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Arc Measurement Of Delambre And Méchain
The arc measurement of Delambre and Méchain was a geodetic survey carried out by Jean-Baptiste Delambre and Pierre Méchain in 1792–1798 to measure an arc section of the Paris meridian between Dunkirk and Barcelona. This arc measurement served as the basis for the original definition of the metre. In 1791, the French Academy of Sciences chose to define the metre as one ten-millionth of the distance from the equator to the North or South Pole. This replaced the earlier definition based on the period of a pendulum, because the force of Earth's gravity varies slightly over the surface of the Earth, which affects the period of a pendulum. To establish a universally accepted foundation for the definition of the metre, more accurate measurements of a meridian were needed. The French Academy of Sciences commissioned an expedition led by Jean Baptiste Joseph Delambre and Pierre Méchain, lasting from 1792 to 1799, which attempted to accurately measure the distance between a b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geodetic Survey
Geodesy ( ) is the Earth science of accurately measuring and understanding Earth's figure ( geometric shape and size), orientation in space, and gravity. The field also incorporates studies of how these properties change over time and equivalent measurements for other planets (known as ''planetary geodesy''). Geodynamical phenomena, including crustal motion, tides and polar motion, can be studied by designing global and national control networks, applying space geodesy and terrestrial geodetic techniques and relying on datums and coordinate systems. The job title is geodesist or geodetic surveyor. History Definition The word geodesy comes from the Ancient Greek word ''geodaisia'' (literally, "division of Earth"). It is primarily concerned with positioning within the temporally varying gravitational field. Geodesy in the German-speaking world is divided into "higher geodesy" ( or ), which is concerned with measuring Earth on the global scale, and "practical geodes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Montjuïc Castle (Barcelona)
Montjuïc Castle ( ca, Castell de Montjuïc, es, Castillo de Montjuich) is an old military fortress, with roots dating back from 1640, built on top of Montjuïc hill in Barcelona, Catalonia, Spain. It currently serves as a Barcelona municipal facility. History The foundation stone for the basic fortification was laid out in 1640. A year later, in January 1641, the fort saw its first battle, during the Catalan Revolt when the Principality of Catalonia challenged Spain's authority. On orders from the King of Spain, Pedro Fajardo, heading an army of 26,000 men, proceeded to crush the revolt. The Spanish recaptured several cities, but they were defeated at the Battle of Montjuïc by Catalan, led by Francesc de Tamarit. At that battle, Colonel Shane O'Neill or known in Spain as Prince Juan O'Neill, died leading his regiment during the Battle of Montjuic near Barcelona, dying from a musket-ball wound to his chest near the town of Castelldefels. In his honor, the King of Spain gr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Meridian Arc
In geodesy and navigation, a meridian arc is the curve between two points on the Earth's surface having the same longitude. The term may refer either to a segment of the meridian, or to its length. The purpose of measuring meridian arcs is to determine a figure of the Earth. One or more measurements of meridian arcs can be used to infer the shape of the reference ellipsoid that best approximates the geoid in the region of the measurements. Measurements of meridian arcs at several latitudes along many meridians around the world can be combined in order to approximate a ''geocentric ellipsoid'' intended to fit the entire world. The earliest determinations of the size of a spherical Earth required a single arc. Accurate survey work beginning in the 19th century required several arc measurements in the region the survey was to be conducted, leading to a proliferation of reference ellipsoids around the world. The latest determinations use astro-geodetic measurements and the method ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
History Of The Metre
The history of the metre starts with the Scientific Revolution that is considered to have begun with Nicolaus Copernicus's publication of '' De revolutionibus orbium coelestium'' in 1543. Increasingly accurate measurements were required, and scientists looked for measures that were universal and could be based on natural phenomena rather than royal decree or physical prototypes. Rather than the various complex systems of subdivision then in use, they also preferred a decimal system to ease their calculations. With the French Revolution (1789) came a desire to replace many features of the Ancien Régime, including the traditional units of measure. As a base unit of length, many scientists had favoured the seconds pendulum (a pendulum with a half-period of one second) one century earlier, but this was rejected as it had been discovered that this length varied from place to place with local gravity. A new unit of length, the ''metre'' was introduced – defined as one ten-mill ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
History Of Geodesy
The history of geodesy deals with the historical development of measurements and representations of the Earth. The corresponding scientific discipline, '' geodesy'' ( /dʒiːˈɒdɪsi/), began in pre-scientific antiquity and blossomed during the Age of Enlightenment. Early ideas about the figure of the Earth held the Earth to be flat (see flat Earth), and the heavens a physical dome spanning over it. Two early arguments for a spherical Earth were that lunar eclipses were seen as circular shadows which could only be caused by a spherical Earth, and that Polaris is seen lower in the sky as one travels South. Hellenic world Initial development from a diversity of views Though the earliest written mention of a spherical Earth comes from ancient Greek sources, there is no account of how the sphericity of Earth was discovered, or if it was initially simply a guess.James Evans, (1998), ''The History and Practice of Ancient Astronomy'', page 47, Oxford University Press A plausible ex ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earth Radius
