A figure obtained by slicing a cone. There are four different types of conic section. If the cone is cut perpendicular to its axis, the resulting figure is a circle. If the cut is not perpendicular to the axis but still produces a closed curve, the curve is an ellipse. If the cone is cut parallel to one of its sloping sides, the resulting curve is a parabola, which is not closed. If the angle of cut is tilted still further, the open figure obtained is a hyperbola. An ellipse has an eccentricity less than 1; a circle is a special case of an ellipse, where the eccentricity is 0. A parabola has an eccentricity of exactly 1. A hyperbola has an eccentricity greater than 1. The orbits of celestial bodies are conic sections.

Figure 1: conic section

Figure 2: conic section