Originally posted by twhitehead
Hey! Thats not 'on Earth'. It doesn't count!
Seriously, the idea of combining scopes to get the resolution of the separation distance is squeezing more information out of radiotelescopes and more recently, optical telescopes as well.
It first started with radioscopes because it was a lot easier to get coordinated phase information at the much lower frequencies of RF telescopes. Recently it has proven possible to get that same kind of phase information from optical scopes as well so they have been able to make scopes that combine to make the resolution the same as a scope the size of the distance between scopes.
I suppose that eventually will extend to X ray scopes as well. The thing that limits the distance between optical scopes is the requirement at least right now of connecting the phase detection lines with fiber optics. Radio telescopes can connect with radio waves or even over the internet so you could theoretically have radio scopes on opposite sides of the solar system giving a scope with the resolution of one billions of kilometers across.
I think optical scopes won't be able to do that trick for a few years yet but the resolution limit of optical scopes is a lot greater than the equivalent radio scope, it's tied to the wavelength of interest, shorter wavelengths means more wavelengths gathered in a given scope size at optical wavelengths, where one wavelength may be 500 nanometers (green color) and so an optical scope system can get much greater bang for the buck, separation wise.
Like a 1 meter scope (1 million micrometers) can collect about 8 E 11 one micron wavelength packets which is in the infrared portion of the optical band. If you wanted to collect 8 E 11 packets of 1 meter wavelengths you would have to have a mirror diameter of 80,000 meters or so. The wavelengths used by most radio telescopes are a lot shorter than 1 meter so those scope would have that much better resolution from the git go.
12,000 km separation of radio scopes listening to 10 cm waves would certainly give better than optical resolution, of course that does not mean you would have the sensitivity of a scope with a single reflector 12,000 km wide, only the resolution.
So you can get more resolution than optical scopes if you separate them further which is possible and done of course, so separating the scopes by 80,000,000 meters would give 1000 times the resolution at 1 meter wavelength than that 1 meter scope reading one micron wavelengths.
That same 1 meter scope, if used at UV wavelengths of say, 100 microns, would give ten times the resolution of the same size used at 1 micron. So the Hubble, about 2 meters across, can give resolution numbers by itself of 1/20th of an arc second.
So connect two hubbles one km apart would give about 500 times the resolution. That kind of resolution is almost happening now on the best optical scope systems and will only get better in the future. It is a great time for astronomers!
Of course all that is based on near perfect optics and in the Earth's atmosphere, active optics that correct for the way light wiggles as it goes through the atmosphere on its way to the scopes. That is a whole other amazing technology in itself!