Stargazing Most powerful telescope system of the future?

[Oldfart]

What do you suppose would be the limiting resolving power of this telescope system? Assume it's built on Earth or nearby with money no object. Could it, for instance, detect a butterfly flitting about on a planet 100 LY from us? If not, what are the limiting factors?

Thanks!

 

[twofish-quant]

What do you suppose would be the limiting resolving power of this telescope system?

The wave nature of light. Since light has wave like properties, and waves spread out, there is some blurring that happens. Google for difraction.

Assume it's built on Earth or nearby with money no object. Could it, for instance, detect a butterfly flitting about on a planet 100 LY from us?

No. You'll be doing really good, if you can detect the planet.

If not, what are the limiting factors?

In addition to the wave nature of light, the atmosphere adds some blurriness. Not to mention the atmosphere of the planet you are looking at.

 

[jnorman]

resolution is determined by the apparent diameter of the objective. since we currently have multiple mirror scopes which combine to achieve large objective diameters, we can envision a variation of such a telescope placed in outer space with no particular limit on how far apart the individual mirrors might be, as long as they can somehow communicate with a control mechanism. but resolution is not the only factor in the problem - you must also be able to pick up enough light to register on the photo-receptor. in the case you present of a butterfly, that could never happen since it is a moving object. however, the detail available from, for example, a distant moon or planet with no atmosphere could perhaps be greatly enhanced by a series of space telescopes like Hubble which could operate as a single multiple mirror scope.

 

[jnorman]

depending on the distance to the object being observed, and the distance between the outermost mirrors of the scope, such a device could also provide some 3D information.

 

[Ryan_m_b]

This is very similar to a thread posted a couple of weeks ago

https://www.physicsforums.com/showthread.php?t=487434

You can work out the diameter needed for a telescope by dividing the wavelength of light you are detecting (visible light ~5e-7) by the object size/object distance.

-For a planet 10,000km in diameter 100ly away the diameter of our telescope would need to be ~47,000km.

-To observe a butterfly 2.5cm in diameter 100ly away the diameter of our telescope would need to be ~20,000,000,000km

And then as jnorman said a butterfly would be moving and impossible to detect

 

[Oldfart]

Thanks to all for your replys!

I was a bit discouraged by twofish's pessimistic outlook on this, then lifted some by jnorman and ryan's collectively cheerier opinions, which suggest that this telescope is doable, given some pretty spectacular state-of-the-art advances and a ton of money. Yeah, it does seem like some sort of "live TV" of moving things like butterflys 100 LY's away is a tough one, but hopefully no different in difficulty than our transition from still civil war pictures to today's movies.

This thread was prompted by my reading a nearby thread about aliens and learning about how difficult it would be to save the human race in the future by launching it off to somewhere. This led to wondering where "somewhere" might be, and it seemed like "somewhere" needs to be selected very carefully. Hence the telescope, a necessary first step. Unless someone else has a better idea...

 

[twofish-quant]

I was a bit discouraged by twofish's pessimistic outlook on this, then lifted some by jnorman and ryan's collectively cheerier opinions, which suggest that this telescope is doable, given some pretty spectacular state-of-the-art advances and a ton of money.

Hmmmmm...

I take back a bit of what I said. I was lazy and I didn't run the numbers, and now that someone has, it turns out to be merely "extremely difficult" rather than "totally impossible given our understanding of physical law."

The Earth's orbit is 150,000,000 km and so if you could do some VLBI, then diffraction is no longer a problem. Now, then there is the problem of getting the mirrors into orbit, and then inventing some way of doing long distance optical interferometry. That puts it in the category of fusion rockets. Nothing that we can do now, but "no physical law were violated in the making of this device."

Yeah, it does seem like some sort of "live TV" of moving things like butterflys 100 LY's away is a tough one, but hopefully no different in difficulty than our transition from still civil war pictures to today's movies.

Yup. It's important to distinguish between the "impossible under known physical law" and "extremely difficult." It's possible that our understanding of the universe is incomplete and what we think is impossible isn't. But the problem with things that are "impossible under known physical law" is that it's possible that it really is impossible, and even if it isn't it's not clear how to build the device.

