Cosmic rays which are mainly coming from outside our solar system can penetrate the hulls of a space ship and also the bodies of astronauts. One possible effect of these charged particles can be broken DNA causing cancer over the course of time.

During Fall 2005 a sunspot named "active region 798/808" released plasma almost every day for two weeks. Consequently, the International Space Station measured reduced radiation levels.

Cosmic rays are composed of charged particles which in turn produce magnetic fields that deflect low-energy-galactic cosmic rays away from Earth. The decreased flux of galactic cosmic rays reaching the Earth is referred to Forbush decrease after Scott E. Forbush who discovered this phenomenon.

For simplicity, the following animation does not show the magnetic field of the Earth which deflects a certain percentage of cosmic rays towards the poles causing auroras. The trajectories of cosmic rays are represented by green arrows. The magnetic field lines are shown in black.