qián nián，前年，the year before last year。
qù nián，去年，last year。
jīn nián，今年，this year。
míng nián，明年，next year。
hòu nián，后年，the year after next year。
shàng gè yuè，上个月，last month。
zhè gè yuè，这个月，this month。
xià gè yuè，下个月，next month。
qián tiān，前天，the day before yesterday。
hòu tiān，后天，the day after tomorrow。
Year, month, and day are a unit of time. People form the concept of “day” according to the rotation of the earth and the phenomenon of alternating day and night; according to the moon’s revolution around the earth, it produces synodic and forms the concept of “moon”, according to the earth’s revolution around the sun The resulting alternation of the four seasons has formed the concept of “year”.
Origin of the concept
Year, month and day, the material movements on which these three concepts are based are independent of each other. According to accurate measurements, the time for the earth to revolve around the sun is about 365.2422 mean solar days, which is called a tropical year. The time interval from one new moon to the next new moon in succession is 29.5306 average solar days, which is called a synodic moon.
The calendar is to calculate the length of the year, month, and day and the relationship between them. The rule of time sequence is called “calendar”. Taking the tropical year as the unit, how many whole-number months are arranged in a year, how many whole-number days are arranged in a month, and how to choose the starting point of the year are called calendars.
The complexity of the calendar problem lies in the fact that the two cycles of the tropical year and the synodic month are too fragmented. The relationship between them and the “day” is not as simple as the relationship between kilometers and meters; moreover, they cannot be negotiated with each other. . Therefore, the calendar always considers one and the other and cannot coordinate two cycles at the same time. Due to these two reasons, calendars are generally divided into three categories; Lunar Calendar, Solar Calendar, and Lunar Calendar. The solar calendar that focuses on coordinating the relationship between the synodic and the calendar month is called the solar calendar; the solar calendar that takes into account the synodic month and the return year, the calendar month and the calendar year is called the lunar calendar.
No matter what kind of calendar, there is a problem of coordinating the relationship between the calendar day cycle and the astronomical cycle. In principle, the calendar month should be equal to the synodic month, and the calendar year should be equal to the return year. However, since the synodic month and the tropical year are not the number of whole days, the calendar month must be divided into a large month and a small month, and the calendar year must be different from a normal year and a leap year. Through the proper collocation and arrangement of large and small moons, normal years and leap years, the average calendar month is equal to the synodic month, or the average calendar year is equal to the tropical year. This is the main content of the calendar.
“Almanac” is a reference book for people to check the year, month and solar terms. The almanac was called Tongshu or Shixianshu in ancient my country. In the era of feudal dynasties, it was also called “imperial calendar” because it was issued by the emperor.