Cosmic rays are streams of high-energy particles that strike Earth’s atmosphere.
The lowest-energy cosmic rays come from the Sun, or are Galactic Cosmic Rays (GCRs) from outside the Solar System.
Medium-energy cosmic rays come from sources within our own Milky Way, including powerful supernova explosions.
Collisions between cosmic rays and the hydrogen gas clouds left by supernovae create a kind of radiation called synchrotron radiation, which can be picked up from places such as the Crab nebula by radio telescopes.
The highest-energy cosmic rays may come from outside our galaxy.
About 85 percent of GCRs are the nuclei of hydrogen atoms, stripped of their electron (see atoms).
Most other GCRs are helium and heavier nuclei, but there are also tiny positrons, electrons and neutrinos.
Neutrinos are so small that they pass almost straight through the Earth without stopping.
The study of cosmic rays gave scientists knowledge about high-energy particles – every subatomic particle except electrons, protons and neutrons.
Most cosmic rays are deflected (pushed aside) by the Earth’s magnetic field or collide with particles in the atmosphere long before they reach the ground.
The Earth is constantly bombarded by cosmic rays — streams of tiny, highly energized particles, traveling at high speed. Some came from exploding stars. Most cosmic rays don’t get through Earth’s atmosphere, but neutrinos pass right through our planet and out the other side.