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Why are many major observatories built on high mountains?
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Telescope
Aerial view of the Keck Observatory's twin domes, which are opened to reveal the telescopes. Keck II is on the left and Keck I on the right.
Major observatories are built on high mountains primarily to improve the quality of astronomical observations by minimizing the interference caused by Earth's atmosphere.12
High-altitude locations offer several critical advantages:
- Reduced Atmospheric Interference: Mountains place telescopes above a significant portion of the atmosphere, resulting in less air to obscure light from distant celestial objects.1
- Improved Clarity and Stability: By operating at high elevations, telescopes experience less atmospheric turbulence, which otherwise causes images to flutter and become diffuse—a phenomenon known as poor "seeing".32
- Lower Humidity: High, dry mountaintops are essential for infrared astronomy. Infrared radiation is easily absorbed by atmospheric water vapor, which is most concentrated at lower altitudes. Sites like Mauna Kea provide the extremely dry conditions necessary to detect these wavelengths.14
- Weather Conditions: Many high-altitude sites are located above the cloud layer, ensuring a higher frequency of clear, calm, and cloudless nights.1
Additionally, these sites are typically chosen to be well away from the light pollution of cities, further enhancing the ability to study faint and distant objects.2