This project addresses the reasons that may motivate efforts to popularize astronomy. Data relevant to this research question were collected by means of focus groups involving professional astronomers at a large Spanish research institute, followed by a questionnaire to the same group of people. The data showed that the main driver for astronomy popularisation is personal satisfaction. Motivations related to the public responsibility of scientists are also important, but less important than the personal ones. These results are discussed in the context of the Spanish Public Understanding of Science (PUS) policy.