Drawing of an ellipse, with two focal points aligned equal distances from the center along the major axis and a perpendicular minor axis also intersecting the center. The Sun is located at one focal point. We can tie two ends of a piece of string to the focal points and then sketch the ellipse with a pencil which draws the string taut. This is a larger image of the ellipse diagram found on the lecture slide.
[NMSU, N. Vogt]