space radiation environment lunar radiation environment The natural radiation environment on or in the vicinity of the Earth's moon, comprising: the free space radiation environment, radiation produced by interactions of the free space radiation environment with the lunar surface, and radiation produced by naturally occurring radioactive elements in the lunar crust. The lunar radiation environment varies with location and time--for example with proximity to the lunar surface, shielding by the Moon itself, and with the solar cycle and periodic solar particle events. It can include both ionizing radiation and non-ionizing radiation such as UVA, UVB and visible light, but often is used to refer to biologically damaging ionizing radiation such as galactic cosmic radiation and solar particles.