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71-542: Longitude ( / ˈ l ɒ n dʒ ɪ tj uː d / , AU and UK also / ˈ l ɒ ŋ ɡ ɪ -/ ) 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
142-532: A prime meridian at the westernmost known land, designated the Fortunate Isles , off the coast of western Africa around the Canary or Cape Verde Islands , and measured north or south of the island of Rhodes off Asia Minor . Ptolemy credited him with the full adoption of longitude and latitude, rather than measuring latitude in terms of the length of the midsummer day. Ptolemy's 2nd-century Geography used
213-413: A prime meridian , is mathematically related to time differences up to 12 hours by a factor of 15. Thus, a time differential (in hours) between two points is multiplied by 15 to obtain a longitudinal difference (in degrees). Historically, times used for calculating longitude have included apparent solar time , local mean time , and ephemeris time , with mean time being the one most used for navigation of
284-415: A spherical or geodetic coordinate system for measuring and communicating positions directly on Earth as latitude and longitude . It is the simplest, oldest and most widely used of the various spatial reference systems that are in use, and forms the basis for most others. Although latitude and longitude form a coordinate tuple like a cartesian coordinate system , the geographic coordinate system
355-400: A circle, as it is for the other planets. Instead it is approximately oval and similar to the shape of a pignon (or pine nut). Some writers have misinterpreted al-Zarqālī's description of an earth-centered oval path for the center of the planet's epicycle as an anticipation of Johannes Kepler 's sun-centered elliptical paths for the planets. Although this may be the first suggestion that
426-474: A difference of 15° longitude corresponds to a one-hour difference in local time, due to the differing position in relation to the Sun. Comparing local time to an absolute measure of time allows longitude to be determined. Depending on the era, the absolute time might be obtained from a celestial event visible from both locations, such as a lunar eclipse, or from a time signal transmitted by telegraph or radio. The principle
497-621: A few of the more prevalent ones. Longitude is given as an angular measurement with 0° at the Prime Meridian , ranging from −180° westward to +180° eastward. The Greek letter λ (lambda) is used to denote the location of a place on Earth east or west of the Prime Meridian. Each degree of longitude is sub-divided into 60 minutes , each of which is divided into 60 seconds . A longitude is thus specified in sexagesimal notation as, for example, 23° 27′ 30″ E. For higher precision,
568-598: A generation of Islamic astronomers in Al-Andalus, and later, after being translated, were very influential in Europe . His invention of the Saphaea (a perfected astrolabe) proved very popular and was widely used by navigators until the 16th century. The crater Arzachel on the Moon is named after him. Al-Zarqālī, of Arab origin, was born in a village near the outskirts of Toledo ,
639-646: A little before 1300; the text was translated into Latin at Florence by Jacopo d'Angelo around 1407. In 1884, the United States hosted the International Meridian Conference , attended by representatives from twenty-five nations. Twenty-two of them agreed to adopt the longitude of the Royal Observatory in Greenwich , England as the zero-reference line. The Dominican Republic voted against
710-416: A location often facetiously called Null Island . In order to use the theoretical definitions of latitude, longitude, and height to precisely measure actual locations on the physical earth, a geodetic datum must be used. A horizonal datum is used to precisely measure latitude and longitude, while a vertical datum is used to measure elevation or altitude. Both types of datum bind a mathematical model of
781-535: A longitudinal degree is 111.3 km. At 30° a longitudinal second is 26.76 m, at Greenwich (51°28′38″N) 19.22 m, and at 60° it is 15.42 m. On the WGS 84 spheroid, the length in meters of a degree of latitude at latitude ϕ (that is, the number of meters you would have to travel along a north–south line to move 1 degree in latitude, when at latitude ϕ ), is about The returned measure of meters per degree latitude varies continuously with latitude. Similarly,
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#1732851836997852-465: 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. 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
