Time Zones

Days and nights occur because the earth is spinning on an axis. Approximately half of the earth's surface is illuminated by the sun, but since the earth is constantly turning, it is necesssary to divide the earth into twenty-four time zones, one for each hour of the day. Some time zone boundaries zigzag so that people living in one region or country can have the same time.

Until the nineteenth century, each city kept local time. Clocks were not often very accurate, but they could be synchronized, or matched, with a sundial. the first time zone were created by railroads in Great Britain. A Canadian named Sanford Fleming first proposed the idea of universal time zones, and by 1900, most nations began to use what became known as "standard time."

The time along the prime meridian in Greenwich, England, is known as Greenwich Mean Time, or GMT. People communicating across two different parts of the globe often use Greenwich Mean Time. The east coast of the United States is five time zones behind GMT, so if it is midnight in Greenwich, it is 7:00 p.m. in Florida. Most of the United States sets their clocks ahead one hour in the summer, so during Daylight Saving Time the east coast is four hours behind Greenwich Mean Time.

There are four time zones in the continental United States. The continental United States refers to the forty-eight contiguous states and does not include Alaska or Hawaii. They are Eastern, Central, Mountain, and Pacific. You might notice that live television programs often begin at 8:00 Eastern, 7:00 Central, 6:00 Mountain and 5:00 Pacific. Alaska is an hour behind Pacific Time and Hawaii is two hours behind Pacific Time.

For convenience, almost all of Alaska uses a single time zone. During the period when Daylight Saving Time is not in use, the sun is overhead at about noon in Alaska's capital, Juneau. Juneau is in the eastern portion of Alaska. Nome is in western Alaska, and while Nome has the same time zone as Juneau, the sun is directly overhead as late as 3:08 p.m.

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