The sun emits lots of electromagnetic radiation at all frequencies from zero up to fairly energetic X-rays. It also is the source of solar wind, a constant flow of energetic protons, electrons, and light nuclei streaming outwards. Charged particles from solar wind spiral in towards Earth along the geomagnetic field lines and create the Aurora.
Other kinds of radiation have close by and faraway sources. Infrared radiation is emitted by all warm objects. Radio waves are emitted by television and radio stations, cell phones and cell phone towers. Microwaves, radar, and lasers are in common use for communication purposes and other uses.
Perhaps you mean nuclear radiation? Most of this kind of radiation people are exposed to comes from the earth in the form of radioactive elements which can decay, such as radon gas (which seeps out of the earth and may collect in people’s basements), and cosmic rays. People are exposed to X-rays when they visit the doctor and the dentist. Nuclear medicine uses radioisotopes to trace the paths of various molecules in the body, or may be used to help provide sharp images of the soft tissues inside the body. Some radiation is used directly on tumors to help kill cancer cells. A much smaller amount of radiation comes from spent nuclear fuel (nuclear waste) and fallout from old nuclear weapons tests. Near Chernobyl, in Russia, it is still rather radioactive due to a fire at a power plant there which caused the release of a sizeable amount of radioactive material in the atmosphere.
(published on 10/22/2007)