Building Has Started On The Extremely Large Telescope

Artist's rendition of what the ELT will look like. The lasers are used to create reference artificial stars in the atmosphere. ESO/L. Calçada

The first stone of the Extremely Large Telescope has been laid in Chile, which means the construction of the dome and telescope has now officially begun. The Extremely Large Telescope (ELT), as the name suggests, will be the biggest optical telescope in the world, with the main mirror 39 meters (128 feet) in diameter.

The ELT is the latest project by the European Southern Observatory (ESO), a 16-nation consortium of European and South-American countries. The telescope is being built near ESO’s Paranal Observatory in Northern Chile, and a ceremony took place there last week to celebrate the beginning of construction.

"With the symbolic start of this construction work, we are building more than a telescope here: it is one of the greatest expressions of scientific and technological capabilities and of the extraordinary potential of international cooperation," Chilean President Michelle Bachelet said during the ceremony.

With a rotating dome 82 meters (269 feet) across, the ELT has already had quite an impact on a specialized sector of astronomy: telescope engineering. The ELT is a tremendous challenge and everything about it is a record breaker. The secondary mirror has just been cast and at 4.2 meters (13.8 feet) in diameter, it is the largest secondary mirror ever and also the largest convex mirror ever produced.

The secondary mirror is larger than the primary mirror of most telescopes. It’s also both strongly curved and aspherical to avoid aberrations in the light the telescope will observe.

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The secondary mirror being transported. SCHOTT/ESO

"This is a milestone in ESO's history, the ELT will be the most powerful and ambitious telescope of its kind," Patrick Roche, president of the ESO Council, added. "We have reached this point thanks to the efforts of many people in the Member States of ESO, in Chile and elsewhere, over many years. I thank them all and am delighted to see many of them here today, celebrating on this occasion."

The scientific goals of the ELT are as ambitious as its size. ESO hopes that the telescope will discover planets as small as Earth, as well as directly image the largest exoplanets. The ELT will take precise measurements of the furthest objects in the universe, which will allow astronomers to learn how they form and better understand the universe as a whole.

"The ELT will produce discoveries that we simply cannot imagine today, and it will surely inspire numerous people around the world to think about science, technology and our place in the Universe," Tim de Zeeuw, director general of ESO, stated. "This will bring great benefit to the ESO Member States, to Chile, and to the rest of the world."

The telescope will see first light in 2024, but it's already being hailed as the beginning of a new era in astronomy.

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