What is the lunar calendar?

[Explanation] 1. A Chinese calendar is a type of lunisolar calendar, generally called the lunar calendar. There are twelve months in an ordinary year, the big month has thirty days, the small month has twenty-nine days, and the whole year has 354 or 355 days (which month is bigger and which month is smaller in a year varies from year to year). Since the average number of days per year is about eleven days less than that of a solar year, seven leap months are set in nineteen years. The year with a leap month has 383 or 384 days in the year. According to the position of the sun, a solar year is divided into twenty-four solar terms to facilitate farming. The chronology is based on the combination of heavenly stems and earthly branches, and the sixty-year cycle begins again and again. This calendar is said to have been created in the Xia Dynasty, so it is also called the Xia calendar. Also called the old calendar.

2. Almanac used in agriculture.

That is the lunar calendar. (The reason why the term "Lunar Calendar" became popular: Due to the proliferation of ultra-left ideological trends during the Cultural Revolution and the "sweeping of the Four Olds", it was believed that the "Xia Calendar" was the mark of the Xia Dynasty and must be renamed; because the traditional calendar was more commonly used in rural areas, it was adopted through newspapers Change of name to "Lunar Calendar": On New Year's Day in 1968, the name of "Xia Calendar" was changed to "Lunar Calendar" in the headlines of newspapers across the country overnight.

Note: The so-called "Lunar Calendar" refers to its significance in guiding agricultural production. But in fact, the lunar month and day are significantly different from the seasonal changes, and the effect of guiding the agricultural season is not good. In ancient my country, what really guided the agricultural season was the "twenty-four Qi", which is actually a special "Gregorian calendar")

The length of the lunar calendar month is based on the synodic month. The big month has 30 days and the small month has 29 days. The big month and the small month complement each other, making the average length of the calendar month close to the synodic month.

The lunar calendar always regards the day of the new moon as the first day of the month - the first day of the month. The so-called "Suo", from an astronomical point of view, has a certain moment, that is, the moment when the celestial longitude of the moon and the celestial longitude of the sun are the same. (The calculation of the ecliptic longitude of the sun and moon is very cumbersome and complicated, so it will not be introduced here)

As for the basis for determining the names of the months in the lunar calendar, it is determined by the "Zhongqi". That is, the month containing "rain" is January; the month containing "vernal equinox" is February; the month containing "grain rain" is March; the month containing "xiaoman" is April; the month containing "summer solstice" is The month containing "Great Heat" is June; the month containing "End Heat" is July; the month containing "Autumnal Equinox" is August; the month containing "Frost" is September; The month containing "light snow" is October; the month containing "winter solstice" is November; the month containing "heavy snow" is December. (The month that does not include the middle energy is regarded as the leap month of the previous month)

The length of the lunar calendar year is based on the tropical year, but a tropical year has more days than 12 synodic months, but shorter than 13 synodic months. When ancient astronomers compiled the lunar calendar, in order to make every day of the month contain the meaning of the moon phase, that is, the first day of the month is a moonless night, and the fifteenth day or so is a full moon, they mainly focus on the synodic moon, while taking into account the seasons. , using the method of seven leap years in nineteen years: in the nineteen years of the lunar calendar, there are twelve ordinary years, which are twelve months in an ordinary year; there are seven leap years, and each leap year is thirteen months.

Why adopt the method of "seven leaps in nineteen years"? The average synodic month is 29.5306 days, and there are 12.368 synodic months in a tropical year. The asymptotic fractions of the decimal part of 0.368 are 1/2, 1/3, 3/8, 4/11, 7/19, 46/125, that is, every two years Add a leap month, or add one leap month every three years, or add three leap months every eight years... After calculation, it is more appropriate to add seven leap months in nineteen years. Because nineteen tropical years = 6939.6018 days, and nineteen lunar years (after adding seven leap months) have 235 synodic months, which is equal to 6939.6910 days, so the two are almost the same.

