Today will be the longest day in three years with scientists adding an additional second onto the final minute of the last hour on June 30. We have had 25 leap seconds since 1975, making this three year gap unusually long.
Leap seconds, like leap years, are added to account for the Earth's slowing rotation as a way to keep the clock in sync with the Earth and its seasons. Since the rotational changes are effected by other celestial bodies' gravitational pull on the Earth, we cannot determine the gravitational outcome prior to feeling these effects, therefore leap seconds are announced only six months prior to implementation.
The short notice can potentially cause problems for some computer systems. Since the time frame for updates is so short, the correction must often be added manually. Error in the update can cause loss of synchronization in communication networks, financial systems, and many other applications which rely on precise timing. During the last leap second, numerous leading websites crashed or incurred system errors.
The is currently a debate taking place in the scientific community to determine whether or not to abolish leap seconds due to the potential problems with our technological systems. But for now, enjoy the extra time!
The clock usually goes from 11:59:59 to 12:00:00. But during leap seconds, the clock should read 11:59:60 to account for the added second.