View source for Overwhelmingly Large Telescope

{{Short description|Proposed extremely large telescope}}
{{Use dmy dates|date=December 2021}}
{{Infobox telescope}}
{{comparison optical telescope primary mirrors.svg|450px}}
The '''Overwhelmingly Large Telescope''' ('''OWL''') was a conceptual design by the [[European Southern Observatory]] (ESO) organisation for an [[extremely large telescope]], which was intended to have a single aperture of 100 metres in diameter. Because of the complexity and cost of building a telescope of this unprecedented size, ESO has decided to focus on the 39-metre diameter [[Extremely Large Telescope]] instead.

==History==
OWL was first proposed in 1998, and at that time was estimated to be technologically feasible by 2010–2015.<ref>{{cite book|last1=Gilmozzi|first1= R.|display-authors=etal |title= Advanced Technology Optical/IR Telescopes VI|chapter= Future of filled aperture telescopes: Is a 100-m feasible?|editor-first1= Larry M.|editor-last1= Stepp|date=1998 |language=en|chapter-url=http://www.eso.org/sci/facilities/eelt/owl/Files/publications/1998_Kona_The_Future_of_Filled_Aperture_Telescopes.pdf|access-date=25 Oct 2018 |series=Proceedings of the SPIE |volume= 3352|pages= 778–791|doi= 10.1117/12.319284|bibcode= 1998SPIE.3352..778G|s2cid= 12512243}}</ref>

While the original 100&nbsp;m design would not exceed the angular resolving power of [[astronomical interferometer|interferometric telescopes]], it would have exceptional light-gathering and imaging capacity.<ref>{{cite web |date=13 April 2006 |title=OWL – a future milestone for Astronomy? |url=https://www.eso.org/sci/facilities/eelt/owl/index_3.html |access-date=26 December 2021 |website=www.eso.org}}</ref> The OWL could be expected to regularly see astronomical objects with an [[apparent magnitude]] of 38, or 1,500 times fainter than the faintest object that has been detected by the [[Hubble Space Telescope]].

All proposed designs for the OWL are variations on a [[segmented mirror]], since there is no technology available to build and transport a monolithic 60- or 100-meter mirror. The operation of a segmented mirror is somewhat more complicated than that of a monolithic one, requiring careful alignment of the segments (a technique called [[cophasing]]). Experience gained in existing segmented mirrors (for example, the [[Keck telescope]]) suggests that the mirror proposed for the OWL is feasible. However, the projected cost (of around €1.5 billion<!-- The €1.5 billion ($1.65 billion) figure listed seems kind of questionable. The ESO website admits the figure given is a preliminary estimate based on engineering/analytical models, and is not final. Given that both the 30 Meter Telescope and the European Extremely Large Telescope are in the ballpark of $1-$2 billion, it seems unlikely a structure or telescope 3x bigger in diameter (9x bigger in area, and 27x bigger in volume) would be so close in cost.

I could be wrong, however if we could find updated estimates, I think the estimated cost of the OWLT will be much higher than their preliminary estimate from years ago. (Is this how I'm supposed to use invisible comments? I hope so, please delete if not.) -->) was considered too high, so the ESO is now building the smaller [[Extremely Large Telescope]] 39,5 m in diameter.<ref>{{Cite web|url=http://www.eso.org/sci/facilities/eelt/owl/FAQs.html|title=OWL 100-m telescope|website=www.eso.org|access-date=2019-10-08}}</ref><ref>{{cite web |title=THE EXTREMELY LARGE TELESCOPE: The World's Biggest Eye In The Sky |url=https://elt.eso.org/ |website=elt.eso.org |date=2021 |access-date=26 December 2021}}</ref><ref>{{cite news| url=https://news.bbc.co.uk/2/hi/science/nature/5252228.stm | work=BBC News | title=Record mirror for Euro telescope | date=2006-08-07 | access-date=2010-03-27}}</ref> Also, there appears to be some inconsistency as to the actual construction costs of the OWL, with some estimating its cost an order of magnitude higher (ELT currently at €1.3 billion,<ref>{{Cite web|last=|title=Funding boost for ESO's Extremely Large Telescope|url=https://www.eso.org/public/announcements/ann20034/|access-date=2020-12-05|website=www.eso.org|language=en}}</ref> equivalent to around $1.3 billion, scaled using {{Math|''D''<sup>2.77</sup>}} proportionality assuming a 100 meter diameter yields $21 billion).<ref>{{Cite web|url=http://www2.lowell.edu/users/gerard/publications/van_belle_meinel2_2004.pdf|title=The Scaling Relationship Between Telescope Cost and Aperture Size for Very Large Telescopes|last=van Belle|first=Gerard T.|website=Lowell Observatory}}</ref>

It has been estimated that a telescope with a diameter of 80 meters would be able to [[spectroscopy|spectroscopical]]ly analyse Earth-size planets around the forty nearest sun-like stars.<ref>{{cite news |first=Roberto |last=Gilmozzi |title=Giant Telescopes of the Future |url=http://www.sciam.com/article.cfm?id=giant-telescopes-of-the-f |work=[[Scientific American]] |date=May 2006 }}</ref> As such, this telescope could help in the exploration of [[exoplanet]]s and [[extraterrestrial life]] (because the spectrum from the planets could reveal [[biosignature|the presence of molecules indicative of life]]).

==See also==
*[[Active optics]]
*[[Adaptive optics]]
*[[Extremely Large Telescope]]
*[[Giant Magellan Telescope]]
*[[List of optical telescopes]]
*[[List of largest optical reflecting telescopes]]
*[[Thirty Meter Telescope]]

==References==
{{Reflist}}

== External links ==
*{{Commons category inline}}
*[https://www.eso.org/sci/facilities/eelt/owl/ The ESO 100-m optical telescope concept]
*[https://www.eso.org/sci/facilities/eelt/owl/Phase_A_Review.html OWL BLUE BOOK] – Phase A design report

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