![]() This standard was known as New Zealand Mean Time. It was based on the longitude 172☃0′ East of Greenwich, that is 11 hours 30 minutes ahead of GMT. On November 2, 1868, the then-British colony of New Zealand officially adopted a standard time to be observed throughout the colony, and was perhaps the first country to do so. Time zones were a compromise, relaxing the complex geographic dependence while still allowing local time to approximate the mean solar time. The problem of differing local times could be solved across larger areas by synchronizing clocks worldwide, but in many places the local time would then differ markedly from the solar time to which people were accustomed. The increase in worldwide communication had further increased the need for interacting parties to communicate mutually comprehensible time references to one another. Some old British clocks from this period have two minute hands-one for the local time, one for GMT. Even though 98% of Great Britain's public clocks were using GMT by 1855, it was not made Britain's legal time until August 2, 1880. About August 23, 1852, time signals were first transmitted by telegraph from the Royal Observatory, Greenwich. This quickly became known as Railway Time. #Timezone horology class portableThe first time zone in the world was established on December 1, 1847, on the island of Great Britain by railway companies using GMT kept by portable chronometers. The use of time zones smooths out these differences. The difference between New York and Boston is about two degrees or 8 minutes, the difference between Sydney and Melbourne, Australia, is about 7 degrees or 28 minutes and the difference between London and Edinburgh is about 3 degrees or 12 minutes. Local solar time became increasingly awkward as railways and telecommunications improved, because clocks differed between places by an amount corresponding to the difference in their geographical longitude, which varied by four minutes for every degree of longitude. Plaque commemorating the Railway General Time Convention of 1883 in North America Greenwich Mean Time (GMT) was established in 1675 when the Royal Observatory was built as an aid to (English) mariners to determine longitude at sea, providing a standard reference time when each city in England kept a different local time. Mean solar time has days of equal length, and the difference between the two averages to zero after a year. Apparent and mean solar time can differ by up to around 15 minutes (as described by the equation of time) due to the non-circular shape of the Earth's orbit around the sun. When well-regulated mechanical clocks became widespread in the early 19th century, each city began to use some local mean solar time. Before the invention of clocks, people marked the time of day with apparent solar time (or "true" solar time) – for example, the time on a sundial – which was typically different for every settlement. ![]()
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