This lesson plan is part of the Center for Educational Resources (CERES), a series of web-based astronomy lessons created by a team of master teachers, university faculty, and NASA researchers. In this lesson, students study the effects of gravity on the planets of the Solar System. They view movies from the Apollo missions, calculate their own weight on other planets, and propose what they might weigh on newly discovered planets around other stars. This lesson contains expected outcomes for students, materials, background information, follow-up questions, and assessment procedures. Educational levels: Intermediate elementary, Middle school