The world is divided into 24 time zones, measured in increments of an hour.

Map by National Geographic Society
  • At noon on November 18, 1883, American and Canadian railroads instituted a system of "standard time," creating the North American time zones. In the mid-19th century, timekeeping was determined by train schedules—and each railroad kept its own time, making travel very complicated. In 1883, the railroad companies agreed to divide the country into four large sections: Eastern, Central, Mountain, and Pacific, corresponding to the 75th, 90th, 105th and 120th longitude meridians. All cities in each zone keep the same standard time, with each zone an hour ahead of the preceding one. At 11:00 a.m. in the Eastern Zone, it is 10:00 a.m. in the Central, 9:00 a.m. in the Mountain Zone, and 8:00 a.m. in the Pacific. This allowed businesses and passengers to coordinate their travel precisely.
    Within a year of the change, 85%of cities in the U.S. were using standard time. Today, most major countries use a similar system of time zones aligned with meridians of longitude. Russia, for instance, has nine time zones. Not all countries follow this pattern, however. China and India each use a single time zone, despite their vast sizes. Stations in Antarctica, where all longitude lines converge, use New Zealand time.
  • Term Part of Speech Definition Encyclopedic Entry
    align Verb

    to put in a straight line.

    converge Verb

    to meet or come together.

    meridian Noun

    line of longitude, dividing the Earth by north-south.

    precise Adjective


    railroad Noun

    road constructed with metal tracks on which trains travel.

    schedule Noun

    set of time tables or deadlines for appointments or completion of tasks.

    time zone Noun

    one of Earth's 24 divisions distinct by one hour, roughly 15 degrees of longitude.

    travel Noun

    movement from one place to another.

    vast Adjective

    huge and spread out.

    zone Noun

    area separated from others by artificial or natural divisions.

    Encyclopedic Entry: zone