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Isn't building a 100m telescope incredibly hard? does that kind of technology exist already? (I genuinely don't know). Also, what would the effect of the atmos

Isn't building a 100m telescope incredibly hard? does that kind of technology exist already? (I genuinely don't know). Also, what would the effect of the atmosphere be in such a large telescope? would a bigger mirror increase or decrease the effects of Earth's atmosphere for these kind of observations?

Balgair 9y ago
Noise is noise. If you put gain on the signal in general, you'll put gain on the noise too. That's why James Webb is in space and the 30 Meter Telescope (TMT) is in Hawaii, less atmosphere and clear air means less noise inputted. Still, the TMT is pretty darn good. So yes, you are correct, bigger telescope means more noise (in gestalt) while in atmosphere. THe reason bigger is better is because you can resolve smaller angles. The Fourier treatment of optics is useful here. The radius of your lenses/reflectors sets the limit of the higher spatial frequency. Low spatial frequencies pass through small lenses/refectors and high spatial frequencies pass through larger ones. Therefore the bigger the telescope, the more higher order spatial frequencies you can collect. https://en.wikipedia.org/wiki/Fourier_optics https://en.wikipedia.org/wiki/Fourier_optics Why not a 100 Meter Telescope? Cost and engineering. With these retro reflectors getting so big, you have to worry a lot about thermal expansion and differential levels of it across the whole surface. Also, the structure to hold it has to be monitored really closely in real time to make sure the calculations are accurate. It's not easy. Also, with modern adaptive optics, you'll have apply all the little piezo-motors across the entire surface which goes as the square of the radius, so costs go up geometrically (plus about 15% more for each doubling in surface area due to cabling, power issues, larger facilities with thicker steel beams, more janitors, etc.). If the TMT costs X, then the 100-MT should cost about 11X, and with the 15% doubling factor, its ~15X for only a 3X increase in radius.
- ExactoKnight 9y ago
  > If the TMT costs X, then the 100-MT should cost about 11X, and with the 15% doubling factor, its ~15X for only a 3X increase in radius. The Thirty Meter Telescope cost $1 billion. So the 100 Metre Overwhelmingly Large Telescope would cost ~$15 billion using your ~15x multiplier. That's large, but for perspective: The F-35 fighter jet program cost $168 billion. Like with the Large Hadron Collider, if the extra cost means the difference between being able to crucially measure the atmospheric spectra of nearby exosolar planets and not being able to, then the extra cost is worth it. I'll take getting definite answers to humanity's most pressing questions, over new tools for killing people, any day.
  - Balgair 9y ago
    As would I! Unfortunately, it seems the Realist sect of International Relations seems to be en vouge these last few decades. That said, there is an existential threat to 'science' in general with these large and impossible to replicate engineering experiments. They kinda get subsumed into the 'Big Science' camp where the budgets mean more than anything else and then incentives get muddied. In the physics field, there is still enough animosity and ego between the researchers to keep it all in 'science' and the results don't get massaged like in bio where it's all 'Big Science' now and the results get tweaked. https://en.wikipedia.org/wiki/Realism_(international_relations) https://en.wikipedia.org/wiki/Realism_(international_relatio...
- saganus 9y ago
  Very nice explanation. Thanks! 15 billion (as per a sibling comment) sounds like a lot, but relative to other, IMO not so important things like said plane, it's not that much. However I wonder if it would be worth it or if that money would be better spent creating a Hubble replacement for example.
  - Balgair 9y ago
    Thanks! I just finished a 14 month class in Optics, so it's fresh for me. The alternative to putting something into space is much more preferable. No matter how big a ground based scope it is, you still have all of that air mucking up the data coming in and you just can't get as good of data. Space is just so much better, as you know, it is mostly empty of the matter we are trying to look at. Granted, for many EM frequencies, ground based is fine. But a lot of atoms we are trying to look at happen to be present in the air too, messing up the data. Space costs a lot more, but I think there is no comparison in the long run. The dark side of the moon would be a good combo of both advantages though. You could build and also maintain and modify a very very large telescope with out any air or other ground based interference. The flip side is that it would be even more remote than current space based telescopes and therefore more expensive to get things to, like people, air, water, food, and fuel. But, hey, it's the flipping Moon! Like, we have a semi-good reason to go back now! For science!
goatlover 9y ago
A quick search shows that the largest optical telescope is only 10.4m, and we would probably want to put it in space, free of atmospheric distortion.

