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Encyclopedia > Longitude
Longitude (λ) Map of Earth Lines of longitude appear curved and vertical in this projection, but are actually halves of great circles. 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°.

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. The geographical western hemisphere of Earth, highlighted in yellow. ... Fig. ... For other uses, see North Pole (disambiguation). ... Latitude,usually denoted symbolically by the Greek letter phi, , gives the location of a place on Earth north or south of the equator. ... Northern hemisphere highlighted in yellow. ...

As opposed to a degree of latitude, which is always around sixty nautical miles or about 111 km (69 statute miles, 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] A nautical mile or sea mile is a unit of length. ... A mile is any of several units of distance, or, in physics terminology, of length. ... This article is about a foot as a unit of length. ... In mathematics, the trigonometric functions are functions of an angle, important when studying triangles and modeling periodic phenomena. ...

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. Coordinated Universal Time (UTC) is a high-precision atomic time standard. ... Timezone and TimeZone redirect here. ... This article is about the astronomical concept. ... A marine chronometer is a timekeeper precise enough to be used as a portable time standard, used to determine longitude by means of celestial navigation. ... Universal Time (UT) is a timescale based on the rotation of the Earth. ... The equation of time is the difference, over the course of a year, between time as read from a sundial and a clock. ...

A line of constant longitude is a meridian, and half of a great circle. For the Brisbane bus routes known collectively as the Great Circle Line (598 & 599), see the following list of Brisbane Transport routes A great circle on a sphere A great circle is a circle on the surface of a sphere that has the same diameter as the sphere, dividing the...

## History of the measurement of longitude GA_googleFillSlot("encyclopedia_square");

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. For the computer wargame, Age of Discovery, see Global Diplomacy. ... Many inventions and institutions are created, including Hans Lippershey with the telescope (1608, used by Galileo the next year), the newspaper Avisa Relation oder Zeitung in Augsburg, and Cornelius Drebbel with the thermostat (1609). ... Events and trends The Bonneville Slide blocks the Columbia River near the site of present-day Cascade Locks, Oregon with a land bridge 200 feet (60 m) high. ... Giovanni Domenico (Jean-Dominique) Cassini Portrait Giovanni Domenico Cassini (June 8, 1625â€“September 14, 1712) was an Italian astronomer, engineer, and astrologer. ... Events March 4 - Charles II of England grants a land charter to William Penn for the area that will later become Pennsylvania. ... Galileo Galilei (15 February 1564 â€“ 8 January 1642) was an Italian physicist, mathematician, astronomer, and philosopher who is closely associated with the scientific revolution. ... Jupiters 4 Galilean moons, in a composite image comparing their sizes and the size of Jupiter (Great Red Spot visible). ... Dava Sobel is a writer of popular expositions of scientific topics. ... John Harrison John Harrison (March 24, 1693â€“March 24, 1776) was an English clockmaker, who designed and built the worlds first successful chronometer (maritime clock), one whose accuracy was great enough to allow the determination of longitude over long distances. ...

### Longitude Act and Harrison's chronometer

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. A portrait of Cloudesley Shovell at the museum in Rochester, Kent, where he was an MP. Sir Cloudesley Shovell (c. ... The longitude prize was a prize offered by the British government through an Act of Parliament in 1714 for the precise determination of a ships longitude. ... John Harrison John Harrison (March 24, 1693â€“March 24, 1776) was an English clockmaker, who designed and built the worlds first successful chronometer (maritime clock), one whose accuracy was great enough to allow the determination of longitude over long distances. ... A marine chronometer is a timekeeper precise enough to be used as a portable time standard, used to determine longitude by means of celestial navigation. ...

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. Rupert Gould (November 16, 1890 - October 5, 1948), was a Lieutenant Commander in the British Royal Navy, and is perhaps most widely known for restoring the chronometers of John Harrison. ... The Board of Longitude was a British Government body formed in 1714 to solve the problem of finding longitude at sea. ... For other uses, see Cornwall (disambiguation). ...

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. Satellite view of the English Channel The English Channel (French: , the sleeve) is an arm of the Atlantic Ocean that separates the island of Great Britain from northern France and joins the North Sea to the Atlantic. ...

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. For other places with the same name, see Portsmouth (disambiguation). ... For other uses, see England (disambiguation). ... â€œWest Indianâ€ redirects here. ... This article does not cite any references or sources. ...

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, 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. The equation of time is the difference, over the course of a year, between time as read from a sundial and a clock. ...

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". Greenwich is a town, now part of the south-eastern urban sprawl of London, England, on the south bank of the River Thames in the London Borough of Greenwich. ... Time zones of Europe: Light colours indicate countries not observing summer time Greenwich Mean Time (Media:Example. ...

### Further refinements

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. 2003 Transit of Mercury The term transit or astronomical transit has two meanings in astronomy: A transit is the astronomical event that occurs when one celestial body appears to move across the face of another celestial body, as seen by an observer at some particular vantage point. ... This article is about the astronomical concept. ... In this July, 1997 still frame captured from video, the bright star Aldebaran has just reappeared on the dark limb of the waning crescent moon in this predawn occultation. ...

