People all have such common sense that there are different months in the Gregorian calendar, that is, there are such provisions in the Gregorian calendar months: "April, June, September and 165438+ 10 have 30 days, and other months have 3 1 day, except for February, which has only 28 days."
The size of the moon began in Caesar's time in the Roman Empire. At that time, Caesar sent someone to modify the calendar and enacted the julian calendar Law, stipulating that all months with special religious significance are 365,438+0 days, and all unimportant months are 30 days. Therefore, the month of 1, March named after the god of war, and July named to show respect for Julius Caesar all have 3 1 day. Because February is an unlucky month for executing prisoners, there are only 29 days. Julius Caesar's successor Augustus's birthday is in August. In order to be on an equal footing with Caesar, he asked to increase August to 3 1 day. In order to make August have 3 1 day, he borrowed another day from February and reduced it to 28 days. In order to avoid the connection of the three big months, it is stipulated that September and 165438+ 10 each have 30 days, and 10 and1February are extended to 3 1 day.
In the Gregorian calendar (Gregorian calendar), a year with leap days is called leap year, which is generally 365 days and 366 days. Because the earth's cycle around the sun is 365 days, 5 hours, 48 minutes and 46 seconds (365,438+09 days), which is the tropic year, the Gregorian calendar defines a year as 365 days, which is called a normal year. The remaining time is about one day in four years, plus February, so the normal year is 365 days, February is 28 days, leap year is 366 days, and February is 29 days. So every 400 years, there are 97 leap years, with one day added at the end of February and 366 days in leap years. Calculation method of leap year: the number of years in the calendar year can be divisible by four, which is a leap year; Divided by 100 but not divided by 400 is an average year; Leap years can be divisible by 100 or 400. For example, 2000 is a leap year, and 1900 is not.
Because a multi-digit, if the last two digits can be divisible by 4, then this number can also be divisible by 4, so you can make a judgment by dividing the last two digits of the year by 4. 1998 is it a flat year or a leap year? Use 98 ÷ 4 = 24...2, so 1998 is the normal year. If the year is 100 years, only the first two digits of the year can be divided by 4, (the dividend and divisor are reduced by 100 times at the same time, and the quotient remains unchanged. ) Is 2400 a normal year or a leap year? Use 24÷4=6, so 2400 is a leap year. . February is neither a big moon nor a small moon. This is a special month. A year with 28 days in February is usually called a flat year, and a year with 29 days is called a leap year.