A 'telescope' is an instrument designed for the observation of remote objects and the collection of
electromagnetic radiation. The earliest known telescopes are credited to three individuals,
Hans Lippershey and
Zacharias Janssen, spectacle-makers in Middelburg, and
Jacob Metius of
Alkmaar also known as Jacob Adriaanszoon (see ''
History of telescopes''). "Telescope" (from the
Greek ''tele'' = 'far' and ''skopein'' = 'to look or see'; ''teleskopos'' = 'far-seeing') was a name invented in 1611 by
Galileo Galilei for his version of the device he based on Hans Lippershey's instrument
[1]. "Telescope" usually refers to
optical telescopes, but there are telescopes that operate in other regions of the
electromagnetic spectrum.

A diagram of a Newtonian telescope.
__TOC__
Types of telescope
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
Main articles: 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 -
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 or studied. Optical telescopes are used for
astronomy and in many non-astronomical instruments including ''
theodolites'', ''
transits'', ''
spotting scopes'', ''
monoculars'', ''
binoculars,'' ''
camera lenses'', and ''spyglasses''. There are three main types:
★ The
refracting telescope which uses solely an arrangement of lenses.
★ The
reflecting telescope which uses solely an arrangement of mirrors.
★ The
catadioptric telescope which uses a combination of mirrors and lenses.
Radio telescopes
Main articles: Radio telescope
Radio telescopes are
directional radio antennae 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.
X-ray and gamma-ray telescopes
X-ray and
gamma-ray telescopes have a problem because these rays go through most metals and glasses. Some x-ray telescopes use 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. Gamma-ray telescopes give up on focusing entirely, 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.
('''see':
X-ray astronomy and
Gamma-ray astronomy'')

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
★
Binoculars
★
spotting scopes
★
monoculars
★
Telephoto lens
★
Solar Telescope
Notable telescopes
★
Anglo-Australian Telescope
★
Arecibo Observatory
★
Atacama Large Millimeter Array
★
Chandra X-ray Observatory
★
CHARA (Center for High Angular Resolution Astronomy) array
★
Hale telescope
★
Hexapod-Telescope
★
Hooker Telescope
★
Hubble Space Telescope
★
IceCube Neutrino Detector
★
Isaac Newton Telescope
★
Keck telescope
★
LIGO
★
McMath-Pierce Solar Telescope
★
McMath-Hulbert Observatory (Solar)
★
Magdalena Ridge Observatory
★
Multiple-Mirror telescope
★
Navy Prototype Optical Interferometer
★
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
See also
★
Amateur telescope making
★
Angular resolution
★
Aperture synthesis
★
ASCOM open standards for computer control of telescopes
★
BOOTES
★
Depth of field
★
Dynameter
★
Eyepiece
★
First light
★
f-number
★
History of telescopes
★
Keyhole problem
★
List of largest optical reflecting telescopes
★
List of largest optical refracting telescopes
★
Microscope
★
Remote Telescope Markup Language
★
Robotic telescope
★
Timeline of telescope technology
★
Timeline of telescopes, observatories, and observing technology
Notes
1. worldwidewords.org, 'The evolving tele- prefix', Michael Quinion, 1996–2007
References
★ 'Contemporary Astronomy - Second Edition',
Jay M. Pasachoff, Saunders Colleges Publishing - 1981, ISBN 0-03-057861-2
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