Solar System Builder & Kepler's Laws
Drag planets to new orbits, change the star's mass and check Kepler's third law.
Drag any planet closer to or further from the star and watch its year get shorter or longer (Kepler's third law). Change the star's mass too.
About the Solar System Builder & Kepler's Laws
Free solar system builder & kepler's laws. Drag planets to new orbits, change the star's mass and check Kepler's third law. Drag, change the sliders and see the result live. No sign-up, works on phone and computer. Built for earth & space, the solar system builder & kepler's laws 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.
Drag planets to new orbits, change the star's mass and check Kepler's third 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 Solar System Builder & Kepler's Laws
- Use the controls to change Star mass (Suns), Time speed (years per second), Distance scale. The simulation reacts instantly.
- Pick an option such as Inner planets, Whole system to switch modes or load an example.
- Press "Reset planets" 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
- Drag Earth to Mars's distance and read the period.
- Double the star's mass.
- Put a planet very close to the star.
Key ideas you can learn
- A planet further from its star takes longer to orbit.
- T² is proportional to a³ (Kepler's third law).
- A heavier star makes planets orbit faster.
- Planets move faster when they are closer to the star.
Where this is used in the real world
Astronomers use the same law to weigh stars 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 third law?
The square of a planet's orbital period is proportional to the cube of its average distance from the star.
How long is a year on Mars?
About 1.88 Earth years, because Mars is 1.52 AU from the Sun.
Is the Solar System Builder & Kepler's Laws 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 Solar System Builder & Kepler's Laws 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.