Niàn means twenty. Often used in the lunar calendar.
The lunar calendar is based on the lunar calendar (summer calendar), because the lunar calendar is based on the change of the moon phase, regardless of the movement of the earth around the sun, so the changes of the four seasons in the summer calendar have no fixed time and cannot reflect the changes of seasons; However, the summer calendar can reflect the tidal phenomenon and is a guide for guiding maritime activities in ancient times.
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A brief history of development
From the ancient times to the opening of the solar calendar in the late Qing Dynasty, it was revised many times in history, and various calendars of 102 were produced in the history of China, which had a great influence on the culture and civilization of China.
For example, the official calendar (photo), the summer calendar, the Shang calendar (lunar calendar), the weekly calendar, the taichu calendar calendar in the Western Han Dynasty, the three-way calendar, the emperor calendar in the Sui Dynasty, the Dayan calendar in the Tang Dynasty and so on. Although some calendars are not officially used, they have played a role in medical care, medicine, ideology, astronomy, mathematics and so on.
After the summer, multi-track calendars appeared, that is, local governors and tribes also had their own local calendars. The Qin Dynasty is the last calendar in the history of China, which takes the four seasons of leap month as the calendar year. In Qin and Han Dynasties, the leap month was placed after September, which was called "the last September". In the first year of Emperor Wu of the Han Dynasty, the leap month was placed in the month without gas in a year as the leap month of the previous month.
At the beginning of Han Dynasty, there was a major turning point in China calendar, and the national unified calendar became a relatively independent science and technology. Emperor Wu of the Han Dynasty instructed, Luo and others to discuss and create the "Han Li", which took him seven years to complete.
In May of that year, the year number was changed to Taichu (that is, the first year of Taichu), and this set of "Han Li" was promulgated and implemented. Later generations called this calendar "taichu calendar", and later Liu Xin wrote "Three Calendars".
The important feature of these two calendars is the unity of age and age. The whole number of days in a year is 365 days, instead of 366 days in the previous calendar. Use "addition" instead of "subtraction" to adjust the time difference. The beginning of the age cycle is quite fixed, and leap months can be determined by mathematical calculation.
reference data
Baidu Encyclopedia -20