IRAS

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Infrared Astronomical Satellite (IRAS)
IRAS and all-sky images
Organization:	NASA, NIVR, SERC
Wavelength:	infrared
Launched:	25 Jan 1983
Deorbited:	21 Nov 1983
Diameter:	0.57 m
Collecting area:	~1 m²
Focal length:	5.5 m, f/9.6
Coolant:	475 L (75 kg) of superfluid He
(main survey instrument):	array of 65 detectors
Low Resolution Spectrometer (LRS):	8–22 µm slitless spectrometer
Chopped Photometric Channel (CPC):	low-quality mapping
Website:	IRAS website

The Infrared Astronomical Satellite (IRAS) was a space-based observatory that performed a survey of the entire sky at infrared wavelengths.

Launched on January 25, 1983, its mission lasted ten months. The telescope was a joint project of the United States (NASA), the Netherlands (NIVR), and the United Kingdom (SERC).

IRAS mapped 96% of the sky four times, at 12, 25, 60 and 100 micrometre wavelengths, with resolutions ranging from 0.5' at 12 micrometers to 2' at 100 micrometers. It discovered about 350,000 sources, many of which are still awaiting identification. About 75,000 of those are believed to be starburst galaxies, still enduring their star-formation stage. Many other sources are normal stars with disks of dust around them, possibly the early stage of a planetary system formation. New discoveries included a dust disk around Vega and the first images of the Milky Way Galaxy's core.

IRAS's life, like most of infrared satellites, was limited by its cooling system: to effectively work in the infrared domain, a satellite must be cooled to impressively low temperatures. In IRAS' case, 475 liters of superfluid helium kept the satellite at a temperature of 1.6 kelvins (about −272 °C), keeping the satellite cool by evaporation. When the fluid totally evaporated, the satellite temperature rose, preventing further observations.

IRAS was designed to catalogue fixed sources, so it scanned the same region of sky several times. Jack Meadows led a team at Leicester University, including John Davies and Simon Green, which searched the rejected sources for moving objects. This led to the discovery of three asteroids, including 3200 Phaethon (an Apollo asteroid and the parent body of the Geminid meteor shower), six comets, and a huge dust trail associated with comet Tempel-2. The comets included the periodic comets 126P/IRAS and 161P/Hartley-IRAS and comet IRAS-Araki-Alcock, which made a close approach to the Earth in 1983.

Today (2004), the Spitzer Space Telescope is the best infrared telescope, allowing astronomers to follow up many detections first made by IRAS.