NationMaster - Encyclopedia: Lines of longitude

Longitude, sometimes denoted by the Greek letter λ, 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: Ferro, 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. Based on a screenshot of a CIA World Factbook PDF. I cropped it, added text labels, and changed file format. ... Based on a screenshot of a CIA World Factbook PDF. I cropped it, added text labels, and changed file format. ... A map of the world by Johannes Kepler A map is a simplified depiction of a space, a navigational aid which highlights relations between objects within that space. ... Earth, also known as Terra, and Tellus mostly in the 19th century, is the third-closest planet to the Sun. ... An object is in a vertical position when it is aligned in an up-down direction, perpendicular to the horizon. ... Lambda (upper case Î›, lower case Î») is the 11th letter of the Greek alphabet. ... Earth, also known as Terra, and Tellus mostly in the 19th century, is the third-closest planet to the Sun. ... A compass rose with east highlighted For other uses, see East (disambiguation). ... A compass rose with west highlighted This article refers to the cardinal direction; for other uses see West (disambiguation). ... Location of the Prime Meridian Prime Meridian in Greenwich The Prime Meridian is the meridian (line of longitude) passing through the Royal Greenwich Observatory, Greenwich, England; it is the meridian at which longitude is 0 degrees. ... This article is about angles in geometry. ... Latitude, sometimes denoted by the Greek letter Ï†, gives the location of a place on Earth north or south of the Equator. ... The equator is an imaginary circle drawn around a planet (or other astronomical object) at a distance halfway between the poles. ... This article is about the astronomical concept. ... Royal Observatory, Greenwich The original site of the Royal Greenwich Observatory (RGO), which was built as a workplace for the Astronomer Royal, was on a hill in Greenwich Park in Greenwich, London, overlooking the River Thames. ... London is the capital city of the United Kingdom and of England. ... El Hierro, a Spanish island, is the smallest and furthest south and west of the Canary Islands, in the Atlantic Ocean off the coast of Africa. ... City motto: Senatus Populusque Romanus â€“ SPQR (The Senate and the People of Rome) Founded 21 April 753 BC mythical, 1st millennium BC Region Latium Mayor Walter Veltroni (Left-Wing Democrats) Area - City Proper 1290 kmÂ² Population - City (2004) - Metropolitan - Density (city proper) 2,823,807 almost 4,000,000 1... Copenhagen (Danish: KÃ¸benhavn) is the capital of Denmark, and the name of the municipality (Danish, kommune) in which it resides. ... Emblem of the Municipality of Jerusalem Jerusalem and the Old City. ... Saint Petersburg (Russian: Санкт-Петербу́рг, English transliteration: Sankt-Peterburg), colloquially known as Питер (transliterated Piter), formerly known as Leningrad (Ленингра́д, 1924–1991) and Petrograd (Петрогра́д, 1914–1924), is a city located in Northwestern Russia on the delta of the river Neva at the east end of the Gulf of Finland... Pisa is a city in Tuscany, central Italy, on the right bank of the mouth of the river Arno on the Tyrrhenian Sea. ... The Eiffel Tower has become a symbol of Paris throughout the world. ... Independence Hall, as it appears today. ... Aerial photo (looking NW) of the Washington Monument and the White House in Washington, DC. Washington, D.C., officially the District of Columbia (also known as D.C.; Washington; the Nations Capital; the District; and, historically, the Federal City) is the capital city and administrative district of the United... 1884 is a leap year starting on Tuesday (click on link to calendar). ... Location of the Prime Meridian Prime Meridian in Greenwich The Prime Meridian is the meridian (line of longitude) passing through the Royal Greenwich Observatory, Greenwich, England; it is the meridian at which longitude is 0 degrees. ...

