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Space Science

World's Largest Telescope Begins Production 138

Posted by Zonk from the big-shiny-thing dept.
JohnnyNapalm writes "The Aggie Daily News is reporting today that the first mirrors have been cast for the world's largest telescope. The result of cooperation from some of the foremost institutions in education and science in the nation, the Giant Magellan Telescope stands to operate at a resolution 10 times larger than the Hubble. The project, set to be constructed in Chile, is slated for completion in 2016."
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World's Largest Telescope Begins Production More

World's Largest Telescope Begins Production

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  • Hubble Telescope (Score:4, Interesting)

    by Ravatar ( 891374 ) on Sunday July 24, 2005 @02:24AM (#13148057)
    Am I alone in feeling that we haven't even used hubble to the fullest extent of its abilities? Not sure why this is a priority right now.

    • Re:Hubble Telescope (Score:1, Interesting)

      by Anonymous Coward
      Except for the fact that we are going to let the Hubble fall out of the sky in the next several years...
    • Why not both? There's plenty to see out there in the cosmos. These programs are usually relatively cheap compared to anything spaced-based. As long as we're getting good science then I say spend the cash.

    • Re:Hubble Telescope (Score:5, Insightful)

      by lightyear4 ( 852813 ) on Sunday July 24, 2005 @02:31AM (#13148076)

      The Hubble will be providing scientific insight long past its stamped expiration date. To quote from TFA:

      The telescope will have four-and-one-half times the collecting area of any current optical telescope and the resolving power of a 25.6-meter (84-foot) diameter telescope - or 10 times the resolution of the Hubble Space Telescope.

      I don't know about you, but given the immense scientific value of the Hubble, investing in further pursuits like this seems a worthwhile and worthy investment.

      • Re:Hubble Telescope (Score:5, Insightful)

        by tempest69 ( 572798 ) on Sunday July 24, 2005 @03:05AM (#13148187) Journal
        The Hubble is a great scope, but we need to go farther. The hubble has flaws of up to 1300 nanometers. Where the magellan has up to 15 nanometer flaws.

        Just for some perspective, a silicon arom has a radius of 1.46 angstroms or .146 nanometers. giving it a .292 nanometers, so were looking at a mirror that is within 50 atoms of perfection.

        Heck, the optic technology alone is enough to have real world impacts. So yea I think the investment is well worth it.

        Storm

        • Heck, the optic technology alone is enough to have real world impacts.

          Because we can point it at the moon to see if they actually landed there and silence all nutjobs?
          • If it's focus is set at the same as Hubble's the moom will still be too close for it to focus on.

          • No, you still can't image the Apollo landers (Score:2, Informative)

            by Anonymous Coward
            The largest dimension on the Apollo landers is 9.07 m, diagonally between the landing legs (it's a 21 foot square). The moon's closest approach to the earth is 363,104 km. Divide those two numbers, and you get the angular size in radians: 2.36e-8 radians, or 0.00487 arcsecond.

            With a 27m diameter, the diffraction limit on telescope resolution is 10^8 cycles/radian. So if there were no atmosphere, it would be barely possible.

            With an atmosphere, there are problems. A typical good seeing limit is 1 arcsec
        • LOL, you said "silicon".
        • Yes, investments in astronomy are usually well worth it. For example, CCD sensors (http://en.wikipedia.org/wiki/Charge-coupled_devic e [wikipedia.org]) were first developed and perfected as a replacement for photographic plates used in telescopes.
        • "The Hubble is a great scope, but we need to go farther. The hubble has flaws of up to 1300 nanometers. Where the magellan has up to 15 nanometer flaws."

          Where'd THAT come from?! hubble was designed to have an abberation less than 1/20 waves at the helium neon laser line of 633 nm (30 nm). It ended up with an error of ~ 1/2 wave and anyway this is irrelevant because the error was corrected completely with costar [asphere.com].
    • in 2016?

      Might as well get to work now!

    • Re:Hubble Telescope (Score:2, Flamebait)

      by tloh ( 451585 )
      Am I alone in feeling that we haven't even used hubble to the fullest extent of its abilities? Not sure why this is a priority right now.

      Have you bothered to reconcile what you feel with what you know? For example, do you know how easy or hard it is to book Hubble for an observation run? Especially when it most matters? Heavenly phenomenons don't exactly conduct themselves by a schedule tailored to you or anyone elses' convenience. You don't really know when a spactacular supernova or comet collision

    • The problem with Hubble is that you have to send the space shuttle each time there is a problem with it. So this is quite a little constraint...

