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time zone

Different time zones exist because of Earth’s rotation. Earth rotates 360 degrees every 24 hours, and therefore different parts of the planet experience daylight and darkness at different times. To coordinate time with daylight, the globe is divided into 24 segments, each 15 degrees of longitude apart. The prime meridian in Greenwich, England, serves as the starting point for these divisions, creating a global framework for timekeeping.

While the theoretical model of time zones is straightforward, practical adjustments are often made to accommodate political, social, and economic factors. For instance, some regions have chosen to adopt time offsets of 30 or 45 minutes instead of the standard one-hour difference. These adjustments are made to better align with local solar time or to unify time within a country, as seen in places such as Newfoundland, Iran, and India.

Before the concept of time zones, each locality set its time based on the Sun’s position, leading to a chaotic array of local times. This system became impractical with the advent of rapid railway transportation in the late 19th century, which required a more uniform timekeeping system to avoid confusion in scheduling. The introduction of standard time zones was a solution to this problem, allowing regions to adopt a consistent time standard.

The Editors of Encyclopaedia Britannica