|History of science and technology in China|
The traditional Chinese calendar (officially known as the Agricultural Calendar [農曆; 农历; Nónglì; ‘farming calendar’], Former Calendar [舊曆; 旧历; Jiùlì], Traditional Calendar [老曆; 老历; Lǎolì] or Yin Calendar [陰曆; 阴历; Yīnlì; ‘yin calendar’]), 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 in overseas Chinese communities. It also gives the traditional Chinese nomenclature of dates within a year which people use for selecting 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 this calendar are used in different parts of the East Asian cultural sphere. Korea, Vietnam, and the Ryukyu Islands adopted the calendar, and it evolved into Korean, Vietnamese, and Ryukyuan calendars. The main difference from the traditional Chinese calendar is the use of different meridians, 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 and end of each month. A sexagenary cycle consists of 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).
One version of the solar calendar is the five-elements calendar (五行曆; 五行历), 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 (行御), 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 (甲子) day (and a 72-day wood phase), followed by a bǐngzǐ day (丙子) and a 72-day fire phase; a wùzǐ (戊子) day and a 72-day earth phase; a gēngzǐ (庚子) day and a 72-day metal phase, and a rénzǐ day (壬子) followed by a water phase. Other days were tracked using the Yellow River Map (He Tu).
Another version is a four-quarters calendar (四時八節曆; 四时八节历; 'four sections, eight seasons calendar', or 四分曆; 四分历). 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 (調曆; 调历). 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 (c. 1600 – c. 1046 BC) was a balanced calendar with 12 to 14 months in a year; the month after the winter solstice was Zhēngyuè.
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(魯曆; 鲁历). Jin issued the Xia calendar (夏曆; 夏历) in AD 102, with a year beginning on the day of the new moon nearest the March equinox. Qin issued the Zhuanxu calendar (顓頊曆; 颛顼历), with a year beginning on the day of the new moon nearest the winter solstice. Song's Yin calendar (殷曆; 殷历) began its year on the day of the new moon after the winter solstice.
These calendars are known as the six ancient calendars (古六曆; 古六历), or quarter-remainder calendars, (四分曆; 四分历; sìfēnlì), since all calculate a year as 365+1⁄4 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.
After Qin Shi Huang unified China under the Qin dynasty in 221 BC, the Qin calendar (秦曆; 秦历) 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 (後九月; 后九月; 'later Jiǔyuè'), was placed at the end of the year. The Qin calendar was used going into the Han dynasty.
Emperor Wu of Han r. 141 – 87 BC introduced reforms halfway through his reign. His Taichu Calendar (太初曆; 太初历; 'grand beginning calendar') defined a solar year as 365+385⁄1539 days, and the lunar month was 29+43⁄81 days. Since the 19 years cycle used for the 7 additional months were 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 (大明曆; 大明历; 'brightest 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 (戊寅元曆; 戊寅元历; 'earth tiger epoch calendar'). The Yuan dynasty Shòushí calendar (授時曆; 授时历; 'season granting 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.
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.
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 "decides the month in sequence, except the intercalary month."[This quote needs a citation] The present traditional calendar follows the Shíxiàn calendar, except:
To optimize the Chinese calendar, astronomers have proposed a number of changes. Gao Pingzi (高平子; 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.
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.
Elements of the traditional Chinese calendar are:
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, (紫微), Supreme Palace (太微), and Heavenly Market. (天市) The eastern mansions are 角, 亢, 氐, 房, 心, 尾, 箕. Southern mansions are 井, 鬼, 柳, 星, 張, 翼, 轸. Western mansions are 奎, 婁, 胃, 昴, 畢, 參, 觜. Northern mansions are 斗, 牛, 女, 虛, 危, 室, 壁. 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 (袁天罡) matched the 28 mansions, seven luminaries and yearly animal signs to yield combinations such as "horn-wood-flood dragon" (角木蛟).
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, 時; 时 or shíchen (時辰; 时辰)) and climatic terms. The 12 characters progress from the first day with the same branch as the month (first Yín day (寅日) of Zhēngyuè; first Mǎo day (卯日) 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.
