Planetary Orbits Part II Read the background pages to answer questions 1 - 6. Give the equation that relates eccentricity, the distance between a focus and the center of the ellipse, and the semimajor axis. Use this equation to determine the eccentricity of an ellipse where the distance between a focus and the center of the ellipse is 76 cm and the semimajor axis is 86 cm. What is the definition of an Astronomical Unit (AU)? Would an ellipse drawn on a piece of paper have a semimajor axis of 20 AU? If the average distance of a planet orbiting our Sun is 4 AU what is the period (P) of the planet is years? If the average distance of a planet orbiting a star that is twice as massive as the Sun is 4 AU, will it have the same period as it would if it were orbiting our Sun? Because planets move in ellipses around the Sun, there must be some force acting upon them. What is that force? If there were no force, what would the planet do? Give the equation for Newton's second law of motion. What force is required to