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Greenwich Meridian
The Greenwich meridian is a prime meridian, a geographical reference line that passes through the Royal Observatory, Greenwich, in London, England. From 1884 to 1974, the Greenwich meridian was the international standard prime meridian, used worldwide for timekeeping and navigation. The modern standard, the IERS Reference Meridian, is based on the Greenwich meridian, but differs slightly from it. This prime meridian (at the time, one of many) was first established by Sir George Airy (in 1851). In 1883, the International Geodetic Association formally recommended to governments that the meridian through Greenwich be adopted as the international standard prime meridian. In October of the following year, at the invitation of the President of the United States, 41 delegates from 25 nations met in Washington, D.C., United States, for the International Meridian Conference. This inter-governmental conference selected the meridian passing through Greenwich as the world standa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Greenwich Observatory Laser
Greenwich ( , , ) is an List of areas of London, area in south-east London, England, within the Ceremonial counties of England, ceremonial county of Greater London, east-south-east of Charing Cross. Greenwich is notable for its maritime history and for giving its name to the Prime meridian (Greenwich), Greenwich Meridian (0° longitude) and Greenwich Mean Time. The town became the site of a royal palace, the Palace of Placentia, from the 15th century and was the birthplace of many House of Tudor, Tudors, including Henry VIII of England, Henry VIII and Elizabeth I. The palace fell into disrepair during the English Civil War and was demolished, eventually being replaced by the Greenwich Hospital (London), Royal Naval Hospital for Sailors, designed by Sir Christopher Wren and his assistant Nicholas Hawksmoor. These buildings became the Old Royal Naval College, Royal Naval College in 1873, and they remained a military education establishment until 1998, when they passed into the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ghana
Ghana, officially the Republic of Ghana, is a country in West Africa. It is situated along the Gulf of Guinea and the Atlantic Ocean to the south, and shares borders with Côte d’Ivoire to the west, Burkina Faso to the north, and Togo to the east. Ghana covers an area of , spanning diverse ecologies, from coastal savannas to tropical rainforests. With nearly 35 million inhabitants, Ghana is the second-most populous country in West Africa. The capital and largest city is Accra; other significant cities include Tema, Kumasi, Sunyani, Ho, Cape Coast, Techiman, Tamale, and Sekondi-Takoradi. The earliest kingdoms to emerge in Ghana were Bonoman in the south and the Kingdom of Dagbon in the north, with Bonoman existing in the area during the 11th century. The Asante Empire and other Akan kingdoms in the south emerged over the centuries. Beginning in the 15th century, the Portuguese Empire, followed by other European powers, contested the area for trading r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carlos Ibáñez E Ibáñez De Ibero
Carlos Ibáñez e Ibáñez de Ibero, 1st Marquis of Mulhacén, (14 April 1825 – 28 or 29 January 1891) was a Spanish divisional general and geodesist. He represented Spain at the 1875 Conference of the Metre Convention and was the first president of the International Committee for Weights and Measures. As a forerunner geodesist and president of the International Geodetic Association, he played a leading role in the worldwide dissemination of the metric system. His activities resulted in the distribution of a platinum and iridium prototype of the metre to all States parties to the Metre Convention during the first meeting of the General Conference on Weights and Measures in 1889. These prototypes defined the metre right up until 1960. He was born in Barcelona. According to Spanish tradition, his surname was a combination of his father's first surname, Martín ''Ibáñez'' y de Prado and of his mother's first surname, Carmen ''Ibáñez de Ibero'' y González del Río. As his par ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
International Association Of Geodesy
The International Association of Geodesy (IAG) is a constituent association of the International Union of Geodesy and Geophysics focusing on the science which measures and describes the Figure of the Earth, Earth's shape, its rotation and gravity field. History The precursors to the IAG were arc measurement campaigns. The IAG was founded in 1862 as the ''Mitteleuropäische Gradmessung'' (Central European Arc Measurement), later became the ''Europäische Gradmessung'' (European Arc Measurement) in 1867, the ''Internationale Erdmessung'' (''Association Geodésique Internationale'' in French and "International Geodetic Association" in English) in 1886, and took its present name in 1946. In the second half of the 19th century, the creation of the International Geodetic Association marked, following Friedrich Wilhelm Bessel and Friedrich Georg Wilhelm von Struve examples, the systematic adoption of more rigorous methods among them the application of the least squares in geodesy. It ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prime Meridian
A prime meridian is an arbitrarily chosen meridian (geography), meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. On a spheroid, a prime meridian and its anti-meridian (the 180th meridian in a degree (angle), 360°-system) form a great ellipse. This divides the body (e.g. Earth) into hemispheres of Earth, two hemispheres: the Eastern Hemisphere and the Western Hemisphere (for an east-west notational system). For Earth's prime meridian, various conventions have been used or advocated in different regions throughout history. Earth's current international standard prime meridian is the IERS Reference Meridian. It is derived, but differs slightly, from the Prime meridian (Greenwich), Greenwich Meridian, the previous standard. Longitudes for the Earth and Moon are measured from their prime meridian (at 0°) to 180° east and west. For all other Solar System bodies, longitude is measured from 0° (their prime meridian) to 360� ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vertical Deflection