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.
As early as the Bronze-Age Xia dynasty, days were grouped into nine- or ten-day weeks known as xún (旬). Months consisted of three xún. The first 10 days were the early xún (上旬), the middle 10 the mid xún (中旬), and the last nine (or 10) days were the late xún (下旬). Japan adopted this pattern, with 10-day-weeks known as jun (旬). In Korea, they were known as sun (순,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 (澣; 浣, "wash").
Grouping days into sets of ten is still used today in referring to specific natural events. "Three Fu" (三伏), 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 (a Central Asian kingdom near Samarkand),[a][b] and is the most-used system in modern China.
Months are defined by the time between new moons, which averages approximately 29+17⁄32 days. There is no specified length of any particular Chinese month, so the first month could have 29 days (short month, 小月) in some years and 30 days (long month, 大月) in other years.
A 12-month-year using this system has 354 days, which would drift significantly from the tropical year. To fix this, traditional Chinese years have a 13-month year approximately once every three years. The 13-month version has the same alternation of long and short months, but adds a 30-day leap month (閏月; rùnyuè) at the end of the year. Years with 12 months are called common years, and 13-month years are known as long years.
Although most of the above rules were used until the Tang dynasty, different eras used different systems to keep lunar and solar years aligned. The synodic month of the Taichu calendar was 29+43⁄81 days long. The 7th-century, Tang-dynasty Wùyín Yuán Calendar was the first to determine month length by synodic month instead of the cycling method. Since then, month lengths have primarily been determined by observation and prediction.
The days of the month are always written with two characters and numbered beginning with 1. Days one to 10 are written with the day's numeral, preceded by the character Chū (初); Chūyī (初一) is the first day of the month, and Chūshí (初十) the 10th. Days 11 to 20 are written as regular Chinese numerals; Shíwǔ (十五) is the 15th day of the month, and Èrshí (二十) the 20th. Days 21 to 29 are written with the character Niàn (廿) before the characters one through nine; Niànsān (廿三), for example, is the 23rd day of the month. Day 30 (as applicable) is written as the numeral Sānshí (三十).
History books use days of the month numbered with the 60 stem-branches:
Tiānshèng 1st year....Èryuè....Dīngsì, the emperor's funeral was at his temple, and the imperial portrait was installed in Nanjing's Hongqing Palace.— History of Song Dynasty, Part 9, Volume 9: Renzong part 1 (in Chinese)
Because astronomical observation determines month length, dates on the calendar correspond to moon phases. The first day of each month is the new moon. On the seventh or eighth day of each month, the first-quarter moon is visible in the afternoon and early evening. On the 15th or 16th day of each month, the full moon is visible all night. On the 22nd or 23rd day of each month, the last-quarter moon is visible late at night and in the morning.
Since the beginning of the month is determined by when the new moon occurs, other countries using this calendar use their own time standards to calculate it; this results in deviations. The first new moon in 1968 was at 16:29 UTC on 29 January. Since North Vietnam used UTC+07:00 to calculate their Vietnamese calendar and South Vietnam used UTC+08:00 (Beijing time) to calculate theirs, North Vietnam began the Tết holiday at 29 January at 23:29 while South Vietnam began it on 30 January at 00:15. The time difference allowed asynchronous attacks in the Tet Offensive.
Lunar months were originally named according to natural phenomena. Current naming conventions use numbers as the month names. Every month is also associated with one of the twelve Earthly Branches.
