# Dictionary:Fig E-12

FIG. E-12.
**Ellipse terminology**. An ellipse is the locus of points for which the sum of the distances from the two foci is constant. A satellite follows an elliptical path about a body at one focus. If *a* = semimajor axis, *b* = semiminor axis, **eccentricity** ; **ellipticity** ; **flattening** ; and = **eccentric** **anomaly** when satellite is at *S*. The polar equation of an ellipse with one focus at the origin is ; where *h* = distance from the focus to a directrix line.