Electromagnetic radiation left over from the original formation of the universe in the Big Bang: Cosmic background radiation is the electromagnetic radiation that penetrates the Earth from unspecified origins in deep space.

Cosmic rays collectively: Streams of high-energy particles from outer space, consist of protons, alpha particles, and light nuclei, which collide with atomic nuclei in the Earth's atmosphere, and produce secondary nuclear particles.

Primarily mesons (elementary particles are responsible for the forces in the atomic nucleus), such as pions and muons (types of subatomic particles), that shower the Earth.

Nuclear and subatomic particles moving through space at high speeds: Cosmic rays are radiated from the Sun and other stars.

Cosmic rays are streams of ionizing radiations from space, largely of protons, alpha particles, and other atomic nuclei.

Cosmic rays are very high energy nuclei moving at velocities close to that of light which are probably produced by supernova explosions.

On striking the Earth's atmosphere, they produce cascades of other particles (by collision with nuclei in the atmosphere) called air showers.

The time it takes the Sun to travel around the center of the galaxy: A cosmic year, the period of revolution of the Sun around the galaxy, takes roughly 22.5 million years.