Examples of four orbital trajectories with different eccentricities

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.