Telescope limitation

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adering

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Not to sound too silly, but what's the limit on resolution for a space-based telescope? Hubble sends back all these amazing images and its looking billions of light years out. Would it be possible to orbit a telescope with sufficient power to actually look at an extra-solar system planet and check it visually for signs of life (e.g. city lights at night)?
 
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MeteorWayne

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Lights at night? No I'm afaraid it's unlikely we can ever get enough resolution for that.<br /><br />The best we can do from here is possibly detect chemicals in the reflected or absorbed light of the star.<br /><br />Great question, welcome to SDC! <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>
 
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docm

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The question is one of angular resolution, not magnifying 'power' per se. You can have a lot of x's and still have a fuzzy image. <br /><br />One way to increase angular resolution for exoplanet imaging is to use an interferometer; multiple telescopes used in an array whose separation (their baseline) lets them collectively act as a much larger instrument. <br /><br />The Keck telescopes in Hawaii are such an instrument using 2 large ground based telescopes, but it's still not adequate for the detailed imaging of exoplanets. Space telescopes are better for that especially if infrared imaging is part of the mix (as it should be).<br /><br />The SIM PlanetQuest mission is a space based interferometer with a 9 meter baseline and 2 imagers which can image down to 1.12 microarcseconds. Nice, but still small for your task.<br /><br />To image exoplanets at the resolution you're talking about would require several fairly large space telescopes flying in formation & arranged into an interferometer with a much longer baseline than SIM's. <br /><br />The NASA Terrestrial Planet Finder (TPF) was such a mission, but it lost funding last year. The ESA also has such a mission under the name of "Darwin" (image below). <div class="Discussion_UserSignature"> </div>
 
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Boris_Badenov

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Actually, somebody figured out what size aperture it would take to image the surface of Gliese 581C (a quick search couldn't find the thread) & at 20.5 light years the aperture needed to be 51 miles in order to image the surface.<br /> While this size telescope is beyond our capabilities now, in 20, 50 or 100 years who knows?<img src="/images/icons/smile.gif" /><img src="/images/icons/smile.gif" /><img src="/images/icons/smile.gif" /><br /> I am an advocate of SpaceDev’s International Lunar Observatory Mission <br />The sooner we build our first Lunar Telescope the sooner we can start building really big ones on the Lunar surface. <div class="Discussion_UserSignature"> <font color="#993300"><span class="body"><font size="2" color="#3366ff"><div align="center">. </div><div align="center">Never roll in the mud with a pig. You'll both get dirty & the pig likes it.</div></font></span></font> </div>
 
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deapfreeze

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Telescopes on the moon would be cool. We can build them when we build the moon base. I think some big scopes on the moon would find a lot more stuff out there that we can't see from earth. <div class="Discussion_UserSignature"> <p><font size="2" color="#0000ff"><em>William ( deapfreeze ) Hooper</em></font></p><p><font size="1">http://deapfreeze-amateur-astronomy.tk/</font></p><p> </p> </div>
 
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dragon04

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<font color="yellow">Telescopes on the moon would be cool. We can build them when we build the moon base. I think some big scopes on the moon would find a lot more stuff out there that we can't see from earth.</font><br /><br />Two would be better. One on each side of the Moon. That way, you get constant viewing as opposed to half a month at a time. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>
 
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docm

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A pair of large 'scopes at L4 and L5 or L1 and L2 would give you a huge baseline for an interferometer, more than enough for planetary imaging. <div class="Discussion_UserSignature"> </div>
 
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Boris_Badenov

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I think the technology to place 2 scopes for an Interferometer thousands or even millions of miles apart in space is beyond our current abilities. But, an Interferometer with a baseline of several hundred miles could be finished in 10 to 20 years time on the Lunar surface without any new technology. It takes the will & the transportation. <div class="Discussion_UserSignature"> <font color="#993300"><span class="body"><font size="2" color="#3366ff"><div align="center">. </div><div align="center">Never roll in the mud with a pig. You'll both get dirty & the pig likes it.</div></font></span></font> </div>
 
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heyscottie

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The problem with very long baseline interferometers is keeping them in formation, or at least knowing their geometry very precisely.<br /><br />In this case "very precisely" means down to a fraction of the wavelengths of light you are interested in. For visible light, this would be a few tens of nanometers...
 
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docm

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Darwin and other proposed space interferometers are infrared which has a far longer wavelength.<br /><br />My understanding is that formation flying would be done using a separate spacecraft from the telescopes equipped with a GPS type system which could detect slight positional changes and correct them with ion thrusters or cold gas jets.<br /><br />(Guesstimating here) if you put the coordinating satellite at L1 and the scopes at L4 and L5 that would minimize the comm time between coordinator and each scope. Skulling this I come up with roughly 8 seconds light time or 16 seconds round trip to L1 for the positioning signals + calculation time for the burn, probably a small fraction of a second. Sound close?<br /><br />The question is would a ~17 second reaction time be fast enough when dealing with infrared? <div class="Discussion_UserSignature"> </div>
 
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heyscottie

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Even the furthest definition of infrared only extends to about 1 mm wavelengths. I still wouldn't want to try to keep an interferometer at Lagrange points on a known baseline with no more than a fraction of a millimeter of error...
 
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erioladastra

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"No I'm afaraid it's unlikely we can ever get enough resolution for that. "<br /><br />I disagree - I don't think you can say never. I think you are trying to tackle the question from pure resolving power of the disk. When I was a young kid interested in astronomy they said we would never resolve the disks of stars. Well that is wrong on 2 fronts. One we have resolved some of the larger ones, albeit crudely. But I agree that is unlilkely to happen with planets in the near future. But with doppler spectroscopy we can get very DETAILED 3-D pictures of stars. I think similar techniques wil one day work for planets. First we will develop maps that show brightness changes, then probably more detailed. Who knows - it will be pretty exciting.
 
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