Atomic clock

Essential information

Royal Observatory, Meridian Line and Historic Royal Observatory, Time & Longitude gallery, Flamsteed House

In 1967, the world changed and time became a matter of atoms rather than stars.

The National Physical Laboratory (NPL) made the first successful atomic clock in 1955. In 1967, the length of a second was redefined as an atomic measurement, rather than an astronomical one.

This particular clock, by Hewlett Packard, was used at the NPL in the 1990s for its contribution to the new global timescale; Coordinated Universal Time (UTC) which is the basis for civil time today. This 24-hour time standard is kept using highly precise atomic clocks combined with the Earth's rotation.

This atomic clock was decommissioned in 1999.