The International Earth Rotation and Reference Systems Service announced for tomorrow the addition of an extra second, which is meant to help match people’s clocks to the Earth’s slowing spin on its axis, which occurs at ever-changing rates affected by tides and many other factors. These leap-seconds have been introduced in 1972 and the last one was added in 2005.

The calculation process is made by the scientists at the IERS organization, which decides when a new second is needed; the extra seconds are known to have occured from six months to seven years of one another. The scientists collect and average the measurements of the Earth's rotation from all over the world. Each January and July it issues a notice letting know whether a leap second is required in the next six months.

The second will be added at 23 hours, 59 minutes and 59 seconds Coordinated Universal Time, also known as UTC. The idea is to make sure clocks vary from the Earth's rotational time by a maximum of 0.9 seconds before an adjustment. This keeps UTC in sync with the position of the sun above the Earth.

UTC is kept by extremely precise atomic clocks, found all over the world, accurate to about a billionth of a second per day.

According to the Tokyo-based National Institute of Information and Communications Technology, which is handling the atomic clock as the basis for civil time, one second will be added once the clock will read 8:59:59 a.m. on January 1, 2009.