Thursday, March 06, 2008

So I've been reading up on the concept of Leap Year since we are experiencing one this very year and just had our Leap Day a few days ago. Of course we've all been taught in grade school that an Earth year is in reality 365.25 days, which is why every four years we add an extra day to our calendar. That way over time, our seasons don't get all out of whack. And for just about everyone alive and able to read this post right now, that rule will suffice just fine until we die.

However, what we aren't taught (at least I wasn't anyway) is that a standard Earth year is in reality 365.2425 days. Doing the math we can quickly deduce that our little add-a-day-every-4-years trick will truck the world ahead a few days after just a few hundred years, reeking havoc for our grandkids' grandkids' grandkids' whom would no longer be able to experience the Winter solstice on December 21 (assuming of course that the Maya calendar that predicts the end of the world on December 21, 2012 is incorrect). So to prevent this cataclysmic catastrophe the powers-that-be devised a sneaky little way to make that work. It gets a little complicated so try to keep up.

We in fact do not simply add a day every four years. Instead the logic goes a little something like this. If the year is evenly divisible by 400, then there will be a Leap Day that year. For example, 1600, 2000, 2400, 2800 are all years that have a Leap Day. If however the year is evenly divisible by 100, but NOT evenly divisible by 400, then there will be no Leap Day. Par exemple, 1800, 1900, 2100, and 2200 are all years that have NO Leap Day. Finally if the year is evenly divisible by 4, but is NOT evenly divisible by 100 UNLESS it is evenly divisible by 400, then there will be a Leap Day. Just like this year, or 2012, or 1980 or 1600. Here is how the math all works out. 365 days a year, plus one day out of every four years, minus one day out of every 100 years, plus one day out of every 400 years. 365 + 1/4 - 1/100 + 1/400 = 365.2425 days a year. Pretty clever considering I would just increase the time of a second by a fraction amount so that a year would be exactly 365 days. This however would eventually result in a completely night time, 12 o' clock "high" noon. Resulting in further changes by me in minutes, hours and days.

But like I said, unless I plan on living until I'm 120 (which I am not unless I look like I do now my entire life) a Leap Day every four years for my entire life should do fine. If we really want to get technical, a year is actually 365.242374 days long anyway, and increasing. Luckily the unpredictability of that increase should be close enought to keep on track with the above algorithm for millennia to come.

1 comment:

The McWhorter Family said...

Thanks for the explanation and the two new posts!