Cosmic rays are high-energy particles that originate from outer space and penetrate the Earth's atmosphere. These particles include protons, muons, electrons, and other subatomic particles. There are several synonyms for the term cosmic ray, including intergalactic radiation, high-energy radiation, and space radiation. Interstellar radiation, galactic radiation, and extraterrestrial radiation are also used to describe the same phenomenon. Cosmic radiation and cosmic particles are other synonyms for cosmic rays. These particles can pose a threat to the health and safety of astronauts and space travelers and can interfere with electronics and communication systems. Scientists continue to study cosmic rays to better understand their origins and effects.