Cosmic rays are electromagnetic waves of extremely short wavelengths. They originate from galaxies outside solar system. As the rays are from outer space or cosmos, they are termed as cosmic rays. The rays consist of protons, alpha particles and positive ions. Almost 85% of cosmic rays are protons. Another 12% are alpha particles.
The distant galaxies are major sources of charged particles, where as sun is a poor contributor. The presence of high electric and magnetic fields in these galaxies accelerate the charged particles.
The charged particles that reach at the outer atmosphere are called primaries. They collide with the particles or molecules in the atmosphere leading to formation of secondaries. The major secondaries are electrons, positively charged particles (positrons) and mesons.
The thick atmosphere around earth functions as a natural blanket and protects us from cosmic rays. Atmosphere of earth is opaque to cosmic rays of lower energy levels and hence only secondaries reach the surface. This radiation is also attenuated by absorption in the atmosphere. As a result people on the ground are not affected by the rays. However, the strength of cosmic rays is more at higher altitudes. Hence, the severity of cosmic rays is more on people like pilots who spend more time at higher altitudes. These radiations are also within bearable limits only.