Semidiameter

Generalizations

A different and incompatible definition is sometimes used for the diameter of a conic section. In this context, a diameter is any chord which passes through the conic's centre. A diameter of an ellipse is any line passing through the centre of the ellipse. Half of any such diameter may be called a semidiameter, although this term is most often a synonym for the radius of a circle or sphere. The longest and shortest diameters are called the major axis and minor axis, respectively. Conjugate diameters are a pair of diameters where one is parallel to a tangent to the ellipse at the endpoint of the other diameter.