Editing Longitude (section)

== History ==
{{Main|History of longitude}}
The concept of longitude was first developed by ancient Greek astronomers. [[Hipparchus]] (2nd century BCE) used a coordinate system that assumed a spherical Earth, and divided it into 360° as we still do today. His [[prime meridian]] passed through [[Alexandria]].<ref name="Dicks">{{cite thesis |type=PhD |last1=Dicks |first1=D.R. |title=Hipparchus : a critical edition of the extant material for his life and works |date=1953 |publisher=Birkbeck College, University of London |url=https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.720566 |access-date=2020-09-26 |archive-date=2021-04-14 |archive-url=https://web.archive.org/web/20210414082903/https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.720566 |url-status=live }}</ref>{{rp|31}} He also proposed a method of determining longitude by comparing the local time of a [[lunar eclipse]] at two different places, thus demonstrating an understanding of the relationship between longitude and time.{{r|Dicks|p=11}}<ref>{{cite book |last1=Hoffman |first1=Susanne M. |title=The Science of Time |chapter=How time served to measure the geographical position since Hellenism|date=2016 |editor-last1=Arias |editor-first1=Elisa Felicitas |editor-last2=Combrinck |editor-first2=Ludwig |editor-last3=Gabor |editor-first3=Pavel |editor-last4=Hohenkerk |editor-first4=Catherine |editor-last5=Seidelmann |editor-first5=P.Kenneth |publisher=Springer International |series=Astrophysics and Space Science Proceedings|volume=50 |doi=10.1007/978-3-319-59909-0_4|pages=25–36|isbn=978-3-319-59908-3 }}</ref> [[Ptolemy|Claudius Ptolemy]] (2nd century CE) developed a mapping system using curved parallels that reduced distortion. He also collected data for many locations, from Britain to the Middle East. He used a prime meridian through the Canary Islands, so that all longitude values would be positive. While Ptolemy's system was sound, the data he used were often poor, leading to a gross over-estimate (by about 70%) of the length of the Mediterranean.<ref>{{cite book |last1=Mittenhuber |first1=Florian |title=Ptolemy in Perspective: Use and Criticism of his Work from Antiquity to the Nineteenth Century|url=https://archive.org/details/ptolemyperspecti00jone |url-access=limited |chapter=The Tradition of Texts and Maps in Ptolemy's Geography |series=Archimedes |date=2010 |volume=23 |editor-last1=Jones | editor-first1=Alexander |publisher=Springer |location=Dordrecht |pages=[https://archive.org/details/ptolemyperspecti00jone/page/n106 95]-119|doi=10.1007/978-90-481-2788-7_4|isbn=978-90-481-2787-0 }}</ref><ref name="Bunbury">{{cite book |last1=Bunbury |first1=E.H. |title=A History of Ancient Geography |volume=2|date=1879 |publisher=John Murray |location=London|url=https://archive.org/details/historyofancientgeographybunburye.h.vol21879_648_H}}</ref>{{rp|551–553}}<ref>{{cite journal |last1=Shcheglov |first1=Dmitry A. |s2cid=129864284 |title=The Error in Longitude in Ptolemy's Geography Revisited |journal=The Cartographic Journal |date=2016 |volume=53 |issue=1 |pages=3–14 |doi=10.1179/1743277414Y.0000000098|bibcode=2016CartJ..53....3S }}</ref>

