A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects, the word telescope now refers to a wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors.
The first known practical telescopes were refracting telescopes with glass lenses and were invented in the Netherlands at the beginning of the 17th century. They were used for both terrestrial applications and astronomy.
The reflecting telescope, which uses mirrors to collect and focus light, was invented within a few decades of the first refracting telescope.
The word telescope 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. In the Starry Messenger, Galileo had used the Latin term perspicillum. The root of the word is from the Ancient Greek τῆλε, romanized tele 'far' and σκοπεῖν, skopein 'to look or see'; τηλεσκόπος, teleskopos 'far-seeing'.
The earliest existing record of a telescope was a 1608 patent submitted to the government in the Netherlands by Middelburg spectacle maker Hans Lipperhey for a refracting telescope. The actual inventor is unknown but word of it spread through Europe. Galileo heard about it and, in 1609, built his own version, and made his telescopic observations of celestial objects.
The idea that the objective, or light-gathering element, could be a mirror instead of a lens was being investigated soon after the invention of the refracting telescope. The potential advantages of using parabolic mirrors—reduction of spherical aberration and no chromatic aberration—led to many proposed designs and several attempts to build reflecting telescopes. In 1668, Isaac Newton built the first practical reflecting telescope, of a design which now 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, and aluminized mirrors in 1932. The maximum physical size limit for refracting telescopes is about 1 meter (39 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 than 10 meters (33 feet), and work is underway on several 30-40m designs.
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 large variety of complex astronomical instruments have been developed.
Since the atmosphere is opaque for most of the electromagnetic spectrum, only a few bands can be observed from the Earth's surface. These bands are visible – near-infrared and a portion of the radio-wave part of the spectrum. For this reason there are no X-ray or far-infrared ground-based telescopes as these have to be observed from orbit. Even if a wavelength is observable from the ground, it might still be advantageous to place a telescope on a satellite due to issues such as clouds, astronomical seeing and light pollution.
The disadvantages of launching a space telescope include cost, size, maintainability and upgradability.
By electromagnetic spectrum
The name "telescope" covers a wide range of instruments. Most detect electromagnetic radiation, but there are major differences in how astronomers must go about collecting light (electromagnetic radiation) in different frequency bands.
As wavelengths become longer, it becomes easier to use antenna technology to interact with electromagnetic radiation (although it is possible to make very tiny antenna). The near-infrared can be collected much like visible light; however, in the far-infrared and submillimetre range, telescopes can operate more like a radio telescope. For example, the James Clerk Maxwell Telescope observes from wavelengths from 3 μm (0.003 mm) to 2000 μm (2 mm), but uses a parabolic aluminum antenna. On the other hand, the Spitzer Space Telescope, observing from about 3 μm (0.003 mm) to 180 μm (0.18 mm) uses a mirror (reflecting optics). Also using reflecting optics, the Hubble Space Telescope with Wide Field Camera 3 can observe in the frequency range from about 0.2 μm (0.0002 mm) to 1.7 μm (0.0017 mm) (from ultra-violet to infrared light).
With photons of the shorter wavelengths, with the higher frequencies, glancing-incident optics, rather than fully reflecting optics are used. Telescopes such as TRACE and SOHO use special mirrors to reflect extreme ultraviolet, producing higher resolution and brighter images than are otherwise possible. A larger aperture does not just mean that more light is collected, it also enables a finer angular resolution.
Telescopes may also be classified by location: ground telescope, space telescope, or flying telescope. They may also be classified by whether they are operated by professional astronomers or amateur astronomers. A vehicle or permanent campus containing one or more telescopes or other instruments is called an observatory.
Radio and submilimeter
Radio telescopes are directional radio antennas that typically employ a large dish to collect radio waves. The dishes are sometimes constructed of a conductive wire mesh whose openings are smaller than the wavelength being observed.
Unlike an optical telescope, which produces a magnified image of the patch of sky being observed, a traditional radio telescope dish contains a single receiver and records a single time-varying signal characteristic of the observed region; this signal may be sampled at various frequencies. In some newer radio telescope designs, a single dish contains an array of several receivers; this is known as a focal-plane array.
