This clock, on top of the information booth at Grand Central Terminal in New York City, is dutifully adjusted twice a year to accomodate Daylight Savings Time.

Photograph by Anthony Ferrara, MyShot

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  • On March 31, 1918, the United States observed the beginning of its first daylight saving time (DST). On this day, Americans set their clocks an hour ahead, increasing the amount of afternoon sunlight. Only two weeks earlier, the Congress legally established DST. The U.S. was motivated by a desire to conserve coal (a major source of heat and light) during World War I.

    While Congress repealed mandatory DST in 1919, it would continue to be widely practiced across the U.S. As many sources of energy become scarce, conservation strategies like DST may become increasingly important parts of energy policy.

  • Term Part of Speech Definition Encyclopedic Entry
    coal Noun

    dark, solid fossil fuel mined from the earth.

    Congress Noun

    legislative branch of the government, responsible for making laws. The U.S. Congress has two bodies, the House of Representatives and the Senate.

    conserve Verb

    to save or use wisely.

    energy Noun

    capacity to do work.

    mandatory Adjective


    motivate Verb

    to inspire or cause.

    policy Noun

    set of actions or rules.

    repeal Verb

    to overturn or reject something that was once guaranteed.

    World War I Noun

    (1914-1918) armed conflict between the Allies (led by the United States, the United Kingdom, and France) and the Central Powers (led by Germany and Austria-Hungary). Also called the Great War.