Coordinated Universal Time serves as the reference point from which all time zones are measured.

The longer version

Every zone is expressed as an offset from one shared reference, so a clock in any country can be converted to any other by simple addition. That reference is maintained by a network of atomic clocks whose readings are combined into a single agreed timescale. The reference replaced earlier systems based on a single observatory's measurements.

It is not tied to any one place's solar time, though it stays closely aligned with the rotation of the planet through occasional leap seconds. Radio signals, satellite links and data networks all distribute it, which is why servers, bank transfers and flight plans can share one unambiguous timestamp. Without it, global scheduling would require constant translation.

Where this entry sits

These facts wander through clocks, calendars, time zones, and the long human effort to measure passing hours. You will find leap years, odd month lengths, ancient sundials, and the reasons modern timekeeping works the way it does. The full list sits on the Time and Calendars page, where every entry is listed in order.