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Longitude by chronometer is a method, in navigation, of determining longitude using a marine chronometer, which was developed by John Harrison during the first half of the eighteenth century. It is an astronomical method of calculating the longitude at which a position line, drawn from a sight by sextant of any celestial body, crosses the ...
Longitude calculations can be simplified using a clock is set to the local time of a starting point whose longitude is known, transporting it to a new location, and using it for astronomical observations. The longitude of the new location can be determined by comparing the difference of local mean time and the time of the transported clock.
A marine chronometer is a precision timepiece that is carried on a ship and employed in the determination of the ship's position by celestial navigation.It is used to determine longitude by comparing Greenwich Mean Time (GMT), and the time at the current location found from observations of celestial bodies.
An accurate determination of longitude was also necessary to determine the proper "magnetic declination", that is, the difference between indicated magnetic north and true north, which can differ by up to 10 degrees in the important trade latitudes of the Atlantic and Indian Oceans. Finding an adequate solution to determining longitude at sea ...
John Harrison (3 April [O.S. 24 March] 1693 – 24 March 1776) was an English carpenter and clockmaker who invented the marine chronometer, a long-sought-after device for solving the problem of how to calculate longitude while at sea.
However, the Board did not meet until at least 1737 [2] when interest grew in John Harrison's marine timekeeper. The Board administered prizes for those who could demonstrate a working device or method. The main longitude prizes were: £10,000 for a method that could determine longitude within 60 nautical miles (110 km; 69 mi) (£1,800,000 as ...
In the mid-1st century AD Lucan writes of Pompey who questions a sailor about the use of stars in navigation. The sailor replies with his description of the use of circumpolar stars to navigate by. [10] To navigate along a degree of latitude a sailor would have needed to find a circumpolar star above that degree in the sky. [11]
The Longitude Act 1714 (13 Ann. c. 14), also known as the Discovery of Longitude at Sea Act 1713, was an act of Parliament of Great Britain passed in July 1714 at the end of the reign of Queen Anne. It established the Board of Longitude and offered monetary rewards ( Longitude rewards ) for anyone who could find a simple and practical method ...