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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 modern telescopes were invented in the [[Netherlands] at 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 who was 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. "Telescopes" can refer to a whole range of instruments operating in most regions of the electromagnetic spectrum.

History

The history of the telescope dates back to the Middle Ages, when Ibn al-Haytham, Robert Grosseteste and other scientists studied magnifying properties of lenses. Although there were some recorded instances of pre-17th century Middle-Eastern and European opticians including Leonard Digges, Taqi al-Din and others creating devices that could have functioned as telescopes, the earliest known working telescopes in the modern sense were the refracting telescopes that appeared in the Netherlands in 1608. These were credited to three individuals: Hans Lippershey and Zacharias Janssen—who were spectacle-makers in Middelburg, and Jacob Metius of Alkmaar—also known as Jacob Adriaanszoon. Galileo greatly improved upon this design the following year. Niccolò Zucchi is credited with constructing the first telescope to use mirrors: a reflecting telescope in 1616. In 1668, Isaac Newton designed an improved a reflecting telescope that bares his name, the "Newtonian reflector."

The invention of the achromatic lens in 1733, in part, corrected color aberrations present in the simple lense and enabled the construction of shorter, higher functioning refracting telescopes. Reflecting telescopes (although 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.^[2], and aluminized mirrors in 1932^[3]. At around 1 meter (40 inches), the maximum physical size limit of the refracting telescope objectives has dictated that the vast majority of large optical researching telescopes built since the turn of the 20th century be reflector-implemented.

The 20th century also saw the development of telescopes that worked in a 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.

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. 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, lenses, or mirrors to gather light and other electromagnetic radiation to bring that light or radiation to a focus. 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:

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 telescope which uses mirrors combined with lenses, in front of the mirror or somewhere within the optical path, to form an image.

Radio telescopes

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, which can also be used to collect radiation when any 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

X-ray and gamma-ray radiation go through most metals and glasses, but some X-ray telescopes use Wolter telescopes composed of ring-shaped 'glancing' mirrors made of heavy metals that are able to 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 patterns of the shadow 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.

Other types

Notable telescopes

Anglo-Australian Telescope
Arecibo Observatory
Atacama Large Millimeter Array
Chandra X-ray Observatory
CHARA (Center for High Angular Resolution Astronomy) array
Giant Metrewave Radio Telescope
Great Paris Exhibition Telescope of 1900
Hale telescope 1948, 200" reflector, Mount Palomar
Hexapod-Telescope
Hooker Telescope 1917, 100" reflector, Mount Wilson
Hubble Space Telescope
IceCube Neutrino Detector
Isaac Newton Telescope
Keck telescope
Leviathan of Parsonstown 1849, 79" reflector, Birr, Ireland
Lick Observatory
LIGO
Lovell Telescope
McMath-Pierce Solar Telescope
McMath-Hulbert Observatory (Solar)
Magdalena Ridge Observatory
Multiple-Mirror telescope
Navy Prototype Optical Interferometer
Overwhelmingly Large Telescope (proposed)
Parkes Observatory
Southern African Large Telescope
Subaru Telescope
UK Schmidt Telescope
Very Large Array
Very Large Telescope
Westerbork Synthesis Radio Telescope
William Herschel Telescope
XMM-Newton
Yerkes 1897, 40" largest optical refractor

Notes

^ omni-optical.com "A Very Short History of the Telescope"
^ madehow.com - Inventor Biographies - Jean-Bernard-Léon Foucault Biography (1819-1868)
^ [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

External links

"The First Telescopes". Part of an exhibit from Cosmic Journey: A History of Scientific Cosmology by the American Institute of Physics
ESO 100 m telescope
The Resolution of a Telescope
Southern African Large Telescope (SALT)
The Digges telescope of the 1570s
The Swedish Solar telescope
History of Refracting Telescope

Template:Link FA

[1] -optical.com "A Very Short History of the Telescope"

[2] w.com - Inventor Biographies - Jean-Bernard-Léon Foucault Biography (1819-1868)

[3] [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."]

[1]

[2]

[3]

