Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
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
Johannes Kepler discovered that planets move in elliptical orbits with the Sun at one focus.
The major axis of an ellipse is the longest diameter, passing through both foci.
The semi-major axis is half of the major axis and represents the average distance from the orbiting body to the Sun.
Eccentricity measures how elongated an ellipse is; an eccentricity of 0 represents a perfect circle.
Kepler's First Law states that all planets move in elliptical orbits with the Sun at one focus.