923-670: A national cartographical organization include the North American Datum , the European ED50 , and the British OSGB36 . Given a location, the datum provides the latitude ϕ {\displaystyle \phi } and longitude λ {\displaystyle \lambda } . In the United Kingdom there are three common latitude, longitude, and height systems in use. WGS 84 differs at Greenwich from
994-556: A perfected kind of astrolabe known as "the tablet of al-Zarqālī" (al-ṣafīḥā al-zarqāliyya), which was famous in Europe under the name Saphaea . There is a record of an al-Zarqālī who built a water clock , capable of determining the hours of the day and night and indicating the days of the lunar months. According to a report found in al-Zuhrī 's Kitāb al-Juʿrāfīyya , his name is given as Abū al-Qāsim bin ʿAbd al-Raḥmān, also known as al-Zarqālī, which has made some historians think that this
1065-841: A simple translation may be sufficient. Datums may be global, meaning that they represent the whole Earth, or they may be local, meaning that they represent an ellipsoid best-fit to only a portion of the Earth. Examples of global datums include World Geodetic System (WGS 84, also known as EPSG:4326 ), the default datum used for the Global Positioning System , and the International Terrestrial Reference System and Frame (ITRF), used for estimating continental drift and crustal deformation . The distance to Earth's center can be used both for very deep positions and for positions in space. Local datums chosen by
1136-401: 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°. 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. The second
1207-500: A year, or 10 m in a century. A weather system high-pressure area can cause a sinking of 5 mm . Scandinavia is rising by 1 cm a year as a result of the melting of the ice sheets of the last ice age , but neighboring Scotland is rising by only 0.2 cm . These changes are insignificant if a local datum is used, but are statistically significant if a global datum is used. On the GRS 80 or WGS 84 spheroid at sea level at
1278-549: Is cos φ decreases from 1 at the equator to 0 at the poles, which measures how circles of latitude shrink from the equator to a point at the pole, so the length of a degree of longitude decreases likewise. This contrasts with the small (1%) increase in the length of a degree of latitude (north–south distance), equator to pole. The table shows both for the WGS84 ellipsoid with a = 6 378 137 .0 m and b = 6 356 752 .3142 m . The distance between two points 1 degree apart on
1349-583: Is where Earth's equatorial radius a {\displaystyle a} equals 6,378,137 m and tan β = b a tan ϕ {\displaystyle \textstyle {\tan \beta ={\frac {b}{a}}\tan \phi }\,\!} ; for the GRS 80 and WGS 84 spheroids, b a = 0.99664719 {\textstyle {\tfrac {b}{a}}=0.99664719} . ( β {\displaystyle \textstyle {\beta }\,\!}
1420-478: Is a different person. Al-Zarqali corrected geographical data from Ptolemy and Al-Khwarizmi . Specifically, he corrected Ptolemy's estimate of the width of the Mediterranean Sea from 62 degrees to the correct value of 42 degrees. In his treatise on the solar year, which survives only in a Hebrew translation, he was the first to demonstrate the motion of the solar apogee relative to the fixed background of
1491-561: Is also referred to in the works of Chaucer , as 'Arsechieles'. In the year 1085, Toledo was taken by the Christian king of Castile Alfonso VI . Al-Zarqālī and his colleagues, such as Al-Waqqashi (1017–1095) had to flee. It is unknown whether the aged Al-Zarqālī fled to Cordoba or died in a Moorish refugee camp. His works influenced Ibn Bajjah (Avempace), Ibn Tufail (Abubacer), Ibn Rushd (Averroës), Ibn al-Kammad , Ibn al-Haim al-Ishbili and Nur ad-Din al-Betrugi (Alpetragius). In
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#17328518369971562-476: Is formed from the Arabic al-Zarqali al-Naqqash , meaning 'the engraver'. He was particularly talented in geometry and astronomy . He is known to have taught and visited Córdoba on various occasions, and his extensive experience and knowledge eventually made him the foremost astronomer of his time . Al-Zarqālī was also an inventor, and his works helped to put Toledo on the intellectual center of Al-Andalus . He
1633-904: Is known as the reduced (or parametric) latitude ). Aside from rounding, this is the exact distance along a parallel of latitude; getting the distance along the shortest route will be more work, but those two distances are always within 0.6 m of each other if the two points are one degree of longitude apart. Like any series of multiple-digit numbers, latitude-longitude pairs can be challenging to communicate and remember. Therefore, alternative schemes have been developed for encoding GCS coordinates into alphanumeric strings or words: These are not distinct coordinate systems, only alternative methods for expressing latitude and longitude measurements. Ab%C5%AB Ish%C4%81q Ibr%C4%81h%C4%ABm al-Zarq%C4%81l%C4%AB Abū Isḥāq Ibrāhīm ibn Yaḥyā al-Naqqāsh al-Zarqālī al-Tujibi ( Arabic : إبراهيم بن يحيى الزرقالي ); also known as Al-Zarkali or Ibn Zarqala (1029–1100),