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. Coastal 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. Alternative meaning: Nineteenth Century (periodical) (18th century &#8212; 19th century &#8212; 20th century &#8212; more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. ... Telegraph and Telegram redirect here. ... (19th century - 20th century - 21st century - more centuries) Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s As a means of recording the passage of time, the 20th century was that century which lasted from 1901&#8211;2000 in the sense of the Gregorian calendar (1900&#8211;1999... For other uses, see Satellite (disambiguation). ... The 1970s decade refers to the years from 1970 to 1979, also called The Seventies. ... The 1980s refers to the years from 1980 to 1989. ... The Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System (GNSS). ...

Longitude is the second part of the ICBM address, latitude being the first. The form used to register a site with the Usenet mapping project before the day of pervasive Internet included a blank for longitude and latitude, preferably to seconds-of-arc accuracy. ... Latitude,usually denoted symbolically by the Greek letter phi, , gives the location of a place on Earth north or south of the equator. ...

## Ecliptic latitude and longitude

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. The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. ... Ecliptic longitude (celestial longitude) is one of the co-ordinates which can be used to define the location of an astronomical object on the celestial sphere in ecliptic coordinates. ... Illumination of Earth by Sun on the day of equinox The vernal equinox (or spring equinox) marks the beginning of astronomical spring. ... The J2000. ...

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 $begin{matrix}2piend{matrix}$ radians in either case. A page from the Hindu calendar 1871-72. ... Hand-coloured version of the anonymous Flammarion woodcut (1888). ... Celestial mechanics is a division of astronomy dealing with the motions and gravitational effects of celestial objects. ... The Julian calendar was introduced in 46 BC by Julius Caesar and came into force in 45 BC (709 ab urbe condita). ... The Gregorian calendar is the most widely used calendar in the world. ... The Chinese calendar is a lunisolar calendar, incorporating elements of a lunar calendar with those of a solar calendar. ... This article is about the Solar System. ... Milankovitch cycles are the collective effect of changes in the Earths movements upon its climate, named after Serbian civil engineer and mathematician Milutin MilankoviÄ‡. The eccentricity, axial tilt, and precession of the Earths orbit vary in several patterns, resulting in 100,000 year ice age cycles of the... The invariable plane of the solar system is the plane passing through its barycenter (center of mass) which is perpendicular to its angular momentum vector, about 98% of which is contributed by the orbital angular momenta of the four jovian planets (Jupiter, Saturn, Uranus, and Neptune). ...

## Longitude on bodies other than Earth

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. Mars is the fourth planet from the Sun in the solar system, named after the Roman god of war (the counterpart of the Greek Ares), on account of its blood red color as viewed in the night sky. ... 3D rendering of an ellipsoid In mathematics, an ellipsoid is a type of quadric that is a higher dimensional analogue of an ellipse. ... Atmosphere Surface pressure: trace Composition: 90% sulfur dioxide Io (eye-oe, IPA: , Greek á¿™ÏŽ) is the innermost of the four Galilean moons of Jupiter and, with a diameter of 3,642 kilometers, is the fourth largest moon in the Solar System. ... Mimas (mee-mÉ™s or mye-mÉ™s, IPA: , Greek ÎœÎ¯Î¼á¾±Ï‚, rarely ÎœÎ¯Î¼Î±Î½Ï‚) is a moon of Saturn that was discovered in 1789 by William Herschel. ... The Mercator projection shows courses of constant bearing as straight lines. ...

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] Airy-0 is a crater on Mars whose location defines the position of the prime meridian of that planet. ...

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. Tidal locking makes one side of an astronomical body always face another, like the Moon facing the Earth. ... Not to be confused with Liberation. ... The analemma photographed, looking east in the northern hemisphere. ...

## Notes

1. ^ Coordinate Conversion
2. ^ "λ = Longitude east of Greenwich (for longitude west of Greenwich, use a minus sign)."
John P. Snyder, Map Projections, A Working Manual, USGS Professional Paper 1395, page ix
3. ^ C.W. Allen, Astrophysical Quantities, 1973, 3rd edition
4. ^ P. Kenneth Seidelmann, ed., Explanatory Supplement to the Astronomical Almanac (Mill Valley, Cal.: University Science Books, 1992) page 700.
5. ^ Where is zero degrees longitude on Mars?
6. ^ First map of extraterrestial planet.

The United States Geological Survey (USGS) is a scientific agency of the United States government. ...

Results from FactBites:

 Latitude and Longitude (1819 words) A lines of longitude is also called a meridian, derived from the Latin, from meri, a variation of "medius" which denotes "middle", and diem, meaning "day." The word once meant "noon", and times of the day before noon were known as "ante meridian";, while times after it were "post meridian."; Today's abbreviations a.m. All points on the same line of longitude experienced noon (and any other hour) at the same time and were therefore said to be on the same "meridian line", which became "meridian"; for short. Longitudes are measured from zero to 180° east and 180° west (or -180°), and both 180-degree longitudes share the same line, in the middle of the Pacific Ocean.
 Latitude and Longitude (779 words) Longitude values are indicate the angular distance between the Prime Meridian and points east or west of it on the surface of the Earth. The 180-degree longitude line is opposite the Prime Meridian on the globe, and is the same going either east or west. At a latitude of 45 degrees, a degree of longitude is approximately 49 miles.
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