Eccentricity

Ratio of the distance between the foci and the major axisLongest diameter of an ellipse; the line from one side of an ellipse to the other that passes through the foci. Click on Term to Read More of an ellipse (planetary orbitThe elliptical path of one body around another, typically the path of a small body around a much larger body. However, depending on the mass distribution of the objects, they may rotate around an empty spot in space • The Moon orbits around the Earth. • The Earth orbits around Click on Term to Read More). Eccentricity is:

where ra = apoapsisPoint in an object’s orbit farthest from a planetary body. Click on Term to Read More distance and rp = periapsis distance.