Balgair 9y ago

Noise is noise. If you put gain on the signal in general, you'll put gain on the noise too. That's why James Webb is in space and the 30 Meter Telescope (TMT) is in Hawaii, less atmosphere and clear air means less noise inputted. Still, the TMT is pretty darn good. So yes, you are correct, bigger telescope means more noise (in gestalt) while in atmosphere. THe reason bigger is better is because you can resolve smaller angles. The Fourier treatment of optics is useful here. The radius of your lenses/reflectors sets the limit of the higher spatial frequency. Low spatial frequencies pass through small lenses/refectors and high spatial frequencies pass through larger ones. Therefore the bigger the telescope, the more higher order spatial frequencies you can collect. https://en.wikipedia.org/wiki/Fourier_optics https://en.wikipedia.org/wiki/Fourier_optics Why not a 100 Meter Telescope? Cost and engineering. With these retro reflectors getting so big, you have to worry a lot about thermal expansion and differential levels of it across the whole surface. Also, the structure to hold it has to be monitored really closely in real time to make sure the calculations are accurate. It's not easy. Also, with modern adaptive optics, you'll have apply all the little piezo-motors across the entire surface which goes as the square of the radius, so costs go up geometrically (plus about 15% more for each doubling in surface area due to cabling, power issues, larger facilities with thicker steel beams, more janitors, etc.). If the TMT costs X, then the 100-MT should cost about 11X, and with the 15% doubling factor, its ~15X for only a 3X increase in radius.

ExactoKnight 9y ago
> If the TMT costs X, then the 100-MT should cost about 11X, and with the 15% doubling factor, its ~15X for only a 3X increase in radius. The Thirty Meter Telescope cost $1 billion. So the 100 Metre Overwhelmingly Large Telescope would cost ~$15 billion using your ~15x multiplier. That's large, but for perspective: The F-35 fighter jet program cost $168 billion. Like with the Large Hadron Collider, if the extra cost means the difference between being able to crucially measure the atmospheric spectra of nearby exosolar planets and not being able to, then the extra cost is worth it. I'll take getting definite answers to humanity's most pressing questions, over new tools for killing people, any day.
- Balgair 9y ago
  As would I! Unfortunately, it seems the Realist sect of International Relations seems to be en vouge these last few decades. That said, there is an existential threat to 'science' in general with these large and impossible to replicate engineering experiments. They kinda get subsumed into the 'Big Science' camp where the budgets mean more than anything else and then incentives get muddied. In the physics field, there is still enough animosity and ego between the researchers to keep it all in 'science' and the results don't get massaged like in bio where it's all 'Big Science' now and the results get tweaked. https://en.wikipedia.org/wiki/Realism_(international_relations) https://en.wikipedia.org/wiki/Realism_(international_relatio...
saganus 9y ago
Very nice explanation. Thanks! 15 billion (as per a sibling comment) sounds like a lot, but relative to other, IMO not so important things like said plane, it's not that much. However I wonder if it would be worth it or if that money would be better spent creating a Hubble replacement for example.
- Balgair 9y ago
  Thanks! I just finished a 14 month class in Optics, so it's fresh for me. The alternative to putting something into space is much more preferable. No matter how big a ground based scope it is, you still have all of that air mucking up the data coming in and you just can't get as good of data. Space is just so much better, as you know, it is mostly empty of the matter we are trying to look at. Granted, for many EM frequencies, ground based is fine. But a lot of atoms we are trying to look at happen to be present in the air too, messing up the data. Space costs a lot more, but I think there is no comparison in the long run. The dark side of the moon would be a good combo of both advantages though. You could build and also maintain and modify a very very large telescope with out any air or other ground based interference. The flip side is that it would be even more remote than current space based telescopes and therefore more expensive to get things to, like people, air, water, food, and fuel. But, hey, it's the flipping Moon! Like, we have a semi-good reason to go back now! For science!

goatlover 9y ago

A quick search shows that the largest optical telescope is only 10.4m, and we would probably want to put it in space, free of atmospheric distortion.