Taichu calendar

The traditional Chinese calendar (also known as the Agricultural Calendar ��曆; 农历; ''Nónglì''; 'farming calendar' Former Calendar ��曆; 旧历; ''Jiùlì'' Traditional Calendar ��曆; 老历; ''Lǎolì'', is a lunisolar calendar which identifies years, months, and days according to astronomical phenomena. In China, it is defined by the Chinese national standard GB/T 33661–2017, "Calculation and Promulgation of the Chinese Calendar", issued by the Standardization Administration of China on May 12, 2017.

Although modern-day China uses the Gregorian calendar, the traditional Chinese calendar governs holidays, such as the Chinese New Year and Lantern Festival, in both China and overseas Chinese communities. It also provides the traditional Chinese nomenclature of dates within a year which people use to select auspicious days for weddings, funerals, moving or starting a business. The evening state-run news program '' Xinwen Lianbo'' in the P.R.C. continues to announce the months and dates in both the Gregorian and the traditional lunisolar calendar.

Like Chinese characters, variants of Chinese calendar were used in different parts of the Sinosphere throughout history. Korea, Vietnam, and the Ryukyu Islands adopted the Chinese calendar, and evolved it into Korean, Vietnamese, and Ryukyuan calendars, with the main difference from the Chinese calendar being the use of different meridians due to geography, which leads to some astronomical events — and calendar events based on them — falling on different dates. The traditional Japanese calendar was also derived from the Chinese calendar (based on a Japanese meridian), but its official use in Japan was abolished in 1873 due to reforms after the Meiji Restoration. Calendars in Mongolia and Tibet have absorbed elements of the traditional Chinese calendar but are not direct descendants of it.

Days begin and end at midnight, and months begin on the day of the new moon. Years start on the second (or third) new moon after the winter solstice. Solar terms govern the beginning, middle, and end of each month. A sexagenary cycle, comprising stems (干, ''gān'') and branches (支, ''zhī''), is used as identification alongside each year and month; including intercalary months or leap months. The length of a month is also annotated as either long (大, literally "big" for months with 30 days) or short (小, literally "small" for months with 29 days).

History

Solar calendars

The traditional Chinese calendar was developed between 771 and 476 BCE, during the Spring and Autumn period of the Eastern Zhou dynasty. Solar calendars were used before the Zhou dynasty period.

One version of the solar calendar is the five-elements calendar (), which derives from the Wu Xing. A 365-day year was divided into five phases of 73 days, with each phase corresponding to a Day 1 Wu Xing element. A phase began with a governing-element day (), followed by six 12-day weeks. Each phase consisted of two three-week months, making each year ten months long. Years began on a ''jiǎzǐ'' () day (and a 72-day wood phase), followed by a ''bǐngzǐ'' day () and a 72-day fire phase; a ''wùzǐ'' () day and a 72-day earth phase; a ''gēngzǐ'' () day and a 72-day metal phase, and a ''rénzǐ'' day () followed by a water phase. Other days were tracked using the Yellow River Map (''He Tu'').

Another version is a four-quarters calendar (, or ). The weeks were ten days long, with one month consisting of three weeks. A year had 12 months, with a ten-day week intercalated in summer as needed to keep up with the tropical year. The 10 Heavenly Stems and 12 Earthly Branches were used to mark days.

A third version is the balanced calendar (). A year was 365.25 days, and a month was 29.5 days. After every 16th month, a half-month was intercalated. According to oracle bone records, the Shang dynasty calendar ( BCE) was a balanced calendar with 12 to 14 months in a year; the month after the winter solstice was ''Zhēngyuè''.

Lunisolar calendars

The first lunisolar calendar was the Zhou calendar (), introduced under the Zhou dynasty. This calendar sets the beginning of the year at the day of the new moon before the winter solstice.

Several competing lunisolar calendars were also introduced, especially by states fighting Zhou control during the Warring States period. The state of Lu issued its own Lu calendar(). Jin issued the Xia calendar () in AD 102, with a year beginning on the day of the new moon nearest the March equinox. Qin issued the Zhuanxu calendar (), with a year beginning on the day of the new moon nearest the winter solstice. Song's Yin calendar () began its year on the day of the new moon after the winter solstice.

