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telescope |
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An optical instrument for viewing distant objects in detail. Rays from an object are brought to a focus where they are magnified by an eyepiece, consisting of one or more lenses in combination. Different methods are used to focus the rays (see the diagram overleaf). Refracting telescopes use lenses; they include the Galilean telescope, now used only in the form of opera-glasses, and the Keplerian telescope, used for terrestrial and small astronomical instruments. Reflecting telescopes use mirrors; the main types are the Newtonian telescope and the Cassegrain telescope. Catadioptric telescopes use a mirror-lens combination; examples are the Schmidt telescope and Schmidt-Cassegrain telescope. All major astronomical instruments use mirrors since large lenses distort under their own weight. Telescopes can also be designed for wavelengths outside the optical range; see, for example, radio telescope.
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| Other Terms : isomorphism | base pairing | acid amide
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