The eccentricity of an elliptical orbit is a measure of the amount by which it deviates from a circle; it is found by dividing the distance between the focal points of the ellipse by the length of the major axis.

How is eccentricity defined?

1a : the quality or state of being eccentric. b : deviation from an established pattern or norm especially : odd or whimsical behavior.

What is eccentricity in Earth's orbit?

Eccentricity measures how much the shape of Earth's orbit departs from a perfect circle. These variations affect the distance between Earth and the Sun.