structural:summarization
Types

Cosmic rays can be divided into two types:

However, the term "cosmic ray" is often used to refer to only the extrasolar flux.

Cosmic rays originate as primary cosmic rays, which are those originally produced in various astrophysical processes. Primary cosmic rays are composed mainly of protons and alpha particles (99%), with a small amount of heavier nuclei (≈1%) and an extremely minute proportion of positrons and antiprotons. Secondary cosmic rays, caused by a decay of primary cosmic rays as they impact an atmosphere, include photons, hadrons, and leptons, such as electrons, positrons, muons, and pions. The latter three of these were first detected in cosmic rays.