What are the main types of calendars?

I. Gregorian calendar: It is the calendar that is currently used all over the world, and it is essentially a solar calendar. The original solar calendar was created by the ancient Egyptians. Initially, the year was taken as 365 days. In order to harmonize the length of the calendar year with the return year, the Roman ruler Julius Caesar modified the solar calendar in 46 BC and formulated the Julian calendar. In 8 B.C., Julius Caesar's nephew, Augustus, adjusted the Julian calendar again. The Julian calendar was divided into a year of twelve months, with an average year of 365 days; a year divisible by four was a leap year, ***366 days. In this way, the average length of the Julian calendar year is 365.25 days, with a difference of 0.7078 days from the length of the return year of 365.2422 days, a difference of about 3 days in 400 years. From the implementation of the Julian calendar to the end of the sixteenth century, the cumulative difference was about 10 days. In order to eliminate this difference, Pope Gregory XIII made the next day of the Julian calendar, October 4, 1582, October 15, eliminating 10 days in between, and also modified the Julian rule of intercalation: years divisible by 4 remained leap years, but for century years (e.g. 1600, 1700,... ...), only years divisible by 400 were leap years. As a result, there were only 97 leap years in 400 years, three fewer than the original, making the average length of a calendar year 365.2425 days, which is closer to the length of a return year. The Julian calendar thus modified is called the Gregorian calendar, also known as the Grecian calendar. The Gregorian calendar was first used in Catholic countries, and then in the early twentieth century it was universally adopted throughout the world, so it is also called the Gregorian calendar. China began to adopt the Gregorian calendar in 1912, but at that time, the Republic of China was still using the Republic of China chronology, and after the founding of the People's Republic of China in 1949, the Gregorian calendar was adopted for the year of the year of the founding of the People's Republic of China. Second, the lunar calendar (Hijri): Lunar Calendar is the calendar used in Islamic countries and regions, also known as the Hijri calendar. It is purely lunar month as the basic unit of the calendar, odd-numbered months for the 30th, even months for the 29th, twelve months for a year, ***354 days. The twelve lunar months are actually about 354.3671 days. In order to make the beginning of the month and the new year start on the day of the appearance of the Ember Moon, the Gregorian calendar adopts the following intercalary method: every 30 years as a cyclic cycle, there are 11 intercalary days. The second, fifth, seventh, tenth, thirteenth, sixteenth, eighteenth, twenty-first, twenty-fourth, twenty-sixth and twenty-ninth years are leap years. December in a leap year is 30 days ****355 days. The beginning of the Hijri calendar was set on the day Mohammed moved from Mecca to Medina, i.e., July 16, 622 AD. Third, the lunar calendar: the lunar calendar is China's adoption of a traditional calendar, also known as the summer calendar, the Chinese calendar, the old calendar, folk also known as the lunar calendar. It uses a strict lunar cycle to determine the month, and the method of setting up intercalary months to make the average length of the year similar to the regression year, both lunar months and the nature of the solar year, so in essence it is a kind of yin and yang calendar. In the lunar calendar, the first day of the month is the day when the sun and the moon coincide with the solstice (the yellow longitude of the sun and the moon are equal). The average length of the lunar month is about 29.53059 days, so some months are 30 days. Some months are 29 days long, and some months are small. The date of the beginning of the month, according to the position of the sun and the moon projected set, not mechanical arrangement. The lunar calendar takes twelve months as a year, ***354 or 355 days, a difference of eleven days from the year of return. This is harmonized by the placement of seven leap months every nineteen years. The arrangement of leap months is determined by the 24 solar terms.