Extraterrestrial Civilizations

The subject of extraterrestrial civilizations is relevant to astronomy in two ways. Firstly, the very existence of life outside Earth is dependent upon the picture that astronomers can draw of the Universe, and we will see how that picture allows us to be very optimistic. Then, if we think that there are intelligent beings in space, the detection of signals from them is an astronomical problem, and we will see that it most probably concerns radio astronomers.