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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 methods of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geodesy
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] |
House Of Wisdom
The House of Wisdom ( ar, بيت الحكمة, Bayt al-Ḥikmah), also known as the Grand Library of Baghdad, refers to either a major Abbasid public academy and intellectual center in Baghdad or to a large private library belonging to the Abbasid caliphs during the Islamic Golden Age. The House of Wisdom was founded either as a library for the collections of the Caliph Harun al-Rashid in the late 8th century (then later turned into a public academy during the reign of al-Ma'mun) or was a private collection created by al-Mansur (reign 754–775) to house rare books and collections of poetry in Arabic. The House of Wisdom and its contents were destroyed in the Siege of Baghdad in 1258, leaving relatively limited archaeological evidence for the House of Wisdom, such that most knowledge about it is derived from the works of contemporary scholars of the era such as al-Tabari and Ibn al-Nadim. Background The House of Wisdom existed as a part of the major Translation Movement taki ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gravity
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the strong interaction, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak interaction. As a result, it has no significant influence at the level of subatomic particles. However, gravity is the most significant interaction between objects at the macroscopic scale, and it determines the motion of planets, stars, galaxies, and even light. On Earth, gravity gives weight to physical objects, and the Moon's gravity is responsible for sublunar tides in the oceans (the corresponding antipodal tide is caused by the inertia of the Earth and Moon orbiting one another). Gravity also has many important biological functions, helping to guide the growth of plants through the process of gravitropism and influencing the circ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jean Richer
Jean Richer (1630–1696) was a French astronomer and assistant (''élève astronome'') at the French Academy of Sciences, under the direction of Giovanni Domenico Cassini. Between 1671 and 1673 he performed experiments and carried out celestial observations in Cayenne, French Guiana, at the request of the French Academy. His observations and measurements of Mars during its perihelic opposition, coupled with those made simultaneously in Paris by Cassini, led to the earliest data-based estimate of the distance between Earth and Mars, which they then used to calculate the distance between the Sun and Earth (the astronomical unit). While there he also measured the length of a seconds pendulum, that is a pendulum with a half-swing of one second, and found it to be 1.25 ''lignes'' (2.8 millimeters*) shorter than at Paris. His methodNewton, Principia Mathematica: "And, first of all, in the year 1672, M Richer took notice of it in the island of Cayenne; for when, in the month of Augus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spherical Earth
Spherical Earth or Earth's curvature refers to the approximation of figure of the Earth as a sphere. The earliest documented mention of the concept dates from around the 5th century BC, when it appears in the writings of Greek philosophers. In the 3rd century BC, Hellenistic astronomy established the roughly spherical shape of Earth as a physical fact and calculated the Earth's circumference. This knowledge was gradually adopted throughout the Old World during Late Antiquity and the Middle Ages.Continuation into Roman and medieval thought: Reinhard Krüger:Materialien und Dokumente zur mittelalterlichen Erdkugeltheorie von der Spätantike bis zur Kolumbusfahrt (1492)Direct adoption by India: D. Pingree: "History of Mathematical Astronomy in India", ''Dictionary of Scientific Biography'', Vol. 15 (1978), pp. 533–633 (554f.); Glick, Thomas F., Livesey, Steven John, Wallis, Faith (eds.): "Medieval Science, Technology, and Medicine: An Encyclopedia", Routledge, New York 20 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Classical Antiquity
Classical antiquity (also the classical era, classical period or classical age) is the period of cultural history between the 8th century BC and the 5th century AD centred on the Mediterranean Sea, comprising the interlocking civilizations of ancient Greece and ancient Rome known as the Greco-Roman world. It is the period in which both Greek and Roman societies flourished and wielded huge influence throughout much of Europe, North Africa, and Western Asia. Conventionally, it is taken to begin with the earliest-recorded Epic Greek poetry of Homer (8th–7th-century BC), and continues through the emergence of Christianity (1st century AD) and the fall of the Western Roman Empire (5th-century AD). It ends with the decline of classical culture during late antiquity (250–750), a period overlapping with the Early Middle Ages (600–1000). Such a wide span of history and territory covers many disparate cultures and periods. ''Classical antiquity'' may also refer to an idealized v ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ellipsoid
