Jun 222019

Castlehill, Edinburgh, EH1 2NG

The One O'Clock Gun positioned in the Half Moon Battery within the walls of Edinburgh Castle

One O’Clock Gun (© Roger Cornfoot via Wikimedia Commons)

Because of the poor Scottish weather, the notorious haar (sea fog), and smog, the time ball at the top of Nelson Monument on Calton Hill was rarely visible to the ship navigators in the ports along Leith and Newhaven who needed to accurately adjust their clocks. As such, in 1861, an 18-pound muzzle-loading cannon from the Half Moon Battery at Edinburgh Castle was commissioned into “Time Gun” service. Its present-day successor is still fired every day at precisely 1 o’clock, except for Sundays, Good Friday and Christmas Day. However, as the speed of sound is 343 metres per second (770 mph) and docks were about 2 miles (3km) away, the navigators had to account for about 10.5s delay when they set their clocks. This can be seen on the “Edinburgh Time Map” prepared by the 1 o’clock gun’s proposer, Charles Piazzi Smyth. Interestingly, the gun has also seen an instance of military action, as it was fired on 2 April 1916 at a German Zeppelin conducting an air raid during WWI.

Find out more

Black and white illustration of the Half Moon Battery within Edinburgh Castle

Half Moon Battery and firing mechanism in 1861 (Wikimedia Commons)

The time signal delay map designed by Piazzi Smyth

Time signal delay map designed by Piazzi Smyth (© Alastair Bruce)

Photograph of Edinburgh Castle showing the smoke after the One O'Clock Gun was fired

Smoke from the One O’Clock Gun (© Kim Traynor via Wikimedia Commons)

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