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Millstone Hill
The Millstone Hill Steerable Antenna, or MISA, is a fully steerable dish antenna, in diameter, designed by the Stanford Research Institute (SRI) in 1959. It is currently located at MIT Haystack Observatory in Westford, Massachusetts. History MISA was originally installed at the Sagamore Hill Radio Observatory in Hamilton, Massachusetts in 1963. The antenna operated at that location until 1978, at which time it was relocated to Millstone Hill. Since that time it has been primarily used as a UHF radar antenna to provide measurements of the near space environment using the incoherent scatter radar technique. It is one of two surviving dish antennas of this type in the world with the other antenna being located at the Stanford University radio science field site in Stanford, California. MISA is used to provide wide radar coverage in latitude and longitude. Capabilities MISA is a broad-based observatory capable of addressing a wide range of atmospheric science investigations. The i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dish Antenna
A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish. The main advantage of a parabolic antenna is that it has high directivity. It functions similarly to a searchlight or flashlight reflector to direct radio waves in a narrow beam, or receive radio waves from one particular direction only. Parabolic antennas have some of the highest gains, meaning that they can produce the narrowest beamwidths, of any antenna type. In order to achieve narrow beamwidths, the parabolic reflector must be much larger than the wavelength of the radio waves used, so parabolic antennas are used in the high frequency part of the radio spectrum, at UHF and microwave ( SHF) frequencies, at which the wavelengths are small enough that conveniently-sized reflectors can be used. Parabolic antennas are use ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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] |
Backscatter
In physics, backscatter (or backscattering) is the reflection of waves, particles, or signals back to the direction from which they came. It is usually a diffuse reflection due to scattering, as opposed to specular reflection as from a mirror, although specular backscattering can occur at normal incidence with a surface. Backscattering has important applications in astronomy, photography, and medical ultrasonography. The opposite effect is forward scatter, e.g. when a translucent material like a cloud diffuses sunlight, giving soft light. Backscatter of waves in physical space Backscattering can occur in quite different physical situations, where the incoming waves or particles are deflected from their original direction by different mechanisms: *Diffuse reflection from large particles and Mie scattering, causing alpenglow and gegenschein, and showing up in weather radar; * Inelastic collisions between electromagnetic waves and the transmitting medium (Brillouin scattering and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coupling, Energetics And Dynamics Of Atmospheric Regions
Coupling, Energetics and Dynamics of Atmospheric Regions"CEDAR" is a US NSF funded program targeting understanding of middle and upper atmospheric dynamics. CEDAR is of relevance to space weather, space physics, and global change. CEDAR involves researchers from institutions within and without the United States, although the funding is almost exclusively directed to US projects. Researchers are funded for observational, theoretical, and simulation work. There is a significant focus on student activities and CEDAR has been tremendously effective at involving a large number of graduate students in front-line research. CEDAR programs produce a significant amount of data which is accessible via th"CEDAR Data Base" a number of Virtual Observatories Virtual may refer to: * Virtual (horse), a thoroughbred racehorse * Virtual channel, a channel designation which differs from that of the actual radio channel (or range of frequencies) on which the signal travels * Virtual function, a pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Peru
, image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = Seal (emblem), National seal , national_motto = "Firm and Happy for the Union" , national_anthem = "National Anthem of Peru" , march = "March of Flags" , image_map = PER orthographic.svg , map_caption = , image_map2 = , capital = Lima , coordinates = , largest_city = capital , official_languages = Peruvian Spanish, Spanish , languages_type = Co-official languages , languages = , ethnic_groups = , ethnic_groups_year = 2017 , demonym = Peruvians, Peruvian , government_type = Unitary state, Unitary Semi-presidential system, semi-presidential republic , leader_title1 = President of Peru, President ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arecibo
