How Time Zones Work: From Solar Noon to Standard Meridians

Time zones are geographical regions where identical standard civil time is enforced. Before railroads in the nineteenth century, each town set its clocks by local solar noon—when the sun stood highest in the sky. As rail and telegraph communication spread, local solar time caused dangerous confusion.

In 1884, the International Meridian Conference established Greenwich, London as the prime meridian (0° longitude). The globe was partitioned into 24 conceptual one-hour time bands of 15 degrees longitude each. Today, geopolitical boundaries, economic ties, and seasonal changes dictate how borders zigzag across time zones. Modern computing relies on the IANA Time Zone Database (tzdb), which tracks historical and current civil clock transitions with atomic precision.