1704-540: Is not cartesian because the measurements are angles and are not on a planar surface. A full GCS specification, such as those listed in the EPSG and ISO 19111 standards, also includes a choice of geodetic datum (including an Earth ellipsoid ), as different datums will yield different latitude and longitude values for the same location. The invention of a geographic coordinate system is generally credited to Eratosthenes of Cyrene , who composed his now-lost Geography at
1775-402: Is straightforward, but in practice finding a reliable method of determining longitude took centuries and required the effort of some of the greatest scientific minds. A location's north–south position along a meridian is given by its latitude , which is approximately the angle between the equatorial plane and the normal from the ground at that location. Longitude is generally given using
1846-731: Is the angle east or west of a reference meridian to another meridian that passes through that point. All meridians are halves of great ellipses (often called great circles ), which converge at the North and South Poles. The meridian of the British Royal Observatory in Greenwich , in southeast London, England, is the international prime meridian , although some organizations—such as the French Institut national de l'information géographique et forestière —continue to use other meridians for internal purposes. The prime meridian determines
1917-405: Is ultimately calculated from latitude and longitude, it is crucial that they clearly state the datum on which they are based. For example, a UTM coordinate based on WGS84 will be different than a UTM coordinate based on NAD27 for the same location. Converting coordinates from one datum to another requires a datum transformation such as a Helmert transformation , although in certain situations
1988-555: The Eiffel Tower in Paris from 1910. These signals allowed navigators to check and adjust their chronometers frequently. 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. They allowed accurate navigation when poor visibility prevented astronomical observations, and became
2059-489: The Library of Alexandria in the 3rd century BC. A century later, Hipparchus of Nicaea improved on this system by determining latitude from stellar measurements rather than solar altitude and determining longitude by timings of lunar eclipses , rather than dead reckoning . In the 1st or 2nd century, Marinus of Tyre compiled an extensive gazetteer and mathematically plotted world map using coordinates measured east from
2130-520: The geodetic normal or the gravity direction . The astronomical longitude can differ slightly from the ordinary longitude because of vertical deflection , small variations in Earth's gravitational field (see astronomical latitude ). 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 . He also proposed
2201-520: The 12th century, Gerard of Cremona translated al-Zarqali's works into Latin. He referred to Al-Zarqali as an astronomer and magician. Ragio Montanous wrote a book in the 15th century on the advantages of the Sahifah al-Zarqalia. In 1530, the German scholar Jacob Ziegler wrote a commentary on one of al-Zarqali's works. In his "De Revolutionibus Orbium Coelestium", in the year 1530, Nicolaus Copernicus quotes
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2272-679: The 12th century, and contributed to the rebirth of a mathematically based astronomy in Christian Europe and were later incorporated into the Tables of Toledo in the 12th century and the Alfonsine tables in the 13th century. Famous as well for his own Book of Tables , of which many had been compiled. Al-Zarqālī's almanac contained tables which allowed one to find the days on which the Coptic, Roman, lunar, and Persian months begin, other tables which give
2343-530: The 12th century, astronomical tables were prepared for a number of European cities, based on the work of al-Zarqālī in Toledo . The lunar eclipse of September 12, 1178 was used to establish the longitude differences between Toledo, Marseilles , and Hereford . 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
2414-694: 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. After the fall of the Roman Empire, interest in geography greatly declined in Europe. Hindu and Muslim astronomers continued to develop these ideas, adding many new locations and often improving on Ptolemy's data. For example al-Battānī used simultaneous observations of two lunar eclipses to determine
