Is 1640 a leap year or a common one? Does it have 365 or 366 days? What is a leap year? The algorithm and steps to calculate
1640: Is it a leap year or a common one?
The leap year algorithm. The three conditions to check in order to know whether a year is a leap or a common one.
1) A leap year is divisible by 4 (evenly divided by 4, having a zero remainder when divided by 4):
1640 is evenly divisible by 4.
2) Except if it's divisible by 100 (evenly divided by 100, having a zero remainder when divided by 100) then it isn't a leap year:
1640 is not evenly divisible by 100.
We could have stopped at this step.
Our year is a leap year and not a common one.
It does not meet this condition.
3) But even for the previous step above, if it's also divisible by 400 (evenly divided by 400, having a zero remainder when divided by 400) then it's a leap year:
1640 is not evenly divisible by 400.
1640 is a leap year. The last leap year before 1640: 1636. The next leap year after 1640: 1644.
1) Each year that is divisible by 4 (divided evenly by 4, having a zero remainder when divided by 4) is a leap year... 2) Unless it is also divisible by 100... 3) But even in this last case, if it is divisible by 400, then it is a leap year. A maximum of three steps to check, in this order.
What is a leap year?
1640, being a leap year has 366 days. A common year has 365.
In a leap year month February has 29 days. February 29th, 1640 is a valid date.
In a common year month February has 28 days. February 29th does not exist.
How often do the leap years occur?
Nearly once every four years is a leap year. More exactly, leap years occur 97 times in every cycle of 400 years.
Why do we need leap years in our calendar?
Leap years keep the calendar year in sync with the astronomical year, preventing us, for example, from celebrating Christmas in the month of November.
The first year in the actual calendar (also called Gregorian, modern, civil) was 1582. Before this year another calendar (Julian) was in use, with different rules. Not all the countries adopted the Gregorian calendar at the same time, in 1582. The adoption process took hundreds of years and is not even now complete. The actual calendar (also called Gregorian, modern, civil) will get out of sync by 1 day with the astronomical calendar around the year of 4818 (after ≈ 3236 of years from its creation in 1582).