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Azimuth
An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematically, the relative position vector from an observer ( origin) to a point of interest is projected perpendicularly onto a reference plane (the horizontal plane); the angle between the projected vector and a reference vector on the reference plane is called the azimuth. When used as a celestial coordinate, the azimuth is the horizontal direction of a star or other astronomical object in the sky. The star is the point of interest, the reference plane is the local area (e.g. a circular area with a 5 km radius at sea level) around an observer on planetary surface, Earth's surface, and the reference vector points to true north. The azimuth is the angle between the north vector and the star's vector on the horizontal plane In astronomy, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Horizontal Coordinate System
The horizontal coordinate system is a celestial coordinate system that uses the observer's local horizon as the fundamental plane to define two angles: altitude and azimuth. Therefore, the horizontal coordinate system is sometimes called as the az/el system, the alt/az system, or the alt-azimuth system, among others. In an altazimuth mount of a telescope, the instrument's two axes follow altitude and azimuth. Definition This celestial coordinate system divides the sky into two hemispheres: The upper hemisphere, where objects are above the horizon and are visible, and the lower hemisphere, where objects are below the horizon and cannot be seen, since the Earth obstructs views of them. The great circle separating the hemispheres is called the celestial horizon, which is defined as the great circle on the celestial sphere whose plane is normal to the local gravity vector. In practice, the horizon can be defined as the plane tangent to a quiet, liquid surface, such as a pool of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Celestial Navigation
Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space (or on the surface of the Earth) without having to rely solely on estimated positional calculations, commonly known as " dead reckoning", made in the absence of satellite navigation or other similar modern electronic or digital positioning means. Celestial navigation uses "sights", or timed angular measurements, taken typically between a celestial body (e.g. the Sun, the Moon, a planet, or a star) and the visible horizon. Celestial navigation can also take advantage of measurements between celestial bodies without reference to the Earth horizon, such as when the Moon and other selected bodies are used in the practice called "lunars" or lunar distance method, used for determining precise time when time is unknown. Celestial navigation by taking sights ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cardinal Direction
The four cardinal directions, or cardinal points, are the four main compass directions: north, east, south, and west, commonly denoted by their initials N, E, S, and W respectively. Relative to north, the directions east, south, and west are at 90 degree intervals in the clockwise direction. The ordinal directions (also called the intercardinal directions) are northeast (NE), southeast (SE), southwest (SW), and northwest (NW). The intermediate direction of every set of intercardinal and cardinal direction is called a secondary intercardinal direction. These eight shortest points in the compass rose shown to the right are: # West-northwest (WNW) # North-northwest (NNW) # North-northeast (NNE) # East-northeast (ENE) # East-southeast (ESE) # South-southeast (SSE) # South-southwest (SSW) # West-southwest (WSW) Points between the cardinal directions form the points of the compass. Arbitrary horizontal directions may be indicated by their azimuth angle value. Determination Ad ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
True North
True north (also called geodetic north or geographic north) is the direction along Earth's surface towards the geographic North Pole or True North Pole. Geodetic north differs from ''magnetic'' north (the direction a compass points toward the Magnetic North Pole), and from grid north (the direction northwards along the grid lines of a map projection). Geodetic true north also differs very slightly from ''astronomical'' true north (typically by a few arcseconds) because the local gravitational field may not point at the exact rotational axis of Earth. The direction of astronomical true north is marked in the skies by the north celestial pole. This is within about 1° of the position of Polaris, meaning the star would appear to trace a tiny circle in the sky each sidereal day. Due to the axial precession of Earth, true north rotates in an arc with respect to the stars that takes approximately 25,000 years to complete. Around 2101–2103, Polaris will make its closest a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sun And Moon Letters
In Arabic and Maltese, the consonants are divided into two groups, called the sun letters or solar letters ( ar, حروف شمسية ', mt, konsonanti xemxin) and moon letters or lunar letters (Arabic: ', mt, konsonanti qamrin), based on whether they assimilate the letter ' ( ') of a preceding Arabic definite article '' al-'' (), which is an important general rule used in Arabic grammar. Phonetically, sun letters are ones pronounced as coronal consonants, and moon letters are ones pronounced as other consonants. These names come from the fact that the word for 'the sun', ', pronounced ''ash-shams'', assimilates the ', while the word for 'the moon', ', doesn't. This also applies to the Maltese language where they are written as ''ix-xemx'' and ''il-qamar''. Rule When followed by a sun letter, the of the Arabic definite article assimilates to the initial consonant of the following noun, resulting in a doubled consonant. For example, "the Nile" is pronounced , not . Whe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
King Alfonso X
