In this laboratory activity, students will use a loop of string and two tacks to draw one circle and four different ellipses. They will then measure the focal distance and major axis of each of these, and use this data to calculate the eccentricity of each ellipse (and the circle). The analysis questions lead students to discover the overall patterns and apply the knowledge learned in this activity to planetary orbits.
Note: Parts of the lab refer to the ESRT. This is New York State's Earth Science Reference Tables. Even if you don't teach in New York State, they are a fantastic resource (both of information and to help students practice finding information elsewhere, which they will often do in the real world). Printable copies can be found at either of the links below.