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An air shower is a "shower" of ionized particles and photons resulting from the interaction of a very high-energy photon or other particle with the atmosphere, such as a cosmic ray or gamma ray entering Earth atmosphere. The incoming particle's interaction with an air molecule results in multiple lower-energy particles and photons, often still with enough energy to trigger the same such interaction, in turn producing more particles and yet more such interactions, a chain-reaction resulting in many such particles and photons, i.e., the "shower". The atmosphere is acting as a scintillator. Resulting sufficiently-low-energy particles can reach the ground, and ground-based detectors spread to record the pattern of the air shower can yield data that can be analyzed to determine characteristics of the original particle or ray.