These calendars are known as the six ancient calendars (), or quarter-remainder calendars, (), since all calculate a year as days long. Months begin on the day of the new moon, and a year has 12 or 13 months. Intercalary months (a 13th month) are added to the end of the year. The Qiang and Dai calendars are modern versions of the Zhuanxu calendar, used by mountain peoples.

Qin and early Han dynasties

After Qin Shi Huang unified China under the Qin dynasty in 221 BCE, the Qin calendar () was introduced. It followed most of the rules governing the Zhuanxu calendar, but the month order was that of the Xia calendar; the year began with month 10 and ended with month 9, analogous to a Gregorian calendar beginning in October and ending in September. The intercalary month, known as the second ''Jiǔyuè'' (), was placed at the end of the year. The Qin calendar was used going into the Han dynasty.

Han-Ming dynasties and Taichu calendar

Emperor Wu of Han introduced reforms halfway through his reign. His Taichu Calendar () defined a solar year as days, and the lunar month had days.
Since $\left(365+\frac\right)\times19=\left(29+\frac\right)\times \left(19\times 12 + 7 \right)$ the 19 years cycle used for the 7 additional months was taken as an exact one, and not as an approximation.

This calendar introduced the 24 solar terms, dividing the year into 24 equal parts. Solar terms were paired, with the 12 combined periods known as climate terms.

The Taichu calendar established a framework for traditional calendars, with later calendars adding to the basic formula. The Dàmíng Calendar (), created in the Liang dynasty by Zu Chongzhi, introduced the equinoxes. The use of a syzygy to determine the lunar month was first described in the Tang dynasty Wùyín Yuán Calendar (). The Yuan dynasty Shòushí calendar () used spherical trigonometry to find the length of the tropical year. The calendar had a 365.2425-day year, identical to the Gregorian calendar.

Modern calendars

Although the Chinese calendar lost its place as the country's official calendar at the beginning of the 20th century, its use has continued. Some calendars followed the last calendar of the Qing dynasty, published in 1908. This caused confusion regarding the date of the 1978 Mid-Autumn Festival, and those areas then switched to the UTC+8-based calendar.

Shíxiàn calendar

During the late Ming dynasty, Xu Guangqi and his colleagues worked out a new calendar based on Western astronomical arithmetic; however, the new calendar was not released before the end of the dynasty. In the early Qing dynasty, Johann Adam Schall von Bell submitted the calendar to the Shunzhi Emperor. The Qing government issued it as the Shíxiàn (seasonal) calendar.

In this calendar, the solar terms are 15° each along the ecliptic and it can be used as a solar calendar. However, the length of the climate term near the perihelion is less than 30 days and there may be two mid-climate terms. The Shíxiàn calendar changed the mid-climate-term rule to "decide the month in sequence, except the intercalary month." The present traditional calendar follows the Shíxiàn calendar, except:
# The baseline is Chinese Standard Time, rather than Beijing local time.
# Astronomical data, rather than mathematical calculations, is used.

Proposals

To optimize the Chinese calendar, astronomers have proposed a number of changes. Gao Pingzi (; 1888–1970), a Chinese astronomer who co-founded the Purple Mountain Observatory, proposed that month numbers be calculated before the new moon and solar terms to be rounded to the day. Since the intercalary month is determined by the first month without a mid-climate and the mid-climate time varies by time zone, countries that adopted the calendar but calculate with their own time could vary from the time in China.

Outlying areas

Calendars of ethnic groups in the mountains and plateaus of southwestern China and the grasslands of northern China are based on their phenology and algorithms of traditional calendars of different periods, particularly the Tang and pre-Qin dynasties.

Structure

Elements

Elements of the traditional Chinese calendar are:
* ''Day'', from one midnight to the next
* ''Month'', the time from one new moon to the next. These synodic months are about days long.
* ''Date'', when a day occurs in the month. Days are numbered in sequence from 1 to 29 (or 30).
* ''Year'', the time of one revolution of the earth around the sun. It is measured from the first day of spring (lunisolar year) or the winter solstice (solar year). A year is about days.
* '' Zodiac'', year, or 30° on the ecliptic. A zodiac is about days.
*'' Solar term'', year, or 15° on the ecliptic. A solar term is about days.
* ''Calendar month'', when a month occurs within a year. Some months may be repeated.
* ''Calendar year'', when it is agreed that one year ends and another begins. The year begins on the first day of spring, defined as the second (sometimes third) new moon after the winter solstice. A calendar year is 353–355 or 383–385 days long.