      If this is possible to do telescopes on earth that can have the same quality as Hubble(I mean, the quality that would have the successor of the Hubble...), then it's pretty interesting because it will be cheaper at the end (maintenance, upgrading, etc). Even if they need huge mirrors for it.
      • The problem with viewing from the earth is that the atmosphere bends the light just enough for the calculations of objects to be off. That's gonna be alot of math over and over.

      • Re:Hubble Telescope (Score:3, Informative)

        by DerekLyons ( 302214 )

        If this is possible to do telescopes on earth that can have the same quality as Hubble(I mean, the quality that would have the successor of the Hubble...), then it's pretty interesting because it will be cheaper at the end (maintenance, upgrading, etc).

        Except it's not possible, despite the hype in the article. No earthbound telescope will ever be able to see the wavelengths that Hubble does - it's a matter of physics, not technology. The light in those wavelenghts never reaches the ground. Nor does H

    • Re:Hubble Telescope (Score:2, Interesting)

      by Wyatt Earp ( 1029 )
      Well, this is a priority because the partners think it's a priority.

      Carnegie Observatories
      Harvard University
      Massachusetts Institute of Technology
      Smithsonian Astrophysical Observatory
      Texas A&M University
      University of Arizona
      University of Michigan
      The University of Texas at Austin

      Look, it's not about having one device, the more devices we have doing research, the better. NASA and ESA run Hubble and will replace it with the James Webb (stupid name IMO) in the next decade.

    • Re:Hubble Telescope (Score:3, Interesting)

      by imsabbel ( 611519 )
      This telescopy will be cheaper in total than a singly shuttle mission to extend hubbles lifetime...
    • Speaking of using it to its fullest potential; what are the chances of somebody turning that puppy towards the moon to see if some imagery of the Apollo landings can be had? Would that not be awesome to actually see Tranquility base, with Armstrong and Aldrin's footprints intermingled with all the Moontian footprints left since they came back? (lol) Or even get a shot of the space station coming over the horizon, or the shuttle lifting off (if and when, if and when). I mean why does it have to just be used
    • Am I alone in feeling that we haven't even used hubble to the fullest extent of its abilities?

      No idea if you're alone in it, but your argument makes no sense.

      You mean we should postpone making something better than hubble because ...? hell, I cant't even see that you have a coherent argument at all.

      Should we have waited to deploy transistors that were ready until we had maxed out everything that could be done with tubes and relays too?

  • Well, if this one is funded by the schools... (Score:3, Insightful)

    by attemptedgoalie ( 634133 ) on Sunday July 24, 2005 @02:30AM (#13148071)
    and not the US Gov't, then THEY get to choose when to pull the plug.

    Not some accountant.

  • Largest Telescope? (Score:4, Insightful)

    by poopdeville ( 841677 ) on Sunday July 24, 2005 @02:30AM (#13148072)
    Largest ptical telescope, perhaps. Arecibo Observatory is still the biggest single telescope, though there are even larger arrays.
    • We're talking optical, not radio. Arecibo is more like an giant antenna than a light gathering device, no?

      -scott

    • Re:Largest Telescope? (Score:3, Informative)

      by luna69 ( 529007 ) *
      Largest optical, perhaps...until OWL!

      "With a diameter of 100 meter, OWL [Overwhelmingly Large Telescope] will combine unrivalled light gathering power with the ability to resolve details down to a milli-arc second."

      Link: OWL [eso.org]

      • Re:Largest Telescope? (Score:3, Informative)

        by Shag ( 3737 )
        Actually, the Thirty-Meter Telescope [ucolick.org] project might be a little easier to build than the OWL, given its smaller size.

        And of course the GMT is being built as a single scope with one focus, while things like the VLT [eso.org], Keck [hawaii.edu] and LBT [arizona.edu] use interferometry to get sharper images.

        (And adaptive optics! I want telescopes with frickin' laser beams strapped to their heads!)

        • Re:Largest Telescope? (Score:3, Informative)

          by luna69 ( 529007 ) *
          I agree, it'll be easier to build (although OWL will use multiple segments/single focus).

          But...when I read "..milli-arcsecond" resolution (in the optical!) on the OWL site, in spite of its competitors, my knees got weak, my toes curled...And I'm a grown man.

          I and the guy who teaches the class I TA for recently had students calculate how large a primary would be necessary to read a homework page on the moon, from Earth. (assuming, of course, diffraction-limited seeing...hah!). Needless to say, even OWL wou

          • Re:Largest Telescope? (Score:3, Informative)

            by Shag ( 3737 )
            Nice. I think there used to be a moon laser out here too, on Maui... LURE [hawaii.edu]. I think it's gone now, though - the MAGNUM [nao.ac.jp] is in part of it, I think, and the Pan-STARRS [hawaii.edu] prototype scope is supposed to be going somewhere around there too.