|Month number||Starts on Gregorian date||Phenological name||Earthly Branch name||Modern name|
|1||between 21 January – 20 February *||陬月; zōuyuè; 'corner month'. square of Pegasus month||寅月; yínyuè; 'tiger month'||正月; zhēngyuè; 'first month'|
|2||between 20 February – 21 March *||杏月; xìngyuè; 'apricot month'||卯月; mǎoyuè; 'rabbit month'||二月; èryuè; 'second month'|
|3||between 21 March – 20 April *||桃月; táoyuè; 'peach month'||辰月; chényuè; 'dragon month'||三月; sānyuè; 'third month'|
|4||between 20 April – 21 May *||梅月; méiyuè; 'plum month'||巳月; sìyuè; 'snake month'||四月; sìyuè; 'fourth month'|
|5||between 21 May – 21 June *||榴月; liúyuè; 'pomegranate month'||午月; wǔyuè; 'horse month'||五月; wǔyuè; 'fifth month'|
|6||between 21 June – 23 July *||荷月; héyuè; 'lotus month'||未月; wèiyuè; 'goat month'||六月; liùyuè; 'sixth month'|
|7||between 23 July – 23 August *||蘭月; 兰月; lányuè; 'orchid month'||申月; shēnyuè; 'monkey month'||七月; qīyuè; 'seventh month'|
|8||between 23 August – 23 September *||桂月; guìyuè; 'osmanthus month'||酉月; yǒuyuè; 'rooster month'||八月; bāyuè; 'eighth month'|
|9||between 23 September – 23 October *||菊月; júyuè; 'chrysanthemum month'||戌月; xūyuè; 'dog month'||九月; jiǔyuè; 'ninth month'|
|10||between 23 October – 22 November *||露月; lùyuè; 'dew month'||亥月; hàiyuè; 'pig month'||十月; shíyuè; 'tenth month'|
|11||between 22 November – 22 December *||冬月; dōngyuè; 'winter month'; 葭月; jiāyuè; 'reed month'||子月; zǐyuè; 'rat month'||冬月; shíyīyuè; 'eleventh month'|
|12||between 22 December – 21 January *||冰月; bīngyuè; 'ice month'||丑月; chǒuyuè; 'ox month'||臘月; 腊月; làyuè; 'end-of-year month'|
Though the numbered month names are often used for the corresponding month number in the Gregorian calendar, it is important to realize that the numbered month names are not interchangeable with the Gregorian months when talking about lunar dates.
One may even find out the heavenly stem and earthly branch corresponding to a particular day in the month, and those corresponding to its month, and those to its year, to determine the Four Pillars of Destiny associated with it, for which the Tung Shing, also referred to as the Chinese Almanac of the year, or the Huangli, and containing the essential information concerning Chinese astrology, is the most convenient publication to consult. Days rotate through a sexagenary cycle marked by a coordination between heavenly stems and earthly branches, hence the referral to the Four Pillars of Destiny as, "Bazi", or "Birth Time Eight Characters", with each pillar consisting of a character for its corresponding heavenly stem, and another for its earthly branch. Since Huangli days are sexagenaric, their order is quite independent from their numeric order in each month, and from their numeric order within a week (referred to as True Animals with relation to the Chinese zodiac). Therefore, it does require painstaking calculation for one to arrive at the Four Pillars of Destiny of a particular given date, which rarely outpace the convenience of simply consulting the Huangli by looking up its Gregorian date.
The solar year (歲; 岁; Suì), the time between winter solstices, is divided into 24 solar terms known as jié qì (節氣). Each term is a 15° portion of the ecliptic. These solar terms mark both Western and Chinese seasons, as well as equinoxes, solstices, and other Chinese events. The even solar terms (marked with "Z", for Chinese: 中氣) are considered the major terms, while the odd solar terms (marked with "J", for Chinese: 節氣) are deemed minor. The solar terms qīng míng (清明) on 5 April and dōng zhì (冬至) on 22 December are both celebrated events in China.