2485-502: The Equator, one latitudinal second measures 30.715 m , one latitudinal minute is 1843 m and one latitudinal degree is 110.6 km. The circles of longitude, meridians, meet at the geographical poles, with the west–east width of a second naturally decreasing as latitude increases. On the Equator at sea level, one longitudinal second measures 30.92 m, a longitudinal minute is 1855 m and
2556-489: The Poles. Also the discontinuity at the ± 180° meridian must be handled with care in calculations. An example is a calculation of east displacement by subtracting two longitudes, which gives the wrong answer if the two positions are on either side of this meridian. To avoid these complexities, some applications use another horizontal position representation . The length of a degree of longitude (east–west distance) depends only on
2627-668: The convention of negative for east is also sometimes seen, most commonly in the United States ; the Earth System Research Laboratories used it on an older version of one of their pages, in order "to make coordinate entry less awkward" for applications confined to the Western Hemisphere . They have since shifted to the standard approach. The longitude is singular at the Poles and calculations that are sufficiently accurate for other positions may be inaccurate at or near
2698-507: 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". 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
2769-619: The early 19th century they started to replace lunars, which were seldom used after 1850. The first working telegraphs were established in Britain by Wheatstone and Cooke in 1839, and in the US by Morse in 1844. It was quickly realised that the telegraph could be used to transmit a time signal for longitude determination. The method was soon in practical use for longitude determination, especially in North America, and over longer and longer distances as
2840-399: The equator is exactly 60 geographical miles or 111.3 kilometers, as there are 60 minutes in a degree. The length of 1 minute of longitude along the equator is 1 geographical mile or 1.855 km or 1.153 miles, while the length of 1 second of it is 0.016 geographical mile or 30.916 m or 101.43 feet. Geographic coordinate system A geographic coordinate system ( GCS ) is
2911-408: The established method for commercial shipping until replaced by GPS in the early 1990s. The main conventional methods for determining longitude are listed below. With one exception (magnetic declination), they all depend on a common principle, which is to determine the time for an event or measurement and to compare it with the time at a different location. Longitude, being up to 180° east or west of
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2982-460: The far western Aleutian Islands . The combination of these two components specifies the position of any location on the surface of Earth, without consideration of altitude or depth. The visual grid on a map formed by lines of latitude and longitude is known as a graticule . The origin/zero point of this system is located in the Gulf of Guinea about 625 km (390 mi) south of Tema , Ghana ,
3053-455: The fifteenth century by Regiomontanus and Peurbach . In the sixteenth century Copernicus employed this model, modified to heliocentric form, in his De Revolutionibus Orbium Coelestium . Al-Zarqālī also contributed to the famous Tables of Toledo , an adaptation of earlier astronomical data by Al-Khwarizmi and Al-Battani , to locate the coordinates of Toledo. His zij and almanac were translated into Latin by Gerard of Cremona in
3124-421: The intervention of Parliament. 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. Chronometers had the advantages that both the observations and the calculations were simpler, and as they became cheaper in
3195-415: The length in meters of a degree of longitude can be calculated as (Those coefficients can be improved, but as they stand the distance they give is correct within a centimeter.) The formulae both return units of meters per degree. An alternative method to estimate the length of a longitudinal degree at latitude ϕ {\displaystyle \phi } is to assume a spherical Earth (to get
3266-473: The motion, while France and Brazil abstained. France adopted Greenwich Mean Time in place of local determinations by the Paris Observatory in 1911. The latitude ϕ of a point on Earth's surface is the angle between the equatorial plane and the straight line that passes through that point and through (or close to) the center of the Earth. Lines joining points of the same latitude trace circles on
