Friday February 29, 2008

Happy Leap Day!

Happy Leap Day! Today, February 29th, comes only once every four years. Of course most of you probably know all of this already. Most of you, but probably somewhat fewer, know *why* we have leap years. The short answer is to keep the calendar in synch with the seasons. A longer explanation can be found here.

A deeper question is, why do we need the calendar to be in synch with the seasons? I'm not sure. Some origins are probably religious, so that we wouldn't have Easter in the winter and Christmas in the fall. Other reasons might be agricultural, so that people know when to plant and when to harvest and when the Nile is likely to flood. In today's modern age this is probably no longer necessary. The fixation on seasons probably originated in the northern hemisphere; the folks in Australia don't seem to complain that Christmas is in the summer. Well, maybe they do, but I haven't heard them.

What's notable about leap year is that it's based on actual astronomical principles: the relationship of the day to the year. This is unlike Daylight Saving Time, which is purely a social construction. DST doesn't actually save anything, and it causes a lot of confusion. Occasionally somebody is an hour off the next day, and occasionally I'm startled by the odd clock that I forgot to reset. Worse, different countries change times on different dates, so the usual time zone differences -- bad enough to begin with -- are temporarily made worse.

Leap years I can live with, but let's just get rid of DST.