            We play with lasers over on Mauna Kea, too... like this nice 20-watt sodium dye [nasa.gov] one. Which, for topicality, is located at the world's current largest optical telescope...

          • Re:Largest Telescope? (Score:5, Informative)

            by luna69 ( 529007 ) * on Sunday July 24, 2005 @08:16AM (#13148895)
            For those of you not familiar with why astronomers would place (frickin') lasers onto telescopes, there are multiple reasons.

            The primary reason is to provide a "fake star" that can be monitored for distortion, which helps adaptive optics systems counteract atmospheric distortion in the final telescope image/data. In other words, it helps remove the "twinkle" caused by the atmosphere.

            The laser at Apache Point, as well as at other locations (see previous message), is used to measure the distance to the moon (which is useful in, among other things, studies looking at the accuracy of general relativity).

            The Apache Point laser is capable of measuring the distance to the moon to a millimeter using this device. (think about it: at a telescope, up on a mountain around 10,000 feet, there's probably more 'flex' in the mountain itself!).

    • Arecibo Observatory is still the biggest single telescope, though there are even larger arrays.

      Yep, like the Very Long Baseline Array [nrao.edu]. Nothin' like being 5,000 miles across to help you see things, I guess. It's interesting to me that at 8.4 meters each, the mirrors will be tied with the Large Binocular Telescope [arizona.edu]'s mirrors which were just installed last year in Arizona. I think the next largest after that may be the 8.3 meter one on the Subaru [naoj.org] telescope (National Astronomical Observatory of Japan)

    • I still think the approach of launching lots of mirrors and bolting them to a rigid bar to form a device using inferometry will be a far better approach. What's to stop us (except money) building a 10km long bar and bolting say 10 smaller telescopes to it, then launching it to a Lagrange point? Insanely high resolution (inferometry again), no atmospheric disturbance...
      • Why bolt them onto a big bar?

        At optical wavelengths, they could keep station using very small thrusters perfectly well to within the required tolerances. You could place one at the leading lagrange, another at the trailing lagrange, and get, what - a couple million km? (too tired to do the calculations here).

        We had one of my former profs come and talk to our astro club about a long-range project he's involved with working on x-ray interferometry in space (there are a couple big projects along these lines)
        • > At optical wavelengths, they could keep station
          > using very small thrusters perfectly well to
          > within the required tolerances.

          You don't actually need to station-keep to within the required tolerances. You just need to measure that accurately. The station-keeping merely has to keep you within the dynamic range of your adaptive optics.

  • Cool! (Score:2, Funny)

    by Anonymous Coward
    The only problem is, where shall we find a Giant Magellan who can operate such a big telescope for us?

  • Capricorn One (Score:5, Funny)

    by pipingguy ( 566974 ) on Sunday July 24, 2005 @02:34AM (#13148094)

    Will it be able to show the moon landings?
    • Will it be able to show the moon landings?
      Obviously not! The moon program is just a clever hoax, remember? Why make it more difficult to pull off? You obviously need to take some at-home coverup classes.

    • Re:Capricorn One (Score:4, Funny)

      by spudchucker ( 680073 ) on Sunday July 24, 2005 @04:00AM (#13148313)
      Trust me, if the moon is going to land, you won't need a telescope.
    • All you need to see the site of the moon landings is to drive to arizona!
      • All you need to see the site of the moon landings is to drive to arizona!

        No, you're wrong, that area is now off limits and is being used by two "Mars" Rovers...
  • The hubble has been obsolete for a while. The VLT, an on-planet operation, has been using it's multiple "world's largest" lenses for interferometry for a while.

    If this is going to beat it out the lenses will have to be tremendous. It was considered a feat of engineering manufacturing and shipping the VLT's lenses

    • I'd love to see a comparison of the VLT and Hubble in the ultraviolet band, for example. ;)
      • And on resolution, too, still. I've got Hubble data coming in this week, imaging, in the optical (600 nm), with a resolution of 0.1 arcseconds. Tell me what telescope I can do that on right now, other than the Hubble. Most of the AO stuff you hear about is for near-infrared observations, which won't always do the job.
        • 0.1", shiny! On the 2.2m where I work, we get all excited when we get 0.3-0.4" infrared or 0.6" visible. I think Keck is supposed to be able to get down to 0.2" or less, conditions permitting, but that might involve the use of AO and/or interferometry. I'm supposed to be up at Keck on Tuesday, so I'll see if I can find out.
    • Oh, and, um, by the way, I think you might mean mirrors, not lenses. Refractors don't really scale all that well. :(

