Background
The UTC standard was officially standardised in 1961 by the International Radio Consultative Committee, having been initiated by several national time laboratories.
The system was adjusted several times until leap seconds were adopted in 1972 to simplify future adjustments. A number of proposals have been made to replace UTC with a new system which would eliminate leap seconds but no consensus has yet been reached.
Today, time zones around the world are expressed as positive or negative offsets from UTC, as in the list of time zones by UTC offset.
UTC is based on International Atomic Time (TAI), a time standard calculated using a weighted average of signals from atomic clocks located in nearly 70 national laboratories around the world. The only difference between the two is that UTC is occasionally adjusted by adding a leap second in order to keep it within one second of UT1, which is defined by the Earth's rotation. In the 41 years up to and including 2012, a total of 25 leap seconds have been added; the most recent was added on 30 June 2012.
Read more about this topic: Coordinated Universal Time
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