Introducing Earth's Orbital Eccentricity

摘要

Most students know that planetary orbits, including Earths, are elliptical; that is Keplers first law, and it is found in many science textbooks. But quite a few are mistaken about the details,thinking that the orbit is very eccentric, or that this effect is somehow responsible for the seasons. In fact, the Earth's orbital eccentricity is small, and its only effect on the seasons is their unequal durations. Here I show a pleasant way to guide students to the actual value of Earths orbital eccentricity, starting from the durations of the four seasons. The date of perihelion is also found.