A new look at orbits

Abstract

Many people assume that the orbits of the planets are far more elliptical than they actually are. However, the orbits of all the planets with the exception of Mercury and Mars are nearly perfect circles. If the orbits of the planets are modeled as 26 inch bicycle wheels, the deviation from a perfect circle is less than one millimeter. The Earth’s orbit around the Sun is normally depicted as being highly elliptical in order to teach students about Kepler’s laws. This has been identified as a possible source of the misconception that it is warmer in summer than winter because the Earth is closer to the Sun. A possible way forward is to first teach students that the orbit of the Earth is essentially circular, like a bicycle wheel, and that seasons are due to the tilt of the Earth’s axis of rotation, and then switch to exaggerated elliptical orbits to teach Kepler’s laws.