Many of the most interesting discoveries about the Universe, which have occurred in the last few decades, have resulted from observations of the sky in light not visible to our eye. To emphasize this point it is only necessary to recall the discovery of the microwave background radiation, still the most convincing evidence for the Big-Bang theory, apart from the discovery of the recession of the galaxies 50 years ago. The discovery of pulsars through radio observations established the existence of neutron stars, which until then had only existed as speculative objects predicted by theoretical astrophysicists to be the end point of stellar evolution for intermediate mass stars. Radio observations first revealed the existence of quasi-stellar objects, now generally believed to be objects at greater distance from us than any known, and therefore offering clues to the early stages of the formation of galaxies and their evolution.