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Tonight you will have one extra second with which to celebrate the new year. A leap second, to be exact. This leap second is not a unique event – in the last 40 years, there have been 22 leap seconds. The last one occured in 1998.

The reason for the leap second is because of disputes between astronomers and physicists. Traditionally, our time scale is based upon the rotation of the Earth on its axis, as well as its rotation around the sun. However, this time is not a constant – that is, the length of a day has been ever-so-slowly increasing for many years. Physicists would rather have time be a constant, and thus invented the atomic clock and an exact time measurement. In order to keep the atomic clock in sync with the rotation of the Earth, leap seconds are added to the clock every few years.

How will you spend your leap second?