The guiding lasers of the ELT

ELT: ESO’s new eye is halfway to completion

ESO has reached half the construction of the biggest optical telescope ever built (ELT) and is promising to revolutionize the way we see the Universe

Many define the sky as the limit, but ask an astronomer, an astronaut, or a pilot and they will deny it. To reach this limit and overtake it, humans are building bigger and more sophisticated telescopes. Today the largest operative optical telescope is the Gran Telescopio Canarias (GranTeCan or GTC) with its 10.4 meters of diameter, but this size is no longer sufficient. ESO (European Southern Observatory) is building a new bigger telescope in the Chilean desert. A telescope with a main mirror diameter of 39 meters, capable to gather 100 million times more light than the human eye and 8 million times more than Galileo’s telescope. This is the Extremely Large Telescope (ELT).

ELT and its laser beams
The ELT and its laser beams. Credits: ESO


How are works going?

It’s news these weeks that the construction of this colossal telescope was half completed. This is a telescope with a five-mirror design. The main giant mirror (M1) is made of 798 hexagonal segments and more than 70% of their supports have been completed, while the second and third mirrors are being polished.

An important feature of this telescope is its adaptive optics system, able to sharpen images that otherwise would be distorted due to atmospheric turbulence. This system couldn’t work without the six laser sources that have been completed and sent to ESO for testing.

Construction development of ELT. Credits: ESO

All the instruments the ELT will be equipped with are in the final part of the design and are about to be produced. Moreover, almost all the support infrastructures for the ELT are in place or on their way to the Cerro Armazones (where the ELT is placed at 3046 m). Among them, are the technical building and the photovoltaic plant that started supplying renewable energy to the ELT site last year.


How much until its completion?

This first half of the observatory encountered a lot of difficulties that slowed down the project. Reaching this point of the project, indeed, required a meticulous process to finalize the design of most components, and some of them, like mirrors and sensors, needed the realization of prototypes and heavy testing. In addition, the pandemic due to COVID-19 closed the construction site for months as well as the telescope components production industries in Europe.

Completing the construction is estimated to require less time. The telescope structure is expected to be concluded by 2026 and become operative by 2028 when the ELT undergoes scientific verification.

The ELT under construction
The ELT under construction. Credits: ESO


Why do we need such a large telescope?

Building larger telescopes has mainly two benefits: more light collected and higher detail. Increasing the diameter of a telescope, then, opens new ways to study the Universe. Just think that the Very Large Telescope (VLT, an array of telescopes part of ESO in Chile) today can discover new planets in other solar systems by studying the behavior and characteristics of a star. With the ELT instead, ESO expects it to be able to take pictures of those planets (in particular the rocky ones) and study their atmosphere. Its tasks, however, don’t stop here. The ELT will explore the first stars and galaxies helping cosmologists in understanding the evolution of the Universe but will also assist in unveiling what dark matter and dark energy are. According to ESO, the most significant contribution is still unexpected, as it will arise from the discoveries that the ELT will achieve as well as the first telescope done during the summer of 1609.

The ELT in construction under the Chilean sky
ELT under the Chilean sky. Credits: ESO

Being halfway to completion of the Extremely Large Telescope, then, set Humanity not only nearer to achieving a marvelous engineering milestone. This set Us a step nearer to answering those questions that have troubled our species since the dawn of time like where did we come from? Or are we alone in the Universe? Projects like the ELT make us aware that we can pursue these answers and are destined to find them.

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Matteo Ferrarini

Matteo Ferrarini

B.Sc in aerospace engineering, now studying the world of renewable energy. Always looking at the stars, but sometimes you can find me underwater.

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