The orbital eccentricity of an astronomical object is a 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 elliptical orbit, 1 is a parabolic escape 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.
In a two-body problem with inverse-square-law force, every orbit is a Kepler orbit. The eccentricity of this Kepler orbit is a non-negative number that defines its shape.
The eccentricity may take the following values:
-circular orbit: e=0
-elliptic orbit: 0<e<1 (see Ellipse)
-parabolic trajectory: e=1 (see Parabola)
-hyperbolic trajectory: e>1 (see Hyperbola)
The eccentricity e is given by the formula shown here.Related formulas
|e||orbital eccentricity (dimensionless)|
|E||total orbital energy (joule)|
|L||angular momentum (joule*s)|
|mred||reduced mass (kg)|
|a||coefficient of the inverse-square law centrl force (N*m2)|