Why do we have time zones?
Time zones establish a regular sequence of time changes around the world. All the places in each zone have the same time. It is called standard time. Travelers often pass through time zones. When it is noon in Chicago, for example, nit is 6 o’clock in the evening in London.
We can understand why time is not the same everywhere, if we think of telling time by the sun. It is apparent noon when the sun is highest in the sky. When it is noon in your town, it is also noon everywhere else straight north and straight south of you. But a difference of only a few miles east or west makes a difference of a minute in sun time.
When it is noon in one town, it is not yet noon in a town 10 miles west, and it is already past noon in a town a few miles east. If every town set its clocks exactly by the sun, few places would be on the same time. For this reason the world has been divided into 24 equal time zones. All the clocks in a time zone are set at the same time. Each zone’s time is one hour earlier than that of the zone east of it. – Dick Rogers