Cosmic ray

Cosmic ray



(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


  1. An energetic particle originating outside our solar system.
  2. Cosmic radiation: a stream of cosmic rays.

Usage notes

The use of the words "ray" and "radiation" implies incorrectly that cosmic rays are electromagnetic waves, similar to light rays and X-rays; cosmic rays were so named before their nature was known.