An ellipsoid is a surface that may be obtained from a sphere by deforming it by means of directional scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a surface that may be defined as the zero set of a polynomial of degree two in three variables. Among quadric surfaces, an ellipsoid is characterized by either of the two following properties. Every planar cross section is either an ellipse, or is empty, or is reduced to a single point (this explains the name, meaning "ellipse-like"). It is bounded, which means that it may be enclosed in a sufficiently large sphere. An ellipsoid has three pairwise perpendicular axes of symmetry which intersect at a center of symmetry, called the center of the ellipsoid. The line segments that are delimited on the axes of symmetry by the ellipsoid are called the ''principal axes'', or simply axes of the ellipsoid. If the three axes have different lengths, the figure is a triaxial ellipsoid (r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 sph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sphere
A sphere () is a Geometry, geometrical object that is a solid geometry, three-dimensional analogue to a two-dimensional circle. A sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the centre (geometry), centre of the sphere, and is the sphere's radius. The earliest known mentions of spheres appear in the work of the Greek mathematics, 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. Bubble (physics), Bubbles such as soap bubbles take a spherical shape in equilibrium. spherical Earth, 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 rolling, roll smoothly in any direction, so mos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Al-Ma'mun
Abu al-Abbas Abdallah ibn Harun al-Rashid ( ar, أبو العباس عبد الله بن هارون الرشيد, Abū al-ʿAbbās ʿAbd Allāh ibn Hārūn ar-Rashīd; 14 September 786 – 9 August 833), better known by his regnal name Al-Ma'mun ( ar, المأمون, al-Maʾmūn), was the seventh Abbasid caliph, who reigned from 813 until his death in 833. He succeeded his half-brother al-Amin after a civil war, during which the cohesion of the Abbasid Caliphate was weakened by rebellions and the rise of local strongmen; much of his domestic reign was consumed in pacification campaigns. Well educated and with a considerable interest in scholarship, al-Ma'mun promoted the Translation Movement, the flowering of learning and the sciences in Baghdad, and the publishing of al-Khwarizmi's book now known as "Algebra". He is also known for supporting the doctrine of Mu'tazilism and for imprisoning Imam Ahmad ibn Hanbal, the rise of religious persecution ('' mihna''), and for the resum ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arc Measurement
Arc measurement, sometimes degree measurement (german: Gradmessung), is the astrogeodetic technique of determining of the radius of Earth – more specifically, the local Earth radius of curvature of the figure of the Earth – by relating the latitude difference (sometimes also the longitude difference) and the geographic distance (arc length) surveyed between two locations on Earth's surface. The most common variant involves only astronomical latitudes and the meridian arc length and is called ''meridian arc measurement''; other variants may involve only astronomical longitude (''parallel arc measurement'') or both geographic coordinates (''oblique arc measurement''). Arc measurement campaigns in Europe were the precursors to the International Association of Geodesy (IAG). History The first known arc measurement was performed by Eratosthenes (240 BC) between Alexandria and Syene in what is now Egypt, determining the radius of the Earth with remarkable correctness. In the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Posidonius
Posidonius (; grc-gre, wikt:Ποσειδώνιος, Ποσειδώνιος , "of Poseidon") "of Apamea (Syria), Apameia" (ὁ Ἀπαμεύς) or "of Rhodes" (ὁ Ῥόδιος) (), was a Greeks, Greek politician, astronomer, astrologer, geographer, historian, mathematician, and teacher native to Apamea, Syria. He was considered the most learned man of his time and, possibly, of the entire Stoicism, Stoic school. After a period learning Stoicism, Stoic philosophy from Panaetius in Athens, he spent many years in travel and scientific researches in Spain, Africa, Italy, Gaul, Liguria, Sicily and on the eastern shores of the Adriatic. He settled as a teacher at Rhodes where his fame attracted numerous scholars. Next to Panaetius he did most, by writings and personal lectures, to spread Stoicism to the Roman world, and he became well known to many leading men, including Pompey and Cicero. His works are now lost, but they proved a mine of information to later writers. The titles an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
