Earth’s orbit around the Sun is not circular, but an ellipse that is slightly elongated with an eccentricity of 0.017. (An eccentricity of 0 is a circle, while the dwarf planet Pluto has a ...

By adjusting the distance between the two slider brackets, the eccentricity of the ellipse can be changed. Eccentricity is a number between zero and one that describes how circular an ellipse is. By ...

In this view, a circle is just a special case of the ellipse, where the eccentricity (a term which, for lack of a better phrase, measures the "stretchiness" of an ellipse) is exactly 0.