Scrutinizing the main activities of the Sociedad Astronomica de Barcelona (SAB), a scientific society that was founded in 1910 and lasted until 1921, this paper analyses how and why its members disseminated astronomy to society at large. Inspired by Camille Flammarion (1842-1925), and with a strong amateur character, the programme of the SAB raised interest among academic scientists, politicians, priests, navy officers, educated audiences, and positivist anticlerical writers. It rapidly conquered the public sphere through well-attended lectures, exhibitions, observations, and publications. In the context of an industrial city, which at that time was suffering serious social tensions, the popularization of astronomy transcended social and cultural boundaries. It created common ground between expert and lay knowledge, science and art, the 'natural' and the 'social', and between science and religion. In addition, it was considered as one of the only possible ways to raise the scientific level of a country such as Spain, which at that time perceived itself as peripheral, even backward, in terms of mainstream innovations in science and technology.