If only Mother Nature had been just a little neater on this one and gotten the day and the year to line up together a little better. Then we wouldn't have all this leap year stuff to deal with.
But no, the earth's trip around the sun, which determines the year, cannot be measured in a neat whole number of rotations of the earth on its axis, which determines the day.
The solar year is approximately 365-1/4 days long, and our current solution to this odd little fraction is to add an extra day every four years – except for round century years (the double-zero ones like 1900) unless they are divisible by 400. Thus the year 2000 was not only "Y2K," with all that meant to strike fear into the hearts of IT departments everywhere; it was a leap year, to boot.
And so is 2008. Today, Friday, Feb. 29, is leap year day – an intercalary day, inserted to keep the calendar, and us, on track.
The idea is that a given date needs to mean something on the calendar from year to year. The vernal equinox, when day and night are equal, happens about March 21 in the Northern Hemisphere. So the relationship between the little numbered boxes in our daybooks and the movements of the heavenly bodies is more or less constant.
In a calendar without a provision for leap year, as in the Muslim lunar calendar, a given date "migrates" across the year. Thus the fasting month of Ramadan sometimes occurs during the high summer, when abstaining from water during the heat of the day represents a particular sacrifice and even a danger.
In a nomadic society, the lack of fixity wasn't much of a problem, but agrarian societies found it useful to plant and harvest according to a fixed calendar.
In the commercialized West, this fixed quality of the calendar assures the merchant class that the days before Christmas will always be short and getting shorter, leaving shoppers particularly susceptible to the suggestion that buying more stuff is a good way to cheer up themselves and their loved ones.
The Roman year started March 1. This explains why all the fiddling around with extra days happens in February, the bedraggled last month of the year.
It also explains why those later months, with their names referring to numbers in Latin, seem two months off. September, for instance, looks as if it ought to be the seventh month.
The Romans originally alternated between months of 30 days and months of 31. But when it was decided to rename the sixth month for Emperor Augustus Caesar, the feeling was that it wouldn't do to have one imperial namesake month (July, already named for Julius Caesar) with 31 days and another one with only 30. And so an extra day was borrowed from February.
Over time, it became clear that the Julian solution was an overcorrection that was pushing the vernal equinox a little earlier, by the calendar, every year. By the time Pope Gregory introduced his reform in 1582, the gap to be made up was 11 days. It took a while for the reform to catch on. It pushed dates back – later, that is. George Washington was born Feb. 11, 1732, by the Julian calendar. But when the British Empire adopted the Gregorian calendar later in the 18th century, his birthday became Feb. 22.
If all this calendar-shifting is beginning to make you think of the way the presidential primaries have been shaken together and mixed up this year, well, hey, you and me both.
In looking into all this, however, I've discovered there is a wonderfully spiffy Latinate term referring to leap years – bissextile. As a noun it means the extra day; as an adjective, it means referring to leap year.