The larger objects is at one of the two foci. For example, the Sun is at one of the foci of Earth's elliptical orbit. If the eccentricity of an ellipse is large, the foci are far apart. If the eccentricity is small, the foci are close together.et's take a look at the mathematical definition of an ellipse. First, place two points on a plane; these will be the foci of the ellipse. Now, pick a distance that is larger than the distance between the two foci. We'll call that distance 2a, for reasons that will become clear in a minute.