An atomic clock keeps time by using the frequency of electromagnetic radiation associated with the natural oscillations of atoms as a standard of measurement. Atomic clocks are the most accurate clocks developed; a cesium-based clock at the National Institute of Standards and Technology in Boulder, Colorado, serves as the official time and frequency standard in the United States and is accurate to 1 second in 100 million years.Continue Reading
A newly developed strontium clock is the most accurate clock ever developed and takes 15 billion years to lose a second. It uses the electromagnetic radiation produced by oscillations of strontium atoms as a standard, while utilizing the relationship of time and gravity predicted by Einstein's theory of relativity to correct for very small temporal errors caused by variations in the local gravitational field. Another innovation is a chip-scale atomic clock small enough to find commercial applications, such as in GPS units.
The official timekeeper for the U.S. Department of Defense is the U.S. Naval Observatory's Master Clock located in Washington, D.C. The Master Clock consists of a bank of many independently operating cesium atomic clocks and hydrogen maser clocks. Colloquially, the term "atomic clock" is sometimes used for clocks that display data received from true atomic clocks via radio or the Internet.Learn more about Time & Calendars