Alfonso X (also known as the Wise, es, el Sabio; 23 November 1221 – 4 April 1284) was King of Castile, León and Galicia from 30 May 1252 until his death in 1284. During the election of 1257, a dissident faction chose him to be king of Germany on 1 April. He renounced his claim to Germany in 1275, and in creating an alliance with the Kingdom of England in 1254, his claim on the Duchy of Gascony as well. Alfonso X fostered the development of a cosmopolitan court that encouraged learning. Jews, Muslims, and Christians were encouraged to have prominent roles in his court. As a result of his encouraging the translation of works from Arabic and Latin into the vernacular of Castile, many intellectual changes took place, including the encouragement of the use of Castilian as a primary language of higher learning, science, and law. Alfonso was a prolific author of Galician poetry, such as the ''Cantigas de Santa Maria'', which are equally notable for their musical content as for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Libros Del Saber De Astronomía
The , ( osp, Libro del saber de astrología), "Books of wisdom of astronomy/astrology of King Alfonso X of Castile", is a series of books of the medieval period, composed during the reign of Alfonso X of Castile. They describe the celestial bodies and the astronomical instruments existing at the time. The collection is a group of treatises on astronomical instruments, like the celestial sphere, the spherical and plane astrolabe, saphea, and universal plate for all latitudes, for uranography or star cartography that can be used for casting horoscopes. The purpose of the rest of the instruments, the quadrant of the type called vetus, sundial, clepsydras, is to determine the time, which was also needed to cast the horoscope. The king looked for separate works for the construction and use of each device. Of the three scientific collections that Alfonso X commissioned between 1276 and 1279, this is the only one that survived with the full original text intact. It is a group of technical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Treatise On The Astrolabe
''A Treatise on the Astrolabe'' is a medieval instruction manual on the astrolabe by Geoffrey Chaucer. It describes both the form and the proper use of the instrument, and stands out as a prose technical work from a writer better known for poetry, written in English rather than the more typical Latin. Significance The ''Treatise'' is considered the "oldest work in English written upon an elaborate scientific instrument". It is admired for its clarity in explaining difficult concepts – although modern readers lacking an actual astrolabe may find the details of the astrolabe difficult to understand. Robinson believes that it indicates that had Chaucer written more freely composed prose it would have been superior to his translations of Boethius and Renaut de Louhans. Chaucer’s exact source is undetermined but most of his ‘conclusions’ go back, directly or indirectly, to ''Compositio et Operatio Astrolabii'', a Latin translation of Messahala's Arabic treatise of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geoffrey Chaucer
Geoffrey Chaucer (; – 25 October 1400) was an English poet, author, and civil servant best known for ''The Canterbury Tales''. He has been called the "father of English literature", or, alternatively, the "father of English poetry". He was the first writer to be buried in what has since come to be called Poets' Corner, in Westminster Abbey. Chaucer also gained fame as a philosopher and astronomer, composing the scientific '' A Treatise on the Astrolabe'' for his 10-year-old son Lewis. He maintained a career in the civil service as a bureaucrat, courtier, diplomat, and member of parliament. Among Chaucer's many other works are '' The Book of the Duchess'', '' The House of Fame'', '' The Legend of Good Women'', and '' Troilus and Criseyde''. He is seen as crucial in legitimising the literary use of Middle English when the dominant literary languages in England were still Anglo-Norman French and Latin. Chaucer's contemporary Thomas Hoccleve hailed him as "the firste fy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astrolabe
An astrolabe ( grc, ἀστρολάβος ; ar, ٱلأَسْطُرلاب ; persian, ستارهیاب ) is an ancient astronomical instrument that was a handheld model of the universe. Its various functions also make it an elaborate inclinometer and an analog calculation device capable of working out several kinds of problems in astronomy. In its simplest form it is a metal disc with a pattern of wires, cutouts, and perforations that allows a user to calculate astronomical positions precisely. Historically used by astronomers, it is able to measure the altitude above the horizon of a celestial body, day or night; it can be used to identify stars or planets, to determine local latitude given local time (and vice versa), to survey, or to triangulate. It was used in classical antiquity, the Islamic Golden Age, the European Middle Ages and the Age of Discovery for all these purposes. The astrolabe's importance comes not only from the early developments into the study of ast ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ballistics
Ballistics is the field of mechanics concerned with the launching, flight behaviour and impact effects of projectiles, especially ranged weapon munitions such as bullets, unguided bombs, rockets or the like; the science or art of designing and accelerating projectiles so as to achieve a desired performance. A ballistic body is a free-moving body with momentum which can be subject to forces such as the forces exerted by pressurized gases from a gun barrel or a propelling nozzle, normal force by rifling, and gravity and air drag during flight. A ballistic missile is a missile that is guided only during the relatively brief initial phase of powered flight and the trajectory is subsequently governed by the laws of classical mechanics; in contrast to (for example) a cruise missile which is aerodynamically guided in powered flight like a fixed-wing aircraft. History and prehistory The earliest known ballistic projectiles were stones and spears, and the throwing stic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
