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Telescopes
A telescope is an instrument designed for the observation of remote objects and the collection of electromagnetic radiation. The first known practically functioning telescope is credited to the German-Dutch lensmaker Hans Lippershey in 1608. more...
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The name \"Telescope\" (from the Greek tele = 'far' and skopein = 'to look or see'; teleskopos = 'far-seeing') was a name given to Galileo Galilei's instrument for viewing distant objects. The name was invented by an unidentified Greek poet/theologian, present at a banquet held in 1611 by Prince Federico Cesi to make Galileo Galilei a member of the Accademia dei Lincei. \"Telescope\" can refer to a whole range of instruments operating in most regions of the electromagnetic spectrum.
Types of telescopes
The name \"telescope\" covers a wide range of instruments and is difficult to define. They all have the attribute of collecting electromagnetic radiation so it can be studied or analyzed in some manner. The most common type is the optical telescope. Other types also exist and are listed below.
Optical telescopes
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An optical telescope gathers and focuses light mainly from the visible part of the Electromagnetic spectrum (although some work in the infrared and ultraviolet). Optical telescopes increase the apparent angular size of distant objects, as well as their apparent brightness. Telescopes work by employing one or more curved optical elements - usually made from glass - lenses or mirrors - to gather light or other electromagnetic radiation and bring that light or radiation to a focus, where the image can be observed, photographed, studied, or sent to a computer. Optical telescopes are used for astronomy and in many non-astronomical instruments, including: theodolites (including transits), spotting scopes, monoculars, binoculars, camera lenses, and spyglasses. There are three main types:
The refracting telescope which uses solely an arrangement of lenses (excluding star diagonals).;
The reflecting telescope which uses solely an arrangement of mirrors (excluding eyepieces).;
The catadioptric telescope which uses a combination of mirrors and lenses, and usually have a glass corrector plate at the front.;
Radio telescopes
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Radio telescopes are directional radio antennae that often have a parabolic shape. The dishes are sometimes constructed of a conductive wire mesh whose openings are smaller than the wavelength being observed. Multi-element Radio telescopes are constructed from pairs or larger groups of these dishes to synthesize large \"virtual\" apertures that are similar in size to the separation between the telescopes: see aperture synthesis. As of 2005, the current record array size is many times the width of the Earth, utilizing space-based Very Long Baseline Interferometry (VLBI) telescopes such as the Japanese HALCA (Highly Advanced Laboratory for Communications and Astronomy) VSOP (VLBI Space Observatory Program) satellite. Aperture synthesis is now also being applied to optical telescopes using optical interferometers (arrays of optical telescopes) and Aperture Masking Interferometry at single reflecting telescopes. Radio telescopes are also used to collect microwave radiation, often used to help study the leftover Big Bang radiation, and also can be used to collect radiation when visible light is obstructed or faint, such as from quasars. Some radio telescopes are used by programs such as SETI and the Arecibo Observatory to search for exterrestrial life. (see also: Wow! Signal)
Read more at Wikipedia.org
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