After the fall of the Roman Empire, interest in geography greatly declined in Europe.<ref name="Wright1925">{{cite book |last1=Wright |first1=John Kirtland |title=The geographical lore of the time of the Crusades: A study in the history of medieval science and tradition in Western Europe |date=1925 |publisher=American geographical society |location=New York |url=https://archive.org/details/geographicallore00wrig}}</ref>{{rp|65}} Hindu and Muslim astronomers continued to develop these ideas, adding many new locations and often improving on Ptolemy's data.<ref name="Ragep">{{cite book |last1=Ragep |first1=F.Jamil |editor-last=Jones |editor-first=A. |title=Ptolemy in Perspective |publisher=Springer |place=Dordrecht |date=2010 |chapter=Islamic reactions to Ptolemy's imprecisions |series=Archimedes |volume=23 |isbn=978-90-481-2788-7 |doi=10.1007/978-90-481-2788-7 |url=https://authors.library.caltech.edu/21360/ |access-date=2022-03-23 |archive-date=2022-07-07 |archive-url=https://web.archive.org/web/20220707133906/https://authors.library.caltech.edu/21360/ |url-status=live }}</ref><ref name="Tibbett">{{cite book |last1=Tibbetts |first1=Gerald R. |editor1-last=Harley |editor1-first=J.B. |editor2-last=Woodward |editor2-first=David |title=The History of Cartography Vol. 2 Cartography in the Traditional Islamic and South Asian Societies |publisher=University of Chicago Press |date=1992 |chapter=The Beginnings of a Cartographic Tradition |chapter-url=https://press.uchicago.edu/books/HOC/HOC_V2_B1/HOC_VOLUME2_Book1_chapter4.pdf |access-date=2020-09-26 |archive-date=2020-09-21 |archive-url=https://web.archive.org/web/20200921202340/https://press.uchicago.edu/books/HOC/HOC_V2_B1/HOC_VOLUME2_Book1_chapter4.pdf |url-status=live }}</ref> For example, [[Al-Battani|al-Battānī]] used simultaneous observations of two lunar eclipses to determine the difference in longitude between [[Antakya]] and [[Raqqa]] with an error of less than 1°. This is considered to be the best that can be achieved with the methods then available: observation of the eclipse with the naked eye, and determination of local time using an [[astrolabe]] to measure the altitude of a suitable "clock star".<ref name="Said2">{{cite journal |last1=Said |first1=S.S. |last2=Stevenson |first2=F.R. |s2cid=117100760 |title=Solar and Lunar Eclipse Measurements by Medieval Muslim Astronomers, II: Observations |journal=Journal for the History of Astronomy |date=1997 |volume=28 |issue=1 |pages=29–48 |doi=10.1177/002182869702800103|bibcode=1997JHA....28...29S }}</ref><ref name="Steele">{{cite thesis |type=PhD |last=Steele|first=John Michael |date=1998 |title=Observations and predictions of eclipse times by astronomers in the pre-telescopic period |publisher=University of Durham (United Kingdom)}}</ref>

In the later Middle Ages, interest in geography revived in the west, as travel increased, and Arab scholarship began to be known through contact with Spain and North Africa. In the 12th century, astronomical tables were prepared for a number of European cities, based on the work of [[Abū Ishāq Ibrāhīm al-Zarqālī|al-Zarqālī]] in [[Toledo, Spain|Toledo]]. The lunar eclipse of September 12, 1178 was used to establish the longitude differences between Toledo, [[Marseille]]s, and [[Hereford]].<ref name="Wright1923">{{cite journal |last1=Wright |first1=John Kirtland |title=Notes on the Knowledge of Latitudes and Longitudes in the Middle Ages |journal=Isis |date=1923 |volume=5 |issue=1 |bibcode=1922nkll.book.....W |url=https://archive.org/details/wright-1923-isisacad-05acaduoft}}</ref>{{rp|85}}

[[Christopher Columbus]] made two attempts to use lunar eclipses to discover his longitude, the first in [[Saona Island]], on 14 September 1494 (second voyage), and the second in [[Jamaica]] on 29 February 1504 (fourth voyage). It is assumed that he used astronomical tables for reference. His determinations of longitude showed large errors of 13° and 38° W respectively.<ref name="Pickering">{{cite journal |last1=Pickering |first1=Keith |title=Columbus's Method of Determining Longitude: An Analytical View |journal=The Journal of Navigation |date=1996 |volume=49 |issue=1 |pages=96–111 |doi=10.1017/S037346330001314X|bibcode=1996JNav...49...95P |s2cid=129232861 }}</ref> Randles (1985) documents longitude measurement by the Portuguese and Spanish between 1514 and 1627 both in the Americas and Asia. Errors ranged from 2° to 25°.<ref name="Randles">{{cite journal |last1=Randles |first1=W.G.L. |title=Portuguese and Spanish attempts to measure longitude in the 16th century |journal=Vistas in Astronomy |date=1985 |volume=28 |issue=1 |pages=235–241|doi=10.1016/0083-6656(85)90031-5 |bibcode=1985VA.....28..235R }}</ref>

