Why do I have to reset my watch if I travel to Asia?

Your question of the month in March (2014)
Jasmin, 10 years old

The Earth is round and completes a full rotation within one day, that is to say in 24 hours. The Sun therefore only shines on one part of the Earth for a certain length of time, our daytime. It is then dark on the opposite side of the world, their nighttime.

Because everybody wants to see the Sun during the same daytime hours the world was divided into separate time zones. There is a one hour’s difference between the various zones. If you fly to China for example, you have to travel through several time zones and therefore have to put your watch forward six hours. China is actually so far away from Germany that it is already the evening there while we are having lunch!

By the way, some countries such as India and Nepal choose a time zone that is not a full hour different to the next time zone. There are various reasons for them doing that. Either the country is exactly between two time zones, or there are historical or political reasons.