A leap year is a year that has an additional day…
A regular year has 365 days.
A leap year has 366 days.
So what year will be a Leap Year?
To be a leap year, a year must match the following criteria (in order):
1. Any year that can be evenly divided by 4, like years 2016 or 2020.
2. But NOT evenly divided by 100, like years 2100 or 2200.
3. Unless, it can also be evenly divided by 400, like years 2000 or 2400
Note: If the year is not evenly divided into 4 (step 1), it is automatically NOT a leap year. You do not need to proceed with the second and third steps.
Is 2015 a leap year?
2015 is not evenly divided into 5, so it is NOT a leap year.
Is 2300 a leap year?
2300 can be divided evenly into 4, BUT it can also be evenly divided into 100, so it is NOT a leap year.
Is 2800 a leap year?
2800 can be divided evenly into 4; it can also be evenly divided into 100, BUT it can also be evenly divided into 400, so it IS a leap year.
Why are there Leap Years?
A year is the amount of time it takes for the earth to orbit (cycle around) around the sun.
Leap Years exist because the earths rotation takes approximately 365.242375 days a year, but we can’t have a fraction of a day in a calendar year. So a year with an additional day is added every four years to account for the 0.242375 of a day missed.
By adding a day every 4 years, we can account for the .25 of a day missed for each of those years. (4 x .25 day = 1 day for every 4 years ) -- Step ONE
But since we rounded up to .25 from .24, we are missing about .01 days (which is about +1 day for every 100 years. We account for that by not having a leap year every 100 years. -- Step TWO
Finally, every 400 years we have a leap year to get us to .2425, which brings us close enough to the actual (365.242375) time and to make the rest negligible. -- Step THREE
So there you have it, why leap years a so important and how to determine when a leap year is going to occur. It is a very creative way to keep the calendar accurate, and to account for the fraction of a day missed each year.