Streams of high-energy particles that strike
the Earth’s atmosphere are called cosmic rays.
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Cosmic Rays
- most cosmic rays are deflected (pushed aside) by the Earth’s magnetic field or collide with particles in our Earth’s atmosphere long before they reach the ground.
. - the study of cosmic rays provided scientists with most of their early knowledge about high-energy particles -these particle can only be made on Earth in huge machines (cosmic rays detection and arrays of detectors) called particle accelerators.
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Energy Cosmic Rays level
- lowest-energy cosmic rays  –  come from the Sun or Galactic Cosmic Rays (GCRs) from outside the Solar System.
- medium-energy cosmic rays  –  come from sources within the Milky-Way, including powerful supernovae explosions.
- highest-energy cosmic rays  –  may come from outside the Milky-Way.
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Galactic Cosmic Rays (GCRs)
- around 90% are nuclei of hydrogen atoms stripped of their electron. (see atom)
- most other CGRs are helium and heavier nuclei – there are also tiny positrons, electrons and neutrinos.
- neutrinos  –  so small that they pass almost straight through our Earth without stopping.
Neutrinos
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