Did you mean: longitude (measure, unit – in geography), Latitude, Longitude, mean longitude, Longitude (2005 Album by Charlie Hunter), Longitude (2000 Adventure Film)
|
Results for longitude
|
On this page:
|
[Middle English, length, a measured length, from Old French, from Latin longitūdō, longitūdin-, from longus, long.]
The east/west location on earth. For details of latitude/longitude positioning, see latitude.
The position of a point on the globe in terms of its meridian east or west of the prime meridian, expressed in degrees. These degrees may be subdivided into minutes and seconds, although decimal parts of the degree are increasingly used.
A measurement, in degrees, of a place's distance east or west of the prime meridian, which runs through Greenwich, England. (Compare latitude.)
The angular distance East or West, between the meridian of a particular place on Earth and that of Greenwich, England, expressed in degrees or time.
The Phoenicians were the world's first great navigators. They determined the location of their ships in terms of the length and width of the Mediterranean, the sea on which they sailed. The Phoenicians taught their navigational methods to the Greeks, from whom the Romans learned. Eventually translated into Latin, the sailors' two perpendicular directions became the longitude (longus, or long) and latitude (latus, or wide). Eratosthenes drew a map of the known world around the third century bce that included lines of latitude and longitude, but his lines were determined by large cities; that is, they were not equally spaced. In the second century bce Hipparchus of Nicaea greatly improved on this by spacing the lines equally around the globe. By assigning 360° to the circumference of Earth, and by using Eratosthenes' nearly correct calculation for the size of Earth, Hipparchus was able to obtain good distances for a degree. Hipparchus's system continues in use today.
Sailors of classical times, however, used only half the system -- the latitude. Early travelers observed the changes in the constellations as one travels north or south. One star, Polaris, is visible every clear night in the Northern Hemisphere, but its position dips closer to the horizon as one travels south. At the North Pole, Polaris is directly overhead; it disappears below the horizon at the equator. Until sailors began to travel in the Southern Hemisphere, all that was needed to find the latitude was an instrument for measuring how high Polaris, the pole star, was above the horizon. The Portuguese sailors who rounded the Cape of Good Hope were terrified because they had lost their main navigational tool on the trip down the side of Africa.
Sailors did not use the longitude because they had no way to measure it. The historian of Magellan's circumnavigation reported that Magellan himself spent long hours trying to find ways to measure the longitude, but those under him were too proud of their navigational skills to speak of it. Common sailors and their pilots believed that they could navigate by a combination of charts, dead reckoning, and the latitude. Governments, however, realized that this was not good enough. The governmental view was particularly brought home to the English when in 1691 and again in 1707 large parts of the British navy were lost because of navigational errors.
Much earlier, in 1598, Philip III of Spain offered the first of several prizes by seagoing nations for the person who could find the longitude. Among the schemes suggested to Philip was one from Galileo. Having discovered the four largest satellites of Jupiter, he proposed that they could be used to locate the longitude. Galileo's idea was based using charts that showed the relative positions of the satellites at different times. By observing the positions, one can determine the time. From the time, one can find the latitude. By telling the time exactly, one can determine the longitude.
As a clock is carried from place to place, it will be off by one hour for each 15° of longitude. This is why there are four time zones in the lower 48 states of the United States. This part of the United States is approximately 4 × 15 or 60° of longitude wide. Comparing universal time with local time helps one to obtain the longitude. Local noon can be obtained easily by determining when the Sun reaches its daily zenith. It is universal time that is hard to obtain.
For example, if you get a long-distance phone call while you are in New York City and you do not know where the call is from, you can ask "What time is it?" If it is noon in New York, and the caller says 11 a.m., then you know the caller's longitude is approximately between 90° W and 107° W, the approximate longitude of Central time in the United States.
To determine the exact longitude, however, you need to forget about time zones and compare Sun times between two places. Specifically, compare local Sun time with Universal Time (UT), formerly known as Greenwich Mean Time (GMT), the time at longitude 0°. If you know it is 1:00 p.m. UT and you observe the sun time where you are to be noon, your longitude is exactly in 15° W.
