World’s largest telescope under construction in Chile that will produce images 15 times sharper than Hubble with a light-collecting area bigger than all existing optical research telescopes combined

The Extremely Large Telescope (ELT) is an astronomical observatory and the world’s largest optical/near-infrared extremely large telescope now under construction. Part of the European Southern Observatory (ESO), it is located on top of Cerro Armazones in the Atacama Desert of northern Chile. The design comprises a reflecting telescope with a 39.3-metre-diameter (126 foot) segmented primary mirror and a 4.2-metre-diameter secondary mirror, and will be supported by adaptive optics, six laser guide star units and multiple large science instruments. The observatory aims to gather 100 million times more light than the human eye, 13 times more light than the largest optical telescopes existing in 2014, and be able to correct for atmospheric distortions. It has around 256 times the light gathering area of the Hubble Space Telescope and, according to the ELT’s specifications, would provide images 16 times sharper than those from Hubble.

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World’s largest telescope under construction in Chile that will produce images 15 times sharper than Hubble with a light-collecting area bigger than all existing optical research telescopes combined

The ELT will tackle the biggest scientific challenges of our time, and aim for a number of notable firsts, including tracking down Earth-like planets around other stars in the “habitable zones” where life could exist — one of the Holy Grails of modern observational astronomy. It will also perform “stellar archaeology” in nearby galaxies, as well as make fundamental contributions to cosmology by measuring the properties of the first stars and galaxies and probing the nature of dark matter and dark energy. On top of this astronomers are also planning for the unexpected — new and unforeseeable questions will surely arise from the new discoveries made with the ELT.

Science goals

General purpose extremely large aperture optical/infrared telescope. Some science areas are to be high redshift galaxies, star formation, exoplanets and protoplanetary systems.

The telescope’s developer is the European Southern Observatory (ESO), an organization founded in 1962 whose 16 members include most of the larger countries in Europe and Brazil. The ELT will be the successor to ESO’s Very Large Telescope, which aggregates the images from four telescopes, each with a 10-foot main mirror.


ELT vs. existing telescopes.

Extremely Large Telescopes are considered worldwide as one of the highest priorities in ground-based astronomy. They will vastly advance astrophysical knowledge, allowing detailed studies of subjects including planets around other stars, the first objects in the Universe, super-massive black holes, and the nature and distribution of the dark matter and dark energy which dominate the Universe.

Since 2005 ESO has been working with its community and industry to develop an extremely large optical/infrared telescopes.

Dubbed ELT for Extremely Large Telescope, this revolutionary new ground-based telescope concept will have a 39-metre main mirror and will be the largest optical/near-infrared telescope in the world: “the world’s biggest eye on the sky”.

The ELT programme was approved in 2012 and green light for construction was given at the end of 2014. The first stone ceremony for the telescope was attended by the President of Chile in May 2017. First light is targeted for 2024.

ESO describes the light-collecting area of the ELT as bigger than all existing optical research telescopes combined. Like all modern earth-based telescopes, it relies on adaptive optics, a computer-controlled system of creating tiny deformations in the surface of the mirror to compensate for atmospheric turbulence.

Oxford University scientists are contributing a spectrograph designed to take 4,000 simultaneous images, each in a different color.

The telescope and supporting infrastructure will weigh some 3,100 tons. It will be housed in a rotating dome, which, itself, will weigh roughly 5,100 tons. Big.

Credit: ESO

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