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Optical Telescope
An optical telescope gathers and focus (optics), focuses light mainly from the visible spectrum, visible part of the electromagnetic spectrum, to create a magnification, magnified image for direct visual inspection, to make a photograph, or to collect data through electronic image sensors. There are three primary types of optical telescope : * ''Refracting telescopes'', which use lens (optics), lenses and less commonly also Prism (optics), prisms (dioptrics) * ''Reflecting telescopes'', which use mirrors (catoptrics) * ''Catadioptric system#Catadioptric telescopes, Catadioptric telescopes'', which combine lenses and mirrors An optical telescope's ability to resolve small details is directly related to the diameter (or aperture) of its objective (optics), objective (the primary lens or mirror that collects and focuses the light), and its light-gathering power is related to the area of the objective. The larger the objective, the more light the telescope collects and the finer det ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aperture
In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image of the aperture and focal length of an optical system determine the cone angle of a bundle of rays that comes to a focus in the image plane. An optical system typically has many structures that limit ray bundles (ray bundles are also known as ''pencils'' of light). These structures may be the edge of a lens or mirror, or a ring or other fixture that holds an optical element in place or may be a special element such as a diaphragm placed in the optical path to limit the light admitted by the system. In general, these structures are called stops, and the aperture stop is the stop that primarily determines the cone of rays that an optical system accepts (see entrance pupil). As a result, it also determines the ray cone angle and brightne ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lens (optics)
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), usually arranged along a common axis. Lenses are made from materials such as glass or plastic and are ground, polished, or molded to the required shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. Devices that similarly focus or disperse waves and radiation other than visible light are also called "lenses", such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses. Lenses are used in various imaging devices such as telescopes, binoculars, and cameras. They are also used as visual aids in glasses to correct defects of vision such as myopia and hypermetropia. History The word ''lens'' comes from , the Latin name of the lentil (a seed of a lentil pla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spectator Sport
A spectator sport is a sport that is characterized by the presence of spectators, or watchers, at its competitions. Spectator sports may be professional sports or amateur sports. They often are distinguished from participant sports, which are more recreational. Overview Most popular sports are both spectator and participant, for example association football, basketball, cricket, tennis, rugby, golf, athletics and volleyball. Less popular sports are mainly participant sports, for example hunting. The increasing broadcasting of sports events, along with media reporting can affect the number of people attending sports due to the ability to experience the sport without the need to physically attend and sometimes an increasingly enhanced experience including highlights, replays, commentary, statistics and analysis. Some sports are particularly known as "armchair sports" or "lounge room sports" due to the quality of the broadcasting experience in comparison to the live experience. S ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Performance Art
Performance art is an artwork or art exhibition created through actions executed by the artist or other participants. It may be witnessed live or through documentation, spontaneously developed or written, and is traditionally presented to a public in a fine art context in an interdisciplinary mode. Also known as artistic action, it has been developed through the years as a genre of its own in which art is presented live. It had an important and fundamental role in 20th century avant-garde art. It involves five basic elements: time, space, body, presence of the artist, and the relation between the artist and the public. The actions, generally developed in art galleries and museums, can take place in any kind of setting or space, and during any time period. Its goal is to generate a reaction, sometimes with the support of improvisation and a sense of aesthetics. The themes are commonly linked to life experiences of the artist themselves, the need for denunciation or social critic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Opera Glass
Opera glasses, also known as theater binoculars or Galilean binoculars, are compact, low-power optical magnification devices, usually used at performance events, whose name is derived from traditional use of binoculars at opera performances. Magnification power below 5× is usually desired in these circumstances in order to minimize image shake and maintain a large enough field of view. A magnification of 3× is normally recommended. The design of many modern opera glasses of the ornamental variety is based on the popular lorgnettes of the 19th century. Often, modern theatre binoculars are equipped with an LED flashlight, which makes it easier to find a place in the dark. In addition to the more stereotypical binocular type, folding opera glasses were another common design. They were made mostly of metal and glass, with a leatherette cover for grip and color. Although folding glasses have existed in one form or another since the 1890s, they were perhaps most popular in the mid- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reconnaissance
