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The smallest radial distance of an Ellipse as measured from a Focus. Taking $v=0$ in the equation of an Ellipse

r = {a(1-e^2 )\over 1+e\cos v}

gives the periapsis distance


Periapsis for an orbit around the Earth is called perigee, and periapsis for an orbit around the Sun is called perihelion.

See also Apoapsis, Eccentricity, Ellipse, Focus

© 1996-9 Eric W. Weisstein