Have you noticed that today is February 22, 2022 in the Gregorian calendar, and it is also the twenty-second day of the first lunar month. But in previous years, there were not so many "2" at the same time, what is going on?
At present, the world's common calendar is the solar calendar, and its starting point is defined internationally on the day of the birth of Jesus, and the cycle is the cycle of the earth around the sun. In addition to the solar calendar, the main calendars actually used are also the lunar calendar and the lunar calendar. The lunar calendar considers the cycle of the moon, while the lunar calendar considers both the moon and the sun.
Since the three cycles of the Earth's rotation, the Earth's orbit around the Sun, and the Moon's orbit around the Earth are not integer multiples, calendar makers need to coordinate these three cycles, and different coordination methods produce different calendars.
The solar calendar determines the length of a year based on the Earth's orbital cycle around the Sun, and then the length of the month. The months of the solar calendar have 28, 29, 30, and 31 days, and the order in which large and small moons appear is somewhat disordered. Why do these phenomena occur? This is the result of scientific and political coordination.
Figure 1. The solar calendar was created based on observations of the Sun (Source: Author)
The formulation of the solar calendar requires the coordination of the earth's rotation cycle and the earth's orbital cycle around the sun. As people's measurement accuracy of the length of "years" continues to improve, the solar calendar is constantly updated.
In 45 BC, the Roman Emperor Julius Caesar used the results of the Egyptian astronomers' measurements of time to determine a year of 365.25 days. The basic idea of formulating the solar calendar at that time was to make the solar calendar year have two lengths, one is smaller than the regression year, set at 365 days, called the common year, and the other is larger than the return year, set at 366 days, called leap years.
Then it is to solve the problem of "a leap year in a few years" and reasonably set a leap year. The zero number of a return year is 6 hours, and the accumulation of 4 years is nearly one day, so it is more reasonable to set "four years and one leap".
Caesar's birthday was in July, so he set the single month as a large month, 31 days a month, 6 large months for a total of 186 days; the bi-months except February as a small month, 30 days per month, and 5 small months for 150 days; February was more special, set to 30 days in leap years, and 29 days in ordinary years. In this way, 366 or 365 days of the year are formed.
This is the Julian calendar.
After Caesar's death, his nephew Octavian took the throne. Octavian was born in August, and August turned out to be a small month, which made him angry and the consequences were very serious.
Astronomers had no choice but to change August to a big moon. Therefore, the even months after August (October and December) were changed to large months, and the odd months (September and November) were changed to small months. In this way, the large month has 1, 3, 5, 7, 8, 10, 12 a total of 7 months and 217 days, and the small month has 4, 6, 9, 11 a total of 4 months and 120 days, at this time, the February has to be changed to 28 days in the common year and 29 days in leap years. Such a solar calendar is called the Augustus calendar.
Figure 2. Schematic diagram of the big and small month (image source: network)
Although the Augustian calendar confused the order of the months and months, this calendar still accurately coordinated the rotation and rotation cycles of the earth, and it was quite convenient to use.
After more than a thousand years of use in the Augustus calendar, astronomers discovered the problem. The "year" measured earlier was slightly longer than the actual one. A year is not 6 hours more than 365 days, but 6 hours more than minus about 650 seconds. Don't underestimate these 650 seconds, the cumulative 400 years will be about 3 days. That is to say, there are 3 more leaps in 400 years.
In 1582, Pope Gregory XIII revised the Julian calendar to the Gregorian calendar. The main reform of the Gregorian calendar is to adjust the method of setting leap years, so that there are fewer leap years every 400 years. The year in which the number of years can be divisible by 4 is a leap year, but the last two digits of the AD number are zeros, such as 1600, 1700, 1800, 1900, 2000... Wait, when it can be divided by 400, it can be set as a leap year. In this way, you can reduce leap years by 3 times every 400 years, and set it to 97 leap years.
The Gregorian calendar, also known as the Gregorian calendar, has been a universal calendar since the 20th century.
After the Gregorian calendar adjusted the leap year setting rules, although it was very accurate, it took thousands of years from the Julian calendar to Gregorian calendar, and there were several errors in the middle, and by 1582, there were 10 more leaps. That is, the date of the calendar is 10 days behind and needs to be turned back. That is, it is necessary to skip 10 days, after October 4, 1582, directly to October 15.
Figure 3. Many cities have solar calendar squares (Source: Author)
Known for their conservative british, Great Britain and its North American colonies did not abandon the Julian calendar until 1752 and switched to the Gregorian calendar. As a result, this is a skip of 11 days, from September 2 directly to September 14. The change caused an uproar in London, with citizens believing they had been cheated out of 11 days' rent, and the slogans of marchers in the streets were even angrier: "Give me back 11 days of life".
At the time, Franklin, who was in the Americas, advised people not to be depressed, because "you can lie down peacefully on the 2nd of this month and not wake up until the morning of the 14th." Russia was even more stubborn, switching to the Gregorian calendar until after the 1918 Revolution, this time skipping 13 days! Thus, when Lenin was preaching that "the last night of capitalism was cold," it was the night of October 24 in the Julian calendar, which is why the anniversary of the October Revolution was set as November 7.
Although chaotic, the calendar year of the solar calendar is very close to the year of return, coinciding with the seasons and solar terms, and is easy to apply in production and life, so it is widely adopted by all countries in the world. However, due to Octavian's messing up of the solar calendar system, and the Gregorian calendar itself is not very perfect, it is in the process of constantly exploring and reforming the solar calendar. In response to the inadequacy of the Gregorian calendar, the United Nations proposed to reform the calendar very early on and proposed the implementation of a new Universal Calendar, but this issue has been discussed in the process and has not reached a unified conclusion.
Source: National Astronomical Observatories, Chinese Academy of Sciences
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