Arecibo (; ) is a city and municipality on the northern coast of Puerto Rico, on the shores of the Atlantic Ocean, located north of Utuado and Ciales; east of Hatillo; and west of Barceloneta and Florida. It is about west of San Juan, the capital city. Arecibo is the largest municipality in Puerto Rico by area, and it is the core city of the Arecibo Metropolitan Statistical Area and part of the greater San Juan Combined Statistical Area. It is spread over 18 ''barrios'' and Arecibo Pueblo (the downtown area and the administrative center of the city). Its population in 2020 was 87,754. The Arecibo Observatory, which housed the Arecibo telescope, the world's largest radio telescope until July 2016, is located in the municipality. The Arecibo telescope collapsed on December 1, 2020. Arecibo is the seat of the Roman Catholic Diocese of Arecibo. Etymology and nicknames The name ''Arecibo'' comes from the Taíno chief Xamaica Arasibo, cacique of the ''yucayeque'' (Taíno ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Greenland
Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is the world's largest island. It is one of three constituent countries that form the Kingdom of Denmark, along with Denmark and the Faroe Islands; the citizens of these countries are all citizens of Denmark and the European Union. Greenland's capital is Nuuk. Though a part of the continent of North America, Greenland has been politically and culturally associated with Europe (specifically Norway and Denmark, the colonial powers) for more than a millennium, beginning in 986.The Fate of Greenland's Vikings , by Dale Mackenzie Brown, ''Archaeological Institute of America'', ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kangerlussuaq
Kangerlussuaq (; ; da, Søndre Strømfjord), is a settlement in western Greenland in the Qeqqata municipality located at the head of the fjord of the same name. It is Greenland's main air transport hub and the site of Greenland's largest commercial airport. The airport dates from American settlement during and after World War II, when the site was known as Bluie West-8 and then Sondrestrom Air Base. The Kangerlussuaq area is also home to Greenland's most diverse terrestrial fauna, including muskoxen, caribou, and gyrfalcons. The settlement's economy and population of 508 is almost entirely reliant on the airport and tourist industry. Geography Kangerlussuaq occupies an alluvial flatland on the far end of the 190 km long Kangerlussuaq Fjord, straddling both sides of the Qinnguata Kuussua river estuary. East of Kangerlussuaq there is a confluence of the two major regional rivers, the Qinnguata Kuussua and Akuliarusiarsuup Kuua. The valley of the latter forms large quicksa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sondrestrom Upper Atmospheric Research Facility
The Sondrestrom Upper Atmospheric Research Facility was an ionospheric and atmospheric research facility situated about west of Kangerlussuaq, Greenland. It was commonly known around the town as Kellyville. The facility was operational from 1983 to 2018. The ionospheric radar was first constructed by SRI International at Stanford, California, then moved to Chatanika, Alaska, where it was operational from November 1971 to March 1982. It was transported to Kangerlussuaq in 1983. It was operated by SRI International for the U.S. National Science Foundation and the Danish Meteorological Institute. This facility hosted more than 20 instruments, the majority of which provided unique and complementary information about the arctic upper atmosphere. The centerpiece instrument of the facility was an L band incoherent scatter Incoherent scattering is a type of scattering phenomenon in physics. The term is most commonly used when referring to the scattering of an electromagnetic wave (usually ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermosphere
The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, creating ions; the thermosphere thus constitutes the larger part of the ionosphere. Taking its name from the Greek θερμός (pronounced ''thermos'') meaning heat, the thermosphere begins at about 80 km (50 mi) above sea level. At these high altitudes, the residual atmospheric gases sort into strata according to molecular mass (see turbosphere). Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation. Temperatures are highly dependent on solar activity, and can rise to or more. Radiation causes the atmospheric particles in this layer to become electrically charged, enabling radio waves to be refracted and thus be received beyond the horizon. In the exosphere, beginning at about 600 km (375&n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Auroral
An aurora (plural: auroras or aurorae), also commonly known as the polar lights, is a natural light display in Earth's sky, predominantly seen in high-latitude regions (around the Arctic and Antarctic). Auroras display dynamic patterns of brilliant lights that appear as curtains, rays, spirals, or dynamic flickers covering the entire sky. Auroras are the result of disturbances in the magnetosphere caused by the solar wind. Major disturbances result from enhancements in the speed of the solar wind from coronal holes and coronal mass ejections. These disturbances alter the trajectories of charged particles in the magnetospheric plasma. These particles, mainly electrons and protons, precipitate into the upper atmosphere (thermosphere/ exosphere). The resulting ionization and excitation of atmospheric constituents emit light of varying colour and complexity. The form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of accelerati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