The arrangement of seven leap months into nineteen years is very particular. The placement of leap months in the lunar calendar has been completely man-made since ancient times, and the placement of leap months in the past dynasties has also been different. Before the Qin Dynasty, the leap month was placed at the end of the year and was called "Twelve Months". In the early Han Dynasty, the leap month was placed after September, which was called "Later September". In the first year of Taichu, Emperor Wu of the Han Dynasty, leap months were inserted into each month of the year. Later, it was stipulated that "the month excluding Zhongqi is regarded as the leap month of the previous month", and this rule is still used until now.

Why do some months have no Qi? The average time between a solar term and a solar term or between a middle gas and a middle gas is 30.4368 days (that is, 65.2422 days in a tropical year are equally divided into 12 equal parts), and the average time of a synodic month is 29.5306 days, so the dates of the solar terms or the middle gas in the lunar month are successively The months pass later, and at a certain point, the middle Qi is no longer in the middle of the month, but moves to the end of the month, and the next middle Qi moves to the beginning of another month. In this way, there is no middle Qi in the middle month, but only one solar term.

As mentioned above, when the ancients compiled the lunar calendar, they used the twelve middle Qi as the symbols of the twelve months, that is, rain is the symbol of the first month, the vernal equinox is the symbol of February, and Grain Rain is the symbol of March. Symbol... Taking the month without Zhong Qi as a leap month makes the calendar month names correspond to Zhong Qi one-to-one, thereby maintaining the original Zhong Qi symbol.

From the seven leap years of the nineteenth year, there are 228 solar terms and 228 middle solar terms in the nineteen tropical years. There are 235 synodic months in the nineteenth year of the lunar calendar. Obviously, there are seven months without solar terms. There is no middle Qi in seven months, so it is natural to designate the month without middle Qi as a leap month.

The size of the lunar months is very irregular. Sometimes there are two, three, four big months in a row or two or three small months in a row. The length of the calendar years is also different, and the gap is huge. The distribution dates of solar terms and middle periods in the lunar calendar are very unstable, and the range of date changes is large. From this point of view, the lunar calendar seems very complicated. actually. The lunar calendar still has a certain cycle: since the number of days in the nineteen tropical years is almost equal to the number of days in the nineteen lunar years, the lunar calendar is almost the same every nineteen years. Every nineteen years, the solar calendar days on the first day of each month in the same lunar month are generally the same or differ by one or two days. Every nineteen years, the dates of the solar terms and the solar terms generally overlap, with some differences of one or two days. Months that are leap months apart in nineteen years repeat or differ by one month.

Stems and Branches

In a literal sense, stems and branches are equivalent to the trunk, branches and leaves of a tree. In ancient my country, the sky was the dominant one and the earth was the subordinate one. The connection between the sky and the branches is called the heavenly stems, the connection between the earth and the branches is called the earthly branches, and together they are called the heavenly stems and earthly branches, referred to as the stems and branches.

There are ten heavenly stems, namely A, Yi, Bing, Ding, Wu, Ji, Geng, Xin, Ren and Gui. There are twelve earthly branches, namely Zi, Chou, Yin, Mao and Chen. , Si, Wu, Wei, Shen, You, Xu, Hai. The ancients combined them in a certain order without repetition. From Jiazi to Guihai, there are sixty pairs, which are called sixty Jiazi.

The ancient Chinese used these sixty pairs of stems and branches to represent the serial numbers of the year, month, day, and hour. They cycle over and over again. This is the discipline of the stems and branches.

It is said that Da Nao, a minister in the Yellow Emperor's time, "had a deep love for the five elements and built it according to the year plan, so he made A and B to name the day and called it a stem; he made Zichou to name the day and called it a branch, and the stems and branches matched each other. "Yicheng sixty years." This is just a legend. Who was the first to create Ganzhi has not yet been confirmed. However, in the oracle bone inscriptions unearthed in the Yin Ruins, there are hieroglyphs representing Ganzhi, indicating that Ganzhi records were used as early as the Yin Dynasty. It’s law.