Friday, February 29, 2008


Today is February 29, 2008 - Leap Year Day in the Gregorian calendar.

Because it takes roughly 365¼ days for the earth to circumnavigate the sun, it’s necessary to add an extra day to our 365-day year every four years so that the months don’t get out of whack with the equinoxes and solstices. Otherwise, you have April showing up in mid-winter.

The Muslim calendar cares not for these things, being a purely lunar calendar. You have a new month whenever you have a new moon, and time of year be damned. It’s why Ramadan shows up in the spring some years, the fall in others. But since agriculture, with its regular planting seasons, is not a big deal to desert nomads, it was never an issue Back In The Day.

The Gregorian calendar - the most widely used calendar today - adds one slight refinement to the older Julian calendar, which has a leap year every four years. But because the solar year is actually about 11 minutes short of 365¼ days, the Julian calendar suffers from “season creep,” with January moving slowly but inexorably towards summer at the rate of just less than three days every 400 years. And so Pope Gregory proposed a slight modification: every year divisible by four is a leap year, but years divisible by 100 are not…unless they are divisible by 400.

So 1900 was not a leap year, and 2100 will not be, even though they’re divisible by four. But 2000 was a leap year, because even though it’s divisible by 100, it’s also divisible by 400. Got that?

That corrects for three days every 400 years. It’s still not perfect, but it will take about four thousand years to pile up a one-day error…and since the day is slowly increasing in length thanks to tidal drag (Tidal Drag! We’re all gonna die!), the error will actually be less than that. And I don’t expect to be around to worry about it.

For us Jews, of course, things get even more complicated. Since our calendar reconciles a lunar month (months always start with the new moon) with a solar year, seven years out of every nineteen are leap years. And we don’t just add a day, oh, no. We add an entire month. Since this year (5768) is a leap year, we have two months of Adar: Adar Rishon and Adar Sheni.

Which means, I guess, that if there were a Jewish equivalent of Sadie Hawkins day, we’d all be in trouble.

Happy Intercalary Day, Esteemed Readers!

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