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Mirror Segment
A segmented mirror is an array of smaller mirrors designed to act as segments of a single large curved mirror. The segments can be either spherical or asymmetric (if they are part of a larger parabolic reflector). They are used as objectives for large reflecting telescopes. To function, all the mirror segments have to be polished to a precise shape and actively aligned by a computer-controlled active optics system using actuators built into the mirror support cell. The concept was pioneered by Guido Horn D'Arturo, who built the first working segmented mirror in 1952, after twenty years of research; It was later independently rediscovered and further developed under the leadership of Dr. Jerry Nelson at the Lawrence Berkeley National Laboratory and University of California during the 1980s, and since then all the necessary technologies have spread worldwide to the point that essentially all future large optical telescopes plan to use segmented mirrors. Application There is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Comparison Optical Telescope Primary Mirrors
Comparison or comparing is the act of evaluating two or more things by determining the relevant, comparable characteristics of each thing, and then determining which characteristics of each are Similarity (psychology), similar to the other, which are Difference (philosophy), different, and to what degree. Where characteristics are different, the differences may then be evaluated to determine which thing is best suited for a particular purpose. The description of similarities and differences found between the two things is also called a comparison. Comparison can take many distinct forms, varying by field: To compare things, they must have characteristics that are similar enough in relevant ways to merit comparison. If two things are too different to compare in a useful way, an attempt to compare them is colloquially referred to in English as "comparing apples and oranges." Comparison is widely used in society, in science and the arts. General usage Comparison is a natural act ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Diffraction
Diffraction is the deviation of waves from straight-line propagation without any change in their energy due to an obstacle or through an aperture. The diffracting object or aperture effectively becomes a secondary source of the Wave propagation, propagating wave. Diffraction is the same physical effect as Wave interference, interference, but interference is typically applied to superposition of a few waves and the term diffraction is used when many waves are superposed. Italian scientist Francesco Maria Grimaldi coined the word ''diffraction'' and was the first to record accurate observations of the phenomenon in 1660 in science, 1660. In classical physics, the diffraction phenomenon is described by the Huygens–Fresnel principle that treats each point in a propagating wavefront as a collection of individual spherical wavelets. The characteristic pattern is most pronounced when a wave from a Coherence (physics), coherent source (such as a laser) encounters a slit/aperture tha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Sutherland, Northern Cape
Sutherland is a town with about 2,841 inhabitants in the Northern Cape province of South Africa. It lies in the western Roggeveld Mountains in the Karoo. History Sutherland was founded in 1855 as a church and market town to serve the area's sheep farmers. By 1872 the town had a population of 138 registered citizens living in 19 houses. The large Dutch Reformed church in the centre of Sutherland was built in 1899. During the Anglo Boer War the church was used as a fort by garrisoned British soldiers. During the war a number of engagements between British and Boer forces occurred in the town. In one such engagement a force of 250 Boer commandos attacked the local British garrison for 10 hours. The ruins of a fort can be found on the outskirts of town on the hill called Rebelskop. This was named after this engagement. Economy Major economic activities include tourism and sheep farming. The area includes at least twelve registered B&B's, guest houses and guest farms. The n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Southern African Large Telescope
The Southern African Large Telescope (SALT) is a 9.2-metre optical telescope designed mainly for spectroscopy. It consists of 91 hexagonal mirror segments each with a 1-metre inscribed diameter, resulting in a total hexagonal mirror of 11.1 by 9.8 m. However, its effective aperture is only 9.2 m. It is located close to the town of Sutherland in the semi-desert region of the Karoo, South Africa. It is a facility of the South African Astronomical Observatory, the national optical observatory of South Africa. SALT is the largest optical telescope in the southern hemisphere. It enables spectroscopic and polarimetric analysis and imaging of the radiation from astronomical objects that are out of reach of northern hemisphere telescopes. It is closely based on the Hobby–Eberly Telescope (HET) at McDonald Observatory, with some changes in its design, especially to the spherical aberration corrector. The main purpose for these changes was to improve the telescope's fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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West Texas