By collecting and correlating signals simultaneously received by several dishes, high-resolution images can be computed. Such multi-dish arrays are known as astronomical interferometers and the technique is called aperture synthesis. The 'virtual' apertures of these arrays are similar in size to the distance between the telescopes. As of 2005, the record array size is many times the diameter of the Earth – using 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, which has the advantage of being able to pass through the atmosphere and interstellar gas and dust clouds.
An optical telescope gathers and focuses light mainly from the visible part of the electromagnetic spectrum. Optical telescopes increase the apparent angular size of distant objects as well as their apparent brightness. 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 and/or mirrors, 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: theodolites (including transits), spotting scopes, monoculars, binoculars, camera lenses, and spyglasses. There are three main optical 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 to form an image.
X-rays are much harder to collect and focus than electromagnetic radiation of longer wavelengths. X-ray telescopes can use X-ray optics, such as 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. In 1952, Hans Wolter outlined 3 ways a telescope could be built using only this kind of mirror. Examples of space observatories using this type of telescope are the Einstein Observatory, ROSAT, and the Chandra X-ray Observatory. In 2012 the NuSTAR X-ray Telescope was launched which uses Wolter telescope design optics at the end of a long deployable mast to enable photon energies of 79 keV.
Higher energy X-ray and 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.
X-ray and Gamma-ray telescopes are usually installed on high-flying balloons or Earth-orbiting satellites since the Earth's atmosphere is opaque to this part of the electromagnetic spectrum. An example of this type of telescope is the Fermi Gamma-ray Space Telescope which was launched in June 2008.
The detection of very high energy gamma rays, with shorter wavelength and higher frequency than regular gamma rays, requires further specialization. An example of this type of observatory is the ground based telescope VERITAS.
Lists of telescopes
- List of optical telescopes
- List of largest optical reflecting telescopes
- List of largest optical refracting telescopes
- List of largest optical telescopes historically
- List of radio telescopes
- List of solar telescopes
- List of space observatories
- List of telescope parts and construction
- List of telescope types
- Amateur telescope making
- Angular resolution
- ASCOM open standards for computer control of telescopes
- Bahtinov mask
- Bioptic telescope
- Carey mask
- Dew shield
- First light
- Hartmann mask
- Keyhole problem
- Remote Telescope Markup Language
- Robotic telescope
- Timeline of telescope technology
- Timeline of telescopes, observatories, and observing technology
- Company, Houghton Mifflin Harcourt Publishing. "The American Heritage Dictionary entry: TELESCOPE". https://www.ahdictionary.com/word/search.html?q=TELESCOPE.
- Sobel (2000, p.43), Drake (1978, p.196)
- Rosen, Edward, The Naming of the Telescope (1947)
- Jack, Albert (2015). They Laughed at Galileo: How the Great Inventors Proved Their Critics Wrong. ISBN 978-1629147581.
- 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, Zacharias Janssen is sometimes associated with the invention
- "NASA – Telescope History". https://www.nasa.gov/audience/forstudents/9-12/features/telescope_feature_912.html.
- Loker, Aleck (20 November 2017). Profiles in Colonial History. Aleck Loker. ISBN 978-1-928874-16-4. https://books.google.com/books?id=Lq1rd1ecFCYC&pg=PA15. Retrieved 12 December 2015.
- Watson, Fred (20 November 2017). Stargazer: The Life and Times of the Telescope. Allen & Unwin. ISBN 978-1-74176-392-8. https://books.google.com/books?id=2LZZginzib4C&q=intitle:Stargazer+digges+coins&pg=PA40. Retrieved 21 November 2020.
- Attempts by Niccolò Zucchi and James Gregory and theoretical designs by Bonaventura Cavalieri, Marin Mersenne, and Gregory among others
- Hall, A. Rupert (1992). Isaac Newton: Adventurer in Thought. Cambridge University Press. p. 67. ISBN 9780521566698.
- "Chester Moor Hall". http://www.britannica.com/biography/Chester-Moor-Hall. Retrieved 25 May 2016.
- Bakich, Michael E. (10 July 2003). "Chapter Two: Equipment". The Cambridge Encyclopedia of Amateur Astronomy. p. 33. ISBN 9780521812986. http://www.cambridge.org/uk/astronomy/features/amateur/files/p28-4.pdf.
