The study of celestial objects by their radiation in the wavelength range 1000 nm1 mm. Absorption by water vapour in our atmosphere poses severe difficulties, some of which are overcome at high-altitude observatories such as Mauna Kea in Hawaii at 4 000 m/13 000 ft, or by using cryogenically cooled telescopes on spacecraft. Many objects emit most of their radiation in the infrared. This type of astronomy has increased in importance with the availability of imaging detector arrays to photograph objects of infrared wavelengths.
Modern infrared astronomy
Near infrared radiation (infrared radiation with wavelengths close to that of visible light) behaves in a very similar way to visible light, and can be detected using similar electronic devices. As infrared is essentially heat radiation, infrared telescopes (which include most major optical telescopes as well as a few dedicated infrared telescopes) need to have their detectors shielded from heat and chilled with liquid nitrogen in order to actually form images.
However, as with visible-light telescopes, space is the ideal place for their use and most optical telescopes launched into space (such as the Hubble Space Telescope) can also perform infrared observations.
Astronomers' infrared spectrum
Infrared space telescopes such as Spitzer, IRAS, ISO and the forthcoming Herschel Space Observatory can observe across the almost all of the infrared spectrum. The main infrared windows are listed below:
| Wavelength range | Astronomical bands | Telescopes |
|---|---|---|
| (micrometres) | ||
| 0.65 to 1.0 | R and I bands | All major optical telescopes |
| 1.25 | J band | Most major optical telescopes and most dedicated infrared telescopes |
| 1.65 | H band | Most major optical telescopes and most dedicated infrared telescopes |
| 2.2 | K band | Most major optical telescopes and most dedicated infrared telescopes |
| 3.45 | L band | Most dedicated infrared telescopes and some optical telescopes |
| 4.7 | M band | Most dedicated infrared telescopes and some optical telescopes |
| 10 | N band | Most dedicated infrared telescopes and some optical telescopes |
| 20 | Q band | Some dedicated infrared telescopes and some optical telescopes |
| 450 | submillimeter | Submillimeter telescopes |
Between these windows there are generally regions where infrared observations are more difficult or impossible from the ground due to the opacity of the atmosphere.
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