Endless February

February 29, 2008 at 7:53 am Leave a comment

images5.jpegLast night I lay awake pondering leap day. Yes, FoHi friends, we are now on Day 29 of February, which really isn’t something to celebrate. With its blasts of cold and otherwise depression-inducing weather, February is not exactly a month many of us are looking to prolong.

There’s one well-known custom for leap day: women can propose marriage to their beaus. Clearly this is a nonstarter for our purposes if you consider how many women already take the initiative (do they give him a ring?); same-sex couples; and that marriage itself is so last generation (regardless of the regrettable piece in this month’s Atlantic) .

So let’s forget about custom and instead focus on understanding how adding 1 day every 4 years keeps the world in order. (Note that I’m pulling from Wikipedia’s entry on this because this is not particularly subjective or hidden information.)

In the Gregorian calendar, the current standard calendar in most of the world, most years whose division by 4 equals an integer are leap years. In a leap year, the month of February has 29 days instead of 28. Adding an extra day to the calendar every four years compensates for the fact that a solar year is almost 6 hours longer than 365 days.

Easy enough, right? But the universe could never be as simple as shtupping 1 extra day into the calendar every 4 years—“almost 6 hours longer”—so here’s where Rule 2 comes in:

However, some exceptions to this rule are required since the duration of a solar year is slightly less than 365.25 days. Years which are evenly divisible by 100 are not leap years, unless they are also evenly divisible by 400, in which case they are leap years. For example, 1600 and 2000 were leap years, but 1700, 1800 and 1900 were not. Going forward, 2100, 2200, 2300, 2500, 2600, 2700, 2900, and 3000 will not be leap years, but 2400 and 2800 will be. By this rule, the average number of days per year will be 365 + 1/4 − 1/100 + 1/400 = 365.2425, which is 365 days, 5 hours, 49 minutes, and 12 seconds.

And here’s where the whole thing breaks down:

The Gregorian calendar was designed to keep the vernal equinox on or close to March 21, so that the date of Easter (celebrated on the Sunday after the 14th day of the Moon that falls on or after 21 March) remains correct with respect to the vernal equinox. The vernal equinox year is about 365.242374 days long (and increasing), whereas the average year length of the Gregorian calendar is 365.2425.

The marginal difference of 0.000125 days means that in around 8,000 years, the calendar will be about one day behind where it is now. But in 8,000 years, the length of the vernal equinox year will have changed by an amount which cannot be accurately predicted. Therefore, the current Gregorian calendar suffices for practical purposes, and Herschel‘s correction (making 4000 AD not a leap year) will probably not be necessary.

The earth and my head are spinning. I’m just glad I won’t be around to see it. In February 8008, let’s face it: no one will want to marry me, regardless of how much I beg and plead and how much Botox I use.

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Entry filed under: Forest Hills, holiday, Rant, timely topic.

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