Each degree of longitude is further sub-divided into 60 minutes, each of which divided into 60 seconds. A longitude is thus specified as 23° 27′ 30" E. For high accuracy, the seconds are specified with a decimal fraction. An alternative representation uses degrees and minutes, where parts of a minute are expressed as a decimal fraction, thus: 23° 27.500′ E. Degrees expressed as a decimal number is also used: 23.45833° E. Sometimes, the West/East suffix is replaced by a negative sign for West. Confusingly, the convention of negative for East is also sometimes seen. The preferred convention that East is positive is consistent with the right-handed x-axis in the Cartesian coordinate system. A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60) of one degree. ... Cartesian means relating to the French mathematician and philosopher Descartes, who, among other things, worked to merge algebra and Euclidean geometry. ...

A specific longitude may then be combined with a specific latitude to give a precise position on the Earth's surface. Latitude, sometimes denoted by the Greek letter Ï†, gives the location of a place on Earth north or south of the Equator. ...

As opposed to a degree of latitude, which always corresponds to about 111 km (69 mi), a degree of longitude corresponds to a distance 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; if the shortest distance, on a great circle were used, the distance would be even a little less. In mathematics, the trigonometric functions are functions of an angle, important when studying triangles and modeling periodic phenomena. ... 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...

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 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 or UTC, also sometimes referred to as Zulu time or Z, is an atomic realization of Universal Time (UT) or Greenwich Mean Time, the astronomical basis for civil time. ... Time zones are areas of the Earth that have adopted the same standard time, usually referred to as the local time. ... This article is about the astronomical concept. ... A chronometer is a clock designed to have sufficient long-term accuracy that it can be used as a portable time standard on a vehicle, usually in order to determine longitude by means of celestial navigation. ... Universal Time (UT) is a timescale based on the rotation of the Earth. ... During the course of the year, the time as read from a sundial can run ahead of clock time by as much as 16 min 33 s (around October 31â€“November 1) or fall behind by as much as 14 min 6 s (around February 11â€“12). ...

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...

1 History of the measurement of longitude
2 Ecliptic latitude and longitude
3 Longitude on bodies other than Earth
4 See also
5 External links

History of the measurement of longitude

The search for a solution

The measurement of longitude is important to both cartography and navigation. Historically, the most important practical application of these was to provide safe ocean navigation. Knowledge of both latitude and longitude was required. Whereas latitude was easy to determine by celestial navigation using the elevation of the pole star or of the sun at noon, for longitude early ocean navigators had to rely on dead reckoning. This was inaccurate on long voyages out of sight of land, and these voyages sometimes ended with shipwrecks. Cartography or mapmaking (in Greek chartis = map and graphein = write) is the study and practice of making maps or globes. ... There are several traditions of navigation. ... Latitude, sometimes denoted by the Greek letter Ï†, gives the location of a place on Earth north or south of the Equator. ... Celestial navigation, also known as astronavigation, is a position fixing technique that was the first system devised to help sailors locate themselves on a featureless ocean. ... For other uses of the words Pole star and Polestar see Polestar (disambiguation). ... Dead reckoning is the process of estimating a global position of a vehicle by advancing a known position using course, speed, time and distance to be traveled. ...

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 the satellites of Jupiter. For application without a professional astronomer at hand, and in particular measurement at sea, the problem was more difficult; see Dava Sobel's book: Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time for a good historical overview. This genius was John Harrison. Categories: 1600s ... 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 Giovanni Domenico Cassini (June 8, 1625 - September 14, 1712) was an Italian-French astronomer and engineer. ... Events March 4 - Charles II of England grants a land charter to William Penn for the area that will later become Pennsylvania. ... Galileo Galilei Galileo Galilei (Pisa, February 15, 1564 â€“ Arcetri, January 8, 1642), was an Italian physicist, astronomer, and philosopher who is closely associated with the scientific revolution. ... For other uses, please see Satellite (disambiguation) A satellite is an object that orbits another object (known as its primary). ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... Dava Sobel is a writer of popular expositions of scientific topics. ... John Harrison. ...

The 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 with his chronometer; the timepiece in question was the one later known as H-4. Sir Cloudesley Shovell c. ... The longitude prize was a prize offered by the British government in 1714 for the precise determination of a ships longitude. ... John Harrison. ... A chronometer is a clock designed to have sufficient long-term accuracy that it can be used as a portable time standard on a vehicle, usually in order to determine longitude by means of celestial navigation. ...

