Orbital eccentricity

In astrodynamics, orbital eccentricity shows how much the shape of an object's orbit is different from a circle.

Eccentricity (${\displaystyle e\,\!}$) is defined for all circular, elliptic, parabolic and hyperbolic orbits. It can take the following values:

• for circular orbits: ${\displaystyle e\,\!}$ is equal to zero,
• for elliptical orbits: ${\displaystyle e\,\!}$ is more than zero but less than 1,
• for parabolic trajectories: ${\displaystyle e\,\!}$ is equal to 1,
• for hyperbolic trajectories: ${\displaystyle e\,\!}$ is more than 1.