Universal Time Coordinated (UTC)

Coordinated Universal Time, UTC, is the world’s reference timescale and the standard time of every modern navigation system, kept by atomic clocks and held to within 0.9 seconds of UT1 by inserting leap seconds. It is the successor to GMT for civil and navigational timekeeping: GNSS, the GMDSS, the Nautical Almanac’s hour entries, and the ship’s chronometer all work to UTC, and a celestial sight is timed in UTC to enter the almanac. The leap second keeps UTC tracking the irregular rotation of the Earth, so it never drifts more than about a second from solar time. Ship’s time is obtained from UTC by applying the zone description, the whole-hour offset for the ship’s longitude.