Conic sections. Animation showing a plane (red) intersecting a cone (green) at different angles to form different shapes. When the plane intersects the cone parallel to the base of the cone, a circle is formed. A circle is a special case of an ellipse, which is a closed geometric figure formed when the plane intersects the cone, but fails to cross the base of the cone. When the intersecting plane lies parallel to the edge of the cone a parabola is formed. When the plane intersects at an angle less than the angle the cone side makes with the cone axis, a hyperbola is formed. In this animation, the plane is at right angles to the base of the cone.