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.
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