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While Congress repealed mandatory DST in 1919, it would continue to be widely practiced across the U.S. As many sources of energy become scarce, conservation strategies like DST may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

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

required.

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.