What is the lunar calendar based on?

The lunar calendar in China, also known as the lunar calendar, should be familiar to everyone. Many traditional festivals, such as the upcoming Spring Festival, are all lunar holidays. However, if you ask about the rules of the lunar calendar, I'm afraid not many people know. Most people know that the first day is the day when the new moon appears, and the day of the full moon is around 15. Many people also know the approximate date of the 24 solar terms in the solar calendar. Most people don't understand the detailed concepts such as leap month. After some searching and reading, I finally have a certain understanding of the rules of the lunar calendar. I want to share it with you here.

First of all, the lunar calendar takes the month as the basic unit, and a month starts from the day when the new moon appears until the day before the next new moon appears. Because the period of the moon's revolution is between 29 and 30 days, a month in the lunar calendar is also 29 or 30 days from the appearance of the new moon. 30 days for the big moon and 29 days for the small moon. Unlike the solar calendar, large and small months are not fixed in different years. For example, the day before the Spring Festival is usually called New Year's Eve, but in many years, such as the 2000 lunar calendar1February, there are only 29 days. Since the period of twelve months is about shorter than that of the solar year 1 1 day, in order to keep the lunar year and the solar year relatively stable, a leap month should be added every two or three years. About every nineteen years, seven leap months will be added. The 24 solar terms are determined by the position of the earth in its orbit around the sun. Starting from the annual winter solstice, every 15 degree is a solar term. Therefore, the 24 solar terms have roughly fixed dates in each month of the solar calendar. In ancient times, the twenty-four solar terms guided farming, which is why the lunar calendar is also called the lunar calendar. Among them, the twelve solar terms in the second half of the solar calendar are also called zhongqi. The time when Qi appears is directly related to the determination of leap month.

The calculation of the lunar calendar has the following four rules:

1. The calculation of the occurrence time of all new moons and solar terms is based on the east longitude 120 degrees, that is, the standard time of the East Eighth District. However, when calculating the lunar calendar time before 1929, Beijing local time, that is, east longitude 1 16 degrees 25, shall prevail.

The day when the new moon appears is the first day of a month. If a solar term appears on this day, whether it appears later than the new moon or not, it will be counted as falling into the new moon.

The annual winter solstice is always in 1 1 month this year. The period from the second day of the winter solstice to the next winter solstice is called one year old. If there are thirteen new moons in a year, then this year is a leap year, plus leap months.

The first month of leap year without gas is leap month. Because there is only twelve breaths in a year, there may be no breath for at least one month or two months in a leap year. But in this case, only the first month without breath is a leap month. When the month before leap month is a month, it is called leap month.

The lunar calendar calculation rules listed above were adopted during the Shunzhi period of the Qing Dynasty, that is, AD 1645. An important feature of the above laws is that they are completely based on astronomical observations in theory, and there is no mathematical relationship between them. This is in stark contrast to the fact that the solar calendar is completely determined by mathematical relations. Of course, when it comes to the calculation of the future lunar calendar, we still need the mathematical model of the movement of the moon and the earth, and the high-precision mathematical model is quite complicated. If there is no computer, it is impossible for ordinary people to calculate the accurate lunar calendar. The mathematical relationship of the solar calendar is very simple, and it is easy to calculate whether it is a leap year or not. This forms another sharp contrast.

However, if we know the lunar calendar of that year, there is a very simple way to calculate the date of next year's Spring Festival. This method is suitable for most years. Find the Gregorian calendar date corresponding to the current lunar calendar 1 1 month 1 day, subtract the number of months, subtract the number of days, and then subtract the number of months. If the date is between February 22nd and February 9th in the next year's Gregorian calendar 1 month, the Spring Festival is the same day, with an error of no more than one day before and after. For example, lunar calendar 1 1 month 1 day in 2002 corresponds to solar calendar 65438+February 4th, so the predicted date of Spring Festival in 2003 is February 1, which is the same as the actual date.