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  2. Caesium standard - Wikipedia

    en.wikipedia.org/wiki/Caesium_standard

    A caesium atomic fountain used as part of an atomic clock. The caesium standard is a primary frequency standard in which the photon absorption by transitions between the two hyperfine ground states of caesium-133 atoms is used to control the output frequency.

  3. Atomic clock - Wikipedia

    en.wikipedia.org/wiki/Atomic_clock

    The main variety of atomic clock uses caesium atoms cooled to temperatures that approach absolute zero. The primary standard for the United States, the National Institute of Standards and Technology (NIST)'s caesium fountain clock named NIST-F2, measures time with an uncertainty of 1 second in 300 million years (relative uncertainty 10 −16 ...

  4. NIST-F1 - Wikipedia

    en.wikipedia.org/wiki/NIST-F1

    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 by Steve Jefferts and Dawn Meekhof of the Time and ...

  5. List of atomic clocks - Wikipedia

    en.wikipedia.org/wiki/List_of_atomic_clocks

    18 cesium atomic clocks and 4 hydrogen maser clocks Cs, H National Institute of Information and Communications Technology; Koganei, ...

  6. NIST-F2 - Wikipedia

    en.wikipedia.org/wiki/NIST-F2

    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]

  7. Atomic fountain - Wikipedia

    en.wikipedia.org/wiki/Atomic_fountain

    The idea of the atomic fountain was first proposed in the 1950s by Jerrold Zacharias. [6] [7] Zacharias attempted to implement an atomic fountain using a thermal beam of atoms, under the assumption that the atoms at the low-velocity end of the Maxwell–Boltzmann distribution would be of sufficiently low energy to execute a reasonably sized parabolic trajectory. [8]

  8. 'Antiques Roadshow:' Clock bought for $1K is actually worth ...

    www.aol.com/entertainment/2014-10-14-antiques...

    The "Antiques Roadshow" appraiser said the clock would have been worth $1,000 to $2,000 more if the dome surrounding the piece was still intact -- but we're guessing the owner is still pretty ...

  9. International Atomic Time - Wikipedia

    en.wikipedia.org/wiki/International_Atomic_Time

    The majority of the clocks involved are caesium clocks; the International System of Units (SI) definition of the second is based on caesium. [6] The clocks are compared using GPS signals and two-way satellite time and frequency transfer. [7] Due to the signal averaging TAI is an order of magnitude more stable than its best constituent clock.