The telescope was invented in the early 17th century. Initially an observation device, developments over the next half century transformed it into an accurate measurement tool.<ref name="Pannekoek">{{cite book |last1=Pannekoek |first1=Anton |title=A history of astronomy |date=1989 |publisher=Courier Corporation |pages=259–276 |url=https://archive.org/details/historyofastrono0000pann}}</ref><ref name="Van Helden">{{cite journal |last1=Van Helden |first1=Albert |title=The Telescope in the Seventeenth Century |journal=Isis |date=1974 |volume=65 |issue=1 |pages=38–58 |doi=10.1086/351216 |jstor=228880 |s2cid=224838258 }}</ref> The [[pendulum clock]] was patented by [[Christiaan Huygens]] in 1657<ref name="Grimbergen">{{cite conference |last1=Grimbergen |first1=Kees |title=Huygens and the advancement of time measurements |journal=Titan - from Discovery to Encounter |conference=Titan - From Discovery to Encounter |editor-last=Fletcher | editor-first=Karen |location=ESTEC, Noordwijk, Netherlands |date=2004 |volume=1278 |pages=91–102 |publisher=ESA Publications Division |bibcode=2004ESASP1278...91G |isbn=92-9092-997-9 }}</ref> and gave an increase in accuracy of about 30 fold over previous mechanical clocks.<ref>{{cite journal |last1=Blumenthal |first1=Aaron S. |last2=Nosonovsky |first2=Michael |title=Friction and Dynamics of Verge and Foliot: How the Invention of the Pendulum Made Clocks Much More Accurate |journal= Applied Mechanics|date=2020 |volume=1 |issue=2 |pages=111–122 |doi=10.3390/applmech1020008|doi-access=free }}</ref> These two inventions would revolutionise observational astronomy and cartography.<ref name="Olmsted">{{cite journal |last1=Olmsted |first1=J.W. |title=The Voyage of Jean Richer to Acadia in 1670: A Study in the Relations of Science and Navigation under Colbert |journal=Proceedings of the American Philosophical Society |date=1960 |volume=104 |issue=6 |pages=612–634 |jstor=985537 }}</ref>

