If everyone on Earth used the same clock, daily life would be confusing. You might wake up at your normal time, even though the clock says 2:00 a.m., eat lunch at 8:00 in the morning, and end your day at 4:00 in the afternoon. As the Earth rotates, different parts of the world move into and out of sunlight. When it is noon in one place, it may be midnight somewhere else. To keep clocks reasonably close to the sun’s position in the sky, most nations have agreed to divide the world into 24 time zones.
Before Universal Time
Until the nineteenth century, each city kept local time. Clocks were not often very accurate, but they could be synchronized with a sundial. Railroad engineers created the first time zones in Great Britain. A railroad would use the same tracks to send trains in different directions, so an inaccurate clock could cause a disaster.
The Prime Meridian
In 1884, American President Chester A. Arthur invited representatives from many nations to the International Meridian Conference in Washington, D.C., to create a standard system for world time and navigation. After much debate, the delegates chose Greenwich, England, just outside London, as the location of the prime meridian.
The time along the prime meridian in Greenwich, England, became known as Greenwich Mean Time, or GMT. People in different time zones often use Greenwich Mean Time. The east coast of the United States is five hours behind Coordinated Universal Time (UTC), so if it is midnight in Greenwich, it is 7:00 p.m. in Washington. During Daylight Saving Time, the difference is four hours.
Time Zones in the United States
There are four time zones in the contiguous United States. The contiguous United States refers to the forty-eight connected states and does not include Alaska or Hawaii. The time zones 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 usually one hour behind Pacific Time, and Hawaii is usually three 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, but even though Nome shares the same time zone as Juneau, the sun reaches its highest point in the sky in Nome as late as 3:08 p.m.
Time Zones Around the World
China has also chosen to use a single time zone, even though it spans a wide area. All of China uses UTC+8. In parts of western China, the sun may not rise until late in the morning.
Much of western Europe also uses a shared time system. Germany occupied France during World War II, and German authorities moved French clocks forward to align them with German time. Spain later decided to keep the same time as Germany and France, even though much of Spain is geographically closer to Greenwich Mean Time.
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Mr. Donn has an excellent website that includes a section on
Geography.
Cite this page:
Dowling, Mike, “Time and Time Zones: Greenwich Mean Time,” mrdowling.com, September 17, 2026. Web. [Date of access].
Sources:
International Meridian Conference, Protocols of the Proceedings (Washington, D.C., October 1884)
Ian R. Bartky, Selling the True Time: Nineteenth-Century Timekeeping in America (Stanford University Press, 2000)