World Time Zones

Time zones were standardised in the late 19th century to coordinate railway schedules across large distances. Before standardisation, every city set its own local time based on the position of the sun — a practical impossibility once fast travel became common.

The world is theoretically divided into 24 zones of 15° longitude each (since the Earth rotates 360° in 24 hours). In practice, political and economic factors mean many countries use offsets that differ from the nearest theoretical zone — China, for example, uses a single time zone across its entire territory despite spanning five theoretical zones.

UTC (Coordinated Universal Time) is the global reference point. All other time zones are expressed as UTC+ or UTC− an offset. The International Date Line roughly follows the 180° meridian in the Pacific, where each calendar day begins and ends.