On land, the period from the development of telescopes and pendulum clocks until the mid-18th century saw a steady increase in the number of places whose longitude had been determined with reasonable accuracy, often with errors of less than a degree, and nearly always within 2° to 3°. By the 1720s errors were consistently less than 1°.<ref>See, for example, Port Royal, Jamaica: {{cite journal |last1=Halley |first1=Edmond |title=Observations on the Eclipse of the Moon, June 18, 1722. and the Longitude of Port Royal in Jamaica |journal=Philosophical Transactions |date=1722 |volume=32 |issue=370–380 |pages=235–236 |url=https://archive.org/details/jstor-103607}}; Buenos Aires: {{cite journal |last1=Halley |first1=Edm. |title=The Longitude of Buenos Aires, Determin'd from an Observation Made There by Père Feuillée |journal=Philosophical Transactions |date=1722 |volume=32 |issue=370–380 |pages=2–4 |url=https://archive.org/details/jstor-103565}}Santa Catarina, Brazil: {{cite journal |last1=Legge |first1=Edward |last2=Atwell |first2=Joseph |title=Extract of a letter from the Honble Edward Legge, Esq; F. R. S. Captain of his Majesty's ship the Severn, containing an observation of the eclipse of the moon, Dec. 21. 1740. at the Island of St. Catharine on the Coast of Brasil |journal=Philosophical Transactions |date=1743 |volume=42 |issue=462 |pages=18–19 |url=https://archive.org/details/jstor-104132}}</ref> At sea during the same period, the situation was very different. Two problems proved intractable; the first was the need of a navigator for immediate results, and the second was the marine environment. Making accurate observations in an ocean swell is much harder than on land, and pendulum clocks do not work well in these conditions.
===The Chronometer===
[[File:Harrison H4 clockwork 1.jpg|thumb|upright=1.2|The clockwork in [[John Harrison]]'s [[Marine_chronometer#First examples|H4 marine chronometer]] on display at the [[Royal Observatory, Greenwich]]]]
In response to the problems of navigation, a number of European maritime powers offered prizes for a method to determine longitude at sea. The best-known of these is the [[Longitude Act]] passed by the British parliament in 1714.<ref name="Siegel">{{cite journal |last1=Siegel |first1=Jonathan R. |title=Law and Longitude |journal=Tulane Law Review |date=2009 |volume=84 |pages=1–66}}</ref>{{rp|8}} It offered two levels of rewards, for solutions within 1° and 0.5°. Rewards were given for two solutions: lunar distances, made practicable by the tables of [[Tobias Mayer]]<ref name="Forbes2006">{{cite journal |last1=Forbes |first1=Eric Gray |title=Tobias Mayer's lunar tables|journal=Annals of Science |volume=22 |issue=2 |year=2006 |pages=105–116 |issn=0003-3790|doi=10.1080/00033796600203075}}</ref> developed into an [[nautical almanac]] by the [[Astronomer Royal]] [[Nevil Maskelyne]]; and for the [[chronometers]] developed by the Yorkshire carpenter and clock-maker [[John Harrison]]. Harrison built five chronometers over more than three decades. This work was supported and rewarded with thousands of pounds from the Board of Longitude,<ref>{{Cite web|date=2012-03-07|title=There was no such thing as the Longitude Prize|url=https://www.rmg.co.uk/discover/behind-the-scenes/blog/there-was-no-such-thing-longitude-prize|access-date=2021-01-27|website=Royal Museums Greenwich|language=en|archive-date=2023-01-22|archive-url=https://web.archive.org/web/20230122155948/https://www.rmg.co.uk/stories/blog/there-was-no-such-thing-longitude-prize|url-status=live}}</ref> but he fought to receive money up to the top reward of £20,000, finally receiving an additional payment in 1773 after the intervention of Parliament.{{r|"Siegel"|p=26}} It was some while before either method became widely used in navigation. In the early years, chronometers were very expensive, and the calculations required for lunar distances were still complex and time-consuming. Lunar distances came into general use after 1790.<ref name="Wess2015">{{cite book|title=Navigational Enterprises in Europe and its Empires, 1730-1850 |editor1-last=Dunn |editor1-first=Richard |editor2-last=Higgitt |editor2-first=Rebekah |last1=Wess|first1=Jane|chapter=Navigation and Mathematics: A Match Made in the Heavens?|year=2015|pages=201–222|publisher=Palgrave Macmillan UK |location=London |doi=10.1057/9781137520647_11|isbn=978-1-349-56744-7 }}</ref> Chronometers had the advantages that both the observations and the calculations were simpler, and as they became cheaper in the early 19th century they started to replace lunars, which were seldom used after 1850.<ref name="Littlehales">{{cite journal |last1=Littlehales |first1=G.W. |title=The Decline of the Lunar Distance for the Determination of the Time and Longitude at |journal=Bulletin of the American Geographical Society |date=1909 |volume=41 |issue=2 |pages=83–86 |doi=10.2307/200792 |jstor=200792 |url=https://archive.org/details/jstor-200792}}</ref>

