| • Science | • People | • Locations | • Timeline |
Time zones are areas of the Earth that have adopted the same standard time. Formerly, people used local solar time (originally apparent and then mean), resulting in time differing slightly from town to town. As telecommunications improved and with the expansion of the railways 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 neighbouring time zones one hour apart. However, the one hour separation is not universal and, as the map below 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, EnglandEngland is the largest, the most populous, and the most densely populated of the four " Home Nations" which make up the United Kingdom of Great Britain and Northern Ireland (UK). Occupying the south-eastern portion of the island of Great Britain, England [1]. For this reason the term Greenwich Mean TimeFor alternate meanings of "GMT", see GMT (disambiguation). Greenwich Mean Time GMT is the mean solar time at the Royal Greenwich Observatory in Greenwich near London in England, which by convention is at 0 degrees geographic longitude. Theoretically, noon ( GMT) is still often used (by the BBCThe British Broadcasting Corporation BBC is primarily a national publicly-funded broadcaster based in the United Kingdom, which also has some international services. Some of the international services (such as BBC cable TV in America, Canada and elsewhere, for example, amongst others) 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.
GMT (UTC) is, incidentally, local time at Greenwich itself only between 01:00 UTC on the last Sunday in October and 01:00 UTC on the last Sunday in March. For the remainder of the year local time is UTC+1—known in the UKThe United Kingdom of Great Britain and Northern Ireland is a state in Western Europe, usually known simply as the United Kingdom the UK Britain or less accurately as Great Britain . The UK was formed by a series of Acts of Union which united the formerly as British Summer TimeBritish Summer Time (BST is the daylight saving time in effect in the United Kingdom between the last Sunday in March and the last Sunday in October each year. In both cases, the change takes place at 01:00 Greenwich Mean Time (GMT). BST is the same as Ce (BST).
The time for a location is given relative to UTC. Some examples:
Where the adjustment for time zones results in a time the other side of midnight from UTC, then the date at the location is one day later or earlier. Some examples:
Note: The time zone adjustment for a specific location may vary due to the use of daylight saving time.
See also: Sidereal time Calculating local time