The greatest radial distance of an ellipse as measured from a focus. Taking in the equation of an ellipse

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
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## Cite this as:

Weisstein, Eric W. "Apoapsis." From *MathWorld*--A Wolfram Web Resource. https://mathworld.wolfram.com/Apoapsis.html

## Subject classifications