The vertical deflection (VD) or deflection of the vertical (DoV), also known as deflection of the plumb line and astro-geodetic deflection, is a measure of how far the gravity direction at a given point of interest is rotated by local mass anomalies such as nearby mountains. They are widely used in geodesy, for surveying networks and for geophysical purposes. The vertical deflection are the angular components between the true zenith–nadir curve ( plumb line) tangent line and the normal vector to the surface of the reference ellipsoid (chosen to approximate the Earth's sea-level surface). VDs are caused by mountains and by underground geological irregularities. Typically angle values amount to less than 10 arc-seconds in flat areas or up to 1 arc-minute in mountainous terrain. Components The deflection of the vertical has a north–south component ''ξ'' ( xi) and an east–west component ''η'' ( eta). The value of ''ξ'' is the difference between the '' astronomi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geodetic Coordinates
Geodetic coordinates are a type of curvilinear orthogonal coordinate system used in geodesy based on a '' reference ellipsoid''. They include geodetic latitude (north/south) , ''longitude'' (east/west) , and ellipsoidal height (also known as geodetic height). The triad is also known as Earth ellipsoidal coordinates (not to be confused with '' ellipsoidal-harmonic coordinates''). Definitions Longitude measures the rotational angle between the zero meridian and the measured point. By convention for the Earth, Moon and Sun, it is expressed in degrees ranging from −180° to +180°. For other bodies a range of 0° to 360° is used. For this purpose, it is necessary to identify a ''zero meridian'', which for Earth is usually the Prime Meridian. For other bodies a fixed surface feature is usually referenced, which for Mars is the meridian passing through the crater Airy-0. It is possible for many different coordinate systems to be defined upon the same reference ellipsoid. Geo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
International Time Bureau
The International Time Bureau (, abbreviated BIH), seated at the Paris Observatory, was the international bureau responsible for combining different measurements of Universal Time. The bureau also played an important role in the research of time keeping and related fields: Earth rotation, reference frames, and atomic time. In 1987 the responsibilities of the bureau were taken over by the International Bureau of Weights and Measures (BIPM) and the International Earth Rotation and Reference Systems Service (IERS). History The creation of the BIH was decided upon during the 1912 ''Conférence internationale de l'heure radiotélégraphique''. The following year an attempt was made to regulate the international status of the bureau through the creation of an international convention. However, the convention wasn't ratified by its member countries due to the outbreak of World War I. In 1919, after the war, it was decided to make the bureau the executive body of the ''International ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
World Geodetic System
The World Geodetic System (WGS) is a standard used in cartography, geodesy, and satellite navigation including GPS. The current version, WGS 84, defines an Earth-centered, Earth-fixed coordinate system and a geodetic datum, and also describes the associated Earth Gravitational Model (EGM) and World Magnetic Model (WMM). The standard is published and maintained by the United States National Geospatial-Intelligence Agency. History Efforts to supplement the various national surveying systems began in the 19th century with Friedrich Robert Helmert, F.R. Helmert's book (''Mathematical and Physical Theories of Physical Geodesy''). Austria and Germany founded the (Central Bureau of International Geodesy), and a series of global ellipsoids of the Earth were derived (e.g., Helmert 1906, John Fillmore Hayford, Hayford 1910 and 1924). A unified geodetic system for the whole world became essential in the 1950s for several reasons: * International space science and the beginning of as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Seconds Of Arc
A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a turn. The nautical mile (nmi) was originally defined as the arc length of a minute of latitude on a spherical Earth, so the actual Earth's circumference is very near . A minute of arc is of a radian. A second of arc, arcsecond (abbreviated as arcsec), or arc second, denoted by the symbol , is a unit of angular measurement equal to of a minute of arc, of a degree, of a turn, and (about ) of a radian. These units originated in Babylonian astronomy as sexagesimal (base 60) subdivisions of the degree; they are used in fields that involve very small angles, such as astronomy, optometry, ophthalmology, optics, navigation, land surveying, and marksmanship. To express even smaller angles, standard SI prefixes can be employed; the milliarcsec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Global Positioning System
The Global Positioning System (GPS) is a satellite-based hyperbolic navigation system owned by the United States Space Force and operated by Mission Delta 31. It is one of the global navigation satellite systems (GNSS) that provide geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. It does not require the user to transmit any data, and operates independently of any telephone or Internet reception, though these technologies can enhance the usefulness of the GPS positioning information. It provides critical positioning capabilities to military, civil, and commercial users around the world. Although the United States government created, controls, and maintains the GPS system, it is freely accessible to anyone with a GPS receiver. Overview The GPS project was started by the U.S. Department of Defense in 1973. The first prototype spacecraft was launched in 1978 an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