Harrison's son 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 Britain, while using astronomical 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 Barbados whose longitude was known. The calculation of the ship's position was only 10 miles in error when it arrived. View over Portsmouth from Portsdown Hill. ... Royal motto (French): Dieu et mon droit (Translated: God and my right) Englands location within the UK Official language English de facto Capital London de facto Largest city London Area â€“ Total Ranked 1st UK 130,395 kmÂ² Population â€“ Total (mid-2004) â€“ Total (2001 Census) â€“ Density Ranked 1st UK 50. ... ... The City of Bridgetown, population 5,928 (1990) metropolitan area 110,000 (2000), formerly the Town of Saint Michael, is the Capital city of the island nation of Barbados. ...

Later developments

Exchanges of chronometers between observatories, to determine the precise differences in local time, used in conjunction with the observation of the transit of stars across the meridian became a standard way of determining longitude. Another method was the observation of occultations of stars at different observatories. From the mid 19th century, instead of exchanging chronometers, telegraph time signals were used; radio time signals followed in the early 20th century. Satellites were used for measurements from the 1970s and 1980s - see GPS. Deimos transits the Sun, as seen by Mars Rover Opportunity on March 4, 2004 The word 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... 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. ... Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — 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. ... The first telegraph links in Europe Telegraphy (from the Greek words tele = far and graphein = write) is the long-distance transmission of written messages without physical transport of letters, originally over wire. ... (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 1901–2000 in the sense of the Gregorian calendar (1900–1999 in the... A satellite is any object that orbits another object (which is known as its primary). ... The 1970s decade refers to the years from 1970 to 1979, inclusive. ... The 1980s decade refers to the years from 1980 to 1989, inclusive. ... Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...

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, sometimes denoted by the Greek letter Ï†, 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 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 radians in either case. A calendar is a system for naming periods of time, typically days. ... An astrological chart (or horoscope) - Y2K Chart â€” This particular chart is calculated for January 1, 2000 at 12:01:00 A.M. Eastern Standard Time in New York City, New York, USA. (Longitude: 074W0023 - Latitude: 40N4251), using the tropical zodiac Example of a natal chart Astrology (from Greek... 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 took force in 45 BC (709 ab urbe condita). ... The Gregorian calendar is the calendar that is used nearly everywhere in the world. ... The Chinese calendar is a lunisolar calendar formed by combining a purely lunar calendar with a solar calendar. ... Presentation of the solar system (not to scale) The solar system comprises our Sun and the retinue of celestial objects gravitationally bound to it. ... Milankovitch cycles is the name given to the collective effect of changes in the Earths movements upon its climate. ... 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

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 (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. A planet is generally considered to be a relatively large mass of accreted matter in orbit around a star that is not a star itself. ... The axis of rotation of a rotating body is a line such that the distance between any point on the line and any point of the body remains constant under the rotation. ... This article is about impact craters, also known as meteor craters. ... The North Pole is the northernmost point on any planet. ... The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. ... A sphere is a perfectly symmetrical geometrical object. ... This article is about retrograde motion. ... This article is about retrograde motion. ...

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. Atmospheric characteristics Atmospheric pressure trace Potassium 31. ... A gas giant is a large planet that is not composed mostly of rock or other solid matter. ... Current flowing through a wire produces a magnetic field (M) around the wire. ... The Sun is the star at the center of our Solar system. ...

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°. Crust composition Oxygen 43% Silicon 21% Aluminium 10% Calcium 9% Iron 9% Magnesium 5% Titanium 2% Nickel 0. ...

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. ... Atmospheric characteristics Atmospheric pressure trace Sulfur dioxide 90% Io (IPA: , eye-oe, Greek Î™ÏŽ, Latin ÄªÅ) is the innermost of the four Galilean moons of Jupiter. ... Mimas (mye-mus) 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. [1] 2002 (MMII) was a common year starting on Tuesday of the Gregorian calendar. ... Airy-0 is a crater on Mars whose location defines the position of the prime meridian of that planet. ...

External links

Categories: Lines of longitude | Navigation | Angle

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