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he period called the day is the time for the Earth to rotate once upon its axis with respect to the Sun. It has arbitrarily been divided into twenty-four hours. The twenty-four hour division has led to a very practical geographical division of the Earth into twenty-four zones, east and west, called time zones. The rotating Earth causes the Sun to appear to move westward, covering one time zone each hour. North-south lines, called standard meridians, are described as passing centrally through each time zone. The standard meridians do not form the boundaries of the zones, but the boundaries lie half-way between these meridians. For political convenience, the boundaries of the time zones are often distorted east or west to include neighboring communities within the same time zone.

During the period of British maritime dominance, the zero, or prime meridian was designated as passing through the observatory at Greenwich, England. The standard meridians then are numbered east and west from there to the one on the opposite side of the Earth, called the international date line.

The system is fundamentally sound, for it permits travel throughout the world under standardized time conditions. All clocks within a time zone read the same under these standardized time conditions and that time is called the standard time of that zone. When one moves from one time zone to an adjacent one, the time must be changed by a full hour. If there were no time zones, as was once the case, each community would set its own time based on the passage of the Sun at that particular location. This, of course, led to a great deal of confusion until time zones were agreed upon. The need for such standardization occurred with the development of the railroads which quickly spanned the continents.


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