TONY CRADDOCK / SCIENCE PHOTO LIBRARY TONY CRADDOCK / SCIENCE PHOTO LIBRARY
Earth's time zones are displayed in this abstract image of a map of Earth set in a clock face. The Earth's surface is divided into 24 time zones, each representing 15 degrees of longitude or one hour of time. Time elapses as the Sun moves in a westerly direction, so that countries to the east of London and the Greenwich Meridian are ahead of Greenwich Mean Time (GMT) and countries to the west are behind. GMT became the legal time in Britain in 1880, followed by the establishment of international time zones in 1884. Standardisation was made necessary by the growth of railways across the larger countries, which made traditional local time-keeping redundant.
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