Observing gamma rays in the atmosphere 

Credit: NASA’s Goddard Space Flight Center/CI Lab
High above Earth’s surface, high-energy gamma rays (magenta) strike the atmosphere. When a gamma ray strikes an air molecule, it shatters into high-speed debris that creates a cascade of particles (blue streaks). These particles are moving so fast they emit light (the blue ring) -- called Cherenkov radiation -- as they travel. Ground-based observatories, such as MAGIC in the Canary Islands, indirectly detect gamma rays through this effect.