Imagine you have been studying in London for two months. It is 1.00 pm. You are thinking about calling your best friend who lives in New York, but right now it is only 5.00 am there. Why are the times dif ferent? Due to the rotation of the Earth , when it is daytime in one part of the planet, it is nighttime in the opposite part. Time zones were created to match the time with the Sun's light. Since Earth is a sphere (360º) and it takes 24 hours to complete one rotation , it moves 15º ever y hour. This is why we have divided the planet into 24 time zones. 24 zones x 15º = 360º. Each time zone is a strip that goes from pole to pole and shares the same time. (25) The Prime Meridian, or Greenwich Meridian , is the base time zone. For ever y 15º we move east or west, the time changes one hour. If we move east of the Prime Meridian, we have to set our clocks forward the same number of hours as the number of time zones we cross. If we move west of the Prime Meridian, we have to set our clocks back the same number of hours as the number of time zones we cross. Sometimes time zones are adjusted for political reasons. Countries can decide whether to apply time zones or not. O T H E R P O I N T S O F V I E W -9 -8 -7 -8 -9 -6 -6 -5 -5 -4 -4 -5:30 -3 -3 -2 -1 0 0 +1 +1 New York São Paulo Mogadishu Moscow Madrid Kashi Yanji Tokyo San Francisco Paris +2 +2 +3 +3 +4 +3:30 +4:30 +5:30 +6:30 +5 +6 +7 +7 +8 +9 +8 +9:30 +10 +10 +11 +11 +12 +12 0 1,800 kilometres Scale Countries on an even standard hour Countries on an odd standard hour Countries with a half hour offset 10 h 11 h 12 h 13 h 14 h 15 h 16 h 17 h 18 h 19 h 20 h 21 h 22 h 23 h 24 h 1 h 2 h 0 h 3 h 4 h 5 h 6 h 7 h 8 h 9 h What time is it really? 26 Calculate. When it is 2.00 pm in Madrid, what time is it in São Paulo? And in Moscow? How many time zones would you cross if you travelled from San Francisco to Paris? Would you have to set your watch forward or back when you arrived? 27 Look at the map. Find China. If the sun rises in Kashi at 5.00 am, what time is sunrise in Yanji? How many time zones are there in the USA? How might this affect its population? 28 UNDERSTAND OTHERS. At what time in London would it be appropriate for you to call your friend in New York? Remember it should be a sociable hour in both cities when you call. 29 Have you ever heard the term jet lag? Find out what it means. Is it related to time zones? Why or why not? 30 What would happen if there were no time zones? Give examples. 25. Time zones 26
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