West Texas is a loosely defined region in the U.S. state of Texas, generally encompassing the desert climate, arid and semiarid climate, semiarid lands west of a line drawn between the cities of Wichita Falls, Texas, Wichita Falls, Abilene, Texas, Abilene, and Del Rio, Texas, Del Rio. No consensus exists on the boundary between East Texas and West Texas. While most Texans understand these terms, no boundaries are officially recognized and any two people are likely to describe the boundaries of these regions differently. The historian and geographer Walter Prescott Webb has suggested that the 98th meridian west, 98th meridian separates East and West Texas; writer A.C. Greene proposed that West Texas extends west of the Brazos River. Use of a single line, though, seems to preclude the use of other separators, such as an area—Central Texas. Texas is part of the Southern United States, South and the American Southwest at the same time, while the semiarid and desert climates of Wes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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McDonald Observatory
McDonald Observatory is an astronomical observatory located near unincorporated community of Fort Davis in Jeff Davis County, Texas, United States. The facility is located on Mount Locke in the Davis Mountains of West Texas, with additional facilities on Mount Fowlkes, approximately to the northeast. The observatory is part of The University of Texas at Austin. It is an organized research unit of the College of Natural Sciences. The observatory produces '' StarDate'', a daily syndicated radio program consisting of short segments related to astronomy that airs on both National Public Radio and commercial radio stations — about 400 affiliates in all. History McDonald Observatory was originally endowed by the Texas banker William Johnson McDonald (1844–1926), who left about $1 million — the bulk of his fortune — to The University of Texas at Austin to endow an astronomical observatory. Edwin Hockaday Fowlkes, step-son of the land's original owner John Chandler Pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Hawaii
Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only state not on the North American mainland, the only state that is an archipelago, and the only state in the tropics. Hawaii consists of 137 volcanic islands that comprise almost the entire Hawaiian Islands, Hawaiian archipelago (the exception, which is outside the state, is Midway Atoll). Spanning , the state is Physical geography, physiographically and Ethnology, ethnologically part of the Polynesian subregion of Oceania. Hawaii's ocean coastline is consequently the List of U.S. states and territories by coastline, fourth-longest in the U.S., at about . The eight main islands, from northwest to southeast, are Niihau, Niihau, Kauai, Kauai, Oahu, Oahu, Molokai, Molokai, Lanai, Lānai, Kahoʻolawe, Kahoolawe, Maui, and Hawaii (island), Hawaii, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Mauna Kea
Mauna Kea (, ; abbreviation for ''Mauna a Wākea''); is a dormant Shield volcano, shield volcano on the Hawaii (island), island of Hawaii. Its peak is above sea level, making it the List of U.S. states by elevation, highest point in Hawaii and List of islands by highest point, the island with the second highest high point, behind New Guinea, the world's largest tropical island with multiple peaks that are higher. The peak is about higher than Mauna Loa, its more massive neighbor. Mauna Kea is unusually Topographic prominence, topographically prominent for its height: its prominence from sea level is List of mountain peaks by prominence, 15th in the world among mountains, at ; its prominence from under the ocean is , rivaled only by Mount Everest. This Topographic prominence#Wet prominence and dry prominence, dry prominence is greater than Everest's height above sea level of , and some authorities have labeled Mauna Kea the tallest mountain in the world, from its underwater ba ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Mauna Kea Observatories
The Mauna Kea Observatories (MKO) are a group of independent astronomical research facilities and large telescope observatories that are located at the summit of Mauna Kea on Hawaii (island), Hawaiʻi, United States. The facilities are located in a 525-acre (212 ha) special land use zone known as the "Astronomy Precinct", which is located within the 11,228-acre (4,544 ha) Mauna Kea Science Reserve. The Astronomy Precinct was established in 1967 and is located on land protected by the National Historic Preservation Act of 1966, Historical Preservation Act for its significance to Hawaiian culture. The presence and continued construction of telescopes Opposition to the Mauna Kea Observatories, is highly controversial due to Mauna Kea's centrality in native Hawaiian religion and culture, as well as for a variety of environmental reasons. The location is near ideal because of its light pollution, dark skies from lack of light pollution, good astronomical seeing, low Relative ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Keck Telescopes
The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and, when completed in 1993 (Keck I) and 1996 (Keck II), they were the largest optical reflecting telescopes in the world. They have been the third and fourth largest since 2006. Overview With a concept first proposed in 1977, telescope designers Terry Mast, of the University of California, Berkeley, and Jerry Nelson of Lawrence Berkeley Laboratory had been developing the technology necessary to build a large, ground-based telescope. In 1985, Howard B. Keck of the W. M. Keck Foundation gave $70 million to fund the construction of the Keck I telescope, which began in September 1985. First light occurred on November 24, 1990, using 9 of the eventual 36 segments. When construction of the first telescope was well advanced, further donations ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |