In the early 1600's, Johannes Kepler came up with his FIRST LAW OF PLANETARY MOTION - "The orbit of each planet is an ellipse with the Sun at one focus point." In this activity, students will create three different ellipses, each one slightly thinner in shape than the last one. Students will learn that there is a number called the eccentricity of an ellipse and will calculate that number for each of their ellipses using a calculator. They then will compare their eccentricities with the same number for each of the planets. All three pages of this activity should be duplicated in quantity for the class.