Cosmic rays can loosely be defined as energetic
particles originating outside of the
Earth. The composition includes
electrons,
protons,
neutrons, and
atomic nuclei from a large region of the
periodic table.
The
kinetic energies of these particles span over fourteen orders of magnitude.
The wide variety of particle energies is reflected in the wide variety of sources.
Cosmic rays originate from energetic processes on the
Sun all the way to the farthest reaches of the visible universe.
Cosmic rays can be conceptually broken into different kinds:
Cosmic rays can have energies up to 10E14 MeV 1
Cosmic rays were initially considered to come from some source other than the Sun. This was because the Sun was thought to emit little but visible light, and, of course, cosmic rays are isotropic and would arrive at Earth from all directions.
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