Why do we need leap years?
Wait, why do we need leap years again? Because the actual time it takes the Earth to orbit the sun is slightly longer than our 365-day calendar.
Why do we leap days every four years?
Because there is a discrepancy between our human-constructed calendars and the actual time it takes the Earth to orbit the sun.
It takes 365.242 days for Earth to complete one trip around the sun. So if we never added a day, our calendars would slowly drift out of sync with the seasons and November would be peak summer at some point.
But it gets more complicated!
Since a trip around the sun takes 365.242 days, and 0.242 is not 0.25, adding a day every four years would also result in a drift out of sync, as pointed out in this very helpful AP article.
To fix this discrepancy, if a year is divisible by 100 then it will not be a leap year: 1700, 1800, and 1900 were not leap years. But if it is also divisible by 400, then it will be a leap year — so 2000 was a leap year.
Because there is a discrepancy between our human-constructed calendars and the actual time it takes the Earth to orbit the sun.
It takes 365.242 days for Earth to complete one trip around the sun. So if we never added a day, our calendars would slowly drift out of sync with the seasons and November would be peak summer at some point.
But it gets more complicated!
Since a trip around the sun takes 365.242 days, and 0.242 is not 0.25, adding a day every four years would also result in a drift out of sync, as pointed out in this very helpful AP article.
To fix this discrepancy, if a year is divisible by 100 then it will not be a leap year: 1700, 1800, and 1900 were not leap years. But if it is also divisible by 400, then it will be a leap year — so 2000 was a leap year.
