false colour

Only a small part of astronomical observations is concerned with visible light, in other words: with electromagnetic radiation visible to the human eye. In order to visualize obervations made at invisible wave-length, such as infra-red light, radio waves or X-rays, the different wave-lengths are mapped to visible colours following some arbitrarily chosen scheme.

Similarly, physical quantities that are not connected with electromagnetic radiation can be mapped to colours; for instance, one can produce images of a star’s interior where different colours stand for different densities.