Ellipse

Definition

An ellipse is a geometric shape that looks like a flattened circle, defined by two focal points. In astronomy, it describes the shape of planetary orbits around the sun.

5 Must Know Facts For Your Next Test

1. Johannes Kepler discovered that planets move in elliptical orbits with the Sun at one focus.
2. The major axis of an ellipse is the longest diameter, passing through both foci.
3. The semi-major axis is half of the major axis and represents the average distance from the orbiting body to the Sun.
4. Eccentricity measures how elongated an ellipse is; an eccentricity of 0 represents a perfect circle.
5. Kepler's First Law states that all planets move in elliptical orbits with the Sun at one focus.

Review Questions

• What are the two focal points of an ellipse in planetary orbits?
• How does eccentricity affect the shape of an ellipse?
• State Kepler's First Law related to elliptical orbits.

Related terms

Eccentricity: A measure of how much an orbit deviates from being circular.

Focal Points: Two fixed points inside an ellipse used to define its shape.

Semi-Major Axis: Half of the major axis, representing the average distance from a planet to its star.