The graphic above is oft-cited in SE questions and answers. I was (a little) sad to see in it that the 100 meter telescope-engineering wunderkind Overwhelmingly Large Telescope or "OWL" has been canceled, leaving the Extremely Large (37 meter) and Thirty Meter (30 meter) Telescopes coming along ("planned 2027") to become the (seemingly) largest two single-aperture optical telescopes for quite some time into the future.

Are they both coming along nicely and on-track for first light circa 2027, now only 4 years away?

Wikimedia's Comparison optical telescope primary mirrors (click link above, or image below for full size & resolution)

Wikimedia's "Comparison optical telescope primary mirrors" https://commons.wikimedia.org/wiki/File:Comparison_optical_telescope_primary_mirrors.svg

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    $\begingroup$ Literally the first News item on their web pages. elt.eso.org/media $\endgroup$
    – ProfRob
    Commented Aug 26, 2023 at 6:33
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    $\begingroup$ @ProfRob literally is better than figuratively when it comes to new items for sure! $\endgroup$
    – uhoh
    Commented Aug 26, 2023 at 23:44

1 Answer 1


The ELT looks basically on track. It’s scheduled to start scientific observations in 2028 and is now half-completed. See https://www.eso.org/public/news/eso2310/

The TMT’s fate is less positive, though, as construction stopped in 2018 due to protests from Native Hawai’ians that it was encroaching a sacred mountain—from what I understood, it had basically been agreed with the Native Council that construction would indeed go forward, but some nonmembers of the Council see things in a different way and disagreed with the Council’s decision, and they are the ones who cause trouble. Wikipedia’s page says that as of June 2022, “no further construction has been announced or initiated” since the 2018 stop.


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