Why are calendars unified all over the world?

At present, the international unified calendar is called the western calendar by foreigners. We call it Gregorian calendar, solar calendar and national calendar, which is an international calendar.

Gregorian calendar is the current international calendar, also called solar calendar, commonly known as solar calendar. The solar calendar, also known as the solar calendar, is based on the fact that the earth revolves around the sun once a year, which is very common in western countries, so it is also called the western calendar. Since the Revolution of 1911, China has adopted the solar calendar since the first year of the Republic of China, so it is also called the "national calendar". In order to be symmetrical with China's old calendar, it is also called the "new calendar". 1949 officially stipulated the calendar year.

He was born in julian calendar BC 1582, and Pope Gregory XIII of Rome designated the second day of julian calendar 1582 10 year 10 day as Gregorian calendar 10 year/0 month/0/5 day. At the same time, julian calendar's leap rules have also been revised.

The earth's orbit around the sun is actually 365.24 19 days (solar year), decreasing by 0.242 19 days every year, decreasing by 0.96876 days every four years and decreasing by 96.876 days every 400 years. So 400 years needs 97 leap years. Leap year adds one day at the end of February, and there are 366 days in the whole year. It took 3333 years to get a day's error.

There are three kinds of years: the earth revolves around the sun for 365 days, 6 hours, 9 minutes and 9 seconds, which is called "sidereal year"; The sun passes through the perigee and travels eastward along the ecliptic, and then passes through the perigee at 6: 13: 48 in 365 days. This year is called "perigee year"; The sun passes through vernal equinox, travels eastward along the ecliptic, and then passes through vernal equinox for 365 days, 5 hours, 48 minutes and 46 seconds. This year is called "the year of the Tropic of Cancer" and "the year of the first year".

Because the vernal equinox (vernal equinox and autumnal equinox) retrogrades westward along the ecliptic for about 50 seconds every year, the time of the return year is shorter than that of the sidereal year, with a difference of 20.23 seconds, which is called "precession". These three years are different. In order to keep the annual solar terms hot and cold, the tropical year is chosen as the calendar year.

It is necessary to remember the time of the Tropic of Cancer. In order to facilitate memory, the song formula is compiled as follows:

How long does it take for the earth to orbit the sun for the first anniversary? Three, six, five hours, 48 minutes and 46 seconds.

From 1 month 1 day to the following year 1 month 1 day, it is called a year. Old people should be equal to their actual age. However, the number of days in a year must be an integer, so it is not convenient to calculate odd hours. Therefore, taking 365 days as a year, there are 5 hours, 48 minutes and 46 seconds left every year, which is about one day in four years. Therefore, one day is added every four years, which is called leap year.

A year without leap days is called an "average year", with 365 days in an average year and 366 days in a leap year. However, the leap in four years is only 23: 15 minutes and 4 seconds. There are too many leap days today. It exceeded 44: 56 seconds and accumulated to 25 leap, that is, 17: 58 minutes and 24 seconds, which is about three quarters of a day. Therefore, a leap will be wasted every hundred years, and it will not be wasted until the 400th year. If you set a leap every four years and reduce it three times every 400 years, it will take eight 400 years, that is, 3200 years, to make up the difference of this day.

The Gregorian calendar began to record dates according to the date of Jesus' birth in the Bible. It is the calendar of westerners, and it is also called Gregorian calendar in China.