Infra Red Astronomy


Astronomy started when the first humans simply looked up at the sky, then, relatively recent (on a historical scale), aided by means of magnification with telescopes. Our ‘window' on the universe has widened tremendously in the past 50 years. With the additional powerful new observing tools of radiotelescopes and space instruments astronomers now have access to a wide spectrum of electromagnetic radiation, all the way from the ultra-short gamma rays to very long radio waves.

While astronomy has thus become a true multi-wavelength discipline, the optical-infrared wavelength range (λ ~ ? to ? ) remains the ‘core region' of the spectrum, where most astronomical observations are made. Not only is this the wavelength region with the highest density of atomic and molecular lines, but it is also the region where the majority of stars, nebulae and galaxies emit most of their radiation. The optical-infrared spectrum is therefore particularly rich in astrophysical information.

Infra Red (IR) observations

Observations at optical and infrared wavelengths require dark and cloudless skies and high atmospheric transparency. Large part of the electromagnetic spectrum is absorbed by our atmosphere.  Absorption is caused by the various gases and dust particles in the atmosphere. The main contributor is water vapour followed (at a distance) by carbon dioxide, ozone and methane. While the concentration of the last three gases is relative stable all over the world, the water vapour content varies extremely, from place to place and from moment to moment. 


In the picture one can see how much of the total incoming electromagnetic radiation the atmosphere typically absorbs.  Most visible and radio wavelengths and limited amounts of infrared (IR) and ultraviolet (UV) (see "optical window" and "radio window") do reach the ground and can be observed by ground-based telescopes. With the space telescopes placed above our atmosphere the atmospheric absorbtion is avoided and the wavelength outside the atmospheric windows can be observed.


NOTE: All distances are approximate. The space telescopes are not shown at

their actual altitudes above the atmosphere. Altitude scale is logarithmic.

SOURCES: Chandra mission website and Space Telescope Science Institute


Special sites with the required conditions of dark, cloudless skies with high atmospheric transparency are exteremely rare, therefore Dutch astronomers rely on observations from remote mountaintops, such as ESO's Very Large Telescope in Chile and the UK-NL telescopes on La Palma (Canary Islands).

By extending the actual telescope size (E-ELT) large improvements can be accomplished regarding the resolution, etc. and the reduction of necessary observing times. However only for the longer wavelengths this scaling up results also in contrast improvements, thus huge steps in IR astronomy can be accomplished with new telescopes and instruments, besides ongoing technological improvements regarding e.g. detector development (larger and denser pizel arrays). For parts of the infrared spectrum, especially at the longest wavelengths (λ≥?), even the best ground-based observatories cannot influence the atmospheric limitations and measurements from space become imperative.

Design: Kuenst.    Development: Dripl.    © 2022 ASTRON