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Optical Telescopes
An optical telescope is a telescope that gathers and focuses light mainly from the visible part of the electromagnetic spectrum, to create a 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 lenses and less commonly also prisms (dioptrics) * Reflecting telescopes, which use mirrors ( catoptrics) * 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 (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 detail it resolves. People use optical telescopes (including monoculars and binoculars) for outdoor activities such as observation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An optical system typically has many openings or structures that limit the 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 ray cone angle and brightness at the image point. In some contexts, especially in photography and astronomy, ''aperture'' refers to the diameter of the aperture stop rather than the physical stop or the opening itself. For example, in a telescope, the aperture ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lens (optics)
A lens is a transmissive optical device which 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 and polished or molded to a desired 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 like 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 '' lēns'', the Latin name of the lentil (a seed of a lentil plant), ... [...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. Most popular sports are both spectator and participant, for example association football, basketball, cricket, tennis, Rugby football, rugby, golf, Sport of athletics, 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 ... [...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 four basic elements: time, space, body, and presence of the artist, and the relation between the creator and the public. The actions, generally developed in art galleries and museums, can take place in the street, 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, or the need of denunci ... [...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. 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-20th Century and many from this era are marked "Made in Japan" or, less commonly, "Made in Occupied Japan". The design can ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reconnaissance
In military operations, reconnaissance or scouting is the exploration of an area by military forces to obtain information about enemy forces, terrain, and other activities. Examples of reconnaissance include patrolling by troops (skirmishers, long-range reconnaissance patrol, U.S. Army Rangers, cavalry scouts, or military intelligence specialists), ships or submarines, crewed or uncrewed reconnaissance aircraft, satellites, or by setting up observation posts. Espionage is usually considered to be different from reconnaissance, as it is performed by non-uniformed personnel operating behind enemy lines. Often called recce (British, Canadian and Australian English) or recon (American English), the word for this activity has at its root the associated verb ''reconnoitre'' or ''reconnoiter''. Etymology The word from the Middle French ''reconoissance''. Overview Reconnaissance conducted by ground forces includes special reconnaissance, armored reconnaissance, amp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hunting
Hunting is the human activity, human practice of seeking, pursuing, capturing, or killing wildlife or feral animals. The most common reasons for humans to hunt are to harvest food (i.e. meat) and useful animal products (fur/hide (skin), hide, bone/tusks, horn (anatomy), horn/antler, etc.), for recreation/taxidermy (see trophy hunting), to remove 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. 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 hunter or (less commonly) huntsman; a natural area used for hunting is called a game reserve; an experienced hun ... [...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 wheth ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ornithology
Ornithology is a branch of zoology that concerns the "methodological study and consequent knowledge of birds with all that relates to them." 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, guilds, island biogeography, phylogeography, and 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 modern biological theories apply across life forms, and the number of scientists w ... [...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 observation, observing celestial objects with the use of telescopes and other astronomical instruments. As a space science, 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 ... [...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, 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 generally is les ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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