The Extremely Large Telescope

The European Southern Observatory (ESO) is planning on building a massive – and I do mean massive – telescope in the next decade. The European Extremely Large Telescope (E-ELT) is a 42-meter telescope in its final planning stages. Weighing in at 5,000 tonnes, and made up of 984 individual mirrors, it will be able to image the discs of extrasolar planets and resolve individual stars in galaxies beyond the Local Group! By 2018 ESO hope to be using this gargantuan scope to stare so deep into space that they can actually see the Universe expanding!

The E-ELT is currently scheduled for completion around 2018 and when built it will be four times larger than anything currently looking at the sky in optical wavelengths and 100 times more powerful than the Hubble Space Telescope – despite being a ground-based observatory.

With advanced adaptive optics systems, the E-ELT will use up to 6 laser guide stars to analyse the twinkling caused by the motion of the atmosphere. Computer systems move the 984 individual mirrored panels up to a thousand times a second to cancel out this blurring effect in real time. The result is an image almost as crisp as if the telescope were in space.

This combination of incredible technological power and gigantic size mean that that the E-ELT will be able to not only detect the presence of planets around other stars but also begin to make images of them. It could potentially make a direct image of a Super Earth (a rocky planet just a few times larger than Earth). It would be capable of observing planets around stars within 15-30 light years of the Earth – there are almost 400 stars within that distance!

The E-ELT will be able to resolve stars within distant galaxies and as such begin to understand the history of such galaxies. This method of using the chemical composition, age and mass of stars to unravel the history of the galaxy is sometimes called galactic archaeology and instruments like the E-ELT would lead the way in such research.

Incredibly, by measuring the redshift of distant galaxies over many years with a telescope as sensitive as the E-ELT it should be possible to detect the gradual change in their doppler shift. As such the E-ELT could allow humans to watch the Universe itself expand!

ESO has already spent millions on developing the E-ELT concept. If it is completed as planned then it will eventually cost about €1 billion. The technology required to make the E-ELT happen is being developed right now all over the world – in fact it is creating new technologies, jobs and industry as it goes along. The telescope’s enclosure alone presents a huge engineering conundrum – how do you build something the size of modern sports stadium at high altitude and without any existing roads? They will need to keep 5,000 tonnes of metal and glass slewing around smoothly and easily once it’s operating – as well as figuring out how to mass-produce more than 1200 1.4m hexagonal mirrors.

The E-ELT has the capacity to transform our view not only of the Universe but of telescopes and the technology to build them as well. It will be a huge leap forward in telescope engineering and for European astronomy it will be a massive 42m jewel in the crown.

Robert Simpson

View Comments

  • Wow, this is the most exciting astronomy news i've heard in a long time. Just how 'clear' will it be able to take images of stars and planets? Will we be able to make out color differences on their 'surfaces'?

  • Will this thing have satellite observatories, too, to allow for interferometry? That way they'll have even better resolution.

  • I would sell all of my limbs to be able to work at this observatory. I would literally spontaneously combust and simultaneously have multiple orgasms upon viewing a telescope mirror of this size.

    I wonder what behemoths they are going to be pointing around in 100 years? Damn you relatively short life span!

  • I read in the AAAS Science about this, and the debate between segmented mirrors and single large mirrors. I think that segmented mirrors are clearly the better option for costs and replacement costs if there is damage to the surface. Optical interferometry is also a good option as well. This can reduce the tendency towards gigantism, and giant budgets as well.


  • Is it possible that a telescope like this could be used in conjunction with a space based telescope like Hubble to get even better images of distant objects, like extra-solar planets?

  • I already heard about this... a friend who is working at Paranal Observatory told me, that they are going to build it there. I really hope, that i will be able to work at this Telescope in 2018...

  • # Molecular Says:
    November 24th, 2009 at 12:10 am

    "Is it possible that a telescope like this could be used in conjunction with a space based telescope like Hubble to get even better images of distant objects, like extra-solar planets?"

    If you mean for interferometry, like commonly employed for radio telescopes and like they do by combining the light from the two Keck telescopes or the four VLT telescopes in Chile, then no - not with any currently available technology, nor any technology that would become available any time soon. To do optical interferometry, you need to combine the light from the different telescopes with path lengths equal to within a small fraction of the wavelength of the shortest wavelength of light you are interested in. So, say you want the full visible spectrum, that would be a small fraction of 400 nanometres. This has only very recently become achievable with stationary ground telescopes separated by no more than a few hundred metres. The Hubble, on the other hand, is wizzing around Earth much faster than a rifle bullet travels, in a roughly though not precisely circular orbit. Relative to the stationary EELT, it's motion would be even more complex. Not to mention slight perturbations to it's orbit due to small gravitational anomalies that would become important at this level of required precision. There is simply no physical way to combine the beams from these telescopes for interferometry, or to record the observations and correlate the signals later on for optical wavelengths.

  • Interferometry requires phase information from the EM radiation detected. For radio telescopes the detected EM radiation is converted into an EM wave on a transmission line from each dish, and these are then combined via wave mechanics to emulate what is detected by a very large dish. This can be done with optical systems, but the wavelengths of light are far smaller and the technical challenge more difficult.

    Optical interferometers employ beam splitters and optical fiber. Optical interferometers are then precise optical bench systems. So optical interferometry involves precise phasing information and exact positioning information. Getting this from a range of scopes in orbit would be difficult in the extreme.


  • This is one of those things where so many items come to mind, I have no idea which one to say... so I'm left speechless.

    I truly hope they can finish it before the end of the next decade.

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