Time zone
Time zones give specific areas on the Earth a time of day that is earlier or later than the neighboring time zones. This is because when it is daytime on one side of the earth, it is night-time on the other side. There are 24 time zones dividing the earth into different times, each with its own name, like the North American Eastern Time Zone. The North American Eastern Time Zone contains large cities in North America like New York City and Miami.
Greenwich Mean Time (GMT) began in 1675. This was when the Royal Observatory, Greenwich was built to help ships find their longitude at sea. GMT was a standard reference for time keeping when each city kept a different local time. When railways began carrying many people quickly among cities keeping different time, they adopted time zones to simplify operations. By about 1900, almost all time on earth was in the form of standard time zones.
Greenwich Mean Time is now called UTC (Coordinated Universal Time). UTC is the time standard of the world. All other parts of the world are offset (plus or minus) according to their longitude. Most of the zones are offset by a full hour, but there are some offset by half an hour or 45 minutes.
In some parts of the world they follow the Daylight Saving Time (DST), and during this period of time in summer they add one hour to their normal solar hour.
In the poles, the time is UTC in the North Pole and UTC+12 in the South Pole.
The time zones are numbered in relation to the UTC, so in Los Angeles the time zone will be UTC−8, in London UTC+0, in Rome UTC+1, and in New Delhi UTC+5:30.
Time Zone Media
Map of current de facto time zones. The map reflects the time actually observed in each location, regardless of legality.
Time zones of the world
World time clock, 2.5 m high. Made in Dresden 1690. Technical Instrument Museum, Dresden
Plaque commemorating the Railway General Time Convention of 1883 in North America
The control panel of the Time Zone Clock in front of Coventry Transport Museum
1913 time zone map of the United States, showing boundaries very different from today
World map of time zones in 1928
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DST observed DST formerly observed* DST never observed
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