A new era of astronomy: Construction of the 39m Extremely Large Telescope dome & main structure officially starts

30 May 2017 by Aprajita Verma

Montage of images related to the ELT's First Stone Ceremony (image credits below)

On Friday 26th May 2017, a major milestone in construction of the world’s largest visible and infrared telescope, the European Southern Observatory’s (ESO) Extremely Large Telescope (ELT), was reached. In the presence of President of the Republic of Chile, Her Excellency Michelle Bachelet Jeria, over 200 people attended the ELT’s ‘First stone’ ceremony at nearby Cerro Paranal, to mark the start of construction of the dome and main structure and the connection of the Cerro Armazones Observatory, where the ELT will be sited, to the Chilean power grid. Oxford Astrophysics’ Professor Patrick Roche, currently serving as President of ESO’s Council, was in attendance at this exciting event.

He said, "This is a milestone in ESO's history, the ELT will be the most powerful and ambitious telescope of its kind. 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."

President Bachelet Jeria emphasised “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.”

The ELT will have a primary mirror of 39 m in diameter, made up of 798 hexagonal segments. This is about 40 per cent the length of a football pitch, enclosed within what will be the world’s largest telescope dome, more akin in size to sports stadia than telescopes! For Oxford locals, the width of the lawn around the Radcliffe Camera is about 39m. The 978 square meter collecting area of this mammoth mirror is larger than the sum of all (2 m and larger) telescopes put together, roughly the area of three and half tennis courts worth of high precision mirrored surface. This large mirror will collect enough light to detect the faintest objects in our Universe, and using adaptive optical elements, the telescope will deliver images that are corrected for distortions caused by turbulence in the Earth’s atmosphere. The ELT will provide vistas of the Universe in exquisite detail, about 16 times sharper than the Hubble Space Telescope. We know that the combination of sensitivity and angular resolution (detail or sharpness) delivered by this telescope has transformational potential in furthering our knowledge of the Universe. It will address numerous areas of research, including studying the earliest galaxies that formed after the Big Bang, constraining dark matter and energy and directly imaging extra-solar planets and the disks in which they form. But the most exciting aspect of this project is actually all the science that it will enable that we can’t even predict yet.

Professor Tim de Zeeuw, Director General of ESO, said: “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. This will bring great benefit to the ESO Member States, to Chile, and to the rest of the world.”

As a member state of ESO, UK scientists will have access to this world leading facility. Moreover, a group of UK Universities and research centres have major involvement in the programme to design and deliver instruments that will be mounted on the telescope. In particular, one of the first two instruments on the telescope is called HARMONI and Oxford’s Professor Niranjan Thatte is leading the European consortium that will build it. HARMONI is a very powerful and versatile instrument that can simultaneously take images of the celestial objects and regions at ~4000 slightly different wavelengths. This type of data allows us to perform scientific studies over a very wide range of astrophysical questions. For example, we will be able to determine the motion and state of stars and gas in regions of the Milky Way but also in distant galaxies, from those nearby to those that reside in the very young Universe. This gives us important information on the interplay of stars, gas and chemistry in these objects, as well as the influence of black holes providing key constraints on the formation and evolutionary history of the galaxies we observe.

Professor Niranjan Thatte said: ‘The ELT will bring many advances in state-of-the-art, it is the combination of a large increase in collecting area and a sharp improvement in spatial resolution (image sharpness) that will open new vistas in observational astronomy. HARMONI is a work-horse instrument, it will tackle many different observing programmes, from planets in our own solar system and around other nearby stars to studying the formation and evolution of the most distant galaxies with unprecedented depth and precision.’

Oxford Astrophysicists are also involved in research and development for the Multi-object Spectrograph for the ELT that can take spectra of many objects over the full ELT 10 arc minute field in one shot. Prof Gavin Dalton leads Oxford’s work on this ambitious instrument that will address many open questions including understanding how galaxies formed and evolved and making a census of stars in nearby galaxies (so called "stellar archaeology"). We are also contributing to R&D for the ELT Planetary Camera & Spectrograph (Oxford lead Dr Matthias Tecza). This instrument will make use of the ELT’s superb sensitivity and resolution to observe faint exoplanets lying close (and possibly within the habitable zone) to their parent stars. We will be able to tell whether the planets are gas giants (like Jupiter) or rocky (like the Earth), and also study their atmospheres. Such observations could lead to the tantalising possibility of detecting “signs of life” on extra terrestrial planets.

With the beginning of construction and first light scheduled for 2024, the forthcoming years are exciting times and members of Oxford Astrophysics are looking forward to contributing to the World’s Biggest Eye on the Sky!

Further information & videos can be found at ESO

The ELT first stone ceremony was covered by Lanisha Butterfield (Oxford)

Further information on the UK involvement in the ELT is available at

Further information on the overall ELT project

Image credits: ELT rendering by ESO/L. Calçada, Pat Roche on a visit to Cerro Armazones with Cerro Paranal in the left background (P. Roche), Panorama from Cerro Armazones (P. Roche), Panorama of the Cerro Paranal Resedencia with VLTs (ESO), Waiting for the First Stone Ceremony (P. Roche), Pat Roche meeting with the President of the Republic of Chile at the first stone ceremony (ESO/Juan Pablo Astorga).

Categories: ELT | E-ELT | Instruments | technology | telescopes | exoplanets | galaxies | stars | stellar populations