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Observational astronomy
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=== Telescopes === [[File:Starwatching.jpg|thumb|200px|An amateur astrophotography setup with an automated guide system connected to a laptop]] The key instrument of nearly all modern observational astronomy is the [[telescope]]. This serves the dual purposes of gathering more light so that very faint objects can be observed, and magnifying the image so that small and distant objects can be observed. Optical astronomy requires telescopes that use optical components of great precision. Typical requirements for grinding and polishing a curved mirror, for example, require the surface to be within a fraction of a wavelength of light of a particular [[cone (geometry)|conic]] shape. Many modern "telescopes" actually consist of arrays of telescopes working together to provide higher resolution through [[aperture synthesis]]. Large telescopes are housed in domes, both to protect them from the weather and to stabilize the environmental conditions. For example, if the temperature is different from one side of the telescope to the other, the shape of the structure changes, due to [[thermal expansion]] pushing optical elements out of position. This can affect the image. For this reason, the domes are usually bright white ([[titanium dioxide]]) or unpainted metal. Domes are often opened around sunset, long before observing can begin, so that air can circulate and bring the entire telescope to the same temperature as the surroundings. To prevent wind-buffet or other vibrations affecting observations, it is standard practice to mount the telescope on a concrete pier whose foundations are entirely separate from those of the surrounding dome and building. To do almost any scientific work requires that telescopes track objects as they wheel across the visible sky. In other words, they must smoothly compensate for the rotation of the Earth. Until the advent of [[computer]] controlled drive mechanisms, the standard solution was some form of [[equatorial mount]], and for small telescopes this is still the norm. However, this is a structurally poor design and becomes more and more cumbersome as the diameter and weight of the telescope increases. The world's largest equatorial mounted telescope is the 200 inch (5.1 m) [[Hale Telescope]], whereas recent 8β10 m telescopes use the structurally better [[altazimuth mount]], and are actually physically ''smaller'' than the Hale, despite the larger mirrors. As of 2006, there are design projects underway for gigantic alt-az telescopes: the Thirty Metre Telescope [https://web.archive.org/web/20150130044644/http://lot.astro.utoronto.ca/], and the 100 m diameter [[Overwhelmingly Large Telescope]].<ref>[http://www.eso.org/projects/owl The ESO 100-m OWL optical telescope concept]</ref> Amateur astronomers use such instruments as the [[Newtonian telescope|Newtonian reflector]], the [[Refracting telescope|Refractor]] and the increasingly popular [[Maksutov telescope]].
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