Even though the educational researchers have developed and implemented various educational strategies to teach the concepts of the phases of the Moon and the formation of the lunar eclipse more effectively, many studies conducted by them in recent years reveal that the teachers still do not understand the causes and scientific processes related to the phases of the Moon phases and lunar eclipse. In addition, this situation shows that there are deep problems in teaching the subjects of Moon phases and lunar eclipse to students. Examining the main causes of learning difficulties in the phases of the Moon and lunar eclipse, this study is designed on the basis of development and implementation of a project supported by STRCT (The Scientific and Technological Research Council of Turkey) in order to discuss the possible solutions. A 5-day activity program including basic astronomy education was applied to science teachers by using the model developed within the scope of the project, and the changes in mental models of the teachers in the subjects of Moon phases and lunar eclipse were examined. This research was carried out with 29 teachers voluntarily participating in the project in the field of Science. In this study in which qualitative and quantitative data collection methods were applied together, as a result of the evaluation of the obtained data, it was observed that the project was very successful in understanding the phases of the Moon and the causes of the lunar eclipse. The obtained results were interpreted by comparing them with the literature.