- noun the study of infrared radiation emitted by astronomical objects
- Infrared light has wavelengths between those of visible light and microwaves. Nearest to light is the near infrared (wavelengths 0.75–2.5 microns), followed by the middle (2.5–30 microns) and far (30–1000 microns) infrared. Infrared light is associated especially with emissions from warm objects, of which astronomers have detected some thousands with ground-based telescopes (which can observe some celestial infrared light) and from space. Gas and dust clouds in space heated by nearby stars are especially readily observed in infrared light, and includes material which may be associated with planetary systems of other stars. In the future, large infra-red telescopes in space such as ISO has begun to yield new information on star-forming areas, interstellar molecules, and the condition of very distant (and therefore old) galaxies, as well as solar system objects. Distant galaxies are so redshifted that we observe the light from them mostly in infrared rather than visible wavelengths. Large ground-based optical telescopes are typically configured to allow them to make infra-red observations as well. Water vapour in the Earth’s atmosphere cuts out much infrared light but mountaintop observatories are sited above most of the water in the atmosphere. In addition, high-flying aircraft can be used for infrared astronomy, as can infrared telescopes in orbit. The first infrared observatory in space was IRAS.