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Why must many infrared telescopes operate at high altitude or in space?

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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.

Infrared telescopes must operate at high altitudes or in space primarily because Earth's atmosphere is largely opaque to infrared radiation.12

Water vapour and carbon dioxide present in the lower atmosphere strongly absorb infrared wavelengths, preventing them from reaching ground-based observatories. While some observations can be conducted through narrow "windows" in the atmosphere from high-altitude sites like Mauna Kea, these locations are chosen specifically for their low humidity.132

To access the full range of infrared data, telescopes must be positioned above the bulk of these absorbing molecules. This is achieved by:2
* High-altitude observatories: Locating telescopes on dry, high mountaintops.13
* Airborne platforms: Using specialized aircraft, such as the Stratospheric Observatory for Infrared Astronomy, to fly above most water vapour.12
* Space-based observatories: Deploying satellites like the Infrared Astronomical Satellite or the James Webb Space Telescope into space, where they are entirely free from atmospheric interference.12