Question

why are optical telescopes located in inhabited places on mountains

Answer 1

Mountaintops also have unobstructed views of the horizon in all directions. Lastly, most cities and towns -- with their accompanying light pollution -- are situated in valleys and plains, so remote mountaintops are among the last places on Earth to find the dark skies so sought after by astronomers.

Earth's Atmosphere

Light Pollution

Space Observatories

Telescopes and Modern Observatories