The Time Realization and Distribution group distributes standard time and frequency signals generated by the Coordinated Universal Time scale, UTC(NIST), maintained at the NIST laboratories in Boulder, Colorado. UTC(NIST) is the U. S. national standard for time-of-day, time interval, and frequency.

One of NIST's mission essential functions is to provide the United States with official sources of time and frequency. Our group fulfills this mission by operating and continuously analyzing a large ensemble of commercial atomic clocks. Briefly, an atomic clock measures the passage of time by counting oscillations of an electronic signal kept resonant with a state transition in an atom, engineered for insensitivity to the surrounding environment or perturbing effects like magnetic field fluctuations.

The stability and robustness of the derived timing signal, calledUTC(NIST), is enhanced by averaging across the clock ensemble. The accuracy of UTC(NIST) is ensured by regular comparisons with primary frequency references---devices like thecesium atomic fountain that attempt to realize a microwave frequency closely based on the definition of the International System (SI) second in terms of an unperturbed state transition in the cesium atom---and by regular comparisons with other national metrology laboratories. We keep UTC(NIST) closely aligned with the international atomic time scale Coordinated Universal Time (UTC); our typical time offsets are at the 1 nanosecond level with frequency offsets of about 1 x 10^-15.

We distribute NIST time and frequency signals freely to the public (e.g.the Internet Time Service,time.gov website,WWV,WWVB, andWWVH radio stations). For customers who need UTC(NIST) at higher accuracies or that require a controlled or calibrated transfer medium, we offer remote calibration services (e.g.TMAS,FMAS) and direct links (e.g.Time over Fiber, Time over Satellite). We publish measurements of UTC(NIST) against timing signals from theGlobal Positioning System (GPS), other global satellite navigation systems (GNSS), and support time transfer methods using GNSS satellites as transfer oscillators. We also offer calibration services for oscillators, commercial atomic clocks, andGPS/GNSS receivers. The group supports US industry and other agencies withCollaborative Research and Development Agreements (CRADAs) and technology transfer partnerships.

Finally, the group incorporates state-of-the-art developments in time and frequency metrology, such asoptical atomic clocks, and supports NIST laboratory research programs.

• Time Distribution
• Time Realization

NBS/NIST Radio Stations: The Story of an Old Timer

Thisseries of webpages will lead you on a journey on the history of the NBS/NIST radio stations. You can watch avideo as well.

News and Updates

What Time Is It on Mars? NIST Physicists Have the Answer.

December 1, 2025

This calculation is necessary for future space navigation and communication networks.

New Atomic Fountain Clock Joins Elite Group That Keeps the World on Time

April 28, 2025

NIST scientists have published results establishing a new atomic clock, NIST-F4, as one of the world’s most accurate timekeepers.

Spotlight: Alejandra Collopy and Atomic Clocks

January 13, 2025

NIST researcher Alejandra Collopy is working to add another piece of timely feedback to help our ensemble of clocks perform at their best 24/7.

Projects and Programs

Frequency Measurement and Analysis Service (FMAS)

Ongoing

Subscribers to the NIST service receive a complete frequency measurement system which includes everything needed to make precision frequency measurements that are traceable to NIST. An easy-to-read instruction manual makes installation a snap. Once the system is installed, it's easy to get started

Time Measurement and Analysis Service (TMAS)

Ongoing

The TMAS meets the requirements of any facility or organization that needs to maintain a high accuracy time standard. TMAS customers include calibration and metrology laboratories, telecommunication providers, instrumentation manufacturers, military installations, defense contractors, government

TMAS Data Service

Ongoing

A commercial time measurement system can also be used to achieve similar results by building-in a comparable GPS receiver to generate the file format compatible with TMAS service. Commercial manufacturers can sell the equipment with this option, which would be activated when customers subscribe to

Trapped Sr+ ion clock; a secondary realization of the SI second

Ongoing

The single 88Sr + clock is attractive for both its frequency accuracy and for its relative simplicity. The 674 nm clock transition has been independently studied at several NMI’s at the 10 -17 level [1-4]. Advances in light source technology [5,6] may allow operation with just two lasers: one for

Publications

Awards

2022 Distinguished Associate Award - Vladislav Gerginov

For long-term and extraordinary contributions in support of NIST’s atomic clock and sensing programs.

Distinguished PTTI Service Award - Michael A. Lombardi

Mr. Lombardi was recognized for system development and leadership in the successful delivery of the U.S. time and frequency standards

2020 - Edward Uhler Condon Award---Glenn Nelson

For his exemplary historical review article commemorating the 100th anniversary of NIST radio station WWV.

2019 Distinguished Associate Award - Jian Yao

For creating and networking the world's best optical atomic clocks for a 100-fold improvement in precision timekeeping over state of the art

Press Coverage

Like I Was Sayin': Time keeps on ticking, but on Mars it's slightly slower

Daily Republic

February 15, 2026

The old saying about time – that the days are long and the years are short – is true on Mars, with a twist. Because on Mars, the days are long and the years are

Mars Time Ticks Faster Than Earth | Einstein Was Right

WION Podcast

January 24, 2026

Scientists have confirmed something straight out of science fiction — time on Mars moves differently than it does on Earth.

What Time Is It on Mars? NIST Physicists Have the Answer

Technology.org

January 12, 2026

Ask someone on Earth for the time and they can give you an exact answer, thanks to our planet’s intricate timekeeping system, built with atomic clocks, GPS

According To Scientists, Time Moves Faster On Mars

Orbital Today

January 6, 2026

For the first time, physicists at the National Institute of Standards and Technology (NIST) have calculated the time on Mars. This is not only remarkable but