It is 3pm in Lagos, 2pm in London, 9am in New York, and 11pm in Tokyo. You would have heard something similar if you watch the news on foreign television stations. But have you ever wondered how it all came about? Why do different parts of the earth have different local times, and how is it calculated?
Well, the reason has to do with the rotation of the earth round the sun as you will learn shortly.
Time zones are based on the fact that Earth moves through 15 degrees of longitude (imaginary vertical lines drawn on the globe) each hour. Therefore, there are 24 standard time zones (24 hours x 15º=360º), which is the sum of angles in a circle.
Time zones are counted from the Prime Meridian (0º longitude), which runs through Greenwich, England. Each time zone is based on a central meridian, counted at 15º intervals from the Prime Meridian, and extends 7½º to either side of the central meridian.
For example, Nigeria lies between the longitudes 3° and 14° E of the Greenwich Meridian, much of which is in the zone of the 15ºE central meridian (GMT+1), and the time zone for this meridian includes all locations between 7½ºE and 22½ºE.
Lagos, though lies at longitude 3° 27′ E, and falls under the time zone for the Greenwich Meridian ( 7½°W – 7½°E), but for the sake of simplicity, and so that all parts of the country will operate at one time, it has been grafted into the GMT+1 time zone.
The need for standard time zones emerged with the spread of high speed transportation systems – first, trains and later, airplanes.The system of time zones that is in use till date was agreed upon by delegates from 27 countries who met in Washington DC in 1884.
Countries like the United States operate at 4 time zones – while it is 9am (GMT -5), Wednesday in New York; it is 6am (GMT -8), Wednesday in Los Angeles – because the country spans about 3,000 miles (over 4,800 km) from East to West. But China, though spanning over 3,000 miles (over 5,000 km) from East to West operates at just one time zone (GMT+8).
Countries like New Zealand start the day first, followed by Japan, Australia, Russia, China and India, followed by countries in Europe and Africa, followed by countries in North and South America, and ending on islands out in the Pacific ocean, like Hawaii and finally Samoa.
