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Eccentricity Demonstrator
Before you start
e = 0 is a circle. The two foci spread apart as e grows. Earth is nearly a circle.
Key idea
A long thin ellipse is still ‘an orbit’ if a focus holds the Sun — that is Kepler I.
What you see
- Ellipse
- Two foci
- e slider
Try this
- e = 0, then e = 0.7
- Note the yellow focus (Sun) leaving the centre
Common mistakes
- Thinking Earth has a very stretched orbit because textbooks draw exaggerated ellipses
Glossary
- Eccentricity
- How stretched an ellipse is, 0–1 for bound orbits.