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China's FAST (Five-hundred-meter Aperture Spherical radio Telescope) is the largest radio telescope in the world.(This is huge!!!) enter image description here

As we all know Space Telescopes are better than Earth-Based telescopes always.(Hubble space telescope was such a tremendous success)Even though ground-based observatories are usually located in highly elevated areas with minimal light pollution, but still they contend with atmospheric turbulence, which limits the sharpness of images taken from this vantage point.

What if all the space agencies collaborate together to build a telescope half the size of China's FAST in moon(Even smaller than half),even then it will be more powerful than the "FAST" right(because the atmosphere of moon is very less dense)?Will it be impractical?It may take decades to build one but still the outcome will be huge(We may even look and find aliens!!)

(Taking in account that Elon Musk is already planning Colonization of Mars)This project looks somewhat tamable than that,right? Is there a possibility of this happening? Is it feasible enough?

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    $\begingroup$ Why you think building it on the Moon is easier/cheaper/better than building it on orbit? $\endgroup$
    – jean
    Jun 6, 2018 at 19:53
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    $\begingroup$ You seem to be talking about telescopes operating in the visual wavelengths but you show a radio telescope. Are you aware of the differences? $\endgroup$
    – Chappo Hasn't Forgotten Monica
    Jun 6, 2018 at 21:10
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    $\begingroup$ @ParanBharali, it is very, very easy to have telescopes in Space. You just build the scope, then sit it on a rocket, and press the button. Building a scope on the moon is incredibly more difficult, and it is more difficult in many, many ways. $\endgroup$
    – Fattie
    Jun 6, 2018 at 22:13
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    $\begingroup$ @Fattie launching a telescope by rocket limits the size of the telescope to what the rocket can carry. Actually building one in space you can build much larger. Rocket launches are limited. $\endgroup$
    – userLTK
    Jun 7, 2018 at 1:21
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    $\begingroup$ This probably should be space exploration not astronomy, but it's obviously gotten a lot of attention here. $\endgroup$
    – userLTK
    Jun 7, 2018 at 2:07

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It's very unlikely that large optical telescopes will ever be built on the Moon, because the Moon is almost the worst possible place to build them. (The surfaces any of the planets other than Earth are worse.) It has no particular advantages over orbit and costs a lot more to build there.

The Moon looked like a good location when observatory technology was film-based, because observatories required people and people needed a base to live in and work best under gravity. But we now have the technology to shade an orbiting telescope from the Sun, point it exquisitely accurately, and take endless photos without changing the film -- all in orbit. Orbit is easier to get to than the Lunar surface -- even the Webb (should it ever launch) which will be parked a million miles from Earth, is easier to get to than the surface of the moon.

If we had the space capabilities to build a giant reflector on the Moon, we could build an even bigger and better one in orbit for the same cost.

You spoke of FAST. FAST is a radio telescope. It's likewise much cheaper to build radio telescopes in orbit than on the Lunar surface. The one possible advantage of the Moon is that the far side of the Moon might have advantages of being especially radio quiet.

But even there, it seems likely that any space radio telescope would be a large array of radio telescopes joined to form a giant synthetic aperture, and that would almost certainly want to be much larger than earth-based instruments -- for which the Moon is already too small.

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    $\begingroup$ +1 for mentioning radio telescope arrays as another example of why the Moon is unrealistic as an option. $\endgroup$
    – Chappo Hasn't Forgotten Monica
    Jun 7, 2018 at 5:41
  • $\begingroup$ The only thing I'm not sure I agree with is "build a better one in orbit for the same cost" When the telescope gets big enough, the primary expense becomes the launching, not the building. Building on the moon circumvents the launching cost. Building on any sizable asteroid could work too, but I think some gravitation is a plus in building. Most asteroids have close to zero gravity. Apart from that one point, I think your answer is spot-on. $\endgroup$
    – userLTK
    Jun 7, 2018 at 14:51
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    $\begingroup$ You don't build it in space in the sense of stacking up bricks and riveting pieces of steel together! A modern telescope is a very complex gadget and would be built in pieces by specialists on the ground using millions of man-hours and then launch with final assembly done in space. In building a big telescope off-earth, gravity is no help at all -- it's a distinct hindrance! $\endgroup$
    – Mark Olson
    Jun 7, 2018 at 14:56
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    $\begingroup$ For anything built on moon, the dust must be considered too. Its sharpness without weathered edges causes serious problems both to humans and machines, plus it electrostatically levitates - prone to cling to optics and everything else. $\endgroup$
    – Juraj
    Jun 8, 2018 at 18:07
  • $\begingroup$ The JWST has indeed launched, and though it's very early days it seems to have deployed as well as or even better than was expected $\endgroup$
    – Richard Ward
    Jan 13, 2022 at 12:15
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There are advantages and disadvantages.

Earth based telescopes have disadvantages because of the atmosphere, which blocks some light and it blocks some wavelengths almost completely and it also bends the incoming light. Some of the atmospheric displacement can be fixed with modern computers, so Earth based telescopes have improved significantly over the last 20-30 years, but they still have the disadvantage Earth's atmosphere blocking some of the light coming in from space. Today's Earth based telescopes are as good as Hubble (I read that somewhere) at least in the visible spectrum, in large part because of computerized imaging. When Hubble was launched (and fixed) at the time if was lightyears better than anything on Earth. Today it's close.