- Tate, Karl (August 30, 2013). "World's Largest Reflecting Telescopes Explained (Infographic)". Space.com. https://www.space.com/22505-worlds-largest-telescopes-explained-infographic.html.
- Stierwalt, Everyday Einstein Sabrina. "Why Do We Put Telescopes in Space?" (in en). https://www.scientificamerican.com/article/why-do-we-put-telescopes-in-space/.
- Siegel, Ethan. "5 Reasons Why Astronomy Is Better From The Ground Than In Space" (in en). https://www.forbes.com/sites/startswithabang/2018/03/22/5-reasons-why-astronomy-is-better-from-the-ground-than-in-space/.
- Siegel, Ethan. "This Is Why We Can't Just Do All Of Our Astronomy From Space" (in en). https://www.forbes.com/sites/startswithabang/2019/11/27/this-is-why-we-cant-just-do-all-of-our-astronomy-from-space/.
- ASTROLab du parc national du Mont-Mégantic (January 2016). "The James-Clerk-Maxwell Observatory" (in en). http://astro-canada.ca/_en/a2111.html.
- "Hubble's Instruments: WFC3 – Wide Field Camera 3" (in en). http://www.spacetelescope.org/about/general/instruments/wfc3/.
- "Observatories Across the Electromagnetic Spectrum". https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum_observatories1.html.
- Dalton, Rex (2000-08-01). "Microsoft moguls back search for ET intelligence" (in en). Nature 406 (6796): 551. doi:10.1038/35020722. ISSN 1476-4687. PMID 10949267.
- Tarter, Jill (September 2001). "The Search for Extraterrestrial Intelligence (SETI)" (in en). Annual Review of Astronomy and Astrophysics 39 (1): 511–548. doi:10.1146/annurev.astro.39.1.511. ISSN 0066-4146. Bibcode: 2001ARA&A..39..511T. https://www.annualreviews.org/doi/10.1146/annurev.astro.39.1.511. Retrieved 20 August 2022.
- "SETI & the Search for Extraterrestrial Life" (in en). 2016-08-02. https://www.space.com/33626-search-for-extraterrestrial-intelligence.html.
- Jones, Barrie W. (2 September 2008) (in en). The Search for Life Continued: Planets Around Other Stars. Springer Science & Business Media. ISBN 978-0-387-76559-4. https://books.google.com/books?id=5wX9aHqfBS0C&pg=PA111. Retrieved 12 December 2015.
- "Who Invented the Telescope?" (in en). 2021-10-26. https://www.space.com/21950-who-invented-the-telescope.html.
- Rupert, Charles G. (1918). "1918PA.....26..525R Page 525". Popular Astronomy 26: 525. Bibcode: 1918PA.....26..525R. https://adsabs.harvard.edu/full/1918PA.....26..525R. Retrieved 2022-08-20.
- "Telescope could focus light without a mirror or lens" (in en-US). https://www.newscientist.com/article/dn13820-telescope-could-focus-light-without-a-mirror-or-lens/.
- Koechlin, L.; Serre, D.; Duchon, P. (2005-11-01). "High resolution imaging with Fresnel interferometric arrays: suitability for exoplanet detection" (in en). Astronomy & Astrophysics 443 (2): 709–720. doi:10.1051/0004-6361:20052880. ISSN 0004-6361. Bibcode: 2005A&A...443..709K. https://www.aanda.org/articles/aa/abs/2005/44/aa2880-05/aa2880-05.html. Retrieved 20 August 2022.
- "Celestron Rowe-Ackermann Schmidt Astrograph – Astronomy Now" (in en-US). https://astronomynow.com/2016/06/01/celestron-rowe-ackermann-schmidt-astrograph/.
- "Telescope (Comet Seeker)" (in en). https://www.si.edu/object/nmah_1183753.
- Stenflo, J. O. (2001-01-01). "Limitations and Opportunities for the Diagnostics of Solar and Stellar Magnetic Fields". Magnetic Fields Across the Hertzsprung-Russell Diagram 248: 639. Bibcode: 2001ASPC..248..639S. https://ui.adsabs.harvard.edu/abs/2001ASPC..248..639S. Retrieved 20 August 2022.
