Jump to content

Telescope: Difference between revisions

Edit links
From Wikipedia, the free encyclopedia
Browse history interactively
← Previous editNext edit →
Content deleted Content added
VisualWikitext
m Reverted edits by 92.21.226.109 to last version by Vsmith (HG)
Line 14: Line 14:
The 20th century also saw the development of telescopes that worked in a wide range of wavelengths from [[radio telescope|radio]] to [[gamma-ray telescope|gamma-rays]]. The first purpose built radio telescope went into operation in 1937. Since then, a tremendous variety of complex astronomical instruments have been developed.
The 20th century also saw the development of telescopes that worked in a wide range of wavelengths from [[radio telescope|radio]] to [[gamma-ray telescope|gamma-rays]]. The first purpose built radio telescope went into operation in 1937. Since then, a tremendous variety of complex astronomical instruments have been developed.


==Types of telescopes==
{{Citations missing|date=July 2008}}
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===
[[Image:Telescope.jpg|thumb|right|160px|50 cm refracting telescope at [[Nice Observatory]].]]
{{main|Optical telescope}}
An optical telescope gathers and [[Focus (optics)|focus]]es 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]]. In order for the image to be observed, photographed, studied, and sent to a computer, telescopes work by employing one or more curved optical elements—usually made from [[glass]]—[[Lens (optics)|lenses]], or [[mirror]]s to gather light and other electromagnetic radiation to bring that light or radiation to a focal point. Optical telescopes are used for [[astronomy]] and in many non-astronomical instruments, including: ''[[theodolite]]s'' (including ''transits''), ''[[spotting scope]]s'', ''[[monocular]]s'', ''[[binoculars]],'' ''[[camera lens]]es'', and ''spyglasses''. There are three main types:
* The [[refracting telescope]] which uses lenses to form an image.
* The [[reflecting telescope]] which uses an arrangement of mirrors to form an image.
* The [[Catadioptric#Catadioptric Telescopes|catadioptric telescope]] which uses mirrors combined with lenses—either in front of the mirror or somewhere within the optical path—to form an image.

===Radio telescopes===
{{main|Radio telescope}}
[[Image:USA.NM.VeryLargeArray.02.jpg|thumb|right|200px|The [[Very Large Array]] at Socorro, New Mexico, United States.]]
Radio telescopes are [[Directional antenna|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 telescope]]s 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; this process is known as [[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 [[Japan]]ese [[HALCA]] (Highly Advanced Laboratory for Communications and Astronomy) [http://www.vsop.isas.ac.jp/ VSOP (VLBI Space Observatory Program) satellite]. Aperture synthesis is now also being applied to optical telescopes using [[Optical interferometry#Astronomical Optical Interferometry|optical interferometers]] (arrays of optical telescopes) and [[aperture masking interferometry]] at single reflecting telescopes. Radio telescopes are also used to collect [[microwave radiation]], which is used to collect radiation when any visible light is obstructed or faint, such as from [[quasar]]s. Some radio telescopes are used by programs such as [[Search for Extraterrestrial Intelligence|SETI]] and the [[Arecibo Observatory]] to search for exterrestrial life. One particularly exciting example is the [[Wow! signal]], recorded in 1977.

===X-ray and gamma-ray telescopes===
{{main|X-ray astronomy|gamma-ray astronomy}}
[[X-ray]] and [[gamma-ray]] radiation go through most metals and glasses, but some X-ray telescopes use [[Wolter telescope]]s composed of ring-shaped 'glancing' [[mirror]]s made of [[heavy metals]] that are able to reflect the rays just a few [[degree (angle)|degree]]s. 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 patterns of the shadow the mask creates can be reconstructed to form an image. These types of telescopes are usually on Earth-orbiting [[satellite]]s or high-flying balloons since the [[Earth's atmosphere]] is opaque to this part of the electromagnetic spectrum.

[[Image:Atmospheric electromagnetic transmittance or opacity.jpg|thumb|center|600px|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==
==Other types==

Revision as of 16:48, 9 December 2008

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 by the collection of electromagnetic radiation. The first known practically functioning telescopes were invented in the Netherlands at the beginning of the 17th century. "Telescopes" can refer to a whole range of instruments operating in most regions of the electromagnetic spectrum.

The name "Telescope" (from the Greek tele = 'far' and skopein = 'to look or see'; teleskopos = 'far-seeing') was coined in 1611 by the Greek mathematician Giovanni Demisiani for one of Galileo Galilei's instruments presented at a banquet at the Accademia dei Lincei[1][2][3]. In the Starry Messenger Galileo had used the term "perspicillum".

History

Main article: History of the telescope

The earliest evidence of working telescopes were the refracting telescopes that appeared in the Netherlands in 1608. Their development is credited to three individuals: Hans Lippershey and Zacharias Janssen, who were spectacle makers in Middelburg, and Jacob Metius of Alkmaar[4]. Galileo greatly improved upon these designs the following year. Niccolò Zucchi is credited with constructing the first reflecting telescope in 1616. In 1668, Isaac Newton designed an improved reflecting telescope that bears his name, the Newtonian reflector.

The invention of the achromatic lens in 1733 partially corrected color aberrations present in the simple lens and enabled the construction of shorter, more functional refracting telescopes. Reflecting telescopes, though not limited by the color problems seen in refractors, were hampered by the use of fast tarnishing speculum metal mirrors employed during the 18th and early 19th century—a problem alleviated by the introduction of silver coated glass mirrors in 1857,[5] and aluminized mirrors in 1932.[6] The maximum physical size limit for refracting telescopes is about 1 meter (40 inches), dictating that the vast majority of large optical researching telescopes built since the turn of the 20th century have been reflectors. The largest reflecting telescopes currently have objectives larger then 10 m (33 feet).

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


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. ^ archive.org "Galileo His Life And Work" BY J. J. FAHIE "Galileo usually called the telescope occhicde or cannocchiale ; and now he calls the microscope occhialino. The name telescope was first suggested by Demisiani in 1612"
  2. ^ Sobel (2000, p.43), Drake (1978, p.196)
  3. ^ Rosen, Edward, The Naming of the Telescope (1947)
  4. ^ galileo.rice.edu The Galileo Project > Science > The Telescope by Al Van Helden "The Hague discussed the patent applications first of Hans Lipperhey of Middelburg, and then of Jacob Metius of Alkmaar... another citizen of Middelburg, Sacharias Janssen had a telescope at about the same time but was at the Frankfurt Fair where he tried to sell it"
  5. ^ madehow.com - Inventor Biographies - Jean-Bernard-Léon Foucault Biography (1819-1868)
  6. ^ 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

Template:Link FA

Retrieved from "https://en.wikipedia.org/enwiki/w/index.php?title=Telescope&oldid=256856863"