The Chinese calendar is lunisolar, similar to the Hindu, Hebrew and ancient Babylonian calendars.

Features

The movement of the sun, moon, Mercury, Venus, Mars, Jupiter and Saturn (known as the seven luminaries) are the references for calendar calculations.
* The distance between Mercury and the sun is less than 30° (the sun's height at ''chénshí'':, 8:00 to 10:00 am), so Mercury was sometimes called the "chen star" (); it is more commonly known as the "water star" ().
* Venus appears at dawn and dusk and is known as the "bright star" () or "long star" ().
* Mars looks like fire and occurs irregularly, and is known as the "fire star" ( or ). Mars is the punisher in Chinese mythology. When Mars is near Antares (), it is a bad omen and can forecast the death of an emperor or removal of a chancellor ().
* The period of Jupiter's revolution is 11.86 years, so Jupiter is called the "age star" (); 30° of Jupiter's revolution is about a year on earth.
* The period of Saturn's revolution is about 28 years. Known as the "guard star" (), Saturn guards one of the 28 Mansions every year.

The Big Dipper is the celestial compass, and its handle's direction determines the season and month.
The stars are divided into Three Enclosures and 28 Mansions according to their location in the sky relative to Ursa Minor, at the center. Each mansion is named with a character describing the shape of its principal asterism. The Three Enclosures are Purple Forbidden, (), Supreme Palace (), and Heavenly Market. () The eastern mansions are , , , , , , . Southern mansions are , , , , , , . Western mansions are , , , , , , . Northern mansions are , , , , , , .
The moon moves through about one lunar mansion per day, so the 28 mansions were also used to count days. In the Tang dynasty, Yuan Tiangang () matched the 28 mansions, seven luminaries and yearly animal signs to yield combinations such as "horn-wood-flood dragon" ().

Codes

Several coding systems are used to avoid ambiguity. The Heavenly Stems is a decimal system. The Earthly Branches, a duodecimal system, mark dual hours (''shí'', or ''shíchen'' ()) and climatic terms. The 12 characters progress from the first day with the same branch as the month (first ''Yín'' day () of ''Zhēngyuè''; first ''Mǎo'' day () of ''Èryuè''), and count the days of the month.

The stem-branches is a sexagesimal system. The Heavenly Stems and Earthly Branches make up 60 stem-branches. The stem branches mark days and years. The five elements of the Wu Xing are assigned to each of the stems, branches, and stem branches.

Day

China has used the Western hour-minute-second system to divide the day since the Qing dynasty. Several era-dependent systems had been in use; systems using multiples of twelve and ten were popular, since they could be easily counted and aligned with the Heavenly Stems and Earthly Branches.

Week

As early as the Bronze-Age Xia dynasty, days were grouped into nine- or ten-day weeks known as ''xún'' (). Months consisted of three ''xún''. The first 10 days were the ''early xún'' (), the middle 10 the ''mid xún'' (), and the last nine (or 10) days were the ''late xún'' (). Japan adopted this pattern, with 10-day-weeks known as . In Korea, they were known as ''sun'' ( ko, label=none, 순, ko, label=none, 旬).

The structure of ''xún'' led to public holidays every five or ten days. During the Han dynasty, officials were legally required to rest every five days (twice a ''xún'', or 5–6 times a month). The name of these breaks became ''huan'' (, "wash").

Grouping days into sets of ten is still used today in referring to specific natural events. "Three Fu" (), a 29–30-day period which is the hottest of the year, reflects its three-''xún'' length. After the winter solstice, nine sets of nine days were counted to calculate the end of winter.

The seven-day week was adopted from the Hellenistic system by the 4th century CE, although its source is unclear. It was again transmitted to China in the 8th century by Manichaeans via Kangju

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