Calendar is a rule to measure the longer time interval than what.

Calendar is a rule to measure the time interval longer than one day. In layman's terms, it is the law of counting days.

Calculate the length of year, month and day and the relationship between them, and formulate the law of time sequence, which is called "calendar". The almanac is a reference book for people to consult by arranging the years and solar terms. In ancient China, the almanac was called the general book or the constitutional book. In the feudal dynasty, it was also called the "imperial calendar" because it was promulgated by the emperor. According to the rotation of the earth, people formed the concept of "day" by alternating day and night; The concept of "moon" is formed according to the new moon generated by the revolution of the moon around the earth, and the concept of "year" is formed according to the phenomenon that the four seasons alternate when the earth revolves around the sun. The material movements on which these three concepts are based are independent of each other. How many integer months are arranged in a year, how many integer days are arranged in a month, and how to choose the starting point of a year are all called calendars.

Calendars are generally divided into three categories; Lunar calendar, solar calendar, lunar calendar. The lunar calendar, which focuses on coordinating the relationship between Wang Shuo and the calendar, is referred to as the lunar calendar; The solar calendar, which focuses on coordinating the relationship between the tropic year and the calendar years, is referred to as the solar calendar for short; The lunar calendar, which takes the moon, tropic year, calendar month and calendar year into account, is called the yin-yang calendar.