Minor axis

The minor axis of an ellipse is its shorter axis. It crosses the ellipse halfway between the foci and perpendicularly to the line joining them. The perpendicular diameter, which crosses the ellipse through the foci, is the major axis. The semi-minor axis is half the minor axis and extends from the centre of the ellipse to one or other of its closest points. The axes are the elliptical equivalents of the diameter of a circle, while the semi-axes are the equivalents of radii.