What is time's 5?

Answer 1

GMT means Greenwich Mean Time, which is the equivalent of UTC (Coordinated Universal Time). The GMT time zone is based on when it is exactly mid-day over Greenwich, London, UK, i.e. when the sun is at its highest point in the sky there, which would be approximately half-way between sunrise and sunset.

As the earth spins, the sun moves over other countries and they experience mid-day at a later time. If a country is in the time zone GMT -5 (minus five), then when it is mid-day GMT in London, such a country would be five hours behind GMT, i.e. seven a.m. (in the morning) in the GMT -5 zone.

Cuba is GMT -5, for example.

Of course, before the sun was over Greenwich, it had travelled accross Asia and Europe.

It was mid-day there before it was mid-day in London. In those areas East of Greenwich (specifically the 'Greenwich meridian' line of zero longitude) their time zones are GMT + (plus) so many hours. If a country is in the time zone GMT +5 (plus five), then when it is mid-day GMT in London, the time in that other country is five hours ahead of GMT, i.e. it is five o'clock in the late afternoon in that GMT +5 zone.

e.g. Calcutta is GMT +5

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