where are the two famous atomic clocks place in the world?

Question

misspellings, placed*

Answer 1

The first atomic clock was built in 1949 at the U.S. National Bureau of Standards (NBS). The first accurate atomic clock, a cesium standard based on the transition of the cesium-133 atom, was built by Louis Essen in 1955 at the National Physical Laboratory in the UK. This led to the internationally agreed definition of the second being based on atomic time.

In August 2004, NIST scientists demonstrated a chip-scaled atomic clock. According to the researchers, the clock was believed to be one hundredth the size of any other. It was also claimed that it requires just 75 mW, making it suitable for battery-driven applications. This device could conceivably become a consumer product. It will presumably be much smaller, much less power-thirsty, and much cheaper to make than the traditional cesium-fountain clocks used by NIST and USNO as reference clocks


The government owns and operates an "Atomic Clock" that is located in Boulder, Colorado. This Atomic Clock keeps time which neither gains or loses a second in 30 million years. The National Institute of Standards and Technology then sends this time to the International Bureau of Weights and Measures in Paris, France. The Bureau receives time scales from other major nations, averages those scales, and distributes the average as the Coordinated Universal Time (UTC). It is this international time scale which NIST distributes via radio stations (including WWVB) and your clock or watch is programmed to interpret. As long as your clock can receive the radio signal, it will update its time to match exactly with UTC and adjusted for your time zone. (Information from NIST - visit for more info)

Answer 2

Not sure what you mean by "famous." There are more than two atomic clocks in the world. The U.S. Naval Observatory maintains an atomic clock that gives the "official" time for the United States:
http://tycho.usno.navy.mil/

To get the official time, go to
http://www.time.gov ...then click on your time zone

A brief history of atomic clocks at the National Institute of Standards and Technology
http://tf.nist.gov/cesium/atomichistory.htm

The most accurate clock in the world:
http://www.units.muohio.edu/dragonfly/time/accurate.htmlx

How atomic clocks work:
http://www.howstuffworks.com/atomic-clock.htm