A butterfly-seeking telescope is "merely very difficult"

This thread was prompted by my reading a nearby thread about aliens and learning about how difficult it would be to save the human race in the future by launching it off to somewhere. This led to wondering where "somewhere" might be, and it seemed like "somewhere" needs to be selected very carefully. Hence the telescope, a necessary first step. Unless someone else has a better idea...

Oh... One problem here is that you may find that you are trying to solve a problem that is more difficult than what you need to. Finding a butterfly at 100 LY is a *lot* more difficult than finding an earth-like planet at 100LY, and we should be able to do that in the next decade or two. (Google for Kepler).

One thing that makes the problem easier is that if you are just looking for earth-like planets, you aren't picky about which stars you want to the planet around. Kepler looks at a lot of stars and then tries to find a blip as the planet passes right in front of another star. It's *very* unlikely for that to happen to one planet, but if you do the math and count the number of stars, then you should see something.

Also, if we develop enough advance technology, then we can use that technology to fix the problem that needs to get us off the planet. The thing about a butterfly-seeking telescope, is that any civilization that could built it is able to do engineering in the Earth's orbit and can colonize Mars or Jupiter.

Then again, it's possible that we'll misuse this technology. It's interesting that the major things that could really screw up the planet are things that we are doing to ourselves. Any civilization that could build a orbital telescope, could screw up the Earth in new and original ways. If you could build a butterfly telescope, you could without too much trouble turn it into an earth-frying weapon.

 

[twofish-quant]

It turns out that Kepler just announced their results, and it's found 54 earth-sized planets in the right area of their stars to support life, and there will likely be more of them as time passes. The thing now is to look at those candidates to see what they are like.

Also, there are some interesting ethical issues, which would make for great science fiction stories. Suppose we've totally screwed up the planet Earth, and we do find an Eden-planet. Do we really have the right to screw up that planet?

Or here is another scary thought (which has already been used in SF). Suppose we have a lot of different civilizations. Some of them which are "nice" (i.e. they don't want to mess up other planets) and some of them are "nasty" (the mess up one planet, and when they are done with that, they go off and mess up other planets). If it turns out that the nasty ones are the ones that end up on more planets, then it's going to be really unpleasant to meet them.

(Greetings planet Earth, we've messed up our planet, and since we've seen the butterflies in your world, we've decided to take over. Put us in charge, or else we'll fry you with the telescopes we've used to look at your butterflies.)

 

[Oldfart]

Hmmmmm...

Oh... One problem here is that you may find that you are trying to solve a problem that is more difficult than what you need to. Finding a butterfly at 100 LY is a *lot* more difficult things that could really screw up the planet are things that we are doing to ourselves. Any civilization that could build a orbital telescope, could screw up the Earth in new and original ways. If you could build a butterfly telescope, you could without too much trouble turn it into an earth-frying weapon.

twofish, thanks for your comments! Just two thoughts:

1. I think we are already screwing up the Earth in new and original ways, the butterfly telescope probably won't add much more risk, percentage-wise...

2. It seems likely that after an enormous investment, no one in their right mind would settle for launching what's left of humanity off to an "earthlike planet". What if the planet is civilized and we all get put in zoos? Or if we all get eaten by lions, tigers, and bears? A closer look is needed first, we need to come fully prepared for our new environment.

 

[Chronos]

metaphysics is always interesting.

 

[Drakkith]

It turns out that Kepler just announced their results, and it's found 54 earth-sized planets in the right area of their stars to support life, and there will likely be more of them as time passes. The thing now is to look at those candidates to see what they are like.

Ohh, where is this at?

 

[IsometricPion]

-To observe a butterfly 2.5cm in diameter 100ly away the diameter of our telescope would need to be ~20,000,000,000km

And then as jnorman said a butterfly would be moving and impossible to detect

I did some calculations, and it seems with a big enough telescope you could get enough photons to see something. I assumed that the solar constant was the same as Earth's and converted that into the equivalent number of 550 nm photons per second, and found one could expect to receive 30 per second with a telescope ~6.7 million km across. So, if instead of building an interferometer 20 billion km across one built an actual mirror that large, one would receive ~270 million photons per second. On the other hand, such a large mirror, even made out of http://en.wikipedia.org/wiki/Aerogel" . I guess one would have to make several and set up an interferometer to get adequate resolution.)

What if the planet is civilized and we all get put in zoos? Or if we all get eaten by lions, tigers, and bears? A closer look is needed first, we need to come fully prepared for our new environment.

