Essential information

Opening times: 
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Royal Observatory, Meridian Line and Historic Royal Observatory, Flamsteed House, Time & Greenwich gallery

Make time to find the master clock at the heart of Britain's time system (and much of the world's) for many a year.

Its time was sent by telegraph wires to London, Edinburgh, Glasgow, Dublin, Belfast and many other cities. By 1866, time signals were sent from this clock to Harvard University in Cambridge, Massachusetts via the new transatlantic submarine cable.

In terms of the distribution of accurate time into everyday life, this is one of the most important clocks ever made.

A slave dial connected to this clock, at the gates of the Royal Observatory, was the first clock ever to show Greenwich Mean Time (GMT) directly to the public.

In 1851 at the famous Great Exhibition held in Hyde Park, London, one of the world's first ever 'master-and-slave' clock systems was installed by Charles Shepherd of Leadenhall Street. It consisted of a central 'master clock' sending regular electrical impulses to a number of ancillary 'slave' dials. George Airy, the seventh Astronomer Royal, saw the potential advantages of such a system and ordered one to be made for the Royal Observatory in Greenwich.

The Shepherd’s system was supplied to Greenwich Observatory the following year and remained the basis of Britain’s time-distribution system for the next 70 years.