Astronomical events that repeat frequently are a good way to obtain Universal Time. Eclipses of the Moon could be used, for example, if they were not too infrequent to be of much use to sailors. The positions of Jupiter's moons are more useful because one or another is frequently eclipsed. Although Galileo's suggestion was ignored by Philip, it was taken up in the 17th century by French astronomers, led by Giovanni Cassini. Using Jupiter's moons, the French were able to establish correctly the longitude of cities in Europe and of islands in the Atlantic. The observations required, however, were too difficult and too time-consuming to be done by sailors at sea.
In 1530, Gemini Frisius suggested that the easy way to solve the problem would be to carry a good clock, set to some universal time, with the ship. Others had the same idea but clocks of the time were inadequate for the degree of precision needed. Even after Huygens developed a pendulum clock that theoretically kept good time, it was too imprecise to find the longitude and too delicate to be used on ships.
Christopher Columbus noted on his first voyage that the compass needle changed its deviation from true north as he sailed across the Atlantic. Many expeditions were launched in the 18th century -- notably that of Edmond Halley -- to chart these magnetic deviations in the hopes that they would lead to the secret of the longitude. It was discovered, however, that the deviations vary in such an unpredictable manner that they are unsuitable for this purpose.
In 1714, the English Parliament provided a reward of [[[sterling.gif]]]20,000 for anyone who could find the longitude and demonstrate the method on a voyage to the West Indies. Many of the leading scientists of the eighteenth century worked on the problem in competition for the prize, but the achievement was accomplished by a self-taught watchmaker, John Harrison. His clock Number Four -- or marine chronometer, as it came to be called -- made the West Indies trip in 1761 and passed the test with flying colors. All along the way Harrison's son, who was in charge of the chronometer, predicted landfalls with greater accuracy by far than the ship's pilots. Unfortunately for Harrison, the board governing the prize included a number of scientists who still hoped to get the money themselves. The board gave him half the prize after four years, and then stalled him again for seven more years. They would probably have stalled longer if King George III had not intervened on Harrison's behalf and obtained the remainder of the prize for him.
Lines of longitude are drawn from the North Pole to the South Pole on the globe.
 |
|
| Map of Earth | |
| Longitude (λ) | |
|---|---|
| Lines of longitude appear curved and vertical in this projection, but are actually halves of great circles. | |
| Latitude (φ) | |
| Lines of latitude appear straight and horizontal in this projection, but are actually circular with different radii. All locations with a given latitude are collectively referred to as a circle of latitude. | |
| The equator divides the planet into a Northern Hemisphere and a Southern Hemisphere, and has a latitude of 0°. |  |
Longitude is the east-west geographic coordinate measurement most commonly utilized in cartography and global navigation.
The Greek letter λ (lambda),[1][2] describes the location of a place on Earth east or west of a north-south line called the Prime Meridian. Longitude is given as an angular measurement ranging from 0° at the Prime Meridian to +180° eastward and −180° westward. Unlike latitude, which has the equator as a natural starting position, there is no natural starting position for longitude. Therefore, a reference meridian had to be chosen. While British cartographers had long used the Greenwich meridian in London, other references were used elsewhere, including: El Hierro, Rome, Copenhagen, Jerusalem, Saint Petersburg, Pisa, Paris, Philadelphia and Washington. In 1884, the International Meridian Conference adopted the Greenwich meridian as the universal prime meridian or zero point of longitude. Each degree of longitude is further sub-divided into 60 minutes, each of which divided into 60 seconds. A longitude is thus specified in sexagesimal notation as 23° 27′ 30" E. For higher precision, the seconds are specified with a decimal fraction. An alternative representation uses degrees and minutes, where parts of a minute are expressed in decimal notation with a fraction, thus: 23° 27.500′ E. Degrees may also be expressed as a decimal fraction: 23.45833° E. For calculations, the angular measure usually must 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 2π.
For calculations, the West/East suffix is replaced by a negative sign in the western hemisphere. Confusingly, the convention of negative for East is also sometimes seen. The preferred convention -- that East be 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 (usually positive in the northern hemisphere) to give a precise position on the Earth's surface.
