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The greatest radial distance of an Ellipse as measured from a Focus. Taking $v=\pi$ in the equation of an Ellipse

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

gives the apoapsis distance


Apoapsis for an orbit around the Earth is called apogee, and apoapsis for an orbit around the Sun is called aphelion.

See also Eccentricity, Ellipse, Focus, Periapsis

© 1996-9 Eric W. Weisstein