One year is equivalent to one rotation made our planet around the sun. Thus, for a calendar to be considered accurate, it must display the correct amount of time that the Earth has taken to make that rotation. One year is supposed to have 365.242 days but since there’s no such thing as a .242 day, the concept of a leap year was created. This year happens every after 4 years and it requires the calendar to have 366 days on it instead of only 365. This counting system is close to perfection but a leap year actually needs .250 of a day to be added to the calendar for it to have a flawless computation. As a result, .008 of a day starts to add up over the years.
The complication in the calendar only ended in the year 1582 when Pope Gregory XIII removed ten days from the month of October during that year. He eliminated the dates Oct 5 to 14 in the calendar that resulted to its peculiar look and a great change in most appointments of individuals around the world for that period of time.
The controversial calendar looked like this:
Sun

Mon

Tue

Wed

Thur

Fri

Sat


1

2

3

4

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31







The Pope was also responsible for coming up with a revised calendar (Gregorian) which no longer has any sort of error in computation. According to the Pope’s calculation, a year can only be considered a leap year if its number can equally be divided into 4. However, if the year can be divided equally into 100, then it won’t have the privilege to be called leap year unless it can be divided into 400 as well.
For example, the year 2000 is both divisible by 400 and 100. Thus, it has 365 days.