The Solar System

How it works

Planet positions are calculated from NASA/JPL Keplerian orbital elements for the chosen moment. Each planet follows an ellipse with the Sun at one focus. Kepler’s third law says that the square of the orbital period grows with the cube of the semi-major axis, so distant planets move much more slowly: Mercury circles the Sun in 88 days, Earth in a year and Neptune in almost 165 years.

Kepler’s third law: T² = a³ (T in years, a in astronomical units)

Try it yourself

1. Select Earth and watch “Position at the chosen time”. Over a year the distance from the Sun changes between 0.983 and 1.017 AU; Earth is closest in early January.
2. Switch to the “Solar System” view, set “Time speed” to 30 days / s and start the clock. Count how many times Mercury orbits the Sun during one Earth orbit (about four).
3. Check Kepler’s third law: Mars has a semi-major axis of about 1.52 AU, so T ≈ √(1.52³) ≈ 1.88 years, or about 687 days. Compare this with its “Length of year”.
4. For Jupiter, open “Planet and moons” and compare how fast nearby Io and distant Callisto orbit.

Model limitations

The NASA/JPL elements are valid for roughly 1800–2050 and ignore the planets’ mutual perturbations. Planet sizes are enlarged when zoomed out so they stay visible. Moon orbits are simplified circles with illustrative starting positions. The simulation needs WebGL.

Related experiments

• Gravity and orbits
• Ray optics
• Projectile motion