A stream of high-energy particles, gamma rays and X-rays, falling to Earth from space. The charged particles interact with the upper layers of the atmosphere and create secondary radiation that reaches the Earth’s surface. Stars, including our Sun, are a source of cosmic rays. Cosmic rays are shielded by the atmosphere, so they are more intense at higher altitudes. Charged particles are deflected by the magnetosphere towards the Earth’s magnetic poles. The annual average dose from cosmic rays in the US is 0.34 mSv.