Final answer:
An X-ray telescope can only be used above the Earth's atmosphere to directly observe high-energy phenomena that are blocked by the atmospheric layer.
Step-by-step explanation:
The type of telescope that can only be used above the Earth's atmosphere is an X-ray telescope. Earth's atmosphere blocks most radiation at wavelengths shorter than visible light, making it impossible for ground-based telescopes to directly observe ultraviolet, X-ray, and gamma-ray emissions. This is why satellites such as the Chandra X-ray Observatory have been launched into orbit, as they can detect high-energy phenomena like supernovae and black holes without atmospheric interference.