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Mural Instrument
A mural instrument is an angle measuring instrument mounted on or built into a wall. For astronomical purposes, these walls were oriented so they lie precisely on the meridian. A mural instrument that measured angles from 0 to 90 degrees was called a mural quadrant. They were utilized as astronomical devices in ancient Egypt and ancient Greece. Edmond Halley, due to the lack of an assistant and only one vertical wire in his transit, confined himself to the use of a mural quadrant built by George Graham after its erection in 1725 at the Royal Observatory, Greenwich. Bradley's first observation with that quadrant was made on 15 June 1742. The mural quadrant has been called the "quintessential instrument" of 18th century (i.e. 1700s) observatories. It rose to prominence in the field of positional astronomy at this time. Construction Many older mural quadrants have been constructed by marking directly on the wall surfaces. More recent instruments were made with a frame that was ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Celestial Coordinate System
In astronomy, coordinate systems are used for specifying positions of celestial objects (satellites, planets, stars, galaxies, etc.) relative to a given reference frame, based on physical reference points available to a situated observer (e.g. the true horizon and north to an observer on Earth's surface). Coordinate systems in astronomy can specify an object's relative position in three-dimensional space or plot merely by its direction on a celestial sphere, if the object's distance is unknown or trivial. Spherical coordinates, projected on the celestial sphere, are analogous to the geographic coordinate system used on the surface of Earth. These differ in their choice of fundamental plane, which divides the celestial sphere into two equal hemispheres along a great circle. Rectangular coordinates, in appropriate units, have the same fundamental () plane and primary (-axis) direction, such as an axis of rotation. Each coordinate system is named after its choice of fund ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ray, Iran
Shahre Ray, Shahr-e Ray, Shahre Rey, or Shahr-e Rey (, ) or simply Ray or Rey (), is the capital of Ray County, Iran, Rey County in Tehran Province, Iran. Formerly a distinct city, it has now been absorbed into the metropolitan area of Greater Tehran as the 20th district of municipal Tehran, the capital city of the country. In historical sources also known as Rhages (), Rhagae, and Arsacia, Ray is the oldest existing city in Tehran Province. In the Classical antiquity, classical era, it was a prominent city belonging to Media (region), Media, the political and cultural base of the Medes. Old Persian cuneiform, Ancient Persian inscriptions and the Avesta (Zoroastrianism, Zoroastrian Religious text, scriptures), among other sources, attest to the importance of ancient Ray. Ray is mentioned several times in the Biblical apocrypha, Apocrypha. It is also shown on the fourth-century Tabula Peutingeriana, Peutinger Map. The city was subject to severe destruction during the Middle Ages, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sextant (astronomical)
In astronomy, sextants are devices depicting a sixth of a circle, used primarily for measuring the position of stars. There are two types of astronomical sextants, mural instruments and frame-based instruments. They are of significant historical importance, but have been replaced over time by transit telescopes, other astrometry techniques, and satellites such as Hipparcos. Mural sextants The first known mural sextant was constructed in Ray, Iran, by Abu-Mahmud al-Khujandi in 994. To measure the obliquity of the ecliptic, al-Khujandī invented a device that he called ''al-Fakhri sextant'' (al-suds al Fakhrī), a reference to his patron, Buwayhid ruler, Fakhr al Dawla (976–997). This instrument was a sixty-degree arc on a wall aligned along a meridian (north–south) line. Al Khujandi's instrument was larger than previous instruments; it had a radius of about twenty meters. Tekeli, Sevim (1958), 'Nasiruddin, Takiyuddin ve Tycho Brahe'nin Rasat Aletlerinin mukayesesi'. ''A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ulugh Beg Observatory
The Ulugh Beg Observatory is an observatory in modern day Samarkand, Uzbekistan, which was built in the 1420s by the Timurid astronomer Ulugh Beg. This school of astronomy was constructed under the Timurid Empire, and was the last of its kind from the Islamic Medieval period. Islamic astronomers who worked at the observatory include Jamshid al-Kashi, Ali Qushji, and Ulugh Beg himself. The observatory was destroyed in 1449 and rediscovered in 1908. History Rise and decline Ulugh Beg, the son of Shah Rukh and grandson of Sultan Timur, became the ruler of Samarkand in the 15th century AD. Ulugh Beg was very skilled in mathematics and astronomy. He taught many important astronomers, including Ali Qushji. Many historians have tried to accurately identify the dates of the events that occurred during the Samarkand or Ulugh Beg Observatory. The differences in interpreting dates and citations of historical sources have caused inaccuracies and neglection of some events during this ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Right Ascension
Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the equinox (celestial coordinates), March equinox to the (hour circle of the) point in question above the Earth. When paired with declination, these celestial coordinate system, astronomical coordinates specify the location of a point on the celestial sphere in the equatorial coordinate system. An old term, ''right ascension'' (), "''Ascensio recta'' Solis, stellæ, aut alterius cujusdam signi, est gradus æquatorus cum quo simul exoritur in sphæra recta"; roughly translated, "''Right ascension'' of the Sun, stars, or any other sign, is the degree of the equator that rises together in a right sphere" refers to the ''ascension'', or the point on the celestial equator that rises with any celestial object as seen from Earth's equator, where the celestial equator perpendicular, intersects the horizon at a right angle. It contrasts wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Declination
