ESO Astronomical Glossary - U
Ultraviolet (UV) radiation
Ultraviolet radiation is a type of electromagnetic radiation with wavelengths shorter, and higher energy, than visible light. As most UV is absorbed in the Earth's atmosphere, it must be observed from space. The UV wavelength range is further subdivided according to the wavelength's proximity to the visible spectrum, into Near-UV (NUV, wavelength 200-380 nm), Far-UV (FUV, wavelength 10-200 nm) and Extreme UV (EUV or XUV, wavelength 1-30 nm).
The Universe is the collective term for all matter and space that exists in which events occur or can occur. The Universe is often referred to in terms of the 'known Universe', which is all matter and space that we can observe from Earth. The study of the Universe in its totality, its history and evolution, is called cosmology.