We present two studies to investigate the extent to which attending a planetarium presentation increases secondary school students' understanding of the apparent motion of the Sun and stars. In the first study, we used the Apparent Motion of Sun and Stars (AMoSS) test in a pretest/post-test/retention test setting to measure learning gains and improved insight of 404 students (16- to 17-year-olds) after attending a classical planetarium presentation at the Brussels Planetarium. The AMoSS test is a questionnaire on the daily and yearly apparent motion and the observer's position. It consists of six multiple-choice questions about the Sun and six similar multiple-choice questions about the stars. We asked the students to explain their choices. The learning gains are rather small and the scores improve more on the Sun questions than on the star questions. This difference is largest for questions about the yearly apparent motion. We found that this is due to the fact that many students copy their knowledge about the Sun to the stars. Based on the results of this survey, we developed a new planetarium presentation with particular attention to the use of the celestial sphere model. We also developed a learning module that prepares students at school for this planetarium presentation. In a second study, we measured the learning gains after attending this new planetarium presentation among 339 students, also 16- to 17-year-olds. Some school groups had worked through the preparatory learning module at school and others had not. We find that the learning gains on the star questions are significantly higher than in the first study, due to better scores on the yearly apparent motion questions. In this regard, it is notable that we do not see significant differences between those students who prepared the presentation at school and those who did not. In the second study, the number of students who answer all questions correctly after attending the planetarium presentation or working through the learning module increases, but only significantly for those students who worked through the learning module at school.