Orbit of Mercury Lab: Understanding planetary orbits and plotting the orbit of Mercury Learning Goals In this activity, the student will learn about planetary orbits. This includes understanding the connection between the planet's position in the sky (versus the Sun in this case), and that planet's orbital motion around the Sun. . The elliptical shape of planetary orbits and application of Kepler's Laws Characteristics related to planetary orbits: semi-major and semi-minor axes; eccentricity; perihelion; aphelion; elongation; conjunction, Orbital versus Synodic Period . How to determine inferior planet orbits Error in measurements Materials . Protractor, straight edge, pencil, and a calculator 1