Greenwich Mean Time

GMT, or Greenwich Mean Time is the mean solar time of the meridian of Greenwich, England. This was the primary basis for calculating standard time
throughout the world until 1972 when it was superceded by UTC. However, although GMT has been replaced by atomic time (UTC) - it is still widely
regarded as the correct time for every international time zone. The atomic time clock is adjusted by leap seconds to maintain synchronicity with GMT.

Standard time, which is based on solar time, was introduced in 1883 by international agreement to avoid the complications that followed in railroad
time schedules when each community used its own local solar time. The earth was divided into 24 time zones. The base position is the zero meridian of
longitude that passes through the Royal Greenwich Observatory, Greenwich, England, and time zones are described by their distance east or west of
Greenwich. Within each time zone all clocks are set to the same time. In the scientific model on which standard time zones are based, each zone spans
15° of longitude; in fact, however, the borders of time zones are bent to conform with state boundaries and international frontiers as well as to
facilitate commercial activities. In 1966 the U.S. Congress passed the Uniform Time Act, which established eight standard time zones for the United
States and its possessions. In navigation, clocks are often set to the local time at Greenwich, which actually is Greenwich Mean Time (GMT).