As opposed to a degree of latitude, which is always around sixty nautical miles or about 111 km (69 Mile#Statute_miless, each of 5280 feet) (exactly 111.1334 - 0.5594 cos (2φ) + 0.0012 cos (4φ) [3]), a degree of longitude varies from 0 to 111 km: it is 111 km times the cosine of the latitude, when the distance is laid out on a circle of constant latitude. More precisely, one degree of longitude = (111.320 + 0.373sin²φ)cosφ km, where φ is latitude).[4]
Longitude at a point may be determined by calculating the time difference between that at its location and Coordinated Universal Time (UTC). Since there are 24 hours in a day and 360 degrees in a circle, the sun moves across the sky at a rate of 15 degrees per hour (360°/24 hours = 15° per hour). So if the time zone a person is in is three hours ahead of UTC then that person is near 45° longitude (3 hours × 15° per hour = 45°). The word near was used because the point might not be at the center of the time zone; also the time zones are defined politically, so their centers and boundaries often do not lie on meridians at multiples of 15°. In order to perform this calculation, however, a person needs to have a chronometer (watch) set to UTC and needs to determine local time by solar observation or astronomical observation. The details are more complex than described here: see the articles on Universal Time and on the Equation of time for more details.
A line of constant longitude is a meridian, and half of a great circle.
The measurement of longitude is important to both cartography and
The discovery of how to measure longitude accurately was among the important discoveries of the 1600s and 1700s. The first effective solution for mapmaking was achieved by Giovanni Domenico Cassini starting in 1681, using Galileo's method based on observing the relative positions of the Galilean moons of Jupiter, which have distinct known orbits. For application without a professional astronomer at hand, and in particular measurement at sea, the problem was more difficult; see Dava Sobel's book about John Harrison, Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time, for a good historical overview.
The tragic wrecking of the British fleet led by Sir Cloudesley Shovell led to the British Longitude Act, which created the Longitude Prize for anyone who could devise a practical method of determining longitude at sea. This was eventually achieved by John Harrison, a humble Yorkshire carpenter, with his marine chronometer; the timepiece in question was the one later known as H-4.
Harrison initially built two timepieces (subsequently designated as H-1 and H-2 by Rupert Gould, who restored them to working order between 1920 and 1933) and partially built a third version (designated the H-3). All of these timepieces used multiple contra-acting pendula with the intention of canceling out the forces caused by pitching and rolling of the ship. They also had a seemingly endless supply of small springs, all designed to correct some aberration or other. In this they initially appeared to succeed and Harrison attempted to persuade the Admiralty to convene the Board of Longitude. The Admiralty initially insisted on a shorter trial voyage to Lisbon in Portugal. The trial voyage to Lisbon revealed that the H-1 ran considerably slow. It lost four minutes during the initial part of the voyage but appeared to keep good time for the last part. The return voyage convinced Harrison that the timepiece was capable of keeping accurate time. In fact Harrison placed the ship some 50 miles west of the position determined by the ship's official navigator. Visual land observations revealed that Harrison was correct, and resulted in the prevention of the ship being wrecked off the coast of Cornwall.
It wasn't until Harrison was constructing the H-3, that he realised that it was the yawing motion of the ship as it tacked down the English Channel against the wind that had caused the clock to run slow. The return journey was free of this effect as the ship effectively ran with the wind. Harrison had to abandon his original mechanism. He then designed and built a totally new (and vastly more compact) model from scratch. This new timepiece was designated the H-4. It was based on a temperature compensated balance wheel, found in virtually every non electronic watch today. It was this model that was presented to the Board of Longitude, which authorised the West Indies trial required by the Longitude Act. By this time Harrison was too frail to undertake sea trials himself.
Harrison's son, William, led a voyage aboard a ship from Portsmouth, England to the Caribbean port city of Bridgetown, Barbados with the H-4 aboard. Harrison demonstrated a method of determining longitude by keeping the exact time of day for Greenwich, Britain, while using standard solar observations to find the exact local time on the ship as it sailed to the island of Barbados. In this way he was able to determine the position of the ship relative to the Greenwich meridian whose longitude was zero degrees exactly. The calculation of the ship's position was only two miles in error when it arrived, better than the half degree required by the act for the full prize to be awarded.
The Board proved very reluctant to pay John Harrison his prize — they didn't want the money to go to a working class carpenter, but rather a gentleman. They initially made a partial award, but then put several obstacles in the way, demanding more and more. Harrison got his prize money in 1773, but only after he persuaded the King to intervene.