@@ Line 1: / Line 1: @@
 {{other}}
 [[Image:100inchHooker.jpg|thumb|right|175px|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 language|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]]<ref>[http://www.omni-optical.com/telescope/ut104.htm omni-optical.com "''A Very Short History of the Telescope''"]</ref>. It was given to a version of the instrument constructed by [[Galileo Galilei]]. "Telescopes" can refer to a whole range of instruments operating in most regions of the [[electromagnetic spectrum]].
+A '''telescope''' is an instrument designed for the observation of remote objects and the collection of [[electromagnetic radiation]]. The first modern telescopes were invented in the [[Netherlands] at the beginning of the [[17th century]]. The name "Telescope" (from the [[Greek language|Greek]] ''tele'' = 'far' and ''skopein'' = 'to look or see'; ''teleskopos'' = 'far-seeing') was invented by an unidentified Greek poet/theologian who was present at a banquet held in 1611 by Prince [[Federico Cesi]]<ref>[http://www.omni-optical.com/telescope/ut104.htm omni-optical.com "''A Very Short History of the Telescope''"]</ref>. It was given to a version of the instrument constructed by [[Galileo Galilei]]. "Telescopes" can refer to a whole range of instruments operating in most regions of the [[electromagnetic spectrum]].
 ==History==
 {{main|History of telescopes}}
-The history of the telescope dates back to the Middle Ages, when [[Ibn al-Haytham]], [[Robert Grosseteste]] and other scientists studied magnifying properties of lenses. Although there were some recorded instances of pre-17th century [[Middle East|Middle-Eastern]] and [[Europe]]an opticians, including [[Leonard Digges]], [[Taqi al-Din]] and others, creating devices that could have functioned as telescopes, the earliest known working telescopes in the modern sense were [[refracting telescope]]s that appeared in the [[Netherlands]] in [[1608]]. These were credited to three individuals, [[Hans Lippershey]] and [[Zacharias Janssen]], spectacle-makers in Middelburg, and [[Jacob Metius]] of [[Alkmaar]] also known as Jacob Adriaanszoon. [[Galileo Galilei|Galileo]] greatly improved upon this design the following year. [[Niccolò Zucchi]] is credited with constructing the first telescope to use mirrors, a [[reflecting telescope]], in 1616. In 1668 [[Isaac Newton]] designed an improved reflecting telescope that bares his name, the [[Newtonian telescope|Newtonian reflector]].
+The history of the telescope dates back to the Middle Ages, when [[Ibn al-Haytham]], [[Robert Grosseteste]] and other scientists studied magnifying properties of lenses. Although there were some recorded instances of pre-17th century [[Middle East|Middle-Eastern]] and [[Europe]]an opticians including [[Leonard Digges]], [[Taqi al-Din]] and others creating devices that could have functioned as telescopes, the earliest known working telescopes in the modern sense were the [[refracting telescope]]s that appeared in the [[Netherlands]] in [[1608]]. These were credited to three individuals: [[Hans Lippershey]] and [[Zacharias Janssen]]—who were spectacle-makers in Middelburg, and [[Jacob Metius]] of [[Alkmaar]]—also known as Jacob Adriaanszoon. [[Galileo Galilei|Galileo]] greatly improved upon this design the following year. [[Niccolò Zucchi]] is credited with constructing the first telescope to use mirrors: a [[reflecting telescope]] in [[1616]]. In 1668, [[Isaac Newton]] designed an improved a reflecting telescope that bares his name, the "[[Newtonian telescope|Newtonian reflector]]."
-The invention of the [[achromatic lens]] in 1733 in part corrected color aberrations present in the simple lense and enabled the construction of shorter, higher functioning refracting telescopes. Reflecting telescopes, although 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<ref>[http://www.madehow.com/inventorbios/39/Jean-Bernard-L-on-Foucault.html  madehow.com - Inventor Biographies - Jean-Bernard-Léon Foucault Biography (1819-1868)]</ref>, and aluminized mirrors in 1932<ref>[http://www.cambridge.org/uk/astronomy/features/amateur/files/p28-4.pdf Bakich sample pages Chapter 2, Page 3 ''"John Donavan Strong, a young
+The invention of the [[achromatic lens]] in 1733, in part, corrected color aberrations present in the simple lense and enabled the construction of shorter, higher functioning refracting telescopes. Reflecting telescopes (although 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.<ref>[http://www.madehow.com/inventorbios/39/Jean-Bernard-L-on-Foucault.html  madehow.com - Inventor Biographies - Jean-Bernard-Léon Foucault Biography (1819-1868)]</ref>, and aluminized mirrors in 1932<ref>[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."'']</ref>.   The maximum physical size limit of the refracting telescope objectives, at around 1 meter (40 inches), has dictated that the vast majority of large optical research telescopes built since the turn of the [[20th century]] be reflectors.
+coated by this technique."'']</ref>. At around 1 meter (40 inches), the maximum physical size limit of the refracting telescope objectives has dictated that the vast majority of large optical researching telescopes built since the turn of the [[20th century]] be reflector-implemented.
-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 [[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 [[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.
+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]]. Telescopes work by employing one or more curved optical elements - usually made from [[glass]] - [[Lens (optics)|lenses]] or [[mirror]]s - to gather light or other electromagnetic radiation and bring that light or radiation to a [[Focus (optics)|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: ''[[theodolite]]s'' (including ''transits''), ''[[spotting scope]]s'', ''[[monocular]]s'', ''[[binoculars]],'' ''[[camera lens]]es'', and ''spyglasses''. There are three main types:
+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 [[Focus (optics)|focus]]. 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.
@@ Line 28: / Line 28: @@
 {{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: 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 [[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]], 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 [[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.  (''see also: [[Wow! Signal]]'')
+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: 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 [[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]] often used to help study the leftover [[Big Bang]] radiation, which can also be 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.  (''see also: [[Wow! Signal]]'')
 ===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, some X-ray telescopes use [[Wolter telescope]]s composed of ring-shaped "glancing" [[mirror]]s, made of [[heavy metals]], that 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 pattern of shadows the mask creates can be reconstructed to form an image.
+[[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.
+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.]]