In military operations, military reconnaissance () or scouting is the exploration of an area by military forces to obtain information about enemy forces, the terrain, and civil activities in the area of operations. In military jargon, reconnaissance is abbreviated to ''recce'' (in British, Canadian, Australian English) and to ''recon'' (in American English), both derived from the root word ''reconnoitre'' / ''reconnoitering''. The types of reconnaissance include patrolling the local area of operations and long-range reconnaissance patrols, which are tasks usually realized in the United States of America by U.S. Army Rangers, cavalry scouts, and military intelligence specialists, using navy ships and submarines, Aerial reconnaissance, reconnaissance aircraft, satellites to collect raw intelligence; and establishing observation posts. Moreover, espionage is different from reconnaissance, because spies work as civilians in enemy territory. Etymology The word is derived from the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hunting
Hunting is the Human activity, human practice of seeking, pursuing, capturing, and killing wildlife or feral animals. The most common reasons for humans to hunt are to obtain the animal's body for meat and useful animal products (fur/hide (skin), hide, bone/tusks, horn (anatomy), horn/antler, etc.), for recreation/taxidermy (see trophy hunting), although it may also be done for resourceful reasons such as removing predators dangerous to humans or domestic animals (e.g. wolf hunting), to pest control, eliminate pest (organism), pests and nuisance animals that damage crops/livestock/poultry or zoonosis, spread diseases (see varmint hunting, varminting), for trade/tourism (see safari), or for conservation biology, ecological conservation against overpopulation and invasive species (commonly called a culling#Wildlife, cull). Recreationally hunted species are generally referred to as the ''game (food), game'', and are usually mammals and birds. A person participating in a hunt is a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pilotage
Piloting or pilotage is the process of navigating on water or in the air using fixed points of reference on the sea or on land, usually with reference to a nautical chart or aeronautical chart to obtain a fix of the position of the vessel or aircraft with respect to a desired course or location. Horizontal fixes of position from known reference points may be obtained by sight or by radar. Vertical position may be obtained by depth sounder to determine depth of the water body below a vessel or by altimeter to determine an aircraft's altitude, from which its distance above the ground can be deduced. Piloting a vessel is usually practiced close to shore or on inland waterways. Pilotage of an aircraft is practiced under visual meteorological conditions for flight. Land navigation is a related discipline, using a topographic map, especially when applied over trackless terrain. Divers use related techniques for underwater navigation. Piloting references Charts Depending on w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ornithology
Ornithology, from Ancient Greek ὄρνις (''órnis''), meaning "bird", and -logy from λόγος (''lógos''), meaning "study", is a branch of zoology dedicated to the study of birds. Several aspects of ornithology differ from related disciplines, due partly to the high visibility and the aesthetic appeal of birds. It has also been an area with a large contribution made by amateurs in terms of time, resources, and financial support. Studies on birds have helped develop key concepts in biology including evolution, behaviour and ecology such as the definition of species, the process of speciation, instinct, learning, ecological niches, guild (ecology), guilds, insular biogeography, phylogeography, and bird conservation, conservation. While early ornithology was principally concerned with descriptions and distributions of species, ornithologists today seek answers to very specific questions, often using birds as models to test hypotheses or predictions based on theories. Most mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Observational Astronomy
Observational astronomy is a division of astronomy that is concerned with recording data about the observable universe, in contrast with theoretical astronomy, which is mainly concerned with calculating the measurable implications of physical models. It is the practice and study of observing celestial objects with the use of telescopes and other astronomical instruments. As a science, the study of astronomy is somewhat hindered in that direct experiments with the properties of the distant universe are not possible. However, this is partly compensated by the fact that astronomers have a vast number of visible examples of stellar phenomena that can be examined. This allows for observational data to be plotted on graphs, and general trends recorded. Nearby examples of specific phenomena, such as variable stars, can then be used to infer the behavior of more distant representatives. Those distant yardsticks can then be employed to measure other phenomena in that neighborhood, inc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Outdoor Activities
Outdoor recreation or outdoor activity refers to recreation done outside, most commonly in natural settings. The activities that encompass outdoor recreation vary depending on the physical environment they are being carried out in. These activities can include fishing, hunting, backpacking, walking and horseback riding — and can be completed individually or collectively. Outdoor recreation is a broad concept that encompasses a varying range of activities and landscapes. Outdoor recreation is typically pursued for purposes of physical exercise, general wellbeing, and spiritual renewal. While a wide variety of outdoor recreational activities can be classified as sports, they do not all demand that a participant be an athlete. Rather, it is the collectivist idea that is at the fore in outdoor recreation, as outdoor recreation does not necessarily encompass the same degree of competitiveness or rivalry that is embodied in sporting matches or championships. Competition generall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
