A view of the universe in which the earth is regarded as being at its centre. Galileo Galilei finally established that the earth revolves round the sun (not the other way round, as the church believed); during the 20th century it became clear from advances in observational astronomy that the earth is no more than one of a number of planets orbiting the sun, which is one of countless millions of similar stars, many of which undoubtedly possess planetary bodies on which life could have evolved.