Space radiation

There are different types of radiation in space. EM radiation is one of them. UV is one of the EM radiation that will cause health problems to astronauts.

Among EM radiation, gamma rays presents more problems than UV in space travel.

More problematic is cosmic rays from various sources (stars and other heavenly bodies). Cosmic rays are ions of mainly protons, alpha particles and electrons. These may be high energy particles moving at high velocities. Secondly effect such as high speed electrons may generate EM radiation (by Compton effect).

On Earth, we are protected by the 100Km thick atmosphere but in space we do not have such luxury therefore, all of these radiations have to be shielded before space travel is possible.

For more information about:
Atmosphere:
http://en.wikipedia.org/wiki/Earth%27s_atmosphere
Cosmic ray:
http://en.wikipedia.org/wiki/Cosmic_ray
Compton effect:
http://en.wikipedia.org/wiki/Compton_effect
Health threat from cosmic radiation:
http://en.wikipedia.org/wiki/Health_threat_from_cosmic_rays