Would it be possible to observe an alien city?

[momo666]

Under what circumstances would a telescope be able to observe an alien city, supposing such a structure was present on a planet?
Are the requirements so high, say the mirror size, that this is simply wishful thinking or is this actually possible?
More specifically, suppose our imagined telescope is 15m in diameter. Is that a fundamental limit that prevents us from achieving such a feat? From what I gather, this kind of observation and detail would require an enormous diameter.

 

[scottdave]

I don't recall the formulas for calculating the necessary mirror size. It might be possible to find evidence of alien activity (assuming they exist) through radio transmissions.

 

[Vanadium 50]

This is far, far out of the realm of possibility. We can't image exoplanets, and indeed most stars.

 

[berkeman]

Under what circumstances would a telescope be able to observe an alien city, supposing such a structure was present on a planet?
Are the requirements so high, say the mirror size, that this is simply wishful thinking or is this actually possible?

https://en.wikipedia.org/wiki/Angular_resolution

 

[Vanadium 50]

So there's your answer - for all but the very nearest stars, the mirror would need to be bigger than the earth.

 

[momo666]

Say the mirror is bigger than the Earth or whatever huge diameter our thought experiment requires. Would that merely give us a picture of the star or would it allow us to observe structures on the orbiting planets?
If it only gives us a picture of the star, are we talking about 2 pixels added together or something like what Hubble gives us when we observe a crater on the Moon?

Edit: So this will clear it up I think.
Suppose the target is 1 light year away and our mirror diameter is 100m. What would be the angular resolution? My math is bad so I got 10m.
What if the mirror diameter is the size of the Earth?

 

[berkeman]

Say the mirror is bigger than the Earth or whatever huge diameter our thought experiment requires. Would that merely give us a picture of the star or would it allow us to observe structures on the orbiting planets?
If it only gives us a picture of the star, are we talking about 2 pixels added together or something like what Hubble gives us when we observe a crater on the Moon?

Edit: So this will clear it up I think.
Suppose the target is 1 light year away and our mirror diameter is 100m. What would be the angular resolution? My math is bad so I got 10m.
What if the mirror diameter is the size of the Earth?

https://en.wikipedia.org/wiki/Angular_resolution

Asked and answered. Thread closed for now.