelve years after an animal. Legend has it that the Lord Buddha summoned all the animals to come to him before he departed from Earth. Only 12 came to bid him farewell and as a reward he named a year after each one in the order they arrived. The Chinese believe the animal ruling the year in which a person is born has a profound influence on personality, saying: "This is the animal that hides in your heart."

 The Chinese year

The Chinese calendar is a combined solar/lunar calendar which strives to have each year coincide with the tropical year and each month coincide with the synodic month. It is not surprising that a few similarities exist between the Chinese and the Hebrew calendars:

An ordinary year has 12 months and a leap year has 13 months. An ordinary year has 353, 354, or 355 days, a leap year has 383, 384, or 385 days.

When determining what a Chinese year looks like, a number of astronomical calculations need to be made:

Firstly, the dates for the new moons must be determined. In the lunar calendar a new moon is a completely "black" moon (when the moon is in conjunction with the sun), not the first visible crescent that used in the Islamic and Hebrew calendars. The date of a new moon is the first day of a new month.

Secondly, the dates when the sun's longitude is a multiple of 30 degrees must be determined. (The sun's longitude is 0 at Vernal Equinox, 90 at Summer Solst, , ice, 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 which case the numbers of the months 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 Chinese communities follow variations on the rules.

To determine if a year is a leap year, the number of new moons between the 11th month of one year (i.e., the month containing the Winter Solstice) and the 11th month of the following year is calculated. If there are 13 new moons 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.

 Early Chinese calendars

Evidence from the Shang (c. 1600-1100 BC) oracle bone inscriptions shows that by at least the 14th century BC the Shang Chinese had established the solar year with 365 and 1/4 days as well as the lunar version with 29 and 1/2 days. In the calendar used by the Shang, the seasons of the year and the phases of the Moon appear to all be accounted for.

In China, the calendar was a sacred document, sponsored and circulated by the reigning monarch. For more than two millennia, a Bureau of Astronomy made astronomical observations, calculated astronomical events such as eclipses, prepared astrological predictions, and maintained the calendar. This practice was very important as a successful calendar not only served practical needs, but also confirmed the consonance between Heaven and the imperial court.

 Analysis of surviving astronomical records inscribed on oracle bones reveals a Chinese lunisolar calendar, with intercalation of lunar months, dating back to theShang Dynastyof the fourteenth century BC. Various intercalation schemes were developed for the early calendars, including the nineteen-year and 76-year lunar phase cycles that came to be known in the West as the Metonic cycle and Callipic cycle.

From the earliest records, the beginning of the year occurred near the winter solstice when a New Moon appeared, but the choice of month for the beginning of the civil year varied with time and place. In the late second century BC, a calendar reform established the practice, which continues today, of requiring the winter solstice to occur in the 11th month. This reform also introduced the intercalation system in which the dates of the New Moons are compared with the 24 solar terms. However, calculations were based on the mean motions resulting from the cyclic relationships. Inequalities in the Moon's motions were incorporated as early as the seventh century AD, but the Sun's mean longitude was used to calculate the solar terms until 1644.

Years were counted from a succession of eras established by reigning emperors. Although the accession of an emperor would mark a new era, an emperor might also declare a new era at various times within his reign. The introduction of a new era was an attempt to reestablish a broken connection between Heaven and Earth, as personified by the emperor. The break might be revealed by the death of an emperor, the occurrence of a natural disaster, or the failure of astronomers to predict a celestial event such as an eclipse. In the latter case, a new era might mark the introduction of new astronomical or calendar models.

Sixty-year cycles were used to count years, months, days, and fractions of a day using the set of Celestial Stems and Terrestrial Branches. While the use of the sixty-day cycle can be seen as far back as the earliest astronomical records, the sixty-year cycle was introduced in the first century AD or possibly a century earlier. Although the practice of counting the days according to the lunar calendar has fallen into disuse in everyday life, it is still tabulated in calendars. The initial year of the current year cycle began on February 2, 1984, which is the third day of the day cycle.