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Sundials were used by many cultures to help the people know what time it was. When the Sun was directly overhead and the shadows of people and objects were at their shortest, it was said to be noon. As technology advanced, clocks and watches took the place of sundials. However, these clocks and watches were still set and checked by using a sundial.

Most towns and cities had a clock tower. This clock tower was the official time keeper for that city or town. Periodically the clock tower would be checked for accuracy using a sundial. This meant that every town had its own local time.

With the invention of the railroad and telegraph, this became very confusing. The need for standardizing the time zones became apparent. The Earth was divided into 24 separate time zones. Each time zone is either one hour ahead or one hour behind the time zone in front and behind it. Over the oceans, these time zones are exactly 15 ° of longitude. However, over land, the time zones are often altered along political and social borders. Most countries are small enough that the entire country easily fits within one time zone. Some larger countries like Russia, Australia, Canada, Brazil, and the U.S. span across multiple time zones.