Time zones exist because the Sun reaches its highest point at different moments around the world.

The longer version

Sunlight strikes a curved surface, so the moment of local noon sweeps steadily westward as Earth turns. Two towns a few hundred kilometres apart differ by minutes in solar terms, and before standardisation each settlement simply set its clocks to its own sky. A traveller moving east gains time, moving west loses it.

Railways broke that arrangement. Timetables listing dozens of local times were unreadable and dangerous, so regions agreed to share a single standard instead. The compromise means clock noon rarely matches the Sun at its highest, and across a wide country the gap at the edges can grow to more than an hour.

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.