# What is apoapsis

1. Jul 23, 2014

### Greg Bernhardt

Definition/Summary

The furthest point of an elliptical orbit from the focus of the orbit

Equations

$$r_A = a(1+e)$$

where:
a is the semi-major axis
e is the eccentricity

Extended explanation

The apoapsis is one of two apsides that are located on the points where a line passing through the focus and bisecting the ellipse along its long dimension intersects the orbit.

The line passing through the two apsides is known as the Line of Apsides.

The segment of the line of apsides that lies between the apsides is the Major Axis of the orbit, and half of this is the Semi-major Axis (a).

For a Sun centered orbit, the apoapsis is called the aphelion and for an Earth centered orbit its is called the apogee. Each major body of the Solar system also has its own specifically named apoapsis.

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