3337-410: The next half century transformed it into an accurate measurement tool. The pendulum clock was patented by Christiaan Huygens in 1657 and gave an increase in accuracy of about 30 fold over previous mechanical clocks. These two inventions would revolutionise observational astronomy and cartography. On land, the period from the development of telescopes and pendulum clocks until the mid-18th century saw
3408-424: The one used on published maps OSGB36 by approximately 112 m. The military system ED50 , used by NATO , differs from about 120 m to 180 m. Points on the Earth's surface move relative to each other due to continental plate motion, subsidence, and diurnal Earth tidal movement caused by the Moon and the Sun. This daily movement can be as much as a meter. Continental movement can be up to 10 cm
3479-408: The position of planets at any given time, and still others facilitating the prediction of solar and lunar eclipses. This almanac that he compiled directly provided "the positions of the celestial bodies and need no further computation", it further simplifies longitudes using planetary cycles of each planet. The work provided the true daily positions of the sun for four Julian years from 1088 to 1092,
3550-520: The proper Eastern and Western Hemispheres , although maps often divide these hemispheres further west in order to keep the Old World on a single side. The antipodal meridian of Greenwich is both 180°W and 180°E. This is not to be conflated with the International Date Line , which diverges from it in several places for political and convenience reasons, including between far eastern Russia and
3621-452: The radius of a circle of latitude. For a sphere of radius a that radius at latitude φ is a cos φ , and the length of a one-degree (or π / 180 radian ) arc along a circle of latitude is When the Earth is modelled by an ellipsoid this arc length becomes where e , the eccentricity of the ellipsoid, is related to the major and minor axes (the equatorial and polar radii respectively) by An alternative formula
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#17328518369973692-414: The same circle of latitude, measured along that circle of latitude, is slightly more than the shortest ( geodesic ) distance between those points (unless on the equator, where these are equal); the difference is less than 0.6 m (2 ft). A geographical mile is defined to be the length of one minute of arc along the equator (one equatorial minute of longitude) therefore a degree of longitude along
3763-430: The same datum will obtain the same location measurement for the same physical location. However, two different datums will usually yield different location measurements for the same physical location, which may appear to differ by as much as several hundred meters; this not because the location has moved, but because the reference system used to measure it has shifted. Because any spatial reference system or map projection
3834-603: 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. Because of the Earth's rotation , there is a close connection between longitude and time measurement . Scientifically precise local time varies with longitude:
3905-538: The same prime meridian but measured latitude from the Equator instead. After their work was translated into Arabic in the 9th century, Al-Khwārizmī 's Book of the Description of the Earth corrected Marinus' and Ptolemy's errors regarding the length of the Mediterranean Sea , causing medieval Arabic cartography to use a prime meridian around 10° east of Ptolemy's line. Mathematical cartography resumed in Europe following Maximus Planudes ' recovery of Ptolemy's text
3976-428: The sea. See also the equation of time for details on the differences. With the exception of magnetic declination, all proved practicable methods. Developments on land and sea, however, were very different. Several newer methods for navigation, location finding, and the determination of longitude exist. Radio navigation , satellite navigation , and Inertial navigation systems , along with celestial navigation , are
4047-625: 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. 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°. The telescope was invented in the early 17th century. Initially an observation device, developments over
4118-473: The seconds are specified with a decimal fraction . An alternative representation uses degrees and minutes, and parts of a minute are expressed in decimal notation, thus: 23° 27.5′ E. Degrees may also be expressed as a decimal fraction: 23.45833° E. For calculations, the angular measure may be converted to radians , so longitude may also be expressed in this manner as a signed fraction of π ( pi ), or an unsigned fraction of 2 π . For calculations,
