## Wednesday, February 29, 2012

### Leap Day

Due to events astronomical, today is Leap Day. Why?

A year is how long it takes the Earth to go around the Sun and back to where it started, and a day is how long it takes the Earth to spin about on its axis. Everyone knows there's 365 days in a year, but that's not quite right. It's more like 365 days and 6 hours, or 365.25 days. Multiply that by two and you find 730.5 days in two years. 1095.75 days in 3 years. 1461 days in 4 years. But wait! There are no quarter-days in the calendar, so the calendar hasn't been keeping track of those! It says there are only 1460 days in 4 years. After 4 years, our calendar is one day behind! What can we do about this? It just doesn't work out!

Well, every four years we'll just throw another day in there somewhere. Hence Leap Years. The problem is the amount of time it takes Earth to go around the Sun, the period of Earth's orbit, isn't an integral multiple of the period of Earth's rotation, which just means if you divide the period of orbit by the period of rotation, you don't get a whole number. Clearly there was no quality control when the solar system was made, because this is totally unreasonable.

If the solar system is a clock, it's as if the teeth on one of the gears aren't spaced evenly, so every once in a while someone has to reset it. But what can you do? We'd have to move the Earth or change the speed of its rotation to 'fix' the clock.

It's actually worse than that because a year isn't really 365 days and 6 hours long, more like 365 days, 5 hours, 49 minutes long. Now we're counting an extra 44 minutes every time we do a Leap Day, so to make up for that we have to skip Leap Day on years ending with 00 (like the year 1900), unless they're divisible by 400 (like the year 2000). Madness...

A sunset, because I don't have any relevant pictures. Sunsets happen on Leap Days.