Skip to definition.
Get the FREE one-click dictionary software for Windows or the iPhone/iPad and Android apps

Noun: cosmic ray  kóz-mik rey
  1. Highly penetrating ionizing radiation of extraterrestrial origin; consisting chiefly of protons and alpha particles; collision with atmospheric particles results in rays and particles of many kinds

Derived forms: cosmic rays

Type of: ionizing radiation

Part of: cosmic radiation

Encyclopedia: Cosmic ray