4189-486: The shape of the earth (usually a reference ellipsoid for a horizontal datum, and a more precise geoid for a vertical datum) to the earth. Traditionally, this binding was created by a network of control points , surveyed locations at which monuments are installed, and were only accurate for a region of the surface of the Earth. Some newer datums are bound to the center of mass of the Earth. This combination of mathematical model and physical binding mean that anyone using
4260-402: The stars. He measured its rate of motion as 12.04 arcseconds per year, which is remarkably close to the modern calculation of 11.77 arcseconds. Al-Zarqālī's model for the motion of the Sun, in which the center of the Sun's deferent moved on a small, slowly rotating circle to reproduce the observed motion of the solar apogee, was discussed in the thirteenth century by Bernard of Verdun and in
4331-458: The surface of Earth called parallels , as they are parallel to the Equator and to each other. The North Pole is 90° N; the South Pole is 90° S. The 0° parallel of latitude is designated the Equator , the fundamental plane of all geographic coordinate systems. The Equator divides the globe into Northern and Southern Hemispheres . The longitude λ of a point on Earth's surface
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#17328518369974402-651: The tables of Tobias Mayer 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, but he fought to receive money up to the top reward of £20,000, finally receiving an additional payment in 1773 after
4473-586: 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
4544-554: The then capital of the newly established Taifa of Toledo . He started work after 1048 under Said al-Andalusi for the Emir Al-Mamun of Toledo and also under Al-Mu'tamid of the Taifa of Seville . Assuming a leading position under Said, Al-Zarqālī conducted solar observations for 25 years from 1050. He was trained as a metalsmith and due to his skills he was nicknamed Al-Nekkach "the engraver of metals". His Latinized name, 'Arzachel'
4615-404: The true positions of the five planets every 5 or 10 days over a period of 8 years for Venus , 79 years for Mars , and so forth, as well as other related tables. In designing an instrument to deal with Ptolemy's complex model for the planet Mercury , in which the center of the deferent moves on a secondary epicycle , al-Zarqālī noted that the path of the center of the primary epicycle is not
4686-466: The west/east suffix is replaced by a negative sign in the western hemisphere . The international standard convention ( ISO 6709 )—that east is positive—is consistent with a right-handed Cartesian coordinate system , with the North Pole up. A specific longitude may then be combined with a specific latitude (positive in the northern hemisphere ) to give a precise position on the Earth's surface. Confusingly,
4757-445: The width per minute and second, divide by 60 and 3600, respectively): where Earth's average meridional radius M r {\displaystyle \textstyle {M_{r}}\,\!} is 6,367,449 m . Since the Earth is an oblate spheroid , not spherical, that result can be off by several tenths of a percent; a better approximation of a longitudinal degree at latitude ϕ {\displaystyle \phi }
4828-527: The works of al-Zarqali and Al-Battani . Al-Zarqālī wrote two works on the construction of an instrument (an equatorium ) for computing the position of the planets using diagrams of the Ptolemaic model. These works were translated into Spanish in the 13th century by order of King Alfonso X in a section of the Libros del Saber de Astronomia entitled the "Libros de las laminas de los vii planetas". He also invented
4899-447: The years 1874–90. This contributed greatly to the accurate mapping of these areas. 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. Wireless time signals for the use of ships were transmitted from Halifax, Nova Scotia , starting in 1907 and from
4970-492: Was an Arab maker of astronomical instruments and an astrologer from the western part of the Islamic world . Although his name is conventionally given as al-Zarqālī, it is probable that the correct form was al-Zarqālluh. In Latin he was referred to as Arzachel or Arsechieles , a modified form of Arzachel , meaning 'the engraver'. He lived in Toledo , Al-Andalus before moving to Córdoba later in his life. His works inspired
5041-639: 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. 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. It offered two levels of rewards, for solutions within 1° and 0.5°. Rewards were given for two solutions: lunar distances, made practicable by
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