- Allen, C. W. (2000). Allen's astrophysical quantities. Arthur N. Cox (4th ed.). New York: AIP Press. ISBN 0-387-98746-0. OCLC 40473741. https://www.worldcat.org/oclc/40473741.
- Ortiz, Roberto; Guerrero, Martín A. (2016-06-28). "Ultraviolet emission from main-sequence companions of AGB stars". Monthly Notices of the Royal Astronomical Society 461 (3): 3036–3046. doi:10.1093/mnras/stw1547. ISSN 0035-8711.
- Wolter, H. (1952), "Glancing Incidence Mirror Systems as Imaging Optics for X-rays", Annalen der Physik 10 (1): 94–114, doi:10.1002/andp.19524450108, Bibcode: 1952AnP...445...94W.
- Wolter, H. (1952), "Verallgemeinerte Schwarzschildsche Spiegelsysteme streifender Reflexion als Optiken für Röntgenstrahlen", Annalen der Physik 10 (4–5): 286–295, doi:10.1002/andp.19524450410, Bibcode: 1952AnP...445..286W.
- Giacconi, R.; Branduardi, G.; Briel, U.; Epstein, A.; Fabricant, D.; Feigelson, E.; Forman, W.; Gorenstein, P. et al. (June 1979). "The Einstein /HEAO 2/ X-ray Observatory" (in en). The Astrophysical Journal 230: 540. doi:10.1086/157110. ISSN 0004-637X. Bibcode: 1979ApJ...230..540G. http://adsabs.harvard.edu/doi/10.1086/157110. Retrieved 20 August 2022.
- "DLR - About the ROSAT mission" (in en). https://www.dlr.de/content/en/articles/missions-projects/past-missions/rosat/rosat-mission.html.
- Schwartz, Daniel A. (2004-08-01). "The development and scientific impact of the chandra x-ray observatory". International Journal of Modern Physics D 13 (7): 1239–1247. doi:10.1142/S0218271804005377. ISSN 0218-2718. Bibcode: 2004IJMPD..13.1239S. https://www.worldscientific.com/doi/abs/10.1142/S0218271804005377. Retrieved 20 August 2022.
- Madejski, Greg (2006). "Recent and Future Observations in the X‐ray and Gamma‐ray Bands: Chandra, Suzaku, GLAST, and NuSTAR". AIP Conference Proceedings 801 (1): 21–30. doi:10.1063/1.2141828. ISSN 0094-243X. Bibcode: 2005AIPC..801...21M. https://aip.scitation.org/doi/abs/10.1063/1.2141828. Retrieved 20 August 2022.
- "NuStar: Instrumentation: Optics". http://www.nustar.caltech.edu/about-nustar/instrumentation/optics.
- Hailey, Charles J.; An, HongJun; Blaedel, Kenneth L.; Brejnholt, Nicolai F.; Christensen, Finn E.; Craig, William W.; Decker, Todd A.; Doll, Melanie et al. (2010-07-29). "The Nuclear Spectroscopic Telescope Array (NuSTAR): optics overview and current status". Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray (SPIE) 7732: 197–209. doi:10.1117/12.857654. Bibcode: 2010SPIE.7732E..0TH. https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7732/77320T/The-Nuclear-Spectroscopic-Telescope-Array-NuSTAR--optics-overview-and/10.1117/12.857654.full.
- Braga, João; D’Amico, Flavio; Avila, Manuel A. C.; Penacchioni, Ana V.; Sacahui, J. Rodrigo; Santiago, Valdivino A. de; Mattiello-Francisco, Fátima; Strauss, Cesar et al. (2015-08-01). "The protoMIRAX hard X-ray imaging balloon experiment" (in en). Astronomy & Astrophysics 580: A108. doi:10.1051/0004-6361/201526343. ISSN 0004-6361. Bibcode: 2015A&A...580A.108B. https://www.aanda.org/articles/aa/abs/2015/08/aa26343-15/aa26343-15.html. Retrieved 20 August 2022.
- "Balloon-borne telescope lifts off to study black holes and neutron stars" (in en). 2022-07-13. https://www.space.com/balloon-telescope-xl-calibur-x-rays-black-holes.
