cosmic radiation

Cosmic flux versus particle energy at the top of Earth's atmosphere Left image: cosmic ray muon passing through a cloud chamber undergoes scattering by a small angle in the middle metal plate and leaves the chamber. Right image: cosmic ray muon losing considerable energy after passing through the plate as indicated by the increased curvature of the track in a magnetic field.

Cosmic rays or astroparticles are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from outside the Solar System — from the Milky Way, from distant galaxies, and from the Sun. Upon impact with Earth's atmosphere, cosmic rays produce showers of secondary particles, some of which reach the surface, although the bulk are deflected into space by Earth's magnetic field (the magnetosphere) or by the heliosphere.