The National Institute of Standards and Technology in Boulder, Colorado, uses its own cesium fountain atomic clock to tell time. This clock, known as NIST-F1, is accurate to one second in 100 million years and serves as the official time and frequency standard in the United States. NIST-F1 is part of an international network of atomic clocks which together define the official world time, known as Coordinated Universal Time or UTC time.Continue Reading
In the late 1940s, NIST was known as the National Bureau of Standards. In 1949, NBS invented the first atomic clock using the frequency of electromagnetic radiation associated with the natural oscillations of ammonia molecules as a standard. In 1952, NBS developed NBS-1, the first cesium-based atomic clock. In 1962, NBS developed NBS-2, a clock more accurate than NBS-1, and in 1963 it developed NBS-3, a clock more accurate and stable than its predecessor. In 1967, the 13th General Conference on Weights and Measures redefined the second based on the natural oscillations of cesium atoms, and NBS-3 became the United States' first atomic clock-based time standard.
NBS continued to improve the accuracy of its atomic clocks with the NBS-4 through NBS-6 series. In 1988, NBS became the National Institute of Standards and Technology. It soon developed NIST-7, which served as the official U.S. time and frequency standard from 1993 to 1999, followed by NIST-F1, which is 10 times as accurate as NIST-7 and has served as the official standard since 2000.Learn more about Time Zones