Leap Second: 07:59:60 on 1 July 2015

Were you aware that there was an “extra second” added on 1 July?  Probably not right? A second more or less is probably insignificant to most as it does not have much impact on people’s lives.

The phenomenon, called a “leap second”, takes place every few years, where an additional second is inserted to the atomic clock, or UTC (Coordinated Universal Time).

So why was there an extra second?

The speed of the Earth's rotation differs from day to day and year to year and in particular to this phenomenon, the Earth’s rotation is known to be slowing down due to factors such as the moon’s gravitational pull and earthquakes. Scientists introduced the atomic time scale in 1967, which is what the world's time system and UTC is based on. But due to irregularities of the Earth's rotation and the precision of the atomic time, a mismatch between both time scales will occur. An extra second has to be inserted when the difference between two time scales exceed 0.9 second.

Isn’t that amazing? But you would have thought how this phenomenon is a big issue and how it affects us right?

Well, during the last leap second on June 30, 2012, more than 400 Qantas flights were delayed when the airline's check-in system crashed, while websites such as Reddit, Mozilla and LinkedIn experienced glitches because the systems could not cope with the extra time. Companies who rely on sub-second precision such as stock markets, i.e. The Singapore Exchange (SGX), adjusted its system’s clock so that it runs 1 second ahead of the UTC.

As we all know, a leap year occurs every 4 years and an extra day is added to the month of February. For leap second, it occurs either on June 30 or December 31 and do not happen very often - about every 3 years.