- Atwood, W. B.; Abdo, A. A.; Ackermann, M.; Althouse, W.; Anderson, B.; Axelsson, M.; Baldini, L.; Ballet, J. et al. (2009-06-01). "The Large Area Telescope on Thefermi Gamma-Ray Space Telescopemission". The Astrophysical Journal 697 (2): 1071–1102. doi:10.1088/0004-637X/697/2/1071. ISSN 0004-637X. Bibcode: 2009ApJ...697.1071A. https://iopscience.iop.org/article/10.1088/0004-637X/697/2/1071. Retrieved 20 August 2022.
- Ackermann, M.; Ajello, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Bissaldi, E. et al. (2017-07-13). "Search for Extended Sources in the Galactic Plane Using Six Years ofFermi-Large Area Telescope Pass 8 Data above 10 GeV" (in en). The Astrophysical Journal 843 (2): 139. doi:10.3847/1538-4357/aa775a. ISSN 1538-4357. Bibcode: 2017ApJ...843..139A. https://doi.org/10.3847/1538-4357/aa775a.
- Krennrich, F.; Bond, I. H.; Boyle, P. J.; Bradbury, S. M.; Buckley, J. H.; Carter-Lewis, D.; Celik, O.; Cui, W. et al. (2004-04-01). "VERITAS: the Very Energetic Radiation Imaging Telescope Array System" (in en). New Astronomy Reviews. 2nd VERITAS Symposium on the Astrophysics of Extragalactic Sources 48 (5): 345–349. doi:10.1016/j.newar.2003.12.050. ISSN 1387-6473. Bibcode: 2004NewAR..48..345K. https://www.sciencedirect.com/science/article/pii/S1387647303003610.
- Weekes, T. C.; Cawley, M. F.; Fegan, D. J.; Gibbs, K. G.; Hillas, A. M.; Kowk, P. W.; Lamb, R. C.; Lewis, D. A. et al. (1989-07-01). "Observation of TeV Gamma Rays from the Crab Nebula Using the Atmospheric Cerenkov Imaging Technique". The Astrophysical Journal 342: 379. doi:10.1086/167599. ISSN 0004-637X. Bibcode: 1989ApJ...342..379W. https://ui.adsabs.harvard.edu/abs/1989ApJ...342..379W. Retrieved 20 August 2022.
- "Silicon 'prism' bends gamma rays – Physics World". 9 May 2012. http://physicsworld.com/cws/article/news/2012/may/09/silicon-prism-bends-gamma-rays.
- Elliott, Robert S. (1966), Electromagnetics, McGraw-Hill
- King, Henry C. (1979). The history of the telescope. H. Spencer Jones. New York: Dover Publications. ISBN 0-486-23893-8. OCLC 6025190. https://www.worldcat.org/oclc/6025190.
- Pasachoff, Jay M. (1981). Contemporary astronomy (2nd ed.). Philadelphia: Saunders College Pub. ISBN 0-03-057861-2. OCLC 7734917. https://www.worldcat.org/oclc/7734917.
- Rashed, Roshdi; Morelon, Régis (1996), Encyclopedia of the History of Arabic Science, 1 & 3, Routledge, ISBN 978-0-415-12410-2
- Sabra, A.I.; Hogendijk, J.P. (2003). The Enterprise of Science in Islam: New Perspectives. MIT Press. pp. 85–118. ISBN 978-0-262-19482-2.
- Wade, Nicholas J.; Finger, Stanley (2001), "The eye as an optical instrument: from camera obscura to Helmholtz's perspective", Perception 30 (10): 1157–1177, doi:10.1068/p3210, PMID 11721819
- Watson, Fred (2007). Stargazer : the life and times of the telescope. Crows Nest, NSW: Allen & Unwin. ISBN 978-1-74176-392-8. OCLC 173996168. https://www.worldcat.org/oclc/173996168.
|Wikimedia Commons has media related to Telescope.|
- Galileo to Gamma Cephei – The History of the Telescope
- The Galileo Project – The Telescope by Al Van Helden
- "The First Telescopes". Part of an exhibit from Cosmic Journey: A History of Scientific Cosmology by the American Institute of Physics
- Outside the Optical: Other Kinds of Telescopes
- Gray, Meghan; Merrifield, Michael (2009). "Telescope Diameter". Sixty Symbols. Brady Haran for the University of Nottingham. http://www.sixtysymbols.com/videos/telescope.htm.
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