Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Time & frequency

Overview

Time and frequency activities at NIST include maintaining standards, providing official time to the U.S., and carrying out a broad program of research and service activities in time and frequency metrology.

The Research

Projects & Programs

Compact Cold Atom Instruments

The cooling of atoms to microkelvin temperatures using lasers is currently enabling a new generation of precision instruments that take advantage of the long

Calcium Thermal Beam Optical Clock

A simple, compact alternative to the highest performing optical standards, the Ca clock uses a thermal beam of neutral atoms with one or two lasers to achieve

Frequency Comb Spectroscopy

We use frequency combs based on ultrafast mode-locked lasers to perform precision spectroscopy in the near- and mid-infrared domains, for rapid, high

Additional Resources Links

What Is Time?

Philosophically, what is "time"? Even if we don’t completely understand what time is, we can precisely measure what time it is, thanks to the atomic clock, humankind’s most accurate measurement device. Atomic clocks have revolutionized navigation. Only time will tell us its future applications.

News

NIST physicist Elizabeth Donley and Compact Atomic Clock

Keeping Time at NIST

Einstein is reported to have once said that time is what a clock measures. Some say that what we experience as time is really our experience of the phenomenon of entropy, the second law of thermodynamics. Entropy, loosely explained, is the tendency for things to become disorganized. Hot coffee always goes cold. It never reheats itself. Eggs don’t unscramble themselves. Your room gets messy and you
A photon is absorbed, creating an electron–hole pair (carrier pair).

Light Fantastic: Counting Single Photons at Unprecedented Rates

Illustration shows two buildings labeled "NIST" and "JILA" facing each other with mountains in the background.

NIST Team Compares 3 Top Atomic Clocks With Record Accuracy Over Both Fiber and Air

optomechanical accelerometer

A Better Way to Measure Acceleration