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Thread: European Extremely Large Telescope (ELT) Gets the Green Light

  1. #1
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    European Extremely Large Telescope (ELT) Gets the Green Light

    Here's a link to the article.

    I'm curious as to how it manages to manipulate the 800 hex segments in order to produce a good image. I thought primary mirrors had to be polished to micrometer tolerances for clarity.

    Are the individual hex segments themselves warped by machine/computer to achieve proper curvature?

    I'm still in awe of the size -- 39 meters! When I first became interested in Astronomy, the Hale Telescope (Mt. Palomar) was still the largest at 200 inches. The ELT, at 1,535 inches, is 7.6 times larger in diameter, but has almost 60 times the light-gathering area!

  2. #2
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    Quote Originally Posted by DoggerDan View Post
    I'm curious as to how it manages to manipulate the 800 hex segments in order to produce a good image. I thought primary mirrors had to be polished to micrometer tolerances for clarity.

    Are the individual hex segments themselves warped by machine/computer to achieve proper curvature?
    Yes, they are. This is not the first telescope to use that technology, you can look up "segmented mirror" and "active optics", for example in Wikipedia:
    http://en.wikipedia.org/wiki/Segmented_mirror
    http://en.wikipedia.org/wiki/Active_optics (this one even has a picture of the actuators)

    The twin Keck telescopes in Hawaii for example are 36 segments each.
    (English is not my first language, so please excuse any mistakes and unintended ambiguities.)

  3. #3
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    It was a huge blow to my region when the decision was made to build it in Chile, not here (Canary Islands), which was quite a good contender at one point. I'm glad that scientific criteria were chosen over political ones.

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    The secondary on that sucker will be almost as large the Hale primary.

  5. #5
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    Don't you just love the naming sheme?

    VLT = Very Large Telescope
    ELT = Extremely Large Telescope

    What comes next?

    The OLT, the Overly Large Telescope?

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    is there any way adaptive optics can be used for larger fields of view i wonder though
    Last edited by mutleyeng; 2012-Jun-17 at 06:48 PM.

  7. #7
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    Quote Originally Posted by Warringer View Post
    Don't you just love the naming sheme?

    VLT = Very Large Telescope
    ELT = Extremely Large Telescope

    What comes next?

    The OLT, the Overly Large Telescope?
    There was OWL -- OverWhelmingly Large. The next size beyond that will probably get a nickname that is not acceptable to a family-oriented forum.
    Information about American English usage here. Floating point issues? Please read this before posting.

    How do things fly? This explains it all.

    Actually they can't: "Heavier-than-air flying machines are impossible." - Lord Kelvin, president, Royal Society, 1895.



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    Quote Originally Posted by swampyankee View Post
    There was OWL -- OverWhelmingly Large. The next size beyond that will probably get a nickname that is not acceptable to a family-oriented forum.
    I suspect that after the overwhelmingly large telescope, if we build Earth-based telescopes bigger, we'll drop the "Large" part of the name, a just give them names about their specific size, like HKOT (the Half-Kilometer Optical Telescope).
    Forming opinions as we speak

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    Quote Originally Posted by antoniseb View Post
    I suspect that after the overwhelmingly large telescope, if we build Earth-based telescopes bigger, we'll drop the "Large" part of the name, a just give them names about their specific size, like HKOT (the Half-Kilometer Optical Telescope).
    They still haven't used RLT -- Ridiculously Large Telescope and LLT -- Ludicrously Large Telescope (dunno if ludicrously is an acutual word, but I had to get a Space Balls reference in there somewhere...)

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    There has been a lot of talk about NASA's NRO gifted spysats. I wonder if they could be broken down and incorporated into a ground based telescope.

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    It would be possible but so costly for the results I doubt anyone would try. NASA has a similar problem. The scope itself is such a small part of the total cost of a space telescope they don't have the budget needed. At one time 2.5 meters was a big ground based scope but today they are so small, except for some very special designs, that size is no longer being built. The Isaac Newton 2.5 meter scope just barely survived the last budget cut that close two other observatories. The EELT has 256 times the light grasp of these "little" scopes.

    Rick

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    Quote Originally Posted by RickJ View Post
    It would be possible but so costly for the results I doubt anyone would try. NASA has a similar problem. The scope itself is such a small part of the total cost of a space telescope they don't have the budget needed. At one time 2.5 meters was a big ground based scope but today they are so small, except for some very special designs, that size is no longer being built. The Isaac Newton 2.5 meter scope just barely survived the last budget cut that close two other observatories. The EELT has 256 times the light grasp of these "little" scopes.

    Rick
    I vote that NASA give the scope to RickJ along with an appropriate mount and a new CCD camera. You could reduce exposure time to just seconds. It's too bad the CCD readout is something like 25 seconds. Then we can scrounge up a bunch of 'busted' playstation 3's and built a cluster for processing. Seriously, find some cheap with bad hard drives and bad BD drives.

    Acquisition, seconds. Processing, still in the hours range.

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    Quote Originally Posted by publiusr View Post
    There has been a lot of talk about NASA's NRO gifted spysats. I wonder if they could be broken down and incorporated into a ground based telescope.
    If their mirrors are good for IR, maybe NASA could make SOFIA II and SOFIA III. Using a new aircraft -- a brand-new 777 is about $275 million -- allowing about $600 million to convert both airframes and $50 million to salvage the telescopes, my WAG is that these two airborne observatories could be up and running for a bit under a billion USD. A pair of used 747-400s would probably cost about $50 million, although they would need more work ($700 million conversion for both?) and would have less airframe life left.
    Information about American English usage here. Floating point issues? Please read this before posting.

    How do things fly? This explains it all.

    Actually they can't: "Heavier-than-air flying machines are impossible." - Lord Kelvin, president, Royal Society, 1895.



  14. #14
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    Extremely Large Telescope, Giant Magellan , Rubin Observatory and others are coming https://astronomy.com/news/2021/03/t...f-the-universe

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