The first working [[Telegraphy|telegraphs]] were established in Britain by [[Charles Wheatstone|Wheatstone]] and [[William Fothergill Cooke|Cooke]] in 1839, and in the US by [[Samuel Morse|Morse]] in 1844. It was quickly realised that the telegraph could be used to transmit a time signal for longitude determination.<ref name="Walker 1850">{{cite journal |last1=Walker |first1=Sears C |title=Report on the experience of the Coast Survey in regard to telegraph operations, for determination of longitude &c. |journal=American Journal of Science and Arts |date=1850 |volume=10 |issue=28 |pages=151–160 |url=https://archive.org/details/appendix-telegraphic-longitude-the-american-journal-of-science-and-arts }}</ref> The method was soon in practical use for longitude determination, especially in North America, and over longer and longer distances as the telegraph network expanded, including western Europe with the completion of transatlantic cables. The United States Coast Survey, renamed the [[United States Coast and Geodetic Survey]] in 1878, was particularly active in this development, and not just in the United States. The Survey established chains of mapped locations through Central and South America, and the West Indies, and as far as Japan and China in the years 1874–90. This contributed greatly to the accurate mapping of these areas.<ref name="Knox">{{cite journal |last1=Knox |first1=Robert W. |title=Precise Determination of Longitude in the United States |journal=Geographical Review |date=1957 |volume=47 |issue=4 |pages=555–563 |doi=10.2307/211865 |jstor=211865|bibcode=1957GeoRv..47..555K }}</ref><ref name="Green1883">{{cite book |last1=Green |first1=Francis Mathews |last2=Davis |first2=Charles Henry |last3=Norris |first3=John Alexander |title=Telegraphic Determination of Longitudes in Japan, China, and the East Indies: Embracing the Meridians of Yokohama, Nagasaki, Wladiwostok, Shanghai, Amoy, Hong-Kong, Manila, Cape St. James, Singapore, Batavia, and Madras, with the Latitude of the Several Stations |date=1883 |publisher=US Hydrographic Office |location=Washington |url=https://archive.org/details/in.ernet.dli.2015.177254}}</ref>

While mariners benefited from the accurate charts, they could not receive telegraph signals while under way, and so could not use the method for navigation. This changed when wireless telegraphy (radio) became available in the early 20th century.<ref name="Munro1902">{{cite journal |last1=Munro |first1=John |s2cid=4021629 |title=Time-Signals by Wireless Telegraphy |journal=Nature |volume=66 |issue=1713 |year=1902 |pages=416 |issn=0028-0836 |doi=10.1038/066416d0 |bibcode=1902Natur..66..416M |url=https://zenodo.org/record/2080631 |access-date=2020-09-26 |archive-date=2021-04-14 |archive-url=https://web.archive.org/web/20210414140852/https://zenodo.org/record/2080631 |url-status=live |doi-access=free }}</ref> Wireless time signals for the use of ships were transmitted from [[Halifax, Nova Scotia]], starting in 1907<ref name="Hutchnson">{{cite journal |last1=Hutchinson |first1=D.L. |title=Wireless Time Signals from the St. John Observatory of the Canadian Meteorological Service. |journal=Proceedings and Transactions of the Royal Society of Canada |date=1908 |volume=Ser. 3 Vol. 2 |pages=153–154 |url=https://archive.org/details/hutchinson-1908-proceedingstrans-32roya}}</ref> and from the [[Eiffel Tower]] in Paris from 1910.<ref name="Lockyer1913">{{cite journal|last1=Lockyer|first1=William J. S.|s2cid=3977506|title=International Time and Weather Radio-Telegraphic Signals |journal=Nature |volume=91 |issue=2263 |year=1913 |pages=33–36 |issn=0028-0836 |doi=10.1038/091033b0 |bibcode=1913Natur..91...33L |doi-access=free}}</ref> These signals allowed navigators to check and adjust their chronometers frequently.<ref name="Zimmerman">{{cite web |last1=Zimmerman |first1=Arthur E. |title=The first wireless time signals to ships at sea |url=https://www.antiquewireless.org/wp-content/uploads/50-the_first_wireless_time_signals_to_ships_at_sea.pdf |website=antiquewireless.org |publisher=Antique Wireless Association |access-date=9 July 2020 |archive-date=11 July 2020 |archive-url=https://web.archive.org/web/20200711122417/https://www.antiquewireless.org/wp-content/uploads/50-the_first_wireless_time_signals_to_ships_at_sea.pdf |url-status=live }}</ref>

[[Radio navigation]] systems came into general use after [[World War II]]. The systems all depended on transmissions from fixed navigational beacons. A ship-board receiver calculated the vessel's position from these transmissions.<ref name="Pierce">{{cite journal |last1=Pierce |first1=J.A. |s2cid=20739091 |title=An introduction to Loran |journal=Proceedings of the IRE |date=1946 |volume=34 |issue=5 |pages=216–234 |doi=10.1109/JRPROC.1946.234564}}</ref> They allowed accurate navigation when poor visibility prevented astronomical observations, and became the established method for commercial shipping until replaced by [[Global Positioning System|GPS]] in the early 1990s.