On June 30, the entire world will get an additional second at midnight.
Midnight will come later on Tuesday as an extra second is added to the official time set by atomic clocks.
The “leap second” means the last minute of June will have 61 seconds in it.
Leap seconds – and leap years – are added as basic ways to keep the clock in sync with the Earth and its seasons.
A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC) in order to keep its time of day close to the mean solar time, or UT1. Without such a correction, time reckoned by Earth’s rotation drifts away from atomic time because of irregularities in the Earth’s rate of rotation.
However, there are concerns the extra second could cause problems for some computer systems because it has to be added manually.
Timekeepers are divided over whether to keep the additional unit of time – and the issue is set to be debated at a meeting later this year.
Basically, our clocks are better at keeping time than the Earth is. UTC is based on an atomic clock, which calculates the length of a second based on (very predictable) changes in cesium atoms. It takes more than a million years to lose a second on atomic time.
News coverage has focused on the potential for software problems that could affect financial trading and other operations around the world.
Because the irregularity of adding leap seconds causes problems for computer networks, several proposals have been put forward to abolish them.
The issue is still being considered by the International Telecommunications Union (ITU) and is set to be discussed at the World Radiocommunication Conference in Geneva in November this year.
Delegates will aim to reach a decision to either end leap seconds or adopt a technical solution to reduce the problems they cause.
Since this system of correction was implemented in 1972, 25 such leap seconds have been inserted. The most recent one happened on June 30, 2012 at 23:59:60 UTC.