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Zenith
The zenith (, ) is an imaginary point directly "above" a particular location, on the celestial sphere. "Above" means in the vertical direction (plumb line) opposite to the gravity direction at that location (nadir). The zenith is the "highest" point on the celestial sphere. Origin The word "zenith" derives from an inaccurate reading of the Arabic expression (), meaning "direction of the head" or "path above the head", by Medieval Latin scribes in the Middle Ages (during the 14th century), possibly through Old Spanish. It was reduced to "samt" ("direction") and miswritten as "senit"/"cenit", the "m" being misread as "ni". Through the Old French "cenith", "zenith" first appeared in the 17th century. Relevance and use The term ''zenith'' sometimes means the highest point, way, or level reached by a celestial body on its daily apparent path around a given point of observation. This sense of the word is often used to describe the position of the Sun ("The sun reached its zenit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zenith Telescope
A zenith telescope is a type of telescope that is designed to point straight up at or near the zenith. They are used for precision measurement of star positions, to simplify telescope construction, or both. A classic zenith telescope, also known as a zenith sector employs a strong altazimuth mount, fitted with levelling screws. Extremely sensitive levels are attached and the telescope has an eyepiece fitted with a micrometer. They are used for the measurement of small differences of zenith distance, and used in the determination of astronomic latitude. Other types of zenith telescopes include the Monument to the Great Fire of London, which includes a central shaft meant for use as a zenith telescope. High-precision (and fixed building) zenith telescopes were also used until the early 1980s to track Earth's north pole position e.g. Earth's rotation axis position ( polar motion). Since then radio astronomical quasar measurements ( VLBI) have also measured Earth's rotation axi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vertical Direction
In astronomy, geography, and related sciences and contexts, a '' direction'' or ''plane'' passing by a given point is said to be vertical if it contains the local gravity direction at that point. Conversely, a direction or plane is said to be horizontal if it is perpendicular to the vertical direction. In general, something that is vertical can be drawn from up to down (or down to up), such as the y-axis in the Cartesian coordinate system. Historical definition The word ''horizontal'' is derived from the Latin , which derives from the Greek , meaning 'separating' or 'marking a boundary'. The word ''vertical'' is derived from the late Latin ', which is from the same root as ''vertex'', meaning 'highest point' or more literally the 'turning point' such as in a whirlpool. Girard Desargues defined the vertical to be perpendicular to the horizon in his 1636 book ''Perspective''. Geophysical definition The plumb line and spirit level In physics, engineering and construction, the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Complementary Angles
In Euclidean geometry, an angle is the figure formed by two rays, called the '' sides'' of the angle, sharing a common endpoint, called the ''vertex'' of the angle. Angles formed by two rays lie in the plane that contains the rays. Angles are also formed by the intersection of two planes. These are called dihedral angles. Two intersecting curves may also define an angle, which is the angle of the rays lying tangent to the respective curves at their point of intersection. ''Angle'' is also used to designate the measure of an angle or of a rotation. This measure is the ratio of the length of a circular arc to its radius. In the case of a geometric angle, the arc is centered at the vertex and delimited by the sides. In the case of a rotation, the arc is centered at the center of the rotation and delimited by any other point and its image by the rotation. History and etymology The word ''angle'' comes from the Latin word ''angulus'', meaning "corner"; cognate words are the Greek ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plumb Line
A plumb bob, plumb bob level, or plummet, is a weight, usually with a pointed tip on the bottom, suspended from a string and used as a vertical reference line, or plumb-line. It is a precursor to the spirit level and used to establish a vertical datum. It is typically made of stone, wood, or lead, but can also be made of other metals. If it is used for decoration, it may be made of bone or ivory. The instrument has been used since at least the time of ancient EgyptDenys A. Stocks. Experiments in Egyptian archaeology: stoneworking technology in ncient Egypt'. Routledge; 2003. . p. 180. to ensure that constructions are "plumb", or vertical. It is also used in surveying, to establish the nadir with respect to gravity of a point in space. It is used with a variety of instruments (including levels, theodolites, and steel tapes) to set the instrument exactly over a fixed survey marker or to transcribe positions onto the ground for placing a marker. Etymology The ''plu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nadir
The nadir (, ; ar, نظير, naẓīr, counterpart) is the direction pointing directly ''below'' a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface. The direction opposite of the nadir is the zenith. Definitions Space science Since the concept of ''being below'' is itself somewhat vague, scientists define the nadir in more rigorous terms. Specifically, in astronomy, geophysics and related sciences (e.g., meteorology), the nadir at a given point is the local vertical direction pointing in the direction of the force of gravity at that location. The term can also be used to represent the lowest point that a celestial object reaches along its apparent daily path around a given point of observation (i.e. the object's ''lower culmination''). This can be used to describe the position of the Sun, but it is only technically accurate for one latitude at a time and only possible at the low latitudes. T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Culmination
