Tuesday, December 09, 2008

Just A Second

Well, it's been a long year, and it looks like it's going to get longer. December 31 will be just a second longer, as a leap second will be added on to the last day of the year. The extra second will be added between 6:59:59 and 7:00:00 pm, Eastern Standard Time.

Apparently, there are two time scales - one based on the Earth's rotation and the other independent of the Earth's rotation. Atomic time is based on a signal emitted by electrons changing energy state within an atom.

The International Earth Rotation Reference Systems Service monitors the two timescales and makes adjustments when necessary. The Earth does not have a steady rotation and is gradually slowing down, causing the time scales to get out of synch. Leap seconds have been added at various intervals since 1972. The last leap second was December 31, 2005.

2008 is the first year with both a leap day and a leap second.

2008 is not, however, the longest year on record. That goes to the year 46 BC, when Julius Ceasar introduced the Julian calendar. In order to correct the difference between the calendar date and the season, determined by the position of the Earth in its rotation around the sun, Ceasar added 2 months and 23 days, making the year a total of 455 days long.

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