infrared astronomy

The study of infrared radiation from astronomical sources. Infrared is electromagnetic radiation with wavelengths in a range between the visible red spectrum and radio waves. The definition is not precise but the wavelength range from about 0.1 to about 100 micrometres is normally considered to be the infrared. It is invisible to the human eye and is absorbed almost completely in the lower layers of the Earth's atmosphere, primarily by water vapour. For this reason, infrared astronomy observations have to be conducted from the highest mountain sites, or from aircraft or satellites. The first infrared observation was made accidentally by William Herschel in 1800 when a thermometer he placed just to one side of the red end of a visible solar spectrum recorded a rise in temperature. Infrared images predominantly show the distribution of heat. All warm objects radiate infrared, so infrared telescopes must be cooled to a few degrees above absolute zero to prevent their being blinded by their own emission. The development of systematic infrared astronomy began in the 1960s, when suitable detectors became available. The first infrared survey of the sky was carried out by Gerry Neugebauer and Robert Leighton of the California Institute of Astronomy (Caltech). They published a list of 5,612 sources in 1969. In 1968, Eric Becklin and Neugebauer announced that the infrared emission from the galactic centre at a wavelength of 2.2 micrometres is more than a thousand times stronger than might have been anticipated from radio observations. Infrared astronomy has made important advances with the development since the 1980s of two-dimensional arrays of infrared detectors, capable of making a complete image in a single exposure. Infrared astronomy received an enormous boost from the successful operation of IRAS, the Infrared Astronomical Satellite, in 1983. Its successor, the Infrared Space Observatory (ISO) was launched in November 1995. The best ground-based site for infrared astronomy is the Mauna Kea Observatories in Hawaii. Three infrared telescopes started operation there in 1979: the United Kingdom Infrared Telescope (UKIRT), NASA's Infrared Telescope Facility (IRTF) and the Canada-France-Hawaii Telescope (CFHT), which also functions as an optical telescope. The telescopes of the Keck Observatories also have infrared capability. Infrared radiation is detected from stars and galaxies, and from dust clouds within the solar system and in the interstellar medium. Strong infrared emission is particularly characteristic of dust that has been heated by shorter-wavelength visible and ultraviolet radiation from stars. Protostars in process of formation and evolved red giant stars are surrounded by shells of dust, giving rise to infrared emission. Unlike visible light, infrared radiation passes relatively unimpeded through dust clouds. So, for example, the galactic centre, which is largely obscured by dust in the visible spectrum, can be explored by means of infrared and radio astronomy. The way in which infrared radiation is scattered from the surfaces of objects in the solar system provides important clues to their composition. Infrared observations are also important for remote objects with large redshift.