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hegemonicon comments on Open Thread: March 4 - 10 - Less Wrong
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Lately I've been wondering about telescope resolving power, and physical limits on the size of features we can see at interstellar distances.
I know about the diffraction limit, which (by my quick and dirty math) seems to imply a telescope on the order of a kilometer in size could resolve objects several meters across, but I imagine it's actually more complicated than that. Does anyone know a good source of information on the topic?
Any introduction to astronomy textbook will help you out. I used BOB.
Instead of having huge individual telescopes which run into issues {How do you keep the mirror clean? What shape do you make it? How do you deal with the atmosphere (Adaptive optics are hard enough for small telescopes)? Constructing a telescope this large in space would be fantastically difficult and expensive.}, you can do interferometry. The largest telescopes these days run into the tens of meters, see E-ELT.
Not sure I've got a good source for you, but if you use the Rayleigh criterion you get that you can just about make out earth-sized objects using visible light at 4 ly. You could use much higher energy photons (better resolution from lower wavelength), but this gives you other problems. Anything beyond visible light won't make it through the atmosphere (1 km is a BIG thing to put into space), and x and gamma rays are really hard to build optics for.
Yeah, if you want to build a space telescope 1km in diameter, you'd better build it out of local materials.