Why European Time is Not Constant


The Sunday Nation


27 March 2005


A fan of the English Premier League football tournament has a puzzling question: why is it that in some months match kick-off is three hours behind Kenyan time and at other times it is two hours behind? Does Greenwich Mean Time (GMT) change and, if so, when?

No: GMT is always constant, what changes is British Standard Time (BST). In the winter months (October to March the following year), BST is equal to GMT, but in summer (March to October) BST is pushed one hour ahead of GMT. This year (2005), the changeover was done last night – at 1:00am, all clocks were pushed one hour ahead to read 2:00am.

Thus while yesterday (March 26) Britain was three hours behind Kenya, today (March 27) it is two hours behind. The reverse adjustment will be done in October – at 2:00am on the 30th day of that month, all clocks will be pushed back to read 1:00am. Obviously, the next question is; why make these changes?

In the regions outside the tropics, daytime in summer is very long – sometimes there can be up to 18 hours of daylight in a 24-hour period during the hot season. The sun may rise at 3:30am and set at ten o’clock at night. The reverse happens in winter – there can be only six hours of daylight on some days.

Now, people generally go to sleep late and wake up early in the morning. Bed time for most of us the world over is around 11pm and we wake up at about 6am or 7am. In summer in Europe, for example, if the sun sets at 10pm, you will turn on your lights for one hour and switch them off at 11pm when you go to sleep.

Thus Benjamin Franklin, (who else!) came up with a bright idea in 1784: what if clocks are pushed ahead by one hour in summer? Instead of sunset being 10pm, the sun will now stay up until 11pm. That way people won’t need to turn on the lights in the evening thus saving on energy – electricity, paraffin or whatever they use for lighting. As with all brilliant ideas, Franklin’s suggestion was scoffed at and it was not until the early 20th century (over 100 years later!) that nations started to give it serious thought. Germany was the first country to implement it in 1916 (during World War I).

In tropical countries, the duration of daytime and nighttime remains fairly constant throughout the year. In Kenya for example, the maximum variation in the length of daylight is less than 15 minutes thus changing clocks would not be of any discernible benefit. Indeed, only two countries in Africa – Egypt and Namibia – have daylight saving time.

But there is still one more question: why is summer daylight time longer than nighttime? That is a story for another day…

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