Today, by other means, we can know the exact time in London (Greenwich Mean Time, Universal Coordinated Time, or "Zulu" Time). By noting the local noon time anywhere in the world, that is, when the sun crosses your meridian (and this can be done quite precisely with a long plumb bob on land), correcting for the Equation of Time, and comparing it with GMT, one's local longitude can be calculated quite accurately. This is the fundamental principle of Harrison's H-4 chronometer, which for use on a sea-going vessel could not use a pendulum. More than anything, this invention marked a breakthrough in clock precision.
It should be noted that Harrison's H-4 marine chronometer did not keep precise time. That would have been well beyond the technology of the time. What Harrison's chronometer did achieve was that it would run fast or slow at a more or less even rate averaged out over time once it had been set at Greenwich. Thus the time at Greenwich (or Greenwich Mean Time) could be ascertained to considerable accuracy by correcting the indication of the chronometer by the calculated accumulated error over the known number of days since it was last set. This daily error in chronometers was simply known as "the rate".
The preferred method of determining longitude became exchanges of chronometers between observatories to accurately determine the differences in local times in conjunction with observation of the transit of stars across the meridian. An alternative method was the simultaneous observation of occultations of stars at different observatories.
From the mid 19th century, telegraph signalling more precisely synchronized star observations to significantly improve longitude measurement accuracy. The Royal Observatory in Greenwich and the U.S. Coast Survey coordinated European and North American longitude measurement campaigns in the 1850s and 1860s resulting in improved map accuracy and navigation safety. Synchronization by radio followed in the early 20th century. Satellites were used to more precisely measure geographic coordinates from the 1970s and 1980s - see GPS.
Longitude is the second part of the ICBM address, latitude being the first.
Ecliptic latitude and longitude are defined for the planets, stars, and other celestial bodies in a similar way to that in which the terrestrial counterparts are defined. The pole is the normal to the ecliptic nearest to the celestial north pole. Ecliptic latitude is measured from 0° to 90° north (+) or south (−) of the ecliptic. Ecliptic longitude is measured from 0° to 360° eastward (the direction that the Sun appears to move relative to the stars) along the ecliptic from the vernal equinox. The equinox at a specific date and time is a fixed equinox, such as that in the J2000 reference frame.
However, the equinox moves because it is the intersection of two planes, both of which move. The ecliptic is relatively
stationary, wobbling within a 4° diameter circle relative to the fixed stars over millions of years under the gravitational
influence of the other planets. The greatest movement is a relatively rapid gyration of Earth's equatorial plane whose pole
traces a 47° diameter circle caused by the Moon. This causes the equinox to precess westward along the ecliptic about 50" per
year. This moving equinox is called the equinox of date. Ecliptic longitude relative to a moving equinox is used whenever
the positions of the Sun, Moon, planets, or stars at dates other than that of a fixed equinox is important, as in
calendars, astrology, or celestial mechanics. The 'error' of the Julian or
Gregorian calendar is always relative to a moving equinox. The years, months, and
days of the Chinese calendar all depend on the ecliptic longitudes of date of
the Sun and Moon. The 30° zodiacal segments used in astrology are also relative to a moving equinox. Celestial mechanics (here
restricted to the motion of solar system bodies) uses both a fixed and moving equinox.
Sometimes in the study of Milankovitch cycles, the invariable plane of the solar system is substituted for the moving ecliptic. Longitude may be
denominated from 0 to 
radians in either case.
Planetary co-ordinate systems are defined relative to their mean axis of rotation and various definitions of longitude depending on the body. The longitude systems of most of those bodies with observable rigid surfaces have been defined by references to a surface feature such as a crater. The north pole is that pole of rotation that lies on the north side of the invariable plane of the solar system (near the ecliptic). The location of the prime meridian as well as the position of body's north pole on the celestial sphere may vary with time due to precession of the axis of rotation of the planet (or satellite). If the position angle of the body's prime meridian increases with time, the body has a direct (or prograde) rotation; otherwise the rotation is said to be retrograde.
In the absence of other information, the axis of rotation is assumed to be normal to the mean orbital plane; Mercury and most of the satellites are in this category. For many of the satellites, it is assumed that the rotation rate is equal to the mean orbital period. In the case of the giant planets, since their surface features are constantly changing and moving at various rates, the rotation of their magnetic fields is used as a reference instead. In the case of the Sun, even this criterion fails (because its magnetosphere is very complex and does not really rotate in a steady fashion), and an agreed-upon value for the rotation of its equator is used instead.
