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Tuesday, 9 July, 2002, 16:34 GMT 17:34 UK
World's largest telescope: Ask the director
Dr Roberto Gilmozzi, director of the Paranal Observatory, answered your questions in a LIVE forum.

  Click here to watch the forum.  

  • Click here to read the transcript

    British astronomers are about to get their hands on the world's largest optical telescope facility.

    UK science is paying millions of pounds to join the European Southern Observatory (Eso) organisation, which includes access to the Very Large Telescope (VLT) on Cerro Paranal in the Atacama Desert, northern Chile.

    This extraordinary facility can delve deep into the Universe, focussing on objects with unprecedented clarity.

    What can the VLT do? How does it differ from the other giant telescopes? What is life like in the middle of the Atacama desert?


    Transcript


    Newshost:

    Hello, I'm Christine McGourty and welcome to this BBC Interactive forum on the future of British astronomy. This week, the UK formally joined the European Southern Observatory organisation. This will give astronomers in this country an input into some of the most exciting telescope projects of the next two decades.

    More immediately, membership gives UK astronomers direct access to the world's largest optical telescope facility - the so-called Very Large Telescope or VLT at the Paranal Observatory in the Atacama Desert in northern Chile.

    The VLT consists of four 8-metre telescopes that can work individually or in tandem, producing remarkable images of the distant reaches of the Universe. I'm pleased to welcome Dr Roberto Gilmozzi, the Director at Paranal, who is going to answer your questions about this amazing facility

    Dr Gilmozzi we have a long list of questions for you here. The first one is from Chennai Ramnath from India who asks: In which areas will the VLT significantly contribute to our understanding of the Universe?


    Dr Roberto Gilmozzi:

    I would say mostly in two areas. One is cosmology because the fact that you have a very powerful telescope means that you can observe very faint objects and mostly in astronomy very faint means also very far. It will allow us to try to understand the evolution of the Universe and go back in time and see what happened back then. The other area certainly is in the search for planets where the VLT, especially in its combined form, is very suited for this task.


    Newshost:

    Gabe from the UK asks: What are the benefits of having the telescope in the Atacama Desert?


    Dr Roberto Gilmozzi:

    The Atacama Desert is one of the driest places on Earth and astronomers like dark skies without clouds. So being in the middle of the desert like that one, where the closest inhabited place is 120 kilometres away, there is no light pollution. It is very, very dry so very rarely, apart from when you were there, there are a lot of clouds; so it is really a fantastic place for astronomy. In fact, it is also protected by Chilean law, to maintain these qualities for astronomy. So, it is really an excellent place.


    Newshost:

    Harjinder Degun from the UK asks: How does the VLT compare to the Hubble Space Telescope (HST)? Is the VLT better?


    Dr Roberto Gilmozzi:

    Well in certain things certainly. It is difficult to make a comparison because the Hubble telescope is outside the atmosphere and therefore can see wavelengths of light that are blocked by the atmosphere for ground-based telescopes and therefore it is an unfair comparison. However, where they do observe in the same wavelength region, before HST had an advantage because being outside the atmosphere it was not suffering from the turbulence of the atmosphere which tends to smear out the images. With the new technology, called the adaptive optics, we now can compensate for this turbulence in the atmosphere and therefore our images begin to be favourably comparable with the ones of the HST.


    Newshost:

    Nicolas Brachet from Canada asks: What can the VLT do that the 10-metre Keck telescopes in Hawaii cannot? Are the Kecks not bigger?


    Dr Roberto Gilmozzi:

    The Kecks are bigger as individual telescopes; the VLT however has twice as many telescopes and so the total collecting area of the VLT is larger than the total collecting area of the two Kecks. Of course, there is a lot of science and scientific capabilities that are in common between the two telescopes and the difference between the two sides accounts for some advantages for the individual Keck telescope.

    The advantage of the VLT, however, is that it has been built as an interferometer from the start. In other words, we planned this project - or Eso planned this project - so that the VLT telescopes could act together, and it is in this sense where the largest advantage of the VLT will come, when the interferometer will be working, joining not only two telescopes at the time but all four of them at the same time, and in a sense mimicking a telescope of 100 metres in diameter in terms of resolution.


    Newshost:

    BF from London asks: The Paranal site is 2,600 metres high, while US Keck facilities in Hawaii are above 4,000 metres high. Is the Paranal site high enough to be free of atmospheric disturbances? Is the air drier there than in Hawaii?


    Dr Roberto Gilmozzi:

    There are statistics in which Paranal has an advantage due to its extreme dryness. It really is amazingly dry.


    Newshost:

    Drier than Hawaii?


    Dr Roberto Gilmozzi:

    Oh yes, definitely. Although the telescopes in Hawaii are most of the time above the cloud bank, like we are. That area of the world is much more prone to perturbations, etc. than the Atacama Desert is.

    So I would say that the two sides compare very favourably with each other and of course the advantage of Mauna Kea is being higher; there is slightly less precipitate vapour in the atmosphere than might be on Paranal some times. But for all the rest, the two sides are very much comparable.


    Newshost:

    Andrew Simpson from the UK asks: Will the VLT be able to image directly a terrestrial-sized planet outside our Solar System?


