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European Extremely Large Telescope (E-ELT)

Despite downsizing its plans over the past 15 years or so, the European Southern Observatory (ESO) will still be building the largest telescope ever. In the late 1990s, engineers came up with an ambitious proposal for developing the 100m Overwhelmingly Large Telescope, but ESO later committed itself to a more realistic 42m instrument, with exactly twice the light-collecting power of the Thirty Meter Telescope (TMT).

European-Extremely-Large-Telescope-E-ELT-300x210 European Extremely Large Telescope (E-ELT)

European Extremely Large Telescope (E-ELT)

In 2011, budget restraints forced ESO to scale back to a 39.2m primary, consisting of 798 hexagonal segments. According to director general Tim de Zeeuw, the ESO Council has approved the European Extremely Large Telescope programme, even though funding is not yet fully secured.

“We’re still awaiting the ratification of Brazil’s ESO membership by the government,” he says. Brazil’s entrance fee is needed to cover a substantial part of the E-ELT’s construction cost. Even though the São Paulo Research Foundation recently partnered with the Giant Magellan Telescope (GMT), de Zeeuw is still optimistic, saying, “We expect ratification within a few months.” The E-ELT will be built at Cerro Armazones in northern Chile, close to ESO’s existing Paranal Observatory, which is home to the Very Large Telescope. The mountain top has already been blasted away and construction work on a mountain road is in progress.

Located in the central part of the Atacama Desert, one of the driest regions on the planet, Cerro Armazones experiences incredibly clear skies and excellent seeing. A near-infrared camera and a nearinfrared spectrograph have been selected as the telescope’s first light instruments. Three high-resolution imagers and spectrometers will follow.

Like the TMT and the GMT, astronomers expect the European monster telescope to shed light on cosmic evolution and galaxy formation. But its sheer size will also enable detailed studies of nearby Earth-like exoplanets.

Then again, as astronomer Martin Harwit once said: “By looking somewhere where no one has been able to look before, one is very likely to make new discoveries.” For all three future telescopes, the greatest scientific excitement will likely lie in the unknown unknowns.


  • Mirror size: 39.2m (made up of 798 hexagonal segments)
  • Location: Cerro Armazones, Chile (altitude 3,050m)
  • Date of completion: 2024
  • Cost: $1.35 billion (£840 million)
  • Trivia: The E-ELT’s segmented primary mirror has a total effective surface area of 978m2 – 2.2 times the area of a basketball court.

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