National Physical Laboratory

60 years of the atomic clock

Here at NPL, atomic clocks keep UK national and international time ticking. In 2015, we celebrated 60 years since the world's first caesium atomic clock was built at NPL - a landmark which has transformed global timekeeping.


NPL and Time

The world's first caesium atomic clock

The world's first caesium atomic clock was developed here at NPL.

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NPL and Coordinated Universal Time

Find out more about NPL's role in the worldwide time system.

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Time Research

Case studies

Discover how past and current research at NPL is helping to shape future technologies.

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Time research highlights

Find out more about the research currently being carried out by NPL's Time and Frequency research group.

Visit NPL's Time research pages

Atomic Clock

A film produced by the NPL Film Unit in the 1950s explaining the principles behind the first accurate atomic clock, designed by Louis Essen and built at the National Physical Laboratory in 1955.

Throughout human history, timekeeping has been based on the rotation of the Earth on its axis. But the Earth's rotation is irregular and the solar day is gradually getting longer. Astronomical time posed a problem: the length of a second was changing.

In 1955, Louis Essen and Jack Parry designed and built the world's first caesium atomic clock at NPL in Teddington, transforming the way we measure and use time.

Louis Essen Experiment
Jack Parry (left) and Louis Essen (right) with the Caesium Mk. 1 atomic clock

Today, the caesium fountain atomic clock at NPL can measure time to an accuracy of one second in 158 million years. The next generation of atomic clocks at NPL, using laser-cooled trapped ions or atoms, should achieve accuracies around 100 times better than the current best atomic clocks - equivalent to gaining or losing no more than one second in the age of the universe.

The current atomic clock system at NPL is the basis of UK time and contributes to the international time scale, Coordinated Universal Time (UTC). Critical elements of the UK's infrastructure, from global communications to satellite navigation, are underpinned by the stable and accurate time scale provided by atomic clocks.

View a timeline of Atomic Time from 1955 to 2015

Time Measurement

The World Time System

How do countries all keep the same time? Find out about the different time systems and how they all link together.

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How do atomic clocks work?

Atomic clocks provide the basis for all precision timekeeping. Discover the science and technology behind the atomic clock.

More on Atomic Clocks

Why do we need accurate time?

The atomic clocks at NPL provide the most accurate time available. Find out more about why we need accurate timekeeping systems.

More on accurate time

MSF radio time signal

The UK time scale

Microwave frequencies provide the standard time for the whole of the UK, and are broadcast via radio signals, telephone lines and the internet.

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Synchronise with NPL's atomic clock

You can set up your computer to synchronise with NPL's atomic clock.

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