infrared astronomy

Study of infrared (IR) radiation produced by relatively cool gas and dust in space, as in the areas around forming stars. Objects at normal temperatures emit infrared radiation, so some critical parts of telescopes designed to observe IR radiation have to be cooled to very low temperatures. IR telescopes are located on high mountains, above most of the IR-absorbing water vapour in the atmosphere, or in space.

In 1983 the US-Dutch-British Infrared Astronomy Satellite (IRAS) surveyed almost the entire sky at infrared wavelengths. It found five new comets, thousands of galaxies undergoing bursts of star formation, and the possibility of planetary systems forming around several dozen stars.

Planets and gas clouds emit their light in the far- and mid-infrared regions of the spectrum. The Infrared Space Observatory (ISO), launched in 1995, observed a broad wavelength (3-200 micrometres) in these regions. It is 10,000 times more sensitive than IRAS, and searches for brown dwarfs (cool masses of gas smaller than the Sun).

The Spitzer Space Telescope, launched in December 2003, is wholly devoted to IR astronomy. It was positioned more than 8 million km/5 million mi from the Earth, trailing our planet in its orbit and far from the Earth's warmth. Among other discoveries it has shown that our galaxy has a pronounced bar across its centre.

The European Space Agency Herschel Space Observatory will be launched in 2007. It will be stationed 1.5 million km/930,000 mi from the Earth. Its 3.5-m/11.5-ft mirror will gather IR radiation from objects much fainter than ever observed before.