Extremely large telescope

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[]

#	Name	Aperture (m)	Area (m²)	Primary mirror	Altitude (m)	First light	Notes	Refs
1	Extremely Large Telescope (ELT)	39.3	978	798 × 1.45 m hexagonal f/1	3060	2027	Under construction at Cerro Armazones Obs. in Chile	^[5]^[6]^[7]
2	Thirty Meter Telescope (TMT)	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 (GMT)	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]^[11]
4	Large Binocular Telescope (LBT)	11.8 (equiv. area) 22.8 (equiv. detail limit)	111	2 × 8.4 m circular	3221	2008	Largest non-segmented mirrors. Located on Mount Graham in Arizona	^[12]
5	Gran Telescopio Canarias (GTC)	10.4	74	36 × 1.9 m hexagonal	2275	2008	Largest single mirror. Located at Roque de los Muchachos Obs. in the Canary Islands	^[13]
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.

The domes of the ELT, the TMT and the GMT compared to other, well known telescopes

Budget[]

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]

$cost\varpropto D^{2.7}$

Name	Cost (est. USD)	Alternate
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)	$148 million	€130 million

Projects[]

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

Under construction

ELT:^[15] Extremely Large Telescope
GMT:^[16] Giant Magellan Telescope

Funded construction

TMT:^[17] Thirty Meter Telescope

Projects

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

GSMT:^[18] , merged into TMT
OWL:^[19] Overwhelmingly Large Telescope, passed over in favor of ELT
VLOT:^[20] , merged into TMT
LAT:^[21]
EURO50:^[22] , merged into ELT
LPT:^[23]
JELT:^[24] ; 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]

References[]

^ As A Skeleton Science Case For Extremely Large (20m–100m) Ground-based Telescopes (ELTs) and first section of ELT Roadmap Archived 2015-05-18 at the Wayback Machine, PDF
^ Jha, Alok (5 August 2006). "Extremely Large Telescope could reveal secrets of life, the universe and everything". The Guardian.
^ Jump up to: ^a ^b "Thirty Meter Telescope Construction Proposal" (PDF). TMT Observatory Corporation. 2007-09-12: 29. Retrieved 2009-07-24. Cite journal requires |journal= (help)
^ Jump up to: ^a ^b "Chapter 6: Optics" (PDF). GMT Conceptual Design Report. GMT Consortium. pp. 6–3. Retrieved 2008-04-02.
^ "Groundbreaking for the E-ELT". 19 June 2014.
^ Schilling, Govert (14 June 2011). "Europe Downscales Monster Telescope to Save Money". Science Insider.
^ "The E-ELT in numbers". Archived from the original on 2009-08-21. Retrieved 2009-08-11.
^ Thirty Meter Telescope timeline page, TMT Observatory Project, retrieved 2010-10-12
^ TMT Timeline, accessed February 11, 2018
^ "Hawaii top court approves controversial Thirty Meter Telescope". BBC News. 31 October 2018.
^ Howell, Elizabeth (29 December 2014). "Giant telescope gets $20m funding boost as design takes shape". Sen.
^ "Large Binocular Telescope Achieves First Binocular Light" (Press release). Large Binocular Telescope Corporation. 2008-02-28. Archived from the original on 2008-03-10.
^ "Giant Canary Islands telescope captures first light". CBC News. 16 July 2007. Retrieved 24 July 2013.
^ Stepp, Larry; Daggert, Larry; Gillett, Paul. "Estimating the costs of extremely large telescopes" (PDF). National Optical Astronomy Observatory.
^ http://www.eso.org/public/teles-instr/elt/
^ "Giant Magellan Telescope".
^ "TMT International Observatory". TIO.
^ "AURA NIO: Home". web.archive.org. October 19, 2006.
^ "The ESO 100-m OWL optical telescope concept". www.eso.org.
^ "VLOT } The Very Large Optical Telescope for CI am Canada". web.archive.org. May 2, 2009.
^ http://astrosun.tn.cornell.edu/atacama
^ "Euro50". web.archive.org. December 14, 2006.
^ "LPT | Large Petal Telescope". web.archive.org. November 23, 2006.
^ [1]^{[permanent dead link]}
^ "index.html". web.archive.org. June 5, 2002.
^ Jump up to: ^a ^b http://www.astro.caltech.edu/~wws/elt.html

External links[]

Media related to Extremely large telescopes at Wikimedia Commons
Australian National Workshop on Extremely Large Telescopes (ELTs)
The OPTICON ELT Working Group a Europe-wide research project
The science case for Extremely Large Telescopes (ELTs) from the Royal Observatory, Edinburgh
Colossus Telescope

[1] As A Skeleton Science Case For Extremely Large (20m–100m) Ground-based Telescopes (ELTs) and first section of ELT Roadmap Archived 2015-05-18 at the Wayback Machine, PDF

[2] Jha, Alok (5 August 2006). "Extremely Large Telescope could reveal secrets of life, the universe and everything". The Guardian.

[constr-3] Jump up to: ^a ^b "Thirty Meter Telescope Construction Proposal" (PDF). TMT Observatory Corporation. 2007-09-12: 29. Retrieved 2009-07-24. Cite journal requires |journal= (help)

[design_optics-4] Jump up to: ^a ^b "Chapter 6: Optics" (PDF). GMT Conceptual Design Report. GMT Consortium. pp. 6–3. Retrieved 2008-04-02.

[eso-groundbreaking2014-5] "Groundbreaking for the E-ELT". 19 June 2014.

[govert-6] Schilling, Govert (14 June 2011). "Europe Downscales Monster Telescope to Save Money". Science Insider.

[7] "The E-ELT in numbers". Archived from the original on 2009-08-21. Retrieved 2009-08-11.

[operations-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. Retrieved 24 July 2013.

[14] Stepp, Larry; Daggert, Larry; Gillett, Paul. "Estimating the costs of extremely large telescopes" (PDF). National Optical Astronomy Observatory.

[15] ttp://www.eso.org/public/teles-instr/elt/

[16] "Giant Magellan Telescope".

[17] "TMT International Observatory". TIO.

[18] "AURA NIO: Home". web.archive.org. October 19, 2006.

[19] "The ESO 100-m OWL optical telescope concept". www.eso.org.

[20] "VLOT } The Very Large Optical Telescope for CI am Canada". web.archive.org. May 2, 2009.

[21] ttp://astrosun.tn.cornell.edu/atacama

[22] "Euro50". web.archive.org. December 14, 2006.

[23] "LPT | Large Petal Telescope". web.archive.org. November 23, 2006.

[24] [1]^{[permanent dead link]}

[25] "index.html". web.archive.org. June 5, 2002.

[elt-26] Jump up to: ^a ^b http://www.astro.caltech.edu/~wws/elt.html

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