Why are many major observatories built on high mountains far from cities?

Major observatories are strategically located on high mountains far from cities primarily to minimize the negative impacts of the Earth’s atmosphere and human-made interference on astronomical observations.1

Atmospheric Conditions

The atmosphere acts as a barrier to clear observation. High-altitude sites offer several advantages:
* Reduced Turbulence: Atmospheric turbulence causes light from celestial objects to "dance" or blur, a phenomenon known as poor seeing. High mountains often provide more stable air, which improves the resolution of telescopic images.21
* Transparency: The atmosphere absorbs certain wavelengths of light, particularly in the infrared spectrum, due to water vapor and carbon dioxide. High-altitude locations typically have lower humidity, allowing for clearer transmission of these signals.1

Light Pollution

Cities produce light pollution, which is excessive or misdirected artificial light that scatters in the atmosphere and creates "skyglow." This brightness severely reduces the visibility of stars and faint celestial objects, making it essential for observatories to be situated well away from urban centers to maintain a dark, clear night sky.3