|Number||Name||Chinese marker||Event||Approximate Date|
|J1||Lì chūn||立春||Beginning of spring||4 February|
|Z1||Yǔ shuǐ||雨水||Rain water||19 February|
|J2||Jīng zhé||驚蟄；惊蛰||Waking of insects||6 March|
|Z2||Chūn fēn||春分||March equinox||21 March|
|J3||Qīng míng||清明||Pure brightness||5 April|
|Z3||Gǔ yǔ||穀雨；谷雨||Grain rain||20 April|
|J4||Lì xià||立夏||Beginning of summer||6 May|
|Z4||Xiǎo mǎn||小滿；小满||Grain full||21 May|
|J5||Máng zhòng||芒種；芒种||Grain in ear||6 June|
|Z5||Xià zhì||夏至||June solstice||22 June|
|J6||Xiǎo shǔ||小暑||Slight heat||7 July|
|Z6||Dà shǔ||大暑||Great heat||23 July|
|J7||Lì qiū||立秋||Beginning of autumn||8 August|
|Z7||Chǔ shǔ||處暑；处署||Limit of heat||23 August|
|J8||Bái lù||白露||White dew||8 September|
|Z8||Qiū fēn||秋分||September equinox||23 September|
|J9||Hán lù||寒露||Cold dew||8 October|
|Z9||Shuāng jiàng||霜降||Descent of frost||24 October|
|J10||Lì dōng||立冬||Beginning of winter||8 November|
|Z10||Xiǎo xuě||小雪||Slight snow||22 November|
|J11||Dà xuě||大雪||Great snow||7 December|
|Z11||Dōng zhì||冬至||December solstice||22 December|
|J12||Xiǎo hán||小寒||Slight cold||6 January|
|Z12||Dà hán||大寒||Great cold||20 January|
The calendar solar year, known as the suì, (歲; 岁) begins at the December solstice and proceeds through the 24 solar terms. Due to the fact that the speed of the Sun's apparent motion in the elliptical is variable, the time between major solar terms is not fixed. This variation in time between major solar terms results in different solar year lengths. There are generally 11 or 12 complete months, plus two incomplete months around the winter solstice, in a solar year. The complete months are numbered from 0 to 10, and the incomplete months are considered the 11th month. If there are 12 complete months in the solar year, it is known as a leap solar year, or leap suì.
Due to the inconsistencies in the length of the solar year, different versions of the traditional calendar might have different average solar year lengths. For example, one solar year of the 1st century BC Tàichū calendar is 365+385⁄1539 (365.25016) days. A solar year of the 13th-century Shòushí calendar is 365+97⁄400 (365.2425) days, identical to the Gregorian calendar. The additional .00766 day from the Tàichū calendar leads to a one-day shift every 130.5 years.
Pairs of solar terms are climate terms, or solar months. The first solar term is "pre-climate" (節氣; 节气; Jiéqì), and the second is "mid-climate" (中氣; 中气; Zhōngqì).
The first month without a mid-climate is the leap, or intercalary, month. In other words, the first month that doesn't include a major solar term is the leap month. Leap months are numbered with rùn 閏, the character for "intercalary", plus the name of the month they follow. In 2017, the intercalary month after month six was called Rùn Liùyuè, or "intercalary sixth month" (閏六月) and written as 6i or 6+. The next intercalary month (in 2020, after month four) will be called Rùn Sìyuè (閏四月) and written 4i or 4+.
The lunisolar year begins with the first spring month, Zhēngyuè (正月; 'capital month'), and ends with the last winter month, Làyuè (臘月; 腊月; 'sacrificial month'). All other months are named for their number in the month order. If a leap month falls after month 11—as it will in 2033—the 11th month will be Shíèryuè (十二月; 'twelfth month'), and the leap month will be Làyuè.
Years were traditionally numbered by the reign in ancient China, but this was abolished after the founding of the People's Republic of China in 1949. For example, the year from 8 February 2016 to 27 January 2017 was a Bǐngshēn year (丙申年) of 12 months or 354 days .
In China, a person's official age is based on the Gregorian calendar. For traditional use, age is based on the Chinese Sui calendar. 100 days after birth, a child is considered one year old,(9 months gestation plus 3) using ordinal numerals (instead of "zero" using cardinal numerals); after each Chinese New Year, one year is added to their traditional age. That is, age is the number of Chinese years in which they have lived. Because of the potential for confusion, infant ages are often given in months instead of years.
After the Gregorian calendar's introduction in China, the Chinese traditional-age was referred to as the "nominal age" (虛歲; 虚岁; xūsuì; 'incomplete age') and the Gregorian age was known as the "real age" (實歲; 实岁; shísùi; 'whole age').
