Chinese New Year's Eve is also called "Chinese New Year's Eve", but why is the upcoming Chinese New Year's Eve not "Chinese New Year's Eve", but "twenty-nine years"? What is the scientific basis for determining the number of days per month in the lunar calendar? Shi Wei, director of the Network Science Popularization Department of shanghai planetarium and deputy secretary general of Shanghai Astronomical Society, made a popular science interpretation for the public.
According to reports, the calendars adopted by various countries and nationalities today can be divided into three categories - the solar calendar, the lunar calendar, and the yin-yang calendar. The solar calendar is a calendar that refers to the "year of return", that is, the earth's rotation cycle. The most widely used solar calendar is the Gregorian calendar, which is based on the Common Era calendar, with 365 days in the common year and 366 days in leap years, with an average of 365.2422 days a year. The lunar calendar is a calendar based on the "synodic month", that is, the cycle of moon phase changes. This type of calendar does not take into account the rotation of the earth, and is added up in a "synodic month" with 354 or 355 days a year.
The Luni-Yang Calendar is a calendar that takes into account the two cycles of the "Year of Return" and the "Synodic Month". The former cycle is followed to reflect the timely change of seasons and to guide agriculture, fisheries and animal husbandry; the latter cycle is to reflect the phases of the moon, facilitate the chronology and chronology, and guide agriculture, fisheries and animal husbandry, and the coastal areas along the river can also associate it with the tides.
The lunar calendar is a luni-yang calendar, and the number of days of the month is determined according to the cycle of moon phase changes. A "synodic month" has an average of 29.5306 days, so the number of days in the lunar month is 30 days or 29 days, 30 days are commonly known as "big moon", and 29 days are called "small moon". The arrangement of large and small moons is not arranged in large and small intervals, but is completely determined by the phases of the moon. The lunar calendar stipulates that the first day of each month, that is, the first day of the first month, is determined by the time of the appearance of Shuo, and this principle is called "Ding Shuo Method".
The past Shuo occurred at 2:33 a.m. on January 3, 2022, so January 3 was determined to be the first day of the first month of the twelfth month of the lunar calendar. The next Shuo will occur at 13:46 on February 1, 2022, so February 1 is determined as the first day of the first lunar month. In this way, this lunar month has only 29 days, so there is no "Chinese New Year's Eve".
The last time Chinese New Year's Eve occurred was the "Year 29" situation, which occurred on February 7, 2016. The next "Year 29" Chinese New Year's Eve appears on January 28, 2025. From 2025 to 2029, the "Chinese New Year's Eve" will be absent for 5 consecutive years. Are there any rules in this? "There are general rules, but locally it seems that the regularity is not very strong." Shi Wei explained that this is because the size of the moon is not very small compared to the earth, so it will constantly swing when it orbits the earth, as if the earth and the moon are dancing a very complicated waltz. "Imagine the extreme: if Shuo happens at 23:59, the number of days in the lunar month will be one day less; if Shuo occurs at 0:01, there will be one more day. It is no exaggeration to say that a minute or two apart can determine whether the Chinese New Year's Eve is 'Chinese New Year's Eve' or 'twenty-nine'. ”
In addition to determining the number of days per month according to the phases of the moon, the lunar calendar also sets up twenty-four solar terms according to the law of the earth's rotation around the sun, which is also the basis for the lunar calendar to set leaps. The purpose of the leap is to combine the laws of the moon and the sun to "coordinate yin and yang". If the lunar calendar year is a total of 12 "synodic months", there are only 354.36 days in a year, which is 10.88 days less than the "return year", so the lunar calendar adopts the method of 19 years and 7 leap months to "catch up with the Gregorian calendar", so that the Difference between the Gregorian calendar and the lunar calendar is only 0.0518 days every 19 years. It can be seen that the lunar calendar is a very scientific yin-yang calendar.