This series of web pages gives an elementary discussion of cosmic rays, followed by sections on high energy particles in the universe and high-energy particles from the Sun.  It describes the existence particles whose velocity approaches that of light, their probable sources, and their measurement.  This is part of a large work, "The Exploration of the Earth's Magnetosphere", that gives a non-mathematical introduction to planetary and solar magnetic fields, space weather, aurora, and charged particle motion. A Spanish translation is available.