Extremely large telescope
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, 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. 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.
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
|5||Extremely Large Telescope
|39.3||978||798 × 1.45 m
|3060||2024||Under construction: Cerro Armazones Obs., Chile|||
|4||Thirty Meter Telescope
|30||655||492 × 1.45 m
|4050||2027||Construction approved  Mauna Kea Obs., Hawaii|||
|3||Giant Magellan Telescope
|24.5||368||7 × 8.4 m
|2516||2024||Under construction: Las Campanas Obs., Chile;
4 mirrors cast (4/7 M1)
|2||Large Binocular Telescope
|11.8 equiv area
22.8 equiv detail limit
|111||2 × 8.4 m
|3221||2008||largest non-segmented mirrors;
Located on Mount Graham in Arizona
|1||Gran Telescopio Canarias
|10.4||74||36 × 1.9 m
|2275||2008||Largest single mirror.
Located on 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.
|Extremely Large Telescope (ELT)||$1189 million||€1055 million (Euros)|
|Thirty Meter Telescope (TMT)||$1400 million|
|Giant Magellan Telescope (GMT)||$1000 million|
|Large Binocular Telescope (LBT)||$120 million|
|Gran Telescopio Canarias (GTC)||$147 million||€130 million (Euros)|
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: Giant Segmented Mirror Telescope, merged into TMT
- OWL: Overwhelmingly Large Telescope, passed over in favor of ELT
- VLOT: Very Large Optical Telescope, merged into TMT
- LAT: Large Atacama Telescope
- EURO50: European 50-metre Telescope, merged into the ELT.
- LPT: Large Petal Telescope
- JELT[permanent dead link]: Japanese ELT Project. Japan joined the TMT project in 2008.
- CELT: California Extremely Large Telescope; CELT became/merged into TMT project.
- Swedish Extremely Large Telescope Project.
- 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.
- "Thirty Meter Telescope Construction Proposal" (PDF). TMT Observatory Corporation. 2007-09-12: 29. Retrieved 2009-07-24.
- "Chapter 6: Optics" (PDF). GMT Conceptual Design Report. GMT Consortium. pp. 6–3. Retrieved 2008-04-02.
- http://www.eso.org/ eso1419 — Organisation Release, Groundbreaking for the E-ELT, 19 June 2014
- Govert Schilling – Europe Downscales Monster Telescope to Save Money ( 14 June 2011) – Science Insider
- TMT Timeline, accessed February 11, 2018
- Thirty Meter Telescope timeline page, TMT Observatory Project, retrieved 2010-10-12
- http://sen.com, Elizabeth Howell, Giant telescope gets $20m funding boost as design takes shape, 29 December 2014
- "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". CBCnews. CBC. 16 July 2007. Retrieved 24 July 2013.