This study aims to analyse the potentialities of using Personal Meaning Maps to assess school children's learning in a visit to a Planetarium. A total of 123 primary students were involved. They were asked to create a PMM, and a drawing, before and after the visit. The results suggest that the visit enhanced the degree to which students generate words and conceptual categories to describe their understanding of the suggested concepts. PMMs seemed to be a good tool to evaluate the impact of the activities on students' ideas about the thematic explored. Drawings helped to understand the main misconceptions.