What is Universal Time Coordinated?

Universal Time Coordinated (UTC) is a time standard based on International Atomic Time with leap seconds added at irregular intervals to compensate for the Earth’s slowing rotation. A leap second is a positive or negative one-second adjustment to the UTC scale that keeps it close to Mean Solar Time at the Royal Observatory, Greenwich. The difference between UTC and Mean Solar Time is not allowed to exceed 0.9 seconds, so if high precision is not required, the general term Universal Time may be used. Time zones are expressed as positive or negative offsets from UTC. While each day contains 24 hours and each hour 60 minutes, the number of seconds in a minute can be 60, 61 or 59.