Phases of the moon, sky charts, UFOs… the sky has inspired a great number of beliefs and continues to raise a great deal of questions. This activity invites students to a great debate about the mysteries of the sky. Assembled in a large group, students are invited to answer three questions: Does the moon impact our behaviour? Has our planet been visited by extraterrestrials? Do the planets have an influence on our personality? Students are offered a chance to explorewhat science has to say about these questions to then build their arguments and defend their point of view during debate. Using their personal opinions and their debating skills, this activity aims to develop their critical thinking skills.