Something peculiar is going to take place today at 10 a. m. Australian Eastern Standard time, as an extra second will be added to the time between 09:59:59 and 10:00:00. This will make 1st July, 2015 or 30th June, 2015 at some other place of world, one second longer than the length of a standard day.

This extras second theory is a result of 'Leap second'. It will be the 26th leap second since it was first introduced in 1972.

Experts in explanation why this extra second is necessary to the day said historically the second had been defined as a fraction of the day. Astronomers in early 2oth century determined that earth's rotation was not constant. They said that it was slowing down.

This meant that a second defined in this fashion would slowly lengthen over time. Later the development of atomic clocks in the 1950s allowed the second to be defined with incredible accuracy, with a variance of only one part in 1014.

As a result, the second was redefined in 1967 by the International Committee for Weights and Measures in 1967. It was then no longer attached to earth's rotation. Instead it was defined in terms of a very particular property of a caesium-133 atom.

As per experts, this mechanical definition disconnected the second from the length of the solar day. According to the new definition 86,400 seconds make up a standard day.

The main reason earth is lagging is tidal friction from the Moon, which by itself would increase the length of the day by 2.3 milliseconds each century.

Therefore a leap second is added to keep the time of noon at Greenwich (Greenwich Mean Time) in line with noon as measured by the atomic clock (International Atomic Time).

The task of adding seconds was initially done by the Bureau International de l'Heure, the executive body of the International Commission of Time, which was part of the International Astronomical Union (IAU).