Astronomy:Extremely large telescope

From HandWiki
Comparison of nominal sizes of apertures of the above extremely large telescopes and some notable optical telescopes

An extremely large telescope (ELT) is an astronomical observatory featuring an optical telescope with an aperture for its primary mirror from 20 metres up to 100 metres across,[1] when discussing reflecting telescopes of optical wavelengths including ultraviolet (UV), visible, and near infrared wavelengths. Among many planned capabilities, extremely large telescopes are planned to increase the chance of finding Earth-like planets around other stars.[2] Telescopes for radio wavelengths can be much bigger physically, such as the 300 metres (330 yards) aperture fixed focus radio telescope of the Arecibo Observatory. Freely steerable radio telescopes with diameters up to 100 metres (110 yards) have been in operation since the 1970s.

These telescopes have a number of features in common, in particular the use of a segmented primary mirror (similar to the existing Keck telescopes), and the use of high-order adaptive optics systems.[3][4]

Although extremely large telescope designs are large, they can have smaller apertures than the aperture synthesis on many large optical interferometers. However, they may collect much more light, along with other advantages.

List of telescopes

# Image Name Aperture (m) Area (m²) Primary mirror Altitude (m) First
Notes Refs
1 Latest Rendering of the E-ELT.jpg Extremely Large Telescope
39.3 978 798 × 1.45 m
hexagonal f/1
3060 2027 Under construction at Cerro Armazones Obs. in Chile [5][6][7]
2 Top view of tmt complex.jpg Thirty Meter Telescope
30.0 655 492 × 1.45 m
hexagonal f/1
4050 2027 Construction approved at Mauna Kea Obs. in Hawaii, halted as of September 2019 due to protests [3][8][9][10]
3 Giant Magellan Telescope - artist's concept.jpg Giant Magellan Telescope
24.5 368 7 × 8.4 m
circular f/0.71
2516 2029 Under construction at Las Campanas Obs. in Chile;
4/7 mirrors cast
4 LBT 2.png Large Binocular Telescope
(equiv. area)
(equiv. detail limit)
111 2 × 8.4 m
3221 2008 Largest non-segmented mirrors.
Located on Mount Graham in Arizona
5 Grantelescopio.jpg Gran Telescopio Canarias
10.4 74 36 × 1.9 m
2275 2008 Largest single mirror.
Located at Roque de los Muchachos Obs. in the Canary Islands
Note: Aperture of LBT: the baseline is obtained via aperture synthesis.

The Keck Observatory (2 x 10 m) and the Very Large Telescope, of the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile, measure 4 × 8.2 m and 4 × 1.8 m, all on separate mounts but in one building for interferometry.


Possible budget figures, which are estimates and can vary over time. For construction costs, it is recommended to estimate the cost of a giant telescope with the following equation:[14]

[math]\displaystyle{ cost \varpropto D^{2.7} }[/math]

Name Cost
(est. USD)
Extremely Large Telescope (ELT) $1590 million €1300 million
Thirty Meter Telescope (TMT) $1400 million
Giant Magellan Telescope (GMT) $1000 million
Large Binocular Telescope (LBT) $120 million
Gran Telescopio Canarias (GTC) $153 million €130 million


European Extremely Large Telescope (39.2m), ChileThirty Meter Telescope (30m), Hawaii
Giant Magellan Telescope (24.5m), Chile Large Binocular Telescope (2x 8.4m, 11.8m)Keck Observatory (2x10m), Hawaii
Very Large Telescope (4x 8.2m, VLTI)Gran Telescopio Canarias (10.4m)
Extremely large telescopes:

Compared to the LBT, Keck, VLT, and GTC

There were several telescopes in various stages in the 1990s and early 2000s, and some developed into construction projects.

Under construction
Funded construction

Some of these projects have been cancelled, or merged into ongoing extremely large telescopes.

  • GSMT:[18] Giant Segmented Mirror Telescope, merged into TMT
  • OWL:[19] Overwhelmingly Large Telescope, passed over in favor of ELT
  • VLOT:[20] Very Large Optical Telescope, merged into TMT
  • LAT:[21] Large Atacama Telescope
  • EURO50:[22] European 50-metre Telescope, merged into ELT
  • LPT:[23] Large Petal Telescope
  • JELT:[24] Japanese ELT Project; Japan joined the TMT project in 2008
  • CELT:[25] California Extremely Large Telescope, became/merged into TMT
  • ELT: Swedish Extremely Large Telescope Project[26]
  • MAXAT[26]

See also


  1. As A Skeleton Science Case For Extremely Large (20m–100m) Ground-based Telescopes (ELTs) and first section of ELT Roadmap , PDF
  2. Jha, Alok (5 August 2006). "Extremely Large Telescope could reveal secrets of life, the universe and everything". The Guardian. 
  3. 3.0 3.1 Thirty Meter Telescope Construction Proposal. TMT Observatory Corporation. 2007-09-12. p. 29. Retrieved 2009-07-24. 
  4. 4.0 4.1 "Chapter 6: Optics". GMT Conceptual Design Report. GMT Consortium. pp. 6–3. Retrieved 2008-04-02. 
  5. "Groundbreaking for the E-ELT". 19 June 2014. 
  6. Schilling, Govert (14 June 2011). "Europe Downscales Monster Telescope to Save Money". Science Insider. 
  7. "The E-ELT in numbers". 
  8. Thirty Meter Telescope timeline page, TMT Observatory Project,, retrieved 2010-10-12 
  9. TMT Timeline, accessed February 11, 2018
  10. "Hawaii top court approves controversial Thirty Meter Telescope". BBC News. 31 October 2018. 
  11. Howell, Elizabeth (29 December 2014). "Giant telescope gets $20m funding boost as design takes shape". Sen. 
  12. "Large Binocular Telescope Achieves First Binocular Light" (Press release). Large Binocular Telescope Corporation. 2008-02-28. Archived from the original on 2008-03-10.
  13. "Giant Canary Islands telescope captures first light". CBC News. 16 July 2007. 
  14. Stepp, Larry; Daggert, Larry; Gillett, Paul. "Estimating the costs of extremely large telescopes". 
  16. "Giant Magellan Telescope". 
  17. "TMT International Observatory". 
  18. "AURA NIO: Home". October 19, 2006. 
  19. "The ESO 100-m OWL optical telescope concept". 
  20. "VLOT } The Very Large Optical Telescope for CI am Canada". May 2, 2009. 
  22. "Euro50". December 14, 2006. 
  23. "LPT | Large Petal Telescope". November 23, 2006. 
  24. [1]
  25. "index.html". June 5, 2002. 
  26. 26.0 26.1

External links