ime zones are areas of the Earth that have adopted the same standard time, usually referred to as the local time. Formerly, people used local solar time (originally apparent and then mean solar time), resulting in time differing slightly from town to town. With the expansion of the railways and as telecommunications improved this became increasingly awkward.

Time zones partially rectified the problem by setting the clocks of a region to the same mean solar time. Time zones are generally centered on meridians of a longitude, that is a multiple of 15°, thus making neighboring time zones one hour apart. However, the one hour separation is not universal and, as the map shows, the shapes of time zones can be quite irregular because they usually follow the boundaries of states, countries or other administrative areas.

All time zones are defined relative to Coordinated Universal Time (UTC). The reference point for Time Zones is the Prime Meridian (longitude 0°) which passes through the Royal Greenwich Observatory in Greenwich, London, United Kingdom. For this reason the term Greenwich Mean Time (GMT) is still often used to denote the "base time" to which all other time zones are relative.

UTC is, nevertheless, the official term for today's atomically measured time as distinct from time determined by astronomical observation as formerly carried out at Greenwich.

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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Time Zones".

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