Eccentricity

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Calculation

For elliptic orbits, eccentricity can be calculated from distance at periapsis and apoapsis:

$e={{d_{a}-d_{p}} \over {d_{a}+d_{p}}}$

$=1-{\frac {2}{(d_{a}/d_{p})+1}}$

where:

• $d_{p}\,\!$ is distance at periapsis (closest approach),
• $d_{a}\,\!$ is distance at apoapsis (farthest approach).