The world’s largest telescope under construction; unironically called Extremely Large Telescope

By Brian Santo, contributing writer

Ground was broken on the foundation for what will be the largest telescope on the planet by far. The Extremely Large Telescope (ELT) will incorporate a main mirror that will be about 128 feet, or farther than you can throw unless you’re an NFL quarterback or MLB player. Its builders expect that it will provide images 15 times sharper than those of the Hubble Space Telescope at the same wavelength.

The ELT is part of an unprecedented boom in advanced telescopes that will let astronomers get much clearer views far deeper into space. Targets could include exoplanets, black holes, novae, developing galaxies, and other objects. They might help identify theorized dark matter. Astronomers are practically giddy about the prospects.

The ELT is being built at Cerro Armazones, Chile, on a levelled-off mountain in a thoroughly sere landscape at just under 10,000 feet altitude and roughly 50 miles south of the nearest city, Antofagasta (pop. 345,000). Remote from city lights, and with a cloudless rate of 89% a year, the general area is already home to a set of other research telescopes. It is scheduled to be operational in 2024.

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.

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.

ELT is one of four enormous ground-based telescopes at various stages of development.

The Giant Magellan Telescope , set to begin operation in 2025, will have a hex of 27-foot mirrors surrounding a seventh; the effective diameter will be about 80 feet. The operator is a consortium of research organizations in the United States, Australia, and Brazil. GMT will be a close neighbor of the ELT in Chile.

Another proposal is the Thirty Meter Telescope which, since we’ve been doing feet, is just about 100 of them. The TMT is backed by a non-profit company whose members include several U.S. and Canadian universities who, before joining together, were pursuing three separate telescope projects. Science academies from China, Japan, and India are also now participating. The fate of the project is uncertain. The plan was to build the observatory on Mauna Kea in Hawaii, but the state is grinding through lawsuits that object to the project on both religious and environmental grounds.

The Large Synoptic Survey Telescope , backed by a non-profit with nearly 40 participating research organizations, will have a 27-foot mirror, smaller than some of the others, but the LSST is aiming at something else. With two subsidiary mirrors and a highly sophisticated 3,200-megapixel camera, it will be able to provide highly detailed wide-field views — hence, the word “survey” in the name. The LSST is scheduled to become operational in 2023.

The cost of lofting and maintaining anything like the ELT, or even the LSST, in space is prohibitive. Space-based telescopes such as the Hubble Space Telescope, meanwhile, have advantages that no terrestrial telescope can hope to even match. They can be smaller, and they can easily detect wavelengths that the Earth’s atmosphere can distort or absorb. And they can be operative all day instead of only at nighttime.

These advantages are why the Hubble is soon to get a partner, the James Webb Space Telescope . The JWST is an infrared telescope with a 20-foot primary mirror. It is scheduled to be launched in October of 2018.