In your above calculation, you're assuming that an object needs to be resolved to be visible. To the contrary, telescopes are able to see un-resolved objects (o

In your above calculation, you're assuming that an object needs to be resolved to be visible. To the contrary, telescopes are able to see un-resolved objects (objects whose angular size is below the angular resolution of the telescope) all the time -- they are called "stars". The relevant parameter here isn't angular size, but flux[0] (brightness). [0] https://en.wikipedia.org/wiki/Radiative_flux https://en.wikipedia.org/wiki/Radiative_flux