Kepler's Laws of Planetary Motion
Change orbit size and shape, see equal-area sectors and check the period–distance law.
Pick a law (1st, 2nd, 3rd or the full lab), then use the filters. Drag the planet to move it, drag the green arrow to change its speed, or use the sliders and presets to build any orbit. Turn on period divisions to see equal areas in equal times, and the T² – a³ graph to test the third law.
About the Kepler's Laws of Planetary Motion
Free kepler's laws of planetary motion. Change orbit size and shape, see equal-area sectors and check the period–distance law. Drag, change the sliders and see the result live. No sign-up, works on phone and computer. Built for earth & space, the kepler's laws of planetary motion runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Change orbit size and shape, see equal-area sectors and check the period–distance law. Use it to explore earth & space ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Kepler's Laws of Planetary Motion
- Use the controls to change Law, Semi-major axis a, Eccentricity e, Star mass, Number of period divisions, and more. The simulation reacts instantly.
- Pick an option such as Full lab, 1st law: ellipse, 2nd law: equal areas, 3rd law: T² ∝ a³ to switch modes or load an example.
- Press "Restart orbit", "Clear path" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Set e = 0.9 and watch the speed.
- Double a and check the period.
- Turn on equal areas.
Key ideas you can learn
- Orbits are ellipses with the star at one focus.
- A line to the star sweeps equal areas in equal times.
- T² is proportional to a³.
- Planets move fastest when closest to the star.
Where this is used in the real world
Kepler's laws are still used to plan satellite orbits and find exoplanets.
Who is this simulation for?
Astronomy and earth-science students, and teachers who need a visual model to explain what is happening in the sky.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
What is Kepler's second law?
The line from the star to the planet sweeps out equal areas in equal times, so the planet speeds up near the star.
What is eccentricity?
A number from 0 (circle) to 1 that says how stretched an ellipse is.
Is the Kepler's Laws of Planetary Motion free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Kepler's Laws of Planetary Motion work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.