In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. The declination angle is measured north (positive) or south (negative) of the celestial equator, along the hour circle passing through the point in question. The root of the word ''declination'' (Latin, ''declinatio'') means "a bending away" or "a bending down". It comes from the same root as the words ''incline'' ("bend forward") and ''recline'' ("bend backward"). In some 18th and 19th century astronomical texts, declination is given as ''North Pole Distance'' (N.P.D.), which is equivalent to 90 – (declination). For instance an object marked as declination −5 would have an N.P.D. of 95, and a declination of −90 (the south celestial pole) would have an N.P.D. of 180. Explanation Declination in astronomy is comparable to geographic latitude, projected onto the celestial sphere, and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astronomical Transit
In astronomy, a transit (or astronomical transit) is the passage of a astronomical object, celestial body directly between a larger body and the observer. As viewed from a particular vantage point, the transiting body appears to move across the face of the larger body, eclipse, covering a small portion of it. The word "transit" refers to cases where the nearer object apparent size, appears smaller than the more distant object. Cases where the nearer object appears larger and completely hides the more distant object are known as occultation, ''occultations''. However, the probability of seeing a transiting planet is low because it is dependent on the alignment of the three objects in a nearly perfectly straight line. Many parameters of a planet and its parent star can be determined based on the transit. In the Solar System One type of transit involves the motion of a planet between a Earth, terrestrial observer and the Sun. This can happen only with inferior and superior pla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sidereal Time
Sidereal time ("sidereal" pronounced ) is a system of timekeeping used especially by astronomers. Using sidereal time and the celestial coordinate system, it is easy to locate the positions of celestial objects in the night sky. Sidereal time is a "time scale that is based on Earth's rate of rotation measured relative to the fixed stars". A sidereal day (also known as the sidereal rotation period) represents the time for one rotation about the planet axis relative to the stars. Viewed from the same location, a star seen at one position in the sky will be seen at the same position on another night at the same time of day (or night), if the day is defined as a sidereal day. This is similar to how the time kept by a sundial (Solar time) can be used to find the location of the Sun. Just as the Sun and Moon appear to rise in the east and set in the west due to the rotation of Earth, so do the stars. Both solar time and sidereal time make use of the regularity of Earth's rot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Guinea (coin)
The guinea (; commonly abbreviated gn., or gns. in plural) was a coin, minted in Great Britain between 1663 and 1814, that contained approximately one-quarter of an ounce of gold. The name came from the Guinea region in West Africa, from where much of the gold used to make the coins was sourced. It was the first English machine-struck gold coin, originally representing a value of 20 shillings in sterling specie, equal to one pound, but rises in the price of gold relative to silver caused the value of the guinea to increase, at times to as high as thirty shillings. From 1717 to 1816, its value was officially fixed at twenty-one shillings. In the Great Recoinage of 1816, the guinea was demonetised and replaced by the gold sovereign. Following the Great Recoinage, the word "guinea" was retained as a colloquial or specialised term, even though the coins were no longer in use; the term ''guinea'' also survived as a unit of account in some fields. Notable usages included professio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sextant (astronomical)
In astronomy, sextants are devices depicting a sixth of a circle, used primarily for measuring the position of stars. There are two types of astronomical sextants, mural instruments and frame-based instruments. They are of significant historical importance, but have been replaced over time by transit telescopes, other astrometry techniques, and satellites such as Hipparcos. Mural sextants The first known mural sextant was constructed in Ray, Iran, by Abu-Mahmud al-Khujandi in 994. To measure the obliquity of the ecliptic, al-Khujandī invented a device that he called ''al-Fakhri sextant'' (al-suds al Fakhrī), a reference to his patron, Buwayhid ruler, Fakhr al Dawla (976–997). This instrument was a sixty-degree arc on a wall aligned along a meridian (north–south) line. Al Khujandi's instrument was larger than previous instruments; it had a radius of about twenty meters. Tekeli, Sevim (1958), 'Nasiruddin, Takiyuddin ve Tycho Brahe'nin Rasat Aletlerinin mukayesesi'. ''A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Elevation
The elevation of a geographic location (geography), ''location'' is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational equipotential surface, surface (see Geodetic datum#Vertical datum, Geodetic datum § Vertical datum). The term ''elevation'' is mainly used when referring to points on the Earth's surface, while ''altitude'' or ''geopotential height'' is used for points above the surface, such as an aircraft in flight or a spacecraft in orbit, and ''three-dimensional space, depth'' is used for points below the surface. Elevation is not to be confused with the distance from the center of the Earth. Due to the equatorial bulge, the summits of Mount Everest and Chimborazo (volcano), Chimborazo have, respectively, the largest elevation and the largest ECEF, geocentric distance. Aviation In aviation, the term ''elevation'' or ''aerodrome elevation'' is defined by the IC ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