  • Photos (Score:4, Informative)

    by spudchucker ( 680073 ) on Sunday July 24, 2005 @02:55AM (#13148156)
    Photos [arizona.edu]
  • They can peer into the bedroom windows of sexy coeds from THOUSANDS of miles away.
  • Can someone please explain how a mirror would work for this (each individual mirror is made up of smaller hex-pieces) if it's made up of many, many small pieces with holes in between? I thought you needed a large, flat unbroken surface for each mirror?
    • nope, many small mirrors are easier to manufacture by far (large mirrors have too many defects to be useful, or cheap), and adaptive optics requires that the mirrors have a modifiable geometry to properly compensate for the atmospheric interference. the break in the mirrors do not reflect light, so as long as the angles are correct it is not noticable.
      • That makes sense. And, after reading more, I may have misunderstood the idea. The hex shapes are the holes in the mirror, not the mirror. Weird.
        • Hmmm... the GMT [gmto.org] site seems to indicate that the mirrors either are hexagonal or are round but in hexagonal frames of a sort. I don't see how this would result in hexagonal holes, though. In the case of the Keck [hawaii.edu] design, the hole to the cassegrain focus is hexagonal because there's one hexagonal segment "missing" to make the hole - but Keck's segments are only something like 1 meter each. In the case of the GMT, the segments are so large that it's simpler to just have a round hole in the middle of one.

      • adaptive optics requires that the mirrors have a modifiable geometry to properly compensate for the atmospheric interference

        Hmm... AO typically uses a thin deformable mirror further down the light path, which has its shape altered a lot of times a second. Active supports like the "wiffle trees" used on Keck do move individual mirror segments to maintain the overall curve of the mirror as the telescope is moved throughout the course of the night, but they're (hopefully!) not actually deforming the m

        • >not actually deforming the mirror segments

          IIRC The mirror segments were deformed during construction. The mirror segments need to be ground to the correct shape (with a pretty tight definition of correct). I belive they were deformed in such a way that the actual shape ground was an easy one to do. When the mirrors were released they sprung back to their original overall shape but with the surface ground to what was needed for the final mirror. Neat way of getting around the problem.

    • Re:A hex-structured mirror? (Score:4, Informative)

      by LMCBoy ( 185365 ) * on Sunday July 24, 2005 @09:23AM (#13149108) Homepage Journal
      It's one piece of glass, with a single, smooth surface on the front, 8.4 m in diameter. The hexagonal "pieces" are holes on the backside. It basically looks like a big honeycomb [arizona.edu]. This design gives you great stiffness and strength, with only 20% the weight that a solid mirror would have.

    • No, you don't need an unbroken surface (Score:2, Informative)

      by Anonymous Coward
      You just need a very, very accurately aligned surface. For moderate sizes, this is easiest to achieve by just making the whole mirror a solid piece. As the mirror gets larger, the stiffness needed to hold its shape to within a fraction of a wavelength of light gets more and more difficult to achieve. Above 5m (the 200 inch Hale telescope), you have to change to active supports, where you measure and compensate for gravity sag rather than just trying to be stiff enough.

      There's still a tradeoff, though.

  • Wow (Score:2, Funny)

    by Suicide Machine ( 902222 )

    I guess scientists suffer from penis envy too.

    "Oh yea, well my telescope is bigger then yours!"

    Or would it go...

    "Hey baby, look, _my_ telescope has a lens that's 40,000 pounds, it'll be 84 feet of girth, and when it gets heated up it takes 3 months to cool"

    • Re:Wow (Score:2)

      by Shag ( 3737 )
      Yeah, there's an ongoing mirror DSW. Mostly in the "largest monolithic mirror" category, which was at 8.3m with Subaru, then went to 8.4 with the LBT and now GMT. Now we need someone to do 8.5m.

      Keck held the "largest segmented mirror" one for quite a while. Still does, depending who you ask. I think Hobby's (in Texas) may be a larger mirror, but Hobby only rotates and doesn't tilt; they move the secondary instead, and thus they end up using less of the primary mirror at a time than Keck does.

  • Southern African Large Telescope... (Score:4, Informative)

    by reg ( 5428 ) <reg@freebsd.org> on Sunday July 24, 2005 @04:28AM (#13148386) Homepage

    For something a little closer to completion than 2016, check out the Southern African Large Telescope [salt.ac.za]. Scheduled to open in November, and will be the biggest optical telescope in the southern hemisphere.

