Telescope

A telescope is an instrument designed for the observation of remote objects and the collection of electromagnetic radiation. The name "Telescope" (from the Greek tele = 'far' and skopein = 'to look or see'; teleskopos = 'far-seeing') was a name given to Galileo Galilei's instrument for viewing distant objects. The name was invented by an unidentified Greek poet/theologian, present at a banquet held in 1611 by Prince Federico Cesi to make Galileo Galilei a member of the Accademia dei Lincei^[1]. "Telescope" 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 their invention in the beginning of the 13th century century with Ibn Al-Haytham's optical research which described 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.

In the history of optics, the properties of lenses and mirrors as image forming devices had been known since antiquity and had been studied widely in the centuries preceding the telescopes development. Although there were some recorded instances of pre-17th century middle eastern and European opticians creating devices that could have functioned as telescopes, the earliest known working telescopes in the modern sense were refracting telescopes 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 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 reflector.

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.

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:

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, 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

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.

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"
^ Sabra, A. I. & Hogendijk, J. P. (2003), The Enterprise of Science in Islam: New Perspectives, MIT Press, pp. 85-118, ISBN 0262194821
^ O. S. Marshall (1950). "Alhazen and the Telescope", Astronomical Society of the Pacific Leaflets 6, p. 4
^ Richard Powers (University of Illinois), Best Idea; Eyes Wide OpenNew York Times, April 18, 1999.
^ 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"

[Sabra2-2] 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] w.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."]

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