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Learning objectives

By the end of this section, you will be able to:

  • Recognize the largest visible-light and infrared telescopes in operation today
  • Discuss the factors relevant to choosing an appropriate telescope site
  • Define the technique of adaptive optics and describe the effects of the atmosphere on astronomical observations

Since Newton’s time, when the sizes of the mirrors in telescopes were measured in inches, reflecting telescopes have grown ever larger. In 1948, US astronomers built a telescope with a 5-meter (200-inch) diameter mirror on Palomar Mountain in Southern California. It remained the largest visible-light telescope in the world for several decades. The giants of today, however, have primary mirrors (the largest mirrors in the telescope) that are 8- to 10-meters in diameter, and larger ones are being built ( [link] ).

Large telescope mirror.

Photograph of one of the 8-meter concave primary mirrors of the European Space Agency’s Very Large Telescope array in Chile.
This image shows one of the primary mirrors of the European Southern Observatory’s Very Large Telescope, named Yepun, just after it was recoated with aluminum. The mirror is a little over 8 meters in diameter. (credit: ESO/G. Huedepohl)

Modern visible-light and infrared telescopes

The decades starting in 1990 saw telescope building around the globe grow at an unprecedented rate. (See [link] , which also includes websites for each telescope in case you want to visit or learn more about them.) Technological advancements had finally made it possible to build telescopes significantly larger than the 5-meter telescope at Palomar at a reasonable cost. New technologies have also been designed to work well in the infrared, and not just visible, wavelengths.

Large Single-Dish Visible-Light and Infrared Telescopes
Aperture (m) Telescope Name Location Status Website
39 European Extremely Large Telescope (E-ELT) Cerro Armazonas, Chile First light 2025 (estimated) www.eso.org/sci/facilities/eelt
30 Thirty-Meter Telescope (TMT) Mauna Kea, HI First light 2025 (estimated) www.tmt.org
24.5 Giant Magellan Telescope (GMT) Las Campanas Observatory, Chile First light 2025 (estimated) www.gmto.org
11.1 × 9.9 Southern African Large Telescope (SALT) Sutherland, South Africa 2005 www.salt.ac.za
10.4 Gran Telescopio Canarias (GTC) La Palma, Canary Islands First light 2007 http://www.gtc.iac.es
10.0 Keck I and II (two telescopes) Mauna Kea, HI Completed 1993–96 www.keckobservatory.org
9.1 Hobby–Eberly Telescope (HET) Mount Locke, TX Completed 1997 www.as.utexas.edu/mcdonald/het
8.4 Large Binocular Telescope (LBT) (two telescopes) Mount Graham, AZ First light 2004 www.lbto.org
8.4 Large Synoptic Survey Telescope (LSST) The Cerro Pachón, Chile First light 2021 www.lsst.org
8.3 Subaru Telescope Mauna Kea, HI First light 1998 www.naoj.org
8.2 Very Large Telescope (VLT) Cerro Paranal, Chile All four telescopes completed 2000 www.eso.org/public/teles-instr/paranal
8.1 Gemini North and Gemini South Mauna Kea, HI (North) and Cerro Pachón, Chile (South) First light 1999 (North), First light 2000 (South) www.gemini.edu
6.5 Magellan Telescopes (two telescopes: Baade and Landon Clay) Las Campanas, Chile First light 2000 and 2002 obs.carnegiescience.edu/Magellan
6.5 Multi-Mirror Telescope (MMT) Mount Hopkins, AZ Completed 1979 www.mmto.org
6.0 Big Telescope Altazimuth (BTA-6) Mount Pastukhov, Russia Completed 1976 w0.sao.ru/Doc-en/Telescopes/bta/descrip.html
5.1 Hale Telescope Mount Palomar, CA Completed 1948 www.astro.caltech.edu/palomar/about/telescopes/hale.html
Practice Key Terms 3

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Source:  OpenStax, Astronomy. OpenStax CNX. Apr 12, 2017 Download for free at http://cnx.org/content/col11992/1.13
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