Therefore, the lunar calendar has both lunar and solar elements. Unlike the Gregorian calendar, which is fixed at 365 days or 366 days, the Gregorian calendar sometimes differs from the Gregorian calendar by one month. In order to coordinate the number of days between the tropic year and the first month of the lunar calendar, the lunar calendar came into being.
Extended data
The ancients observed the movement law of astronomical phenomena, and adopted the era of dry branches in ancient times. According to the Ming Dynasty historian Wan Mingying, it was invented when he determined that the main branch was the emperor's home according to the clear records in the ancient documents of China, and it was recorded in detail in his book "Three Rings". The invention of trunks and branches marked the emergence of the most primitive calendar, which was used to calculate the age by numbers. 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 integration of calendar and year. 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.