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Why are X-ray and gamma-ray telescopes placed above Earth’s atmosphere?

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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.

X-ray and gamma-ray telescopes must be placed above Earth’s atmosphere because the atmosphere absorbs most of this high-energy radiation, preventing it from reaching the ground.123

In the electromagnetic spectrum, X-rays and gamma rays are blocked by atmospheric atoms and molecules through processes such as electronic excitation. Because of this atmospheric absorption, astronomers must use balloons, rockets, or satellites to carry detectors to high altitudes or into orbit to observe these celestial sources.4123

While most gamma-ray telescopes operate in space, some ground-based facilities can indirectly observe gamma rays by detecting Cherenkov radiation—the light produced when gamma rays strike the upper atmosphere. However, for direct detection and high-resolution imaging, space-based observatories remain essential.312