I have a confession to make.  Before researching this post I had only the most rudimentary understanding of leap years.  Digging deep into the recesses of my educational memory I recalled that the time it takes for the earth to travel around the sun differs slightly from our 365 days, so we add an extra day every four years to keep the calendar on track.

Good basic knowledge.  I’m sure I’d make my science teacher proud.

Writing a blog gives me a perfect excuse to dig around the internet about random things, especially the kind of general knowledge most everyone else remembers from elementary school.  Google is a good friend of mine.

Facts about leap years that I learned this weekend:

  • The Earth takes approximately 365.242189 days – or 365 days, 5 hours, 48 minutes, and 45 seconds – to travel around the sun one time.  (I can’t quite wrap my brain around all 6 of those decimal places.)
  • Without adding the leap day every four years we’d lose about 6 hours per calendar year. After 100 years our calendar would be off track by approximately 24 days, so basically we would lose an entire month per century.  I wonder which one they’d skip.
  • Julius Caesar initiated the first leap year over 2,000 years ago.  (“I came, I saw, I conquered…and in my spare time I padded every fourth February.”)

All interesting facts about leaps years, sure, but not earth shattering.  What did take me by surprise was the algorithm used to determine which years qualify for that extra day in February.  It had me flashing back to high school math proofs.

Apparently three criteria must be considered before declaring a leap year for the Gregorian calendar:

  • The year can be evenly divided by 4.
  • If the year can be evenly divided by 100, it is NOT a leap year, unless;
  • The year is also evenly divisible by 400.  Then it is a leap year.

Um, okay.  When the kids ask, I think I’ll just stick to that whole “every four years” thing. Otherwise we’d be looking at a whole new memory device…

30 days hath September,

April, June, and November;

All the rest have 31,

Except February alone.

Which only has but 28 days clear

And 29 in each leap year.

[As long as the year divides evenly by 4,

NOT by 100, which would close that door,

Unless 400 divides it also quite even,

Which makes it a Leap Year, you’d best be believin’!]

Rolls right off the tongue, doesn’t it.


Source: What is a Leap Year?