    Regards,
    -Jeremy

  • it's not as obsolete as you may think... (Score:3, Interesting)

    by randumspin ( 902235 ) on Sunday July 24, 2005 @05:08AM (#13148500)
    I had the wonderful experience of being an undergraduate in astrophysics at UC Santa Cruz, where a grant in adaptive optics was paving the way for ground-based telescopes. By shining a laser straight where the telescope is pointed, aberrations and distortions from the atmosphere can be measured and exactly countered by the telescope, effectively cancelling atmospheric effects to a remarkable degree. Check out http://cfao.ucolick.org./ [cfao.ucolick.org] The main telescope was outside of San Jose, CA, which might seem a strange location for a telescope due to its proximity to a large city. But since all of the streetlamps in San Jose are sodium (whose spectral properties are well known and simple), those features can be subtracted from any measured spectra and in conjunction with adaptive optics, the telescope outside northern california's largest city produces world-class astronomy. This telescope being built should be pretty neat. I wonder how they will deal with gravitational aberrations. Plus scientists won't ever need to face the threat of government letting their instrument "deorbit" while still producing good data.
  • While i dont like multi-face mirrors optically (like in good-loooking, not good optical properties :D ), those are really impressive.

    Its also interesting just how long those mirrors need to cool down... in our modern, fast-paced world a mirror cooling for more than half a year or so seems like something from another age...

  • Report from the lab (Score:5, Informative)

    by LMCBoy ( 185365 ) * on Sunday July 24, 2005 @09:58AM (#13149232) Homepage Journal
    The Steward Observatory Mirror Lab [arizona.edu] had an open house yesterday for observatory personnel, which I attended.

    The spin-cast oven is huge. [arizona.edu] In these pictures, you only see the top portion of it, it actually fills the floor below as well. I believe this is the only large spin-cast mirror facility in the world. The idea behind spin-casting is that, by spinning the molten glass as it is slowly cooled, you automatically get a paraboloid top surface. This makes the final shaping of the mirror much easier, since the first-order shape is already there.

    Actually, in the case of the GMT, it will use seven mirrors [gmto.org], six of which are off-axis. The off-axis mirrors will obviously have a more complicated surface than a typical on-axis paraboloid. The mirror being cast now is an off-axis mirror; it is a proof-of-concept that they can grind an eight-meter chunk of glass to an off-axis paraboloid shape with a surface RMS of 20 nanometers (!).

    In a few months when the mirror has cooled and solidified, it will be removed from the oven, cleaned, ground, and eventually, polished. The stress-lap polisher [arizona.edu] is very impressive. It has a network of stress actuators above it, which can dynamically change the shape of the polisher's surface as it travels across the mirror.

    It's interesting that the "Aggie Daily News" was chosen as the linked story, which makes it sound like UT Austin and Texas A&M are the major players in the GMT, along with a handful of other, unnamed institutions. In fact, the Carnegie Institute is the impetus behind the project, and the U of Arizona is providing the mirrors. I think this UA News article [uanews.org] is much more informative.

  • somethiing to keep in mind (Score:3, Interesting)

    by RayBender ( 525745 ) on Sunday July 24, 2005 @03:31PM (#13151029) Homepage
    People keep comparing this large ground-based telescope to Hubble, and invariably say seomthing like "we can do just as good as Hubble at 1/10th the price". Nonsense, for three reasons:

    1) Absorption. The atmosphere absorbs in many wavelengths of interest, including the UV and parts of the IR. There are some projects that can never be done on the ground.

    2) Background emission. The atmosphere "glows" at a number of wavelengths; this acts as a source of background contamination and reduces your sensitivity.

    3) Blurring. The stars twinkle. This reduces the sharpness of ground-based images by an enormous factor (for GMT in the optical, excluding AO, by a factor of about 200).

    People keep mentioning "adaptive optics" as a way to overcome the blurring from the atmosphere. But the harsh truth is that AO doesn't work all that well, for situations where you actually need to get rid of the effects of the atmosphere. Sure, it sharpens up pictures of binary stars pretty well, but it leaves a bunch of uncalibrated "scruff" near the star that e.g. makes it impossible to look for planets near that star. Another limitation of AO is that it requires a bright star to guide on - although lasers are becoming available. Mind you, the laser stuff seems to have even worse issues with calibration. Finally, AO has a very limited effective field of view; you can only correct over a small patch at a time. It makes it hard to do wide-field surveys that way.

    Sooo, the upshot is that you need both, and will continue to need bothy for a long time. That being said, I wish the GMT guys lots of luck.

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