No matter how you look, you will be looking at an image that left that planet 100 years ago, and it will take you over 100 years to get there (so you would be sending people based on data that would be over 200 years old by the time they arrive). If we had the capability to get there I don't think any planet-bound civilization/creatures would be a match for us (if we decided we really needed their planet, which probably isn't very likely since there are lots of pieces of rock around).

In fact, if humans could spend (at least) a significant fraction of the mass of asteroid belt building a telescope, I seriously doubt that would be the best option. Such a civilization would be on par with ones that could build http://en.wikipedia.org/wiki/Dyson_sphere" (i.e., capable of rearranging a solar system's planets/planetary material at will).

 

[Arch2008]

http://en.wikipedia.org/wiki/Astronomical_optical_interferometry

Don’t forget interferometry. An array of large telescopes receiving photons that are then combined using computers can mimic the effect of an enormous telescope. Such an array orbiting the Sun would be possible, although the technical problems are daunting to our present level of ability. Certainly in the not too distant future, surface images of any exoplanets orbiting the several dozen nearest stars should be possible for such an array.
We’ll see Earth II before we claim it. ;)

 

[abuguchie]

http://kepler.nasa.gov/news/mmu/index.cfm?FuseAction=ShowNews&NewsID=109
Here is the official site about the Kepler findings.

 

[abuguchie]

As well as this one:
http://www.nasa.gov/mission_pages/kepler/news/kepler_data_release.html

 

[Oldfart]

Thanks, everyone -- fastinating stuff!

And good timing! Now that Kepler has spoken, it seems clearly the time to start designing an early version of the butterfly telescope, one which will at least reveal oceans and mountains, maybe forests and maybe even sailing ships at anchor! I suspect that once signs of life are found on other star's planets, there will be no stopping a massive effort to look deeper, out of both scientific curiosity and to spy upon civilizations more advanced than ours, to try to learn their secrets. Suddenly I'm confident that the butterfly telescope is not just a dream!

All of which makes me wonder who, out there, is watching our butterflies...

 

[Neandethal00]

What do you suppose would be the limiting resolving power of this telescope system? Assume it's built on Earth or nearby with money no object. Could it, for instance, detect a butterfly flitting about on a planet 100 LY from us? If not, what are the limiting factors?

Thanks!

I don't think future telescopes will be built from glass materials because of the limitation pointed out by many posters.

Long ago I read a few papers where researchers found holograms of certain artificial patterns have lensing effects. I don't know why those dicoveries have not been pushed further. Anyway, instead of glass or glass-like materials, we must wait for a breakthough in material science to watch a butterfly on a flower 100LY away.

 

[twofish-quant]

What if the planet is civilized and we all get put in zoos? Or if we all get eaten by lions, tigers, and bears? A closer look is needed first, we need to come fully prepared for our new environment.

One of the more interesting books that I read was a book on space law, and the last chapter was a discussion of the legal status of aliens. There are three possibilities. One is that we meet aliens that are more technologically advanced. That is legally easy. We do whatever they tell us to do. The second case was we meet aliens that are equal technologically advanced. That's tricky, but still not hard because we'd develop something similar to diplomatic relations.

The hard part is if we meet aliens that are technologically less advanced, and the book spent about fifty pages going over the legal issues. The solution would probably be to put the planet under the jurisidiction of the United Nations and use the United Nations as a forum for figuring out what to do, but even that would be messy because the major powers surrender a great deal of power to the UN, which they might not be willing to do.

 

[twofish-quant]

I don't think future telescopes will be built from glass materials because of the limitation pointed out by many posters.

I think they well be. Glass is a pretty good material for telescopes.

Long ago I read a few papers where researchers found holograms of certain artificial patterns have lensing effects. I don't know why those dicoveries have not been pushed further

It's just that the technology is hard, and there are easier ways of pending light.

Anyway, instead of glass or glass-like materials, we must wait for a breakthough in material science to watch a butterfly on a flower 100LY away.

It's not so much materials science as signal processing and astro-engineering. What we *can* do right now, is to put to radio telescopes on different parts of the Earth and then electronically combine the radio signals to create something that works like a giant telescope the size of the earth.

 

[twofish-quant]

And good timing! Now that Kepler has spoken, it seems clearly the time to start designing an early version of the butterfly telescope, one which will at least reveal oceans and mountains, maybe forests and maybe even sailing ships at anchor!

