Cosmic rays are high energy charged particles.

Energy

Cosmic Rays typically have energies ranging between 10⁶ - 10²⁰ eV (around 10^-13 - 10^-10 Joules). Although in these terms this does not sound a very large amount of energy, the energy is very concentrated; the particles are extremely small (typically 10^-29kg and of the order 10^-18m in radius, or 0.000000000000000001 metres in radius) it can be appreciated that this is a large energy for each of these minute particles to have.

Cosmic rays originate in outer space, (mainly from supernova explosions but also from stars see "where do cosmic rays come from" to read more) travel at the speed of light and strike the Earth from all directions.

The cosmic rays strike the Earth's surface at the rate of about 1 cosmic ray every square centimetre every minute. Perhaps a more meaningful way to look at this is that during an average nights sleep a person will have on average of a million cosmic rays traveling through their body!

Cosmic rays are very penetrating; so much so that they have also been detected under the ground, such as in the London Underground system and down deep mines. The table below gives some comparison of penetration for different types of radiation, so that cosmic rays can be compared.