Jump to content

Telescope

Edit links
From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by InternetHero (talk | contribs) at 17:03, 19 July 2008 (Nonsense. I think we're going to have to get an admin.). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

For other uses, see Telescope (disambiguation).
The 100 inch (2.5 m) Hooker reflecting telescope at Mount Wilson Observatory near Los Angeles, California.

A telescope is an instrument designed for the observation of remote objects and the collection of electromagnetic radiation. The first known practically functioning telescopes were invented in the Netherlands in the beginning of the 17th century. The name "Telescope" (from the Greek tele = 'far' and skopein = 'to look or see'; teleskopos = 'far-seeing') was invented by an unidentified Greek poet/theologian, present at a banquet held in 1611 by Prince Federico Cesi[1]. It was given to a version of the instrument constructed by Galileo Galilei. "Telescope" can refer to a whole range of instruments operating in most regions of the electromagnetic spectrum.

History

Main article: History of telescopes

The history of the telescope dates back to the their invention in the beginning of the 13th century century with Ibn Al-Haytham's optical research which descibed the first magnifying device to be used in an instrument.[2] His descriptions in the Book of Optics helped set the parameters in Europe for the later advances in telescopic and microscopic technology,[3][4]but the first known practically functioning telescope is credited to the German-Dutch lensmaker Hans Lippershey in 1608.

The invention of the achromatic lens in 1733 that corrected some of the color aberration of simple lenses allowed for more functional shorter refracting telescopes. Reflecting telescopes, although not limited by the color problems seen in refractors, were limited in their usefulness due to the fast tarnishing speculum metal mirrors used during the 18th and 19th centuries. The introduction of silver coated glass mirrors in 1857[5], aluminized mirrors in 1932[6], and the maximum physical size limit of the refracting telescope objectives, at around 1 meter (40 inches), meant almost all of the large research telescopes built since the turn of the 20th century have been reflectors.

The 20th century also saw the development of telescopes that worked in wide range of wavelengths from radio to gamma-rays. The first radio telescope went into operation in 1937. Since then a tremendous variety of complex astronomical instruments have been developed.

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

50 cm refracting telescope at Nice Observatory.
Main article: Optical telescope

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:

Radio telescopes

Main article: Radio telescope
The Very Large Array at Socorro, New Mexico, United States.

Radio telescopes are directional radio antennas 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)

X-ray and gamma-ray telescopes

Main articles: X-ray astronomy and gamma-ray astronomy

X-ray and gamma-ray radiation go through most metals and glasses, some X-ray telescopes use Wolter telescopes composed of ring-shaped "glancing" mirrors, made of heavy metals, that reflect the rays just a few degrees. The mirrors are usually a section of a rotated parabola and a hyperbola or ellipse. Gamma-ray telescopes refrain from focusing completely, and use coded aperture masks; the pattern of shadows the mask creates can be reconstructed to form an image.

These types of telescopes are usually on Earth-orbiting satellites or high-flying balloons, since the Earth's atmosphere is opaque to this part of the electromagnetic spectrum.

A diagram of the electromagnetic spectrum with the Earth's atmospheric transmittance (or opacity) and the types of telescopes used to image parts of the spectrum.

Other types

Notable telescopes

See also

Wikimedia Commons has media related to Telescopes.
File:Newtonian Telescopes.JPG
A group of Newtonian Telescopes at Perkins Observatory, Delaware, Ohio

Notes

  1. ^ omni-optical.com "A Very Short History of the Telescope"
  2. ^ Sabra, A. I. & Hogendijk, J. P. (2003), The Enterprise of Science in Islam: New Perspectives, MIT Press, pp. 85-118, ISBN 0262194821
  3. ^ O. S. Marshall (1950). "Alhazen and the Telescope", Astronomical Society of the Pacific Leaflets 6, p. 4
  4. ^ Richard Powers (University of Illinois), Best Idea; Eyes Wide OpenNew York Times, April 18, 1999.
  5. ^ madehow.com - Inventor Biographies - Jean-Bernard-Léon Foucault Biography (1819-1868)
  6. ^ [http://www.cambridge.org/uk/astronomy/features/amateur/files/p28-4.pdf Bakich sample pages Chapter 2, Page 3 "John Donavan Strong, a young physicist at the California Institute of Technology, was one of the first to coat a mirror with aluminum. He did it by thermal vacuum evaporation. The first mirror he aluminized, in 1932, is the earliest known example of a telescope mirror coated by this technique."]

References

  • Contemporary Astronomy - Second Edition, Jay M. Pasachoff, Saunders Colleges Publishing - 1981, ISBN 0-03-057861-2
  • Sabra, A. I. & Hogendijk, J. P. (2003), The Enterprise of Science in Islam: New Perspectives, MIT Press, pp. 85-118, ISBN 0262194821

Template:Link FA

Retrieved from "https://en.wikipedia.org/w/index.php?title=Telescope&oldid=226655962"