eli5 How time zones were made and how the lines for time zones were created?
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In 1884 a bunch of countries met in Washington DC to decide where longitude 0 was.
They eventually decided that 0 would be running across a science place in the English town of Greenwich.
So from then on that because 0 for the time zones as well.
Called Greenwich Mean Time or GMT, later called Universal Time Coordinated or UTC after some minor tweaks were added.
And after that, each country decided which parts were which time zones, completely free to mess around with it however they wanted for any reason. Because no one could stop them.
For example, the USA decided that it would have 4 time zones for their continental places, while China decided to have 1, and the whole country follows the time zone of where their capital was. Despite China being wide enough to cover 3 / 24ths of the world’s longitude.
The UK moved the time zone for their South East Asia holdings into the time zone to the east, so they wouldn’t have to change times between those and Hong Kong.
Australia has a bunch of places that aren’t even full hours off UTC.
Northern Territory is UTC +9:30.
Time zones arose out of necessity as fast travel along long distances (East-West) became more feasible. At first it only really mattered to companies and individuals who traveled in such a fashion and they came up with time zones as they saw fit.
Over time different zones over different countries merged and combined to form a world wide time zone system.
For the most part, local governments decide the time zones within their borders, and the lines are generally drawn to align with geographical and political boundaries, to be the obtrusive to the people that live within.
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