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# What does leap month mean? How to calculate the lunar leap month

What does leap month mean? How many leap months a year? Leap month is a special day in our national lunar calendar. It refers to a day set up to maintain the normal operation of the 24 solar terms in our country. Do you know what leap month means? Let's have a look

What does leap month mean

What is a leap month? Leap month is a calendar leap month. In Asia (especially in China), leap month refers to an additional month in every leap year in the Han calendar (also known as the lunar calendar in folk society) (in order to coordinate the contradiction between the year of return and the year of Han calendar and prevent the disconnection between the year of return and the four seasons in the Han calendar, one leap is set every 2 to 3 years. In ancient times, the leap week of 7 leap in 19 years was adopted, and the Linde calendar in the Tang Dynasty In addition to the fixed leap week, the non seasonal month is used to place the leap, so it is the leap time to place the leap). Sometimes, leap month also refers to the month containing leap days in the leap year of the Gregorian calendar (i.e. February of the leap year of the Gregorian calendar).

Leap months occur every few years

Every two or three years. There is a generalization of "seven leap in nineteen years" among the people. On the lunar calendar, because the total number of days in the 12 months of the weekday (let's call it "lunar month" for the time being) is 11 days less than that in the Gregorian calendar, the calendar stipulates that every two or three years, a leap month must be added to make up for the difference of about one month. And because the difference is not a regular number, it is not very regular which year needs to add a leap month. However, with the increase of years, people have summed up a law of "seven leap months in nineteen years", that is, in nineteen years, China's lunar calendar should have seven leap months. It depends on the difference between the month and the 24 solar terms, because the 24 solar terms of the lunar calendar are basically consistent with the date of the Gregorian calendar. But generally, there is no leap month after the twelfth month and the first month of the lunar calendar.

The mid month of the lunar year is based on the length of the new moon of 29.5306 days, so the big month is 30 days and the small month is 29 days. In order to ensure that the first day of each month (the first day of the new year) must be a new day, the arrangement of large and small months is not fixed, but needs to be determined through strict observation and calculation. Therefore, it is common for two consecutive months in the lunar calendar to be the big month or the small month. There have even been rare exceptions, such as March and April in 1990 being the small month and September, October, November and December being the big month.

So how long does it take to add a leap month? The best way is to find the least common multiple of the number of days in the regression year and the number of days in the new moon: we hope that the number of days in M regression years is equal to the number of days in n new moon, that is, there should be an equation:

m× 365.2422=n× 29.5306 in this equation, we cannot directly find m and N, but we can find their proportion:

The approximate value is:

In these fractions, the numerator represents the number of regression years and the denominator represents the number of new moon. For example, the sixth fractional formula = means that 7 leap months must be added in the 19 regression years.

Comparison of the results of adding 7 leap months in 19 regression years: 19 regression years = 19 & times; 365.2422 = 6939.6018 (days)

A new moon has 29.5306 days, 235 new moons = 235 & times; 29.5306 = 6939.6910 (days)

After adding 7 leap months to the 19 regression years, the contradiction is only eliminated: 6939.6910-6939.6018 = 0.0892 (days) -- that is, more than 2 hours and 9 minutes, which is accurate enough.

Therefore, the lunar calendar adopts the method of 19 years plus 7 leap months, that is, the '19 years and 7 leap method', which well coordinates the return year with the lunar year, so that the Lunar New Year's Day (Spring Festival) is always maintained at the end of winter and the beginning of spring. The ancients called 235 new moon as' leap week '.

The method of placing leap in the lunar calendar can make the average length of the lunar year close to the regression year, and the moon in the lunar calendar has distinct lunar phase characteristics, maintaining the best of both the Gregorian and lunar calendar.