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Telescopes

The interior of one of the four 8.2-m telescopes at the Very Large Telescope (VLT) in Chile. During the day, the housing is kept...Read More >>The interior of one of the four 8.2-m telescopes at the Very Large Telescope (VLT) in Chile. During the day, the housing is kept shut to protect the delicate scientific equipment inside, as well as to ensure the temperature differences between the telescope and the air outside is kept to a minimum at opening. A telescope is an instrument that makes distant objects appear closer, allowing the viewer to see details that are not visible with the naked eye. Terrestrial telescopes are used for spotting wildlife (binoculars are made up of two telescopes, one for each eye) and on gunsights and in periscopes. Astronomical telescopes are used to study objects in space. Terrestrial telescopes and most astronomical telescopes are optical telescopes, which collect light coming from distant objects and use it to produce images of the objects. A powerful astronomical telescope will reveal details of planets, nebulae (clouds of dust or gas) and galaxies that are invisible to the naked eye.



A diagram of a reflecting telescope housed inside an observatory

Refractors and reflectors

There are two main types of optical telescope—refracting telescopes and reflecting telescopes. In a refracting telescope, a convex lens (bulging shape) collects light from the distant object and focuses it to form an image of the object. This image is very small, but is much larger than the image formed in the human eye.

The word telescope comes from two Greek words: tele meaning "far" and skopein "to look or see".  The word was created in 1611 to describe one of Galileo's instruments, which Galileo himself called a perspicillum.

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