False-color image of the solar corona as seen in deep ultraviolet light at 17.1 nm by the Extreme ultraviolet Imaging Telescope instrument aboard the SOHO spacecraft

An ultraviolet photograph of the Earth taken from the Moon by Apollo 16 astronauts. Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays. It is so named because the spectrum consists of electromagnetic waves with frequencies higher than those that humans identify as the color violet (purple). UV light is typically found as part of the radiation received by the Earth from the Sun. Most humans are aware of the effects of UV through the painful condition of sunburn. The UV spectrum has many other effects, including both beneficial and damaging changes to human health.