Gamma rays come from some of the most mysterious and powerful objects in the universe: black holes, quasars, supernovae, and neutron stars. They speed across the universe, past galaxies, racing between the stars … until they reach the earth, where the atmosphere stops them like a brick wall.
It’s a good thing it does — gamma radiation is highly dangerous to living things. It breaks up molecules and causes mutations. On the unfortunate side, astronomers on Earth can’t see or detect gamma radiation.
So in 1991, NASA launched the Compton Gamma Ray Observatory, CGRO. The observatory, named after the astronomer Arthur Holly Compton, spent 9 years orbiting the Earth.

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| Year launched: | 1991 |
| Telescope type: | Detector |
| Light collector: | Gamma ray counter |
| Light observed: | Gamma ray |