How long is a second - NIST History

Before 1901, America had eight different definitions of a gallon. So the government created a national laboratory to standardize measurements. It began in Washington, DC, as the National Bureau of Standards. Today, it is NIST, headquartered in Gaithersburg, Maryland.^{[1], [2], [3]}

During World War II, its researchers helped develop a radio fuse that detonated explosives just before impact.^[4]

But one of its most important breakthroughs was changing how we measure time. In 1949, researchers at the original Washington lab built the world's first atomic clock. It used ammonia molecules and microwaves to generate a precise signal. It was not actually more accurate than existing clocks, but it proved atoms could be used to keep time, rather than measuring it by the Earth's rotation. Later, in 1967, scientists redefined the second using cesium atoms. That precision helped make technologies like GPS possible.^{[4], [5], [2]}

NIST also designed protective enclosures for the original Declaration of Independence, Constitution, and Bill of Rights. Today, the Gaithersburg campus continues research that affects everyday life. The campus is also the setting of Al Donley's short story Timekeeper, about what happens when the clocks stop.^{[4], [2], [6]}