Telescopes TodayDuring the 20th century several large reflecting
Telescopes have been built on mountain sites in clear-air
regions. Telescope sizes have also escalated in recent decades, and
instruments larger than 100 in (2.5 m) in diameter are now common (see observatory, astronomical). Multiple-mirror and other designs have also been developed. For work in other regions of the
spectrum, different forms of devices are used to perform functions generally more or less equivalent to telescopic instruments. These include, for example, the parabolic antennas of radio
astronomy. For the remaining regions of the spectrum, see gamma-
ray astronomy, infrared astronomy, ultraviolet astronomy, and X-ray astronomy.
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