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NIST-F1, source of the official time of the United States. NIST-F1 is a cesium fountain clock, a type of atomic clock, in the National Institute of Standards and Technology (NIST) in Boulder, Colorado, and serves as the United States' primary time and frequency standard. The clock took fewer than four years to test and build, and was developed ...
WWVB's Colorado location makes the signal weakest on the U.S. east coast, where urban density also produces considerable interference. In 2009, NIST raised the possibility of adding a second time code transmitter, on the east coast, to improve signal reception there and provide a certain amount of robustness to the overall system should weather or other causes render one transmitter site ...
NIST physicists Steve Jefferts (foreground) and Tom Heavner with the NIST-F2 cesium fountain atomic clock, a civilian time standard for the United States. NIST-F2 is a caesium fountain atomic clock that, along with NIST-F1, serves as the United States' primary time and frequency standard. [1] NIST-F2 was brought online on 3 April 2014. [1] [2]
Boulder, Colorado United States [8] ... 18 cesium atomic clocks and 4 hydrogen maser clocks Cs, H ... DOST-PAGASA Juan Time [27]
The tz database partitions the world into regions where local clocks all show the same time. This map was made by combining version 2023d with OpenStreetMap data, using open source software. [1] This is a list of time zones from release 2025a of the tz database. [2]
Before the adoption of four standard time zones for the continental United States, many towns and cities set their clocks to noon when the sun passed their local meridian, pre-corrected for the equation of time on the date of observation, to form local mean solar time. Noon occurred at different times but time differences between distant ...
The high frequency of caesium allows for more accurate measurements. Caesium reference tubes suitable for national standards currently last about seven years and cost about US$35,000. Primary frequency and time standards like the United States Time Standard atomic clocks, NIST-F1 and NIST-F2, use far higher power. [34] [70] [71] [72]
The master atomic clock ensemble at the U.S. Naval Observatory in Washington D.C., which provides the time standard for the U.S. Department of Defense. [1] The rack mounted units in the background are caesium beam clocks. The black units in the foreground are hydrogen maser standards.