Orbital eccentricity

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An elliptic Kepler orbit wi an eccentricity o 0.7 (reid ellipse), a parabolic Kepler orbit (green) an a hyperbolic Kepler orbit wi an eccentricity o 1.3 (blue ooter line)

The orbital eccentricity o an astronomical object is a parameter that determines the amoont bi which its orbit aroond anither body deviates frae a perfect circle. A value o 0 is a circular orbit, values atween 0 an 1 form an elliptical orbit, 1 is a parabolic escape orbit, an greater than 1 is a hyperbola. The term derives its name frae the parameters o conic sections, as every Kepler orbit is a conic section. It is normally uised for the isolatit twa-body problem, but extensions exist for objects follaein a rosette orbit through the galaxy.