when you travel east or west to a different country, you have to change the time on your watch. this happens because the earth turns , so when it is daytime in some parts of the world , it is night - time in others. we divide the earth into 24 time zones, one for each hour of the day . all the places in the same time zone have the same time. we start counting form Greenwich,England .when it is 12 pm in Greenwich and you travel east to a place in the next zone, Rome for example, it is 1 pm. if you travel west to a place in the next zone, The Azores for example , it is 11 am.