An Etymological Dictionary of Astronomy and Astrophysics

Half the → latus rectum.

For an ellipse, semilatus rectum has the expression l = b²/a, where a and b are semi-major and minor axes of the ellipse. It can also be expressed in terms of → eccentricity, e, as: l = a(1 - e²).

See also: → semi-; → latus rectum.