Boom! Mountain makes way for a telescope

This week, 3000 metres up a Chilean mountain, scientists pressed the button to blow up half a million tonnes of rock....
24 June 2014

Interview with 

Gerry Gilmore, Institute of Astronomy, Cambridge University


This week, 3000 metres up a Chilean mountain, scientists pressed the button to blow up half a million tonnes of rock. The mountain's called Cerro Armazones and the reason it was being blown up was to create the site for what will become the world's biggest most powerful optical telescope. With typical scientific understatement, it's known as the European Extremely Large Telescope or EELT. Gerry Gilmore, from the Institute of Astronomy at Cambridge University, is part of the the E-ELT initiative and spoke to Chris Smith about the work...

Gerry -  It's designed to be the biggest optical and near-infrared telescope yet built.  It will be maybe twice as big as its nearest computer, four times bigger than the biggest that we have today.  And will allow us by the way of these things to go maybe a hundred times deeper and fainter into the universe.

Chris -  When we say optical telescope, what does that mean?

Gerry -  It means this thing is especially designed to work on the same light that we see by eye, but also on the heat that we feel on our skin.  So, it doesn't study radio waves.  It doesn't study the frequency that this programme is going out on.  It doesn't study the far-infrared because that invisible from the ground.  You have to go into space to do that, but the sort of warm end visible light is where all the normal star shine actually, that's why we look that way.

Chris -  When we say big and extremely large, this imaginative name for this telescope, how big actually is it?

Gerry -  They're pretty dull names, aren't they?  The predecessor was called the very large telescope so we go ahead and ran into humongous soon I think, but is big.  The mirror is just under 40 meters which is about 40% of a size of a football field.  So, it's big and that's the glass, the mirror.  The telescope structure itself is maybe twice that size.  It's a huge big thing.

Chris -  When we say 40 meters is the mirror, is that one single piece of glass or is it the mirror equivalent of an insect eye - lots of little mirrors that all work together?

Gerry -  It's exactly the second, yes.  You can't make one big mirror or even if you could, that would be kind of difficult to carry at the side of a mountain.  So, it's actually made of over a thousand small mirrors each which is about a meter in size actually.  They're little hexagons that'll fit together just like the panels on a football.  Except there's about a thousand of these things and they're all each individually controlled so that they're acting as if they're a single large mirror.

Chris -  And this means that you can - I presume - focus or tweak the performance of the telescope very, very accurately because you can move each of these individual elements and therefore, overcome aberrations in the moving a little bit or gravity or the atmosphere.

Gerry -  Yeah, that's the reason that these things are multi-mirror.  Any structure that big sags under its own weight, it gets blown around by the wind, and it shakes, there are these little earthquakes shaking things all time anywhere on Earth.  And so, having a large number of mirrors, each of which is fine-tuned about a thousand times a second, allows us to correct for this real-time disturbance function and produce a telescope that works.  Although it's big, bigger than anything else, it will work very much higher precision than anything we have done before as well.  So, we get really, really sharp image quality.

Chris -  Why at the top of a mountain in Chile?

Gerry -  Yes, you're right.  We have a little bang so that we do better at studying the Big Bang.  But the reason we go to high mountains is basically to get away from the water and dust in the air.  The reason that stars twinkle and everything blue is out at night is because of water in air.  So, you have to high and dry.  And the highest and driest place on Earth is the northern Andes in Chile.  So, there are a lot of telescopes up there.  It's the best site on Earth in which to actually do astronomy.

Chris -  And the bang was to level off the top of the mountain just to make the site good.

Gerry -  Yes. Mountain tops in general don't come flat and so, telescopes need to be on a flat base and hard rocks.  So, you got to get rid of all the fractured rubbish and clean it off so that you get a good solid foundation.

Chris -  You've said that this will return stunningly good quality images which are far more powerful, much than we've ever been able to see before.  But what exactly will you be able to do with this telescope?  What are the goals of this mission?

Gerry -  Well, size matters in telescopes for two reasons.  The first is, bigger collection gives you more light so you see fainter objects.  And so, you can get much more detailed studies on the oldest things in the universe, the first things that had formed only a few hundred million years after the Big Bang.  And we can detect these things for things like the Hubble Space telescope and no more than that.  This telescope is designed to allow us to study them in detail.  But the other thing you can do with the big telescopes is you have a lot more magnification.  If you've got good image quality, so that you can then look at things that are very close to other things and a particular challenge here is to look for planets around other stars, measure their colours and see if we can find an Earth-like planet at the right distance from its parent star and see if it goes white in winter and green in summer.

Chris -  In other words, we'll be able to see bodies - these distant planets, which are much smaller than those we can see at the moment because we can see loads of planets around other stars, these exoplanets.  But they're all big ones, aren't they?

Gerry -  Yeah, they're big ones and also, they're mostly seen only indirectly.  We see them by actually measuring all of the light plus the star, plus planet and then subtracting off what we see when the planet goes around the back.  And so, you're actually measuring a difference between two very large numbers which is quite hard to do accurately.  With enough magnification, and enough light collection, you'll actually see the planet as a planet.  So, you'll have a real image of a real independent planet.

Chris -  I'd like to finish by asking you about the price tag and the delivery date for this.  So, when will this telescope go live and how much is it costing?

Gerry -  The cost will be about one and a quarter billion Euros in today's money.  The project started a bit going on for 15 years right now.  It should be finished in principle in another 10 years from now, that depends on cash flow and technical issues.

Chris -  And who is paying for this?

Gerry -  It's funded by Europe, the European Southern Observatory, that's a collection of 20 odd countries, all obvious western European countries, but with a couple of other significant partners including Chile of course - the host country - and Brazil, which is joining European Southern Observatory as part of a much bigger programme to combine Brazilian science with European science.  And so, their joining fee provides the crucial extra money.  So, we're all hoping though they win this World Cup and feel happy, and turn up with a cheque pretty soon.

Chris -  Have they not paid yet?

Gerry - It takes a long time to get things through the Brazilian parliament.  The deal was signed by President Lula 5 years ago.  But getting things through multicomplex political structures takes time.

Chris -  How much do Brazil owe you?

Gerry -  It's only a third of a billion,  I mean, it's small change compared to a football game.

Chris -  Do you think they've invested it in the World Cup rather than in your telescope then?  Is that why they're late?

Gerry -  They might have borrowed it, yeah...!


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