The term 'light' is usually associated with colours and brightness, but there are other kinds of light,
such as ultraviolet or infrared light, invisible to the human eye. The Universe looks completely different when seen in each kind of light,
and all these different 'views' are needed to perform a complete exploration. The 'infrared view' of the Universe is the last astronomers
have been able to get.
Although the discovery of infrared light was reported exactly 200 years ago, astronomers had to wait until the eighties to gain full
access to the infrared sky -with the IRAS satellite-, and until 1995 to have a true Infrared Space Observatory, ESA's ISO. ISO
stopped observing in May 1998, but the infrared community says its results have only now started to be exploited. Also, in 1997 ESA's
participation in the NASA/ESA Hubble Space Telescope gave Europe access to an important high-resolution near-infrared instrument
called NICMOS (Near Infrared Camera and Multi-Object Spectrograph).
These missions have unveiled a face of the Universe that is much more interesting that expected. The idea that infrared observations were
simply an adjunct to the observations in visible light is proven wrong: the infrared has allowed the study, for the first time in any detail, of how stars
are born and how they die; it has triggered the study of many molecules in space, for example the water molecule; it has shown astronomers
that, in the past, the Universe had many more stars than previously thought.
ESA is also very active in future infrared astronomy projects. It is launching the Herschel Space Observatory and
participating in the NASA/ESA/CSA Next Generation Space Telescope (NGST), which is the infrared successor to the Hubble Space Telescope.