    Dr Roberto Gilmozzi:

    That's an interesting question. It depends very much on the assumption that you make to give such an answer. Certainly the VLTI (interferometer), when it will work with the four telescopes together, will give it the best shot that they can and it will be able to image some planets. Now, an Earth-like planet is not something easy to image. Consider the Earth and the Sun for a moment. The brightness of the two, even at favourable wavelengths of light, is of the order of ten billion times. And to detect something 10 billion times fainter next to something very, very bright is not easy and you have to try to increase your resolution very much so you can separate them out. And even the VLTI can do that only up to something like 50-60 light-years from us, which means that if there are planets there, yes we would be able to image them but it is not a certainty - we certainly hope so.


    Newshost:

    And the VLTI is a VLT working as an interferometer?


    Dr Roberto Gilmozzi:

    Yes, it is called a VLT interferometer.


    Newshost:

    Zinedine from Malaysia asks: How can people follow the latest findings of the VLT?


    Dr Roberto Gilmozzi:

    That's easy. We have a website where we publish all our press releases which very often contain the latest results that have been achieved with the telescopes. The website is www.eso.org.


    Newshost:

    Kyle McDonald from the USA asks: If you could see it, what would you expect the edge of the Universe to look like within the visible spectrum of light?


    Dr Roberto Gilmozzi:

    It is not an easy question to answer. The edge of the Universe, in astronomical terms, is actually the beginning of the Universe because the further away we look, since the speed of light is finite, the more back in time we look; and so looking at the edge of the Universe is a strange expression to be used in astronomy but I take it to mean going backward as much as possible - as far away from us as we can.

    It is not easy to answer because it depends - we don't really know exactly how the Universe went from the Big Bang to what we see today which is galaxies, stars, planets, people, etc. Therefore, what is really down there is what we would like to understand and to study and that's why we are building all these telescopes. Now there is an epoch up to about 300,000 years after the Big Bang which will never be visible to us at visible wavelengths. The Universe is too hot for the light to not be continuously absorbed by the matter that was there. After that, we presumably would be able to see the proto-galaxies, the beginning, just the first wave of star formation when the first common formation of matter started collapsing and becoming hot enough to produce the nuclear reactions that created stars. But this is just what we expect to see but we want to go and see to give the proper answer.


    Newshost:

    Another question from one of our readers: How hard was it to manufacture the mirrors for the VLT?


    Dr Roberto Gilmozzi:

    Very. These mirrors are special in a sense. The VLT uses a technology called the active optics in which the mirror is maintained at its almost ideal shape all through the observations and all through the pointings that a telescope does through the 150 actuators below the mirror that push and pull to maintain the shape. The mirror has to be flexible in a sense to allow you to do that and although this flexibility is of the order of microns - it is not moved by millimetres - means that the mirror is very, very thin compared with its size - it is 8.2 metres in diameter but only 17 centimetres thick to allow you to be able to apply these forces. This has meant that the fabrication of this mirror has been particularly difficult and a careful exercise and also polishing it was a very, very long activity that took about a year and a half.


    Newshost:

    Dr Jain from Canada asks: Is it possible at all to use this facility to observe and detect potential Earth-impacting asteroids?


    Dr Roberto Gilmozzi:

    Not as such. Large telescopes do not have a very wide field of view although they can go very deep; typically they don't do it on a very large portion of the sky and to detect asteroids the larger your field of view the likelier it is that you can see them. Therefore, smaller telescopes with a much wider field of view are used to detect asteroids. Of course, a telescope like this would then be able, once an asteroid is detected, to make very detailed studies of its chemical composition - how it's kept together, etc. But I would say it has no direct impact in detecting asteroids. Of course, there are some asteroids that we see in our pictures just as streaks going across our deep exposures, but it is very difficult for us to even find them afterwards because this is not something that we do. We study asteroids but we go and look for them explicitly.


    Newshost:

    Boris Zupanic from Croatia asks: With improvements provided by adaptive optics systems, do we need space-based telescopes?


    Dr Roberto Gilmozzi:

    There are wavelengths of light that cannot be seen from the ground and therefore in those wavelengths there is no doubt that the space-based telescopes are our only option. However, now that adaptive optics is beginning to give very good results, then there are some wavelength regions where things can be done from the ground probably with a much cheaper experiment than you would be able to do from space or for the same amount of money with much bigger telescopes. So, indeed there is a sort of specialisation now for these facilities in which each one can concentrate on the things that they can do best. Certainly today observing in the very near infra-red with adaptive optics is competitive from the ground with regard to space-based operations.


    Newshost:

    Graham Little from the UK asks: How do you decide who gets time on the telescope, and does money play a major part in this, i.e. the biggest contributor financially gets the most time on the telescope?


    Dr Roberto Gilmozzi:

    Time is allocated by a time allocation committee that is made up of people that do not belong to the organisation and they meet together and judge the scientific validity of proposals and then they make a list and we try to get as many as we can fitted in during a certain period of time. The committee meets every six months.

    There is no provision to have a direct link between the contribution of a country to the Eso budget and the number of nights that they get. On the other side is a self-regulating process because a country that pays more typically means that it has more people which means that there are also more astronomers putting in more proposals. And the number of good proposals to the total number of proposals is more or less the same everywhere and therefore in the end it does happen that larger countries do get more time than smaller countries. But it is not decided before - it just happens to be that way.

  • The UK joins the European Southern Observatory.


    VLT FORUM

    FACT FILE
    See also:

    05 Dec 01 | Science/Nature
    04 Dec 01 | Science/Nature
    25 Mar 99 | Science/Nature
    25 Mar 99 | Science/Nature
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