Chandra and Spitzer see in wavelengths that don't make it to Earth, so they need to be in orbit to work. James Webb will also view in the infra-red as well as visible wavelengths, so it needs to be in space to take advantage of it's infrared imaging.

Space is much better because it gets a much cleaner picture and it receives all wavelengths. There are disadvantages to being in space too, like cosmic rays, solar storms and the occasional near-light-speed proton but on average, space is better than Earth and the surface of the Moon is similar to being in space due to there being essentially no atmosphere.

A big problem with telescopes in space is that launching that much material is very expensive. It costs about $10,000 per pound to launch something into space. That's why there's so few you can count space telescopes on your fingers (fingers and toes actually, I think there's 13).

It's also important to keep large telescopes somewhat cold. (James Webb will have a large sun shield). That's especially important for infrared imaging. Provided the area is shaded, the moon will remain sufficiently cold.

The big advantage the Moon has is that it's full of silicon, which is what mirrors are made of, so by using lunar material, much less stuff needs to be launched and that saves a ton of money and increases the size of this theoretical telescope. That's the real advantage. We can't launch a 100 or 200 foot telescope from Earth because it's too big, but we could in theory, built one that size on the moon because there's lots and lots of stuff to use.

A smaller advantage is that the body of the moon acts as a shield for what's below it, but the real advantage is that the Moon is made of stuff that can be turned into a telescope. Really any large body a few miles in diameter would work, though working on a surface with gravity might be easier. Personally I think Ceres would be a great place to build. Very low gravity (but enough where you can set things down and not worry about them bouncing away) farther from the sun so a smaller sun-shield. Any reasonably large body in space could theoretically be used to build a telescope.

The moon, however, is closer, so it's both more easily repaired and it's close enough that it's easier to transmit images back to Earth as opposed to a Phobos based or Ceres based telescope.

This shouldn't be mistaken for easy though. It's never been done and might run into unanticipated problems and end up being quite difficult, but it's a nice idea.

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    $\begingroup$ The silicon is full of feldspar, pure silicon on earth comes from geothermal water and sea action. Youd need hot crucibles of moon rock and refine feldspar silicon mix, un unkown industry. Youd need gold, aluminium, vapor deposition chambers, dust free clean-rooms, the moons dust is abrasive. A flintstonoscope on the moon would not be optimal use of money. After building the silicon refinery for 10billion dollars. The list of costs would exceed 200 billion in todays money... lifting machines,cranes, it would be cheaper to make homes there than big machines. $\endgroup$
    – bandybabboon
    Jun 7, 2018 at 9:55
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    $\begingroup$ It would be insanely expensive to set up that manufacturing infrastructure just to build a telescope. Of course, if you were building a base big enough to warrant that setup, or a long-term colony, then sure you might as well build a scope at some stage. $\endgroup$
    – PM 2Ring
    Jun 7, 2018 at 11:23
  • $\begingroup$ @com.prehensible I was going off this NASA article, which you critiqued in the other answer. space.com/5628-nasa-envisions-huge-lunar-telescope.html I have no idea how feasible it actually is, but I did mention that it's never been done and could be quite difficult. Probably not something we'll see anytime remotely soon, if at all. $\endgroup$
    – userLTK
    Jun 7, 2018 at 14:55
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This 2004 article although a little dated now, discusses the relative merits of three possible novel sites for new major optical/IR telescopes: Dome A in Antarctica, the South pole of the Moon, and the Earth-Sun L2 point (or an orbit around it). Each is best for different purposes. A particular attraction of the Lunar site is the ability to stare at the same part of the sky for very long periods to detect very faint objects.

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Telescopes on the moon are a fantastic idea. If you "thought it up yourself" congratulations, because it's a great idea for the future.

As you may know we already have many fantastic telescopes in space (that is to say, generally orbiting or near our Earth). The next step would be telescopes on the Moon. (It is far, far, harder to build one on the moon, than simply lift one up to orbit.)

You can easily find many beginning studies about it; for example here is one by NASA on your great idea, from ten years ago!

Your idea is a good one, and hopefully it comes sooner rather than later. I bet we are 30 years away from telescopes on the moon. But they will come.

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    $\begingroup$ I don't know why you'd call the Moon the "next step". I voted you up for your NASA article though. That pretty well covers it. The point is that a telescope, built out of lunar material, could be larger and set up more cheaply than anything we can launch from Earth . . . in that sense, I guess it is a next step but there are several next steps already on the way, the next one is James Webb, that will unfold in space if all goes according to plan. The real advantage to the Moon is lunar material could be used, so stuff doesn't need to be launched from Earth. $\endgroup$
    – userLTK
    Jun 7, 2018 at 2:10
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    $\begingroup$ Nanotubes? In the resin mirror? Sounds silly. Why? Nanotubes, carbon fiber is more rigid than steel. Aluminium vapor deposition? On the moon? That researcher needs a 20meter mirror to be taken seriously. Better build microscopes for malians and sudanese first or you can make a ladder to the moon from them? $\endgroup$
    – bandybabboon
    Jun 7, 2018 at 10:12
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    $\begingroup$ Building a lunar base is actually scifi, a dark side of the moon base with the industrial capacity of building high-tech telescopes is more suited to WolrdBuilding SE than Space Exploration SE $\endgroup$
    – jean
    Jun 7, 2018 at 11:08

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