- Subatomic particles entering the Earth’s atmosphere from above. Most cosmic rays are of solar origin and their composition reflects the Sun’s own, consisting mainly of neutrons and alpha particles, since the Sun consists mainly of hydrogen and helium. But other cosmic rays appear to come from deep space, especially from supernovae, which accounts for the appearance of heavier nuclei among cosmic rays.
- high energy particles which travel through space at nearly the speed of light, and which consist mostly of protons and alpha particles. Cosmic rays have many sources, including solar flares, and impinge upon the earth from every direction. Also called cosmic radiation, or primary cosmic rays.
- synonym cosmic radiation
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