The original solar calendar was founded by the ancient Egyptians. At first, a year was considered as 365 days. In order to coordinate the length of the calendar year and the tropic year, the Roman ruler Julius Caesar revised the solar calendar in 46 BC and formulated the julian calendar. In the 8th year BC, Augustus, Caesar's nephew, adjusted julian calendar. Julian calendar is divided into twelve months a year, with an average of 365 days a year; A leap year divisible by 4 in a year is 366 days in total. In this way, the average length of julian calendar over the years is 365.25 days, which is 0.7078 days different from that of the Tropic of Cancer (365.2422 days) and about 3 days different in 400 years. From the implementation in julian calendar to the end of16th century, the cumulative difference was about10th day. In order to eliminate this difference, Pope Gregory XIII set the second day of julian calendar 1582/kloc-0 10 on the 4th of October as15, and eliminated10 in the middle. At the same time, julian calendar's leap year rule is modified: the year divisible by 4 is still a leap year, but for century years (such as 1600, 1700, ...), only the year divisible by 400 is a leap year. In this way, there are only 97 leap years in 400 years, three less than the original, making the average length of the calendar year 365.2425 days, which is closer to the length of the tropical year. After this modification, julian calendar was called the Gregorian calendar, also known as the Gregorian calendar. The Gregorian calendar was first used in Catholic countries, and was widely used all over the world at the beginning of the twentieth century, so it is also called Gregorian calendar. China adopted the Gregorian calendar in 19 12, but still used the year of the Republic of China. 1949 After the establishment of People's Republic of China (PRC), the Gregorian calendar was adopted.
Second, the lunar calendar (hijri): The lunar calendar is a calendar adopted by Islamic countries and regions, also known as hijri. It takes the new moon as the basic unit of the calendar. There are 30 days in odd-numbered months, 29 days in even-numbered months, and 12 months in a year, totaling 354 days. In fact, there are about 354.38+0 days in the twelve lunar months. In order to make the beginning of the month and the New Year start from the day when the waning moon appears, the following leap method is adopted in the hijri calendar: every 30 years is a cycle, and 1 1 leap day is set. 2, 5, 7, 10, 13, 16, 18, 2 1, 24, 26 and 29 years are leap years. 65438+February in leap year is 30th, with a total of 355 days. The beginning of hijri was set on the day when Muhammad moved from Mecca to Medina, that is, July 16, AD 622.
Third, the lunar calendar: the lunar calendar is a traditional calendar adopted in China, also known as the summer calendar, the middle calendar and the old calendar. Some people call it the lunar calendar. It uses the strict lunar cycle to determine the month, and sets the leap month to make the average length of a year close to the tropic year, which has the attributes of lunar month and solar year, so it is essentially a kind of yin-yang calendar. In the lunar calendar, the date when the sun and the moon meet (the ecliptic is equal) is the first day of the month, that is, the first day. The average length of the first month of the lunar calendar is about 29.53059 days, so some months are 30th. Call the moon big; Some months are the 29th, called abortion. The date of the beginning of the month is calculated according to the position of the sun and the moon, not mechanically arranged. The lunar calendar takes1February as a year, with a total of 354 days or 355 days, which is different from the tropical year 1 1 day. Therefore, coordination is achieved by inserting 7 leap months every 19 years. The arrangement of leap month is determined by the 24 solar terms.