Eccentricity

Definition

Eccentricity is a measure of how much an orbit deviates from being a perfect circle. It ranges from 0 (a perfect circle) to 1 (a parabolic trajectory).

5 Must Know Facts For Your Next Test

1. Eccentricity determines the shape of an orbit, with values closer to 0 indicating more circular orbits.
2. Johannes Kepler's first law states that planets move in elliptical orbits with the Sun at one focus, which directly relates to eccentricity.
3. Earth's orbit has a low eccentricity, making it nearly circular compared to other planets like Pluto, which has a higher eccentricity.
4. An orbit with an eccentricity value of 1 or greater is not bound and will result in an object escaping the central body’s gravitational pull.
5. The semi-major axis and the distance between the foci are used to calculate the eccentricity of an ellipse.

Review Questions

• What does an eccentricity value of 0 indicate about an orbit?
• Why is Earth's orbit considered nearly circular?
• How does Kepler's first law relate to the concept of eccentricity?

Related terms

Semi-Major Axis: The longest diameter of an ellipse, half of which extends from the center to the furthest point on the edge.

Elliptical Orbit: An oval-shaped path followed by celestial bodies around a focal point due to gravitational forces.

Kepler's First Law: States that planets move in elliptical orbits with the Sun at one focus.