page_title: Optical telescope
section_title: Astronomical research telescopes
hierarchical_section_title: Optical telescope / Astronomical research telescopes
caption_attribution_description: English: On a remote mountaintop, 2600 metres above sea level in the Chilean Atacama Desert, lies the world’s most advanced visible-light observatory. The European Southern Observatory’s Very Large Telescope (VLT) is not only a window on the Universe; it is also a celebration of modern science and technology. This photograph shows two of the four Unit Telescopes that make up the VLT. With its giant 8.2-metre diameter mirrors, sensitive detectors, and state-of-the art adaptive optics system, the VLT uses cutting-edge technology at every opportunity. Even the telescope enclosures — the domes — are highly advanced, being thermally controlled to reduce air turbulence in the telescope structure. Every night the VLT studies the sky to make discoveries about the Universe. Visible in this photo, sweeping between the two Unit Telescopes, is the plane of the Milky Way. Containing billions of stars, it is our own corner of the cosmos, but the VLT's vision can peer much deeper than this, our home galaxy, and look out to the extremes of space, all in the name of science and discovery.
context_page_description: 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 view, or to make a photograph, or to collect data through electronic image sensors.
  There are three primary types of optical telescope:
  refractors, which use lenses
  reflectors, which use mirrors
  catadioptric telescopes, which combine lenses and mirrors
  A telescope's ability to resolve small detail is directly related to the diameter of its objective, 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 telescopes and binoculars for activities such as observational astronomy, ornithology, pilotage and reconnaissance, and watching sports or performance arts.
context_section_description: Optical telescopes have been used in astronomical research since the time of their invention in the early 17th century. Many types have been constructed over the years depending on the optical technology, such as refracting and reflecting, the nature of the light or object being imaged, and even where they are placed, such as space telescopes. Some are classified by the task they perform such as Solar telescopes.
caption: Two of the four Unit Telescopes that make up the ESO's VLT, on a remote mountaintop, 2600 metres above sea level in the Chilean Atacama Desert.
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