In ancient China, years were numbered from a new emperor's assumption of the throne or an existing emperor's announcement of a new era name. The first recorded reign title was Jiànyuán (建元), from 140 BC; the last reign title was Xuāntǒng (宣統; 宣统), from AD 1908. The era system was abolished in 1912, after which the current or Republican era was used.
The 60 stem-branches have been used to mark the date since the Shang dynasty (1600–1046 BC). Astrologers knew that the orbital period of Jupiter is about 4,332 days. Since 4332 is 12 × 361, Jupiter's orbital period was divided into 12 years (歲; 岁; suì) of 361 days each. The stem-branches system solved the era system's problem of unequal reign lengths.
Nomenclature similar to that of the Christian era has occasionally been used:
No reference date is universally accepted. The most popular is the Gregorian calendar (公曆; 公历; gōnglì; 'common calendar').
On 2 January 1912, Sun Yat-sen announced changes to the official calendar and era. 1 January was 14 Shíyīyuè 4609 Huángdì year, assuming a year 1 of 2698 BC, which makes 4719 at 2021 AD. The change was adopted by many overseas Chinese communities, such as San Francisco's Chinatown.
During the 17th century, the Jesuits tried to determine the epochal year of the Han calendar. In his Sinicae historiae decas prima (published in Munich in 1658), Martino Martini (1614–1661) dated the ascension of the Yellow Emperor to 2697 BC and began the Chinese calendar with the reign of Fuxi (which, according to Martini, began in 2952 BC. Philippe Couplet's 1686 Chronological table of Chinese monarchs (Tabula chronologica monarchiae sinicae) gave the same date for the Yellow Emperor. The Jesuits' dates provoked interest in Europe, where they were used for comparison with Biblical chronology. Modern Chinese chronology has generally accepted Martini's dates, except that it usually places the reign of the Yellow Emperor at 2698 BC and omits his predecessors Fuxi and Shennong as "too legendary to include".[This quote needs a citation]
Publications began using the estimated birth date of the Yellow Emperor as the first year of the Han calendar in 1903, with newspapers and magazines proposing different dates. The province of Jiangsu counted 1905 as the year 4396 (using a year 1 of 2491 BC, and implying that 4512 is 2021 AD), and the newspaper Ming Pao (明報) reckoned 1905 as 4603 (using a year 1 of 2698 BC, and implying that 4719 is 2021 AD). Liu Shipei (劉師培, 1884–1919) created the Yellow Emperor Calendar, with year 1 as the birth of the emperor (which he determined as 2711 BC, implying that 4732 is 2021 AD). There is no evidence that this calendar was used before the 20th century. Liu calculated that the 1900 international expedition sent by the Eight-Nation Alliance to suppress the Boxer Rebellion entered Beijing in the 4611th year of the Yellow Emperor.
The date of the Chinese New Year accords with the patterns of the lunisolar calendar and hence is variable from year to year. However, two general rules govern the date. Firstly, Chinese New Year transpires on the second new moon following the December solstice. If there is a leap month after the eleventh or twelfth month, then Chinese New Year falls on the third new moon after the December solstice. Alternatively, Chinese New Year will fall on the new moon that is closest to lì chūn, or the solar term that begins spring (typically falls on 4 February). However, this rule is not as reliable since it can be difficult to determine which new moon is the closest in the case of an early or late Chinese New Year.
It has been found that Chinese New Year moves back by either 10, 11, or 12 days in some years. If it falls before 21 January, then it moves forward in the next year by either 18, 19, or 20 days.
The plum-rains season (梅雨), the rainy season in late spring and early summer, begins on the first bǐng day after Mangzhong (芒種) and ends on the first wèi day after Xiaoshu (小暑). The Three Fu (三伏; sānfú) are three periods of hot weather, counted from the first gēng day after the summer solstice. The first fu (初伏; chūfú) is 10 days long. The mid-fu (中伏; zhōngfú) is 10 or 20 days long. The last fu (末伏; mòfú) is 10 days from the first gēng day after the beginning of autumn. The Shujiu cold days (數九; shǔjǐu; 'counting to nine') are the 81 days after the winter solstice (divided into nine sets of nine days), and are considered the coldest days of the year. Each nine-day unit is known by its order in the set, followed by "nine" (九).