Earth radius (denoted as ''R''🜨 or R_E) is the distance from the center of Earth to a point on or near its surface. Approximating the figure of Earth by an Earth spheroid, the radius ranges from a maximum of nearly (equatorial radius, denoted ''a'') to a minimum of nearly (polar radius, denoted ''b''). A ''nominal Earth radius'' is sometimes used as a unit of measurement in astronomy and geophysics, which is recommended by the International Astronomical Union to be the equatorial value. A globally-average value is usually considered to be with a 0.3% variability (±10 km) for the following reasons. The International Union of Geodesy and Geophysics (IUGG) provides three reference values: the ''mean radius'' (R) of three radii measured at two equator points and a pole; the ''authalic radius'', which is the radius of a sphere with the same surface area (R); and the ''volumetric radius'', which is the radius of a sphere having the same volume as the ellipsoid (R). All three ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earth's Circumference
Earth's circumference is the distance around Earth. Measured around the Equator, it is . Measured around the poles, the circumference is . Measurement of Earth's circumference has been important to navigation since ancient times. The first known scientific measurement and calculation was done by Eratosthenes, who achieved a great degree of precision in his computation. Treating the Earth as a sphere, its circumference would be its single most important measurement. Earth deviates from spherical by about 0.3%, as characterized by flattening. In modern times, Earth's circumference has been used to define fundamental units of measurement of length: the nautical mile in the seventeenth century and the metre in the eighteenth. Earth's polar circumference is very near to 21,600 nautical miles because the nautical mile was intended to express one minute of latitude (see meridian arc), which is 21,600 partitions of the polar circumference (that is 60 minutes × 360 degrees). The p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cartography Of France
The history of French cartography can be traced to developments in the Middle Ages. This period was marked by improvements in measuring instruments and also by an upgrade of work in registers of all types. What is thought to be the oldest land map in Europe, the Saint-Bélec slab, representing an area of the Odet valley, was found in 1900, and rediscovered in a castle cellar in France in 2014. The Bronze-Age stone is thought to be 4,000-years old. The first map of France was drawn by Oronce Finé and printed in woodcuts in 1525. It testifies to the will of the political power to mark its presence on the territory; to affirm, to build limits, borders, to arrange its territory, and to consolidate the internal economic markets. In the 16th century, Dieppe appeared as an important school of cartography. Pierre Desceliers allowed the realization of many maps. At the same time, the Portolan maps of the Portuguese sailors had the most recent knowledge obtained by the Dieppois sailors i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Flattening
Flattening is a measure of the compression of a circle or sphere along a diameter to form an ellipse or an ellipsoid of revolution ( spheroid) respectively. Other terms used are ellipticity, or oblateness. The usual notation for flattening is and its definition in terms of the semi-axes of the resulting ellipse or ellipsoid is :: \mathrm = f =\frac . The ''compression factor'' is \frac\,\! in each case; for the ellipse, this is also its aspect ratio. Definitions There are three variants of flattening; when it is necessary to avoid confusion, the main flattening is called the first flattening.Torge, W. (2001). ''Geodesy'' (3rd edition). de Gruyter. and online web textsOsborne, P. (2008). The Mercator Projections'' Chapter 5.Rapp, Richard H. (1991). ''Geometric Geodesy, Part I''. Dept. of Geodetic Science and Surveying, Ohio State Univ., Columbus, Ohio/ref> In the following, is the larger dimension (e.g. semimajor axis), whereas is the smaller (semiminor axis). All fl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geoid
The geoid () is the shape that the ocean surface would take under the influence of the gravity of Earth, including gravitational attraction and Earth's rotation, if other influences such as winds and tides were absent. This surface is extended through the continents (such as with very narrow hypothetical canals). According to Gauss, who first described it, it is the "mathematical figure of the Earth", a smooth but irregular surface whose shape results from the uneven distribution of mass within and on the surface of Earth. It can be known only through extensive gravitational measurements and calculations. Despite being an important concept for almost 200 years in the history of geodesy and geophysics, it has been defined to high precision only since advances in satellite geodesy in the late 20th century. All points on a geoid surface have the same geopotential (the sum of gravitational potential energy and centrifugal potential energy). The force of gravity acts everywhere ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oblate Spheroid
A spheroid, also known as an ellipsoid of revolution or rotational ellipsoid, is a quadric surface obtained by rotating an ellipse about one of its principal axes; in other words, an ellipsoid with two equal semi-diameters. A spheroid has circular symmetry. If the ellipse is rotated about its major axis, the result is a ''prolate spheroid'', elongated like a rugby ball. The American football is similar but has a pointier end than a spheroid could. If the ellipse is rotated about its minor axis, the result is an ''oblate spheroid'', flattened like a lentil or a plain M&M. If the generating ellipse is a circle, the result is a sphere. Due to the combined effects of gravity and rotation, the figure of the Earth (and of all planets) is not quite a sphere, but instead is slightly flattened in the direction of its axis of rotation. For that reason, in cartography and geodesy the Earth is often approximated by an oblate spheroid, known as the reference ellipsoid, instead of a s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sphere
A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the centre of the sphere, and is the sphere's radius. The earliest known mentions of spheres appear in the work of the ancient Greek mathematicians. The sphere is a fundamental object in many fields of mathematics. Spheres and nearly-spherical shapes also appear in nature and industry. Bubbles such as soap bubbles take a spherical shape in equilibrium. The Earth is often approximated as a sphere in geography, and the celestial sphere is an important concept in astronomy. Manufactured items including pressure vessels and most curved mirrors and lenses are based on spheres. Spheres roll smoothly in any direction, so most balls used in sports and toys are spherical, as are ball bearings. Basic terminology As mentioned earlier is th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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