Is 2020 a normal year or a leap year?
Gregorian calendar and lunar calendar have different historical origins and calendar regulations. The Gregorian calendar has a leap year every four years. Every year in the solar calendar where the number of years can be divided by 4 is a leap year, with 29 days in February, an endless year is a flat year and 28 days in February. 2020 is divisible by 4, so it is a leap year. But for the whole century year, such as 1900, 2000, 2 100, only the first two digits can be divided by 4, which is a leap year, otherwise it is a flat year.
China lunar calendar determines the date and month according to the moon phase and the age according to the 24 solar terms. There are 24 solar terms from 1 winter to the 24th, and the odd ones are called Zhongqi. The 24 solar terms reflect the annual movement of the sun. Because the number of days in1February is not old enough and exceeds1March, leap months are added in time for adjustment. A year with a leap month is also called the lunar leap year, which includes 13 lunar months. The year of the rat in China lunar calendar includes leap April. The rule of adding leap month is that every month, any month containing neutral gas is considered as a normal month, and any month without neutral gas is considered as a leap month of the previous month. The leap April of the Lunar Year of the Rat is the leap month of the previous month.
The establishment of leap year is to make up for the time difference between the number of days in a year and the actual period of revolution of the earth caused by man-made calendar regulations, and the year to make up for the time difference is leap year.
Leap year has 29 days in February and 366 days in the whole year, which is divided into ordinary leap year and century leap year. Ordinary leap year means that the Gregorian calendar year is a multiple of 4, not a multiple of 100, and the century leap year must be a multiple of 400.
The most fundamental reason for leap year is that the earth's orbit around the sun is 365 days, 5 hours, 48 minutes and 46 seconds (365 days +09 days), which is the tropic year. The Gregorian calendar has an average of only 365 days a year, which is about 0.2422 days shorter than the tropical year, and the remaining time is about one day every four years. So 1 day is added at the end of February of the fourth year, making the calendar year of that year 366 days, and this year is a leap year. The current Gregorian calendar has 97 leap years every 400 years. According to a leap year every four years, it will count as 0.0078 days per year on average, so after 400 years, it will count as 3 days. So every 400 years, three leap years will be reduced. Therefore, the Gregorian calendar stipulates that when the year is a whole hundred, it must be a multiple of 400 to be a leap year; It is not a century year with multiples of 400, and even a multiple of 4 is not a leap year.
This is what is usually said: jump in four years, not jump in a hundred years, and jump again in four hundred years. For example, 2000 is a leap year, and 2 100 is a normal year.