There are several traditional and religious holidays shared by communities throughout the world that use the Chinese (Lunisolar) calendar:
The Chinese New Year (known as the Spring Festival/春節 in China) is on the first day of the first month and was traditionally called the Yuan Dan (元旦) or Zheng Ri (正日). In Vietnam it is known as Tết Nguyên Đán (節元旦) and in Korea it is known as 설날. Traditionally it was the most important holiday of the year. It is an official holiday in China, Hong Kong, Macau, Taiwan, Vietnam, Korea, the Philippines, Malaysia, Singapore, and Indonesia. It is also a public holiday in Thailand's Narathiwat, Pattani, Yala, and Satun provinces and is an official public school holiday in New York City.
The Double Third Festival is on the third day of the third month and in Korea is known as 삼짇날 (samjinnal).
The Dragon Boat Festival, or the Duanwu Festival (端午節), is on the fifth day of the fifth month and is an official holiday in China, Hong Kong, Macau, and Taiwan. It is also celebrated in Vietnam where it is known as Tết Đoan Ngọ (節端午) and in Korea where it is known as 단오 (端午) (Dano) or 수릿날 (戌衣日/水瀨日) (surinal) (both Hanja are used as they are homonyms).
The Qixi Festival (七夕節) is celebrated in the evening of the seventh day of the seventh month. It is also celebrated in Vietnam where it is known as Thất tịch (七夕) and in Korea where is known as 칠석 (七夕) (chilseok).
The Double Ninth Festival (重陽節) is celebrated on the ninth day of the ninth month. It is also celebrated in Vietnam where it is known as Tết Trùng Cửu (節重九) and in Korea where it is known as 중양절 (jungyangjeol).
The Lantern Festival is celebrated on the fifteenth day of the first month and was traditionally called the Yuan Xiao (元宵) or Shang Yuan Festival (上元節). In Vietnam it is known as Tết Thượng Nguyên (節上元) and in Korea it is known as 대보름 (大보름) Daeboreum (or the Great Full Month).
The Zhong Yuan Festival is celebrated on the fifteenth day of the seventh month. In Vietnam, it is celebrated as Tết Trung Nguyên (中元節) or Lễ Vu Lan (禮盂蘭) and in Korea it is known as 백중 (百中/百種) Baekjong or 망혼일 (亡魂日) Manghongil (Deceased Spirit Day) or 중원 (中元) Jungwon.
The Mid-Autumn Festival is celebrated on the fifteenth day of the eighth month. In Vietnam, it is celebrated as Tết Trung Thu (節中秋) and in Korea it is known as 추석 (秋夕) Chuseok.
The Xia Yuan Festival is celebrated on the fifteenth day of the tenth month. In Vietnam, it is celebrated as Tết Hạ Nguyên (節下元).
The Laba Festival is on the eighth day of the twelfth month. It is the enlightenment day of Sakyamuni Buddha and is celebrated in Korea as 성도재일 (seongdojaeil) and in Vietnam is known as Lễ Vía Phật Thích Ca Thành Đạo.
The Kitchen God Festival is celebrated on the twenty-third day of the twelfth month in northern regions of China or on the twenty-fourth day of the twelfth month in southern regions of China. In Vietnam it is known as Tết Táo Quân (節竈君).
Chinese New Year's Eve is also known as the Chuxi Festival and is celebrated on the evening of the last day of the lunar calendar. It is celebrated wherever the lunar calendar is observed.
Many of the above holidays were celebrated in pre-Meiji Japan based on the lunar calendar, but are now celebrated based on the Gregorian calendar.
In the case where there is a corresponding intercalary month, the holidays may be celebrated twice. For example, in the hypothetical situation where there is an additional intercalary seventh month, the Zhong Yuan Festival will be celebrated on the seventh month followed by another celebration on the intercalary seventh month.