Why are there solar calendars and lunar calendars?

Gregorian calendar: Also called Gregorian calendar. A calendar based on the time that the earth goes around the sun once. The time for the earth to make one revolution around the sun is 365.2422 days (5: 48: 46 on 365), which is called the tropic of cancer. Because the calendar stipulates that a year must be a whole day, it usually takes 365 days as a year, which is called a normal year; About every four years, one day is added to leap, and a year of 366 days is called leap year. The length of a month is decided by people and has nothing to do with the moon. The Gregorian calendar widely used in modern countries is adapted from the Gregorian calendar.

Lunar calendar: also known as the old calendar, is a kind of yin-yang calendar, which was mistakenly called the lunar calendar in the past. Legend has it that it originated in the Xia Dynasty, so it is also called the Xia calendar. Because it has been used in China for many years, it is customarily called lunar calendar. It is characterized by not only paying attention to the round changes of the moon, but also taking care of all the seasons. In order to coordinate the running laws of the sun and the moon in the calendar, the 7-leap method of 19 is adopted, that is, 7 years plus 1 month (leap month) of 19, and other years are still 12 months. There are 13 months in a year, also called leap year, and there are 383 ~ 385 days in a year; The year of 65438+February is also called the average year, with 353 ~ 355 days in the whole year. The accuracy of this leap calendar is quite high. This calendar divides a solar year into 24 solar terms according to the position of the sun on the ecliptic to facilitate farming. Its disadvantage is that the number of days in a normal year is very different from that in a leap year.