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Why no telescopes on the moon?

  1. Jun 1, 2015 #1
    We are placing everyday more telescopes in satellites in orbit. Would't it be convenient to have some permanent telescopes placed on the moon's surface? I guess if we don't do that it's because that would be much more expensive than launching satellites? Are there no plans to place telescopes on the moon and why?
     
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  3. Jun 1, 2015 #2

    Drakkith

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    Partly, yes. Satellites in orbit don't require heavy and expensive hardware that's required to land it on the Moon's surface. In addition, a telescope in orbit can be turned to point in nearly any direction at any time, whereas a telescope on the Moon is limited to whatever area of the sky is currently in view.
     
  4. Jun 1, 2015 #3

    Vanadium 50

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    If you Google this, you will find many objections. There are two immediate questions, though - 1) what question can be answered better by a lunar telescope than the alternatives, and 2) how will you get the images back to earth, given that the moon is between the telescope and the planet,
     
  5. Jun 1, 2015 #4
    Now this has raised the question of why such a telescope couldn't be positioned on the lunar poles to allow for observations, communications, and power? It wouldn't be ideal, but it would allow for a very large telescope.
     
  6. Jun 1, 2015 #5

    epenguin

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    Er, no it doesn't have to be. And we could take astronomical selfies with it.
     
  7. Jun 1, 2015 #6

    Vanadium 50

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    You want to put it on the near side?
     
  8. Jun 1, 2015 #7

    epenguin

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    I can see an advantage.
     
  9. Jun 1, 2015 #8
    The moon isn't ideal either, it has a very thin "atmosphere" of dust. The Apollo astronauts noticed a haze on the moon which turned out to be dust help in position by electro-static forces.
     
  10. Jun 1, 2015 #9
    But indeed a moon telescope could be much larger than one in orbit. Having rotation so it can be pointed to any direction (except the sky area blocked by the moon itself of course) doesn't seem a big problem either, and the moon / Earth rotation would allow for observing (I guess) any point in space. I don't know how much the dust could be a problem though.
     
  11. Jun 1, 2015 #10
    A single telescope you may be right, but not for a telescope array. An array of small telescopes is much more powerful than one large one, and the further you put them away from each other they better.
     
  12. Jun 1, 2015 #11
    What could we observe from the surface of the Moon that we could not observe from other Earth orbiting scopes?
     
  13. Jun 1, 2015 #12

    Drakkith

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    How so?
     
  14. Jun 1, 2015 #13

    davenn

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    Exactly, nothing, and having scopes based on the moon adds an even bigger headache for maintenance issues
    I cant see any point in moon based observatories unless there is already established significant manned moonbase

    Dave
     
  15. Jun 1, 2015 #14

    Chronos

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    A moon teledcope would be fabulous if we had a moon base, that is the bigger question in my mind - why do we not have a moon base on the drawing board? That is the logical first step for space exploration.
     
  16. Jun 2, 2015 #15
    I have read that a moon telescope's mirror could be largely made out from lunar dust, so the payload to take from Earth would be rather limited. This article says that with this method a 50 meter telescope could be built on the moon, far larger than anything in orbit.

    http://www.technologyreview.com/news/410253/a-moon-based-telescope/
     
  17. Jun 2, 2015 #16

    russ_watters

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    That doesn't make any sense: You wouldn't have to carry the mirror to the moon...just an entire manufacturing plant for making mirrors, which, necessarily, would be larger than the mirrors it is making.
     
  18. Jun 2, 2015 #17

    Janus

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    I can think of one type of telescope that could benefit by being placed on the far side of the Moon, a radio telescope. The distance and intervening bulk of the Moon would shield it from Earth based electromagnetic interference. Whether or not this benefit would be worth it is another question.
     
  19. Jun 2, 2015 #18

    mfb

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    You would make the primary mirror segmented. A small plant that makes many mirrors. I think it would still need more material than the primary mirror, but the comparison is not as obvious as it might look like.
     
  20. Jun 2, 2015 #19
    50m is nice, but an array of smaller telescopes put far apart in orbit can have an effective apature way beyond 50m.

    Not all telescopes orbit earth, we have several at the L points and several orbiting the sun.

    Money. Both Russian and China have plans for a base in the later part of the 2020s, but they're still way too expensive.
     
  21. Jun 2, 2015 #20
    My apologies for the brevity of my post. This is off the cuff without all the links to references that a more scholarly reply would have.

    Drakkith is correct. And there are a couple of other factors as well.

    Space telescopes in orbit around the Earth are closer than the Moon, so control signals don't take as long to get there. Remember the delays between asking a question of the astronauts on the Moon and receiving their reply?

    It costs somewhat less to put a satellite telescope in orbit than it does to take it to the moon; much less land it as Drakkith mentions.

    If you intend to perform periodic maintenance and upgrades on your telescope, it's much cheaper and faster to get to it in Earth orbit than on the Moon.
    The Moon has a limited amount of surface area which limits the practical size of of a telescope, even if you build an array. You can theoretically build a much larger free floating array in orbit than you can on the surface of the Earth or the Moon.

    In orbit, there's no gravity to distort the shape of your lens. While the Moon has only about 1/6th the gravity of the Earth, that would still limit the size of the reflective lens you can use; although that might be surmountable by placing actuators behind the lens to bend it into whatever curvature you needed. A lens 6 times larger than the Mount Palomar one would definitely flex, even if the backing was a glass honeycomb; although I don't know how brittle it would be in those temperatures (probably very.)

    All of this applies to optical telescopes. Now there might be a good reason to place a radio telescope on the far side of the Moon as the bulk of the Moon should shield the telescope from most Earth radio transmissions.
     
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