Wednesday, December 31, 2008

Happy 2009!

As you're waiting for the ball to drop tonight (or whatever other marker you like), remember that 2008 will be hanging around for just a bit longer than the last few years. A leap second has been introduced for the first time since 2005 and only the second time this century.

Leap seconds are interesting (and somewhat problematic) to anyone interested in keeping a computer's clock exactly in sync with the official timekeepers because, unlike leap years, they do not follow a predetermined rule. Rather, the International Earth Rotation and Reference Systems Service (IERS) announces them based on observations of the earth's rotation. Despite what the name might suggest, the IERS does not actually cause the earth to rotate.

The Wikipedia link above has a good rundown. The official version is on the IERS site, but be advised that it's a bit technical. Evidently "How much is the accuracy of precession/nutation improved by MHB2000 and corrections to the precession constant and obliquity rate over the current IAU models?" is a frequently asked question.

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