For "planetographic longitude", west longitudes (i.e., longitudes measured positively to the west) are used when the rotation is prograde and east longitudes (i.e., longitudes measured positively to the east) when the rotation is retrograde. However, "planetocentric longitude" is measured positively to the east. Because of tradition, the Earth, Sun, and Moon do not conform with this definition: their rotations are prograde and longitudes run both east and west 180° instead of the usual 360°.
The reference surfaces for some planets (such as Earth and Mars) are ellipsoids of revolution for which the equatorial radius is larger than the polar radius. Smaller bodies (Io, Mimas, etc.) tend to be better approximated by triaxial ellipsoids; however, triaxial ellipsoids would render many computations more complicated, especially those related to map projections. Many projections would lose their elegant and popular properties. For this reason spherical reference surfaces are frequently used in mapping programs.
The modern standard for maps of Mars (since about 2002) is to use planetocentric coordinates. The meridian of Mars is located at Airy-0 crater.[5]
Tidally-locked bodies have a natural reference longitude passing through the point nearest to their parent body.[6] However, libration due to non-circular orbits or axial tilts causes this point to move around any fixed point on the celestial body like an analemma.
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Nederlands (Dutch)
lengtegraad, geografische lengte
Français (French)
n. - longitude
Deutsch (German)
n. - (geographische) Länge
Ελληνική (Greek)
n. - γεωγραφικό μήκος
Italiano (Italian)
longitudine
Português (Portuguese)
n. - longitude (f)
Español (Spanish)
n. - longitud
Svenska (Swedish)
n. - (geogr., astr.) longitud, längd, (geogr. äv.) längdgrad
中文（简体） (Chinese (Simplified))
经度, 经线
中文（繁體） (Chinese (Traditional))
n. - 經度, 經線
日本語 (Japanese)
n. - 経度, 経線, 黄経
العربيه (Arabic)
(الاسم) طول, خط الطول في الجغرافيا
עברית (Hebrew)
n. - קו-אורך, מצהר
If you are unable to view some languages clearly, click here.
To select your translation preferences click here.
Some good "longitude" pages on the web:
 Math mathworld.wolfram.com |
| Longitude Swim Suit | Nautica Latitude Longitude Conditioning Shampoo |
Did you mean: longitude (measure, unit – in geography), Latitude, Longitude, mean longitude, Longitude (2005 Album by Charlie Hunter), Longitude (2000 Adventure Film)
Join the WikiAnswers Q&A community. Post a question or answer questions about "longitude" at WikiAnswers.
Copyrights:
 |
 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved. Read more |
 |
| Computer Desktop Encyclopedia. THIS COPYRIGHTED DEFINITION IS FOR PERSONAL USE ONLY. All other reproduction is strictly prohibited without permission from the publisher. © 1981-2008 Computer Language Company Inc. All rights reserved. Read more |
 |
| Geography Dictionary. A Dictionary of Geography. Copyright © Susan Mayhew 1992, 1997, 2004. All rights reserved. Read more |
 |
| Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/ Read more |
 |
| Geography. The New Dictionary of Cultural Literacy, Third Edition Edited by E.D. Hirsch, Jr., Joseph F. Kett, and James Trefil. Copyright © 2002 by Houghton Mifflin Company. Published by Houghton Mifflin. All rights reserved. Read more |
 |
| Cosmic Lexicon. Copyright 1996 Planetary Science Research Discoveries. Read more |
|
| Essay. History of Science and Technology, edited by Bryan Bunch and Alexander Hellemans. Copyright © 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved. Read more |
 |
| Word Tutor. Copyright © 2004-present by eSpindle Learning, a 501(c) nonprofit organization. All rights reserved. eSpindle provides personalized spelling and vocabulary tutoring online; free trial. Read more |
 |
| Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Longitude". Read more |
 |
| Translations. Copyright © 2007, WizCom Technologies Ltd. All rights reserved. Read more |
Search for answers directly from your browser with the FREE Answers.com Toolbar!
Click here to download now. 
Get Answers your way! Check out all our free tools and products.
Mentioned In:
