Apse line
An apse line, or line of apsides, is an imaginary line defined by an orbit's eccentricity vector. It is strictly defined for elliptic, parabolic, and hyperbolic orbits.
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The line of apsides of an ellipse connects point 1 and 2 (major axis).
For such orbits the apse line is found:[1]
- for elliptical orbits – between the orbit's periapsis and apoapsis (also known as the major axis)
- for parabolic and hyperbolic orbits – between the orbit's periapsis and focus
For circular orbits, the apse line is not defined because the eccentricity is equal to zero. As it is required as a base for the definition of true anomaly, it is usually arbitrarily assumed (as a line pointing into the direction of the vernal equinox).
See also
- Apsidal precession
- Apsis
- Eccentricity (orbit)
- Orbit: circular, elliptic, parabolic and hyperbolic
- True anomaly
References
- "Line of apsides – Astronomy". Encyclopædia Britannica. Retrieved 23 August 2015.
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