Coordinated Universal Time date-time scale, based on the second, is equivalent to mean solar time at the prime meridian (0° longitude), formerly expressed in GMT.
UTC divides up time into days, hours, minutes and seconds. Days are conventionally identified using the Gregorian calendar. Each day contains 24 hours and each hour contains 60 minutes, but the number of seconds in a minute can be 60, or sometimes 61 or 59 (leap seconds added at irregular intervals to compensate for the Earth's slowing rotation).
UTC was defined in 1970 by the International Radio Consultative Committee, now ITU (ITU-R Recommendation TF.460-5).
