Electromagnetic radiation with a shorter wavelength (100 to 4000 ≈) than visible light. Ultraviolet radiation is produced by stars and, naturally, also by the Sun, which is our UV source.
Ultraviolet light is divided into three groups: UV-A, UV-B and UV-C. The one with the longest wavelength, UV-A, reaches all the way to the Earth's surface. Other wavelengths are usually halted by the ozone layer.
One nm (nanometre) equals 10 ≈ (Ângstrˆm) = 10-10 metres.
UV radiation has harmful effects on humans, such as cancer and even genetic change. Powerful UV rays destroy cells. This is why life could not move to land until the protective shield of ozone had been formed some 500 million years ago. Pictured here life in Cambrian seas before life emerged on Earth.
