The Liverpool Time Ball and one o'clock gun



Liverpool's one o'clock gunThe Liverpool Time Ball and one o'clock gun was built at Waterloo Dock, Liverpool in 1845 and one of its objectives was to establish Greenwich time and to indicate it each day to the citizens of the Port of Liverpool. Eventually many towns and cities developed their own time ball systems, but it was particularly important for maritime ports to have a precise time signal. Chronometers on board ship had to be exact in order for the ships position to be accurately known.
 
John Hartnup at the Liverpool Observatory determined sidereal time from the stars by means of the transit telescope situated in one of the domes on the Observatory roof.

A sidereal clock at the Observatory kept sidereal time, and solar time was calculated from it. A time ball was fitted to the outside wall of the Observatory and was dropped each day at exactly one o'clock so that the citizens and mariners could check their timepieces. A time ball is a sphere, which slides up and down a vertical mast and can be abruptly dropped at an appointed hour. It was similar in all respects to that used at Greenwich and also at Portsmouth, which were also dropped at one o'clock.

 more information from here:  http://www.pol.ac.uk/home/history/gun.html

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