Ultraviolet Astronomy

We often refer to electromagnetic radiation in terms of its wavelength, the distance from one peak of a light wave to the next peak. A convenient unit of wavelength ROSAT (Roentgensatellit) satellite prior to its launch on June 1, 1990. This German/United Kingdom/NASA satellite is capable of detecting both x rays and extreme ultraviolet (EUV) light. © Dornier Space/Science Photo Library, National Audubon Society Collection/Photo Researchers, Inc. Reproduced by permission. is the Angstrom Å. One Angstrom equals one 10 billionth of a meter.

Visual light, the light our eyes are sensitive to, has wavelengths from about 4,000-7,000 Angstroms. Beyond the visual is infrared light—we cannot see it, but we can feel it as heat. On the short wavelength side of the visual part of the spectrum is the ultraviolet. Ultraviolet (often just called UV) light has wavelengths from 100-4,000 Angstroms.

Earth's atmosphere is opaque to UV light, meaning UV radiation cannot penetrate it. This is fortunate for us, since UV light is what causes sunburn and in sufficiently large doses, skin cancer. Optical telescopes cannot see wavelengths much shorter than 3,600 Angstroms, and to observe UV radiation from astronomical objects it is therefore necessary to go above the atmosphere. Orbiting, space-based telescopes are needed, and only in the past few decades have they been available.