What Part Has The Greenwich Observatory Played In Determining UK Time And International Time Zones?

The Royal Observatory at Greenwich, being at zero degrees, has played a fundamental role.

Before the invention of the electric telegraph, Greenwich had a large ball erected above Flamsteed House in 1833. This ball runs up and down a vertical shaft and its purpose was as a visual time signal for ships sailing on the Thames. At 12.55 hours the ball was hoisted halfway up the mast. At 12.58 the ball was moved to the top of the mast and at exactly 13.00 hours the ball was dropped suddenly from the top. When the ball dropped mariners on the River Thames could set their chronometers to Greenwich Mean Time.

Nineteen years later the Observatory began making use of this new technology afforded by the invention of the electric telegraph. An electric master clock was built to send out time pulses by telegraph wire to other clocks around the country to signal Greenwich Mean Time.