John Harrison was a self-educated English carpenter and clockmaker who invented the marine chronometer, a long-sought-after device for solving the problem of calculating longitude while at sea.
Longitude is a geographic coordinate that specifies the east–west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda (λ). Meridians are imaginary semicircular lines running from pole to pole that connect points with the same longitude. The prime meridian defines 0° longitude; by convention the International Reference Meridian for the Earth passes near the Royal Observatory in Greenwich, south-east London on the island of Great Britain. Positive longitudes are east of the prime meridian, and negative ones are west.
Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another. The field of navigation includes four general categories: land navigation, marine navigation, aeronautic navigation, and space navigation.
Nevil Maskelyne was the fifth British Astronomer Royal. He held the office from 1765 to 1811. He was the first person to scientifically measure the mass of the planet Earth. He created the British Nautical Almanac and Astronomical Ephemeris for the Meridian of the Royal Observatory at Greenwich using Johann Tobias Mayer's corrections for Euler's Lunar Theory tables.
The Royal Observatory, Greenwich is an observatory situated on a hill in Greenwich Park in south east London, overlooking the River Thames to the north. It played a major role in the history of astronomy and navigation, and because the Prime Meridian passes through it, it gave its name to Greenwich Mean Time, the precursor to today's Coordinated Universal Time (UTC). The ROG has the IAU observatory code of 000, the first in the list. ROG, the National Maritime Museum, the Queen's House and the clipper ship Cutty Sark are collectively designated Royal Museums Greenwich.
The longitude rewards were the system of inducement prizes offered by the British government for a simple and practical method for the precise determination of a ship's longitude at sea. The rewards, established through an Act of Parliament in 1714, were administered by the Board of Longitude.
Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space without having to rely solely on estimated positional calculations, commonly known as "dead reckoning", made in the absence of satellite navigation or other similar modern electronic or digital positioning means.
Charles Mason was an English astronomer who made significant contributions to 18th-century science and American history, particularly through his survey with Jeremiah Dixon of the Mason–Dixon line, which came to mark the border between Maryland and Pennsylvania (1764–1768). The border between Delaware and Maryland is also defined by a part of the Mason–Dixon line.
John Arnold was an English watchmaker and inventor.
Charles Green was a British astronomer, noted for his assignment by the Royal Society in 1768 to the expedition sent to the Pacific Ocean in order to observe the transit of Venus aboard James Cook's Endeavour.
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 observer's assumed latitude. In order to calculate the position line, the time of the sight must be known so that the celestial position i.e. the Greenwich Hour Angle and Declination, of the observed celestial body is known. All that can be derived from a single sight is a single position line, which can be achieved at any time during daylight when both the sea horizon and the sun are visible. To achieve a fix, more than one celestial body and the sea horizon must be visible. This is usually only possible at dawn and dusk.
In celestial navigation, lunar distance is the angular distance between the Moon and another celestial body. The lunar distances method uses this angle, also called a lunar, and a nautical almanac to calculate Greenwich time if so desired, or by extension any other time. That calculated time can be used in solving a spherical triangle. The theory was first published by Johannes Werner in 1524, before the necessary almanacs had been published. A fuller method was published in 1763 and used until about 1850 when it was superseded by the marine chronometer. A similar method uses the positions of the Galilean moons of Jupiter.
The Longitude Act 1714 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 for anyone who could find a simple and practical method for the precise determination of a ship's longitude. The Act of 1714 was followed by a series of other Longitude Acts that revised or replaced the original.
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. When first developed in the 18th century, it was a major technical achievement, as accurate knowledge of the time over a long sea voyage was vital for effective navigation, lacking electronic or communications aids. The first true chronometer was the life work of one man, John Harrison, spanning 31 years of persistent experimentation and testing that revolutionized naval navigation and enabling the Age of Discovery and colonialism to accelerate.
The history of longitude describes the centuries-long effort by astronomers, cartographers and navigators to discover a means of determining the longitude of any given place on Earth. The measurement of longitude is important to both cartography and navigation. In particular, for safe ocean navigation, knowledge of both latitude and longitude is required, however latitude can be determined with good accuracy with local astronomical observations.
Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time is a best-selling book by Dava Sobel about John Harrison, an 18th-century clockmaker who created the first clock (chronometer) sufficiently accurate to be used to determine longitude at sea—an important development in navigation. The book was made into a television series entitled Longitude. In 1998, The Illustrated Longitude was published, supplementing the earlier text with 180 images of characters, events, instruments, maps and publications.
A nautical chronometer made by Thomas Earnshaw (1749–1828), and once part of the equipment of HMS Beagle, the ship that carried Charles Darwin on his voyage around the world, is held in the British Museum. The chronometer was the subject of one episode of the BBC's series A History of the World in 100 Objects.
William Harrison was an English instrument maker, the son of John Harrison, inventor of the marine chronometer.
Thomas Mercer Chronometers is a British company specialising in the design and production of bespoke chronometers.
Robert Waddington was a mathematician, astronomer and teacher of navigation. He is best known as one of the observers appointed by the Royal Society to observe the 1761 transit of Venus with Nevil Maskelyne on the island of Saint Helena. On that voyage they made successful use of the lunar-distance method of establishing longitude at sea. Waddington subsequently taught the method at his academy in London and published a navigation manual, A Practical Method for Finding the Longitude and Latitude of a Ship at Sea, by Observations of the Moon (1763).