Being worked on.

But whatever we see, it will be interesting. If we point out telescopes at Earth like planets and we find that they are all environmental disasters that never quite got to the point where anything like life existed, then that will be also pretty amazing.

I suspect that once signs of life are found on other star's planets, there will be no stopping a massive effort to look deeper, out of both scientific curiosity and to spy upon civilizations more advanced than ours, to try to learn their secrets.

And if we find no signs of life on other star's, there will be no stopping a massive effort to look deeper, because at that point we'd really want to know what makes Earth special. The knowledge that we are alone would be as revolutionary as to find out that we are not.

Within the next two or three decades, we will know if life-supporting Earth planets-like are common or not.

There is one important thing that we *have* learned already. The solar system has some planets in nicely behaved circular orbits, with all of the big planets way out in the other solar system where they can knock a comet or so, but where they don't bother the earth.

We've already figured out that this is somewhat unusual for a solar system, and most solar systems aren't as "nicely laid out."

All of which makes me wonder who, out there, is watching our butterflies...

Maybe someone. Maybe no one. Either way, it's really mind blowing.

The really mind blowing part is if it turns out that we are the first civilization in the Milky Way, and a billion years from now, some astro-archeologist will be trying to piece together the legend of the lost ancients, who happen to be us.

 

[stany]

yeah maybe we are being watched right now millions of years in the future by our ancestors on planet X in another galaxy

 

[matt.o]

I would think that if a buttefly were to exist on an extrasolar planet, then this planet must have a significant atmosphere in order to support flight. This atmosphere would likely have some level of turbulence, thus affecting what could be resolved by this "uber-telescope." I suspect this would become a limiting factor in observing objects at the butterfly scale!

 

[Oldfart]

Being worked on.

By whom, where? I'm 75 and would like to speed things up a bit, don't have all day, so to speak. Do they take money?

 

[twofish-quant]

By whom, where?

Rus Belikov at NASA Ames

I'm 75 and would like to speed things up a bit, don't have all day, so to speak. Do they take money?

Yes. One thing that you can do is to subscribe to www.spacenews.com and call your congressman whenever there is talk of budget cuts.

 

[FtlIsAwesome]

How powerful of a telescope would we need to see other planets (suppose one is around Alpha Centauri A or B) as good as we can see Pluto with our current telescopes?

EDIT: Pluto's angular diameter is 0.11". Hubble has made the highest resolution images. So what's that resolution? Looking at the images I guess they have a resolution somewhere between 1/4 and 1/8 of Pluto's diameter.

 

[AwesomeSN]

It turns out that Kepler just announced their results, and it's found 54 earth-sized planets in the right area of their stars to support life, and there will likely be more of them as time passes. The thing now is to look at those candidates to see what they are like.

Also, there are some interesting ethical issues, which would make for great science fiction stories. Suppose we've totally screwed up the planet Earth, and we do find an Eden-planet. Do we really have the right to screw up that planet?

Or here is another scary thought (which has already been used in SF). Suppose we have a lot of different civilizations. Some of them which are "nice" (i.e. they don't want to mess up other planets) and some of them are "nasty" (the mess up one planet, and when they are done with that, they go off and mess up other planets). If it turns out that the nasty ones are the ones that end up on more planets, then it's going to be really unpleasant to meet them.

(Greetings planet Earth, we've messed up our planet, and since we've seen the butterflies in your world, we've decided to take over. Put us in charge, or else we'll fry you with the telescopes we've used to look at your butterflies.)

So that would make us nasty, eh? :)

 

[IsometricPion]

How powerful of a telescope would we need to see other planets (suppose one is around Alpha Centauri A or B) as good as we can see Pluto with our current telescopes?

Using the formula ryan_m_b gave earlier in the thread (post #5), at 562nm the diameter (for http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html" light-years away, the formula yields: 19.4km, for a telescope the same fraction larger than this value as the Hubble was larger than the Pluto value the diameter would have to be 23.1km.

 

[Ryan_m_b]

Using the formula ryan_m_b gave earlier in the thread (post #5), at 562nm the diameter (for http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html" light-years away, the formula yields: 19.4km, for a telescope the same fraction larger than this value as the Hubble was larger than the Pluto value the diameter would have to be 23.1km.

