Those eager to put 2008 behind them will have to hold their good-byes for just a moment this New Year's Eve. The world's official timekeepers have added a “leap second” to the last day of the year, to help match clocks to the Earth's slowing spin on its axis, which takes place at ever-changing rates affected by tides and other factors. The International Earth Rotation and Reference Systems Service made the decision based on its monitoring of the Earth's rotation, to make sure clocks vary from the Earth's rotational time by no more than 0.9 seconds before an adjustment. The first leap second was introduced on June 30, 1972. The last was added on Dec. 31, 2005. They have been added at intervals ranging from six months to seven years. __
