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Orbital eccentricity
Amount by which an orbit deviates from a perfect circle / From Wikipedia, the free encyclopedia
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This article is about eccentricity in astrodynamics. For other uses, see Eccentricity (disambiguation).
In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values between 0 and 1 form an elliptic orbit, 1 is a parabolic escape orbit (or capture orbit), and greater than 1 is a hyperbola. The term derives its name from the parameters of conic sections, as every Kepler orbit is a conic section. It is normally used for the isolated two-body problem, but extensions exist for objects following a rosette orbit through the Galaxy.
![](http://upload.wikimedia.org/wikipedia/commons/thumb/b/b7/Kepler_orbits.svg/320px-Kepler_orbits.svg.png)
Elliptic (eccentricity = 0.7)
Parabolic (eccentricity = 1)
Hyperbolic orbit (eccentricity = 1.3)
![](http://upload.wikimedia.org/wikipedia/commons/thumb/f/fa/Animation_of_Orbital_eccentricity.gif/320px-Animation_of_Orbital_eccentricity.gif)
0 · 0.2 · 0.4 · 0.6 · 0.8