The Onset of Extremely Large Telescopes

01 Feb 2022



Last month, I shared with you my excitement about the new golden age we are currently living through; from state-of-the-art heavy lift launchers to shiny new robotic probes whizzing across our solar system, space science and exploration have never looked more promising. And yet, within the list of missions and projects I described, I failed to mention another important advancement that will soon change the way scientists look at the sky: the advent of extremely large optical reflecting telescopes.


The largest telescopes currently in operation were built around twenty years ago (give or take 5 years) and have roughly 10 meters in diameter for their primary mirror, with the biggest of them being the Gran Telescopio Canarias at 10.4 m. It is worth noting that some telescopes combine relatively smaller mirrors (+/- 8 m) to create a larger reflective surface such as the Large Binocular Telescope or the Very Large Telescope.


Soon though, all these will look tiny next to the crop of giant telescopes currently in construction: the Giant Magellan Telescope (GMT), the Thirty Meters Telescope (TMT), and the Extremely Large Telescope (ELT). Let’s look at them briefly.


GMT will consist of seven 8.4 m primary mirrors placed in a petal pattern that, when combined, will have the effect of 24.5 m. Based in Chile, it should start operations in 2029.


TMT will have, as its name indicates, a 30 m primary mirror formed by 492 hexagonal mirrors 1.4 m in diameter that will be able to change shape and position. The telescope will be based on the top of Mauna Kea in Hawaii and should see first light in 2027 (although this might change if local protests are renewed).


ELT will be the biggest of them all with a whopping 39.9 m primary mirror consisting of 798 hexagonal mirrors 1.4m in diameter similar to TMT. Planned for completion in 2027, it will scan the skies from the top of a Chilean mountain.


Needless to say, the next decade will see a revolution in astronomy as these behemoths will capture faint lights and reveal whole new facets of our universe. If only astronomers could come up with better names for these extraordinary machines…