In observational astronomy, culmination is the passage of a celestial object (such as the Sun, the Moon, a planet, a star, constellation or a deep-sky object) across the observer's local meridian. These events were also known as meridian transits, used in timekeeping and navigation, and measured precisely using a transit telescope. During each day, every celestial object appears to move along a circular path on the celestial sphere due to the Earth's rotation creating two moments when it crosses the meridian. Except at the geographic poles, any celestial object passing through the meridian has an upper culmination, when it reaches its highest point above the horizon, and nearly twelve hours later, is followed by a lower culmination, when it reaches its lowest point. The time of ''culmination'' (when the object culminates) is often used to mean upper culmination. An object's altitude (''A'') in degrees at its upper culmination is equal to 90 minus the observer's latitude (''L'') ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Altitude Angle
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 mer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mecca
Mecca (; officially Makkah al-Mukarramah, commonly shortened to Makkah ()) is a city and administrative center of the Mecca Province of Saudi Arabia, and the Holiest sites in Islam, holiest city in Islam. It is inland from Jeddah on the Red Sea, in a narrow valley above sea level. Its last recorded population was 1,578,722 in 2015. Its estimated metro population in 2020 is 2.042million, making it the List of cities in Saudi Arabia by population, third-most populated city in Saudi Arabia after Riyadh and Jeddah. Pilgrims more than triple this number every year during the Pilgrimage#Islam, pilgrimage, observed in the twelfth Islamic calendar, Hijri month of . Mecca is generally considered "the fountainhead and cradle of Islam". Mecca is revered in Islam as the birthplace of the Prophets and messengers in Islam, Islamic prophet Muhammad. The Hira cave atop the ("Mountain of Light"), just outside the city, is where Muslims believe the Quran was first revealed to Muhammad. Vis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tropic Of Cancer
The Tropic of Cancer, which is also referred to as the Northern Tropic, is the most northerly circle of latitude on Earth at which the Sun can be directly overhead. This occurs on the June solstice, when the Northern Hemisphere is tilted toward the Sun to its maximum extent. It also reaches 90 degrees below the horizon at solar midnight on the December Solstice. Using a continuously updated formula, the circle is currently north of the Equator. Its Southern Hemisphere counterpart, marking the most southerly position at which the Sun can be directly overhead, is the Tropic of Capricorn. These tropics are two of the five major circles of latitude that mark maps of Earth, the others being the Arctic and Antarctic circles and the Equator. The positions of these two circles of latitude (relative to the Equator) are dictated by the tilt of Earth's axis of rotation relative to the plane of its orbit, and since the tilt changes, the location of these two circles also changes. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tropic Of Capricorn
The Tropic of Capricorn (or the Southern Tropic) is the circle of latitude that contains the subsolar point at the December (or southern) solstice. It is thus the southernmost latitude where the Sun can be seen directly overhead. It also reaches 90 degrees below the horizon at solar midnight on the June Solstice. Its northern equivalent is the Tropic of Cancer. The Tropic of Capricorn is one of the five major circles of latitude marked on maps of Earth. Its latitude is currently south of the Equator, but it is very gradually moving northward, currently at the rate of 0.47 arcseconds, or 15 metres, per year. Less than 3% of the world's population lives south of it; this is equivalent to about 30% of the population of the Southern Hemisphere. Name When this line of latitude was named in the last centuries BC, the Sun was in the constellation Capricornus at the December solstice. This is the date each year when the Sun reaches zenith at this latitude, the southernmost l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Islamic Astronomy
Islamic astronomy comprises the Astronomy, astronomical developments made in the Islamic world, particularly during the Islamic Golden Age (9th–13th centuries), and mostly written in the Arabic language. These developments mostly took place in the Middle East, Central Asia, Al-Andalus, and North Africa, and later in the Far East and History of India, India. It closely parallels the genesis of other Islamic sciences in its assimilation of foreign material and the amalgamation of the disparate elements of that material to create a science with Islamic characteristics. These included Greek astronomy, Greek, Sassanid Empire, Sassanid, and Indian astronomy, Indian works in particular, which were translated and built upon. Islamic astronomy played a significant role in the revival of Byzantine science, Byzantine and Science in Medieval Western Europe, EuropeanSaliba (1999). astronomy following the Dark Ages (historiography), loss of knowledge during the early medieval period, notably ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Noon
Noon (or midday) is 12 o'clock in the daytime. It is written as 12 noon, 12:00 m. (for meridiem, literally 12:00 noon), 12 p.m. (for post meridiem, literally "after noon"), 12 pm, or 12:00 (using a 24-hour clock) or 1200 (military time). Solar noon is the time when the Sun appears to contact the local celestial meridian. This is when the Sun reaches its apparent highest point in the sky, at 12 noon apparent solar time and can be observed using a sundial. The local or clock time of solar noon depends on the longitude and date, with Daylight Savings Time tending to place solar noon closer to 1:00pm. Etymology The word ''noon'' is derived from Latin ''nona hora'', the ninth canonical hour of the day, in reference to the Western Christian liturgical term none, one of the seven fixed prayer times in traditional Christian denominations. The Roman and Western European medieval monastic day began at 6:00 a.m. (06:00) at the equinox by modern timekeeping, so the ninth hour star ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
