cosmic rays

plural noun

1. Also called: cosmic radiation. radiation consisting of particles, esp protons, of very high energy that reach the earth from outer space

cosmic rays

1. Elementary particles, mainly protons, that are produced by the sun and other stars and then strike the upper atmosphere of the Earth. Some of these particles are absorbed, some help form the Van Allen belt, and some reach the Earth's surface, where they form a part of the background radiation that constantly surrounds us.