Friday, February 29, 2008

Happy Leap Day!

Sincerely. Happy Leap Day! If you know me at all, you might think I am being disingenuous, sarcastic, or hypocritical by saying this. Not at all. Leap Day is the only day in popular culture that is an acknowledgement of our intellectual progress rather than of our stupidity. It is the only day that, while arbitrarily placed, does not exist arbitrarily.

The Earth rotates on its axis once a day, and travels around the Sun once every 365.256366 days. A year does not divide evenly into days. Therefore, if we held to a firm 365 days in a "human" year, our seasons would flip about every 700 years. To keep things stable, we insert an extra day every 4 years. But because the fractional portion is slightly larger than 0.25, we need to remove a few leap days once in a while. Every 400 years, we remove 3 leap days. 1700, 1800, and 1900 did not have leap days, and 2100, 2200, and 2300 will not. 1600 and 2000 did.

As humans, we have known about the day/year problem for thousands of years. How many people today do you think could explain the meaning of February 29th?


At 3:56 AM, Blogger Mikael Ölmestig said...

It is generally taught in school here in Sweden, but I don't know if people remember it. The seasons here has changed here anyway, now we seem to have autumn the year around. But that is another problem.

At 12:17 PM, Blogger Jeff said...

Since a year is 365.256366 days, shouldn't we have to ADD an extra leap day every 157 years instead of leaving one out every so often?

At 3:02 PM, Blogger ekted said...

Consider if you had a stick that was 12.1 inches long and you were measuring out yards. Every 10 sticks you would be adding an extra inch. Every 360 sticks you would be adding an extra yard.

At 9:01 AM, Blogger Jeff said...

Right. I understand why we have leap days.

But why do we skip having one occasionally, when EVERY year has that extra quarter-day that has to be accounted for? And when does that extra 0.006366 get accounted for? (I know the answer to that second one actually - we occasionally have 'leap minutes' that take care of it.)

At 9:06 AM, Blogger ekted said...

By removing 3 leap days every 400 years, we are removing about 10.8 minutes per year.

At 9:16 AM, Blogger Jeff said...

OK, found my answer at Wikipedia:

"However, some exceptions to this rule are required since the duration of a solar year is slightly less than 365.25 days."


Post a Comment

<< Home