It's a useful little equation that. It's important to remember that this is why we don't use light sensing telescopes to look for planets but then again this is a thread about future potential

 

[twofish-quant]

Using the formula ryan_m_b gave earlier in the thread (post #5), at 562nm the diameter (for http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html" light-years away, the formula yields: 19.4km, for a telescope the same fraction larger than this value as the Hubble was larger than the Pluto value the diameter would have to be 23.1km.

Which is less difficult than it might sound. The VLI telescope in New Mexico is a radio telescope that is 21 km long, and there are proposals for space based telescopes of this size.

http://olbin.jpl.nasa.gov/

In particular you there are proposals for a satellite telescopes whose mirrors are 100 km apart.

http://olbin.jpl.nasa.gov/links/index.html

 

[Zentrails]

Which is less difficult than it might sound. The VLI telescope in New Mexico is a radio telescope that is 21 km long, and there are proposals for space based telescopes of this size.

http://olbin.jpl.nasa.gov/

In particular you there are proposals for a satellite telescopes whose mirrors are 100 km apart.

http://olbin.jpl.nasa.gov/links/index.html

Actually astronomers have already combined images from telescopes of various sorts aiming at the same part of the sky from opposite spots in the Earth's orbit, which is a lot longer than 21 km.

The Hubble telescope was once pointed at the same spot for a week and found 3,000 new galaxies. Theoretically, you could do the same thing for six months and get even better resolution. The law of diminishing returns applies, though.

The best telescopes already exist, IMO: Gravitational lensing.
It's hard to imagine humans doing better than that.

 

[twofish-quant]

Actually astronomers have already combined images from telescopes of various sorts aiming at the same part of the sky from opposite spots in the Earth's orbit, which is a lot longer than 21 km.

With radio yes. Not with optical.

There are two things to worry about. Detail and brightness. You can have extremely detailed images which aren't sensitive to faint objects, or you can have extremely sensitive but somewhat blurry images,

The Hubble telescope was once pointed at the same spot for a week and found 3,000 new galaxies. Theoretically, you could do the same thing for six months and get even better resolution. The law of diminishing returns applies, though.

No you can't. The fact that the telescope has a finite size means that you won't get any better resolution. You will see dimmer and dimmer galaxies, but that's something different.

 

[Zentrails]

With radio yes. Not with optical.

There are two things to worry about. Detail and brightness. You can have extremely detailed images which aren't sensitive to faint objects, or you can have extremely sensitive but somewhat blurry images,

No you can't. The fact that the telescope has a finite size means that you won't get any better resolution. You will see dimmer and dimmer galaxies, but that's something different.

No, you should get slightly better resolution, because of parallax, certainly very small for nearly all other galaxies, but not small for stars in our own galaxies. Combine that with computer enhancement and you should get better resolution - it's effectively like using a Newtonian reflector telescope with a bigger mirror - Earth based optical telescopes are always categorized by mirror diameter and there are telescopes out there now with multiple mirrors that are aimed by computerized coordinated control. I agree that the effect is probably insignificant for a single telescope. If you could combine many telescopes from a variety of orbits around the sun, the effect should be more pronounced.

We might have differing definitions of resolution. All stars that are lightyears away are detected by a single photon over a certain period of time - so there is a limit to the resolution you can get with an optical telescope because of that. I'm talking about objects that are large enough or close enough to have a optically measurable diameter.

The one week Hubble photograph which identified 3,000 new galaxies was more than just a long exposure, simply collecting more photons in a particular region of the sky, IIRC.

And as a bonus you can calculate distances to these stars as well. They can even eliminate noise due to atmospheric scattering by sending particle into the sky and measuring the scatter of the particles, then computer correcting the images. That certainly enhances resolution - and you eliminate one of the advantages of an orbiting telescope.

It occurs to me that the Cobe background study (currently being refined with more and more detail) could be called the best telescope of them all, if you define the power of a telescope as it's ability to detect the farthest away objects. The resolution keeps getting better but it's nothing like the resolution of an optical telescope. It's a radio wave (microwave) detecting telescope, but it works by digitally subtracting the microwaves of known objects.

I spend a lot of time trying to grasp what the COBE backround is really showing us. Not only is it far, far back in time, in a manner of speaking, but the images come from a universe which had a much, much smaller volume than what we think the volume of the universe is today. It's exceedingly difficult to visualize, at least for me.