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Solar system simulator

A solar system simulator moves the planets around the Sun by gravity, so you can speed up time and watch their orbits, or change something and see what happens. This one is free in your browser with no download: the eight planets start where they really are today, at their true distances, orbit shapes and masses, and every body pulls on every other. Add a planet, throw one, or make Jupiter a hundred times heavier.

Mercury, Venus, Earth and Mars where they are today, at their real distances, orbit shapes and masses: a year takes 8 seconds at 1×. The planets are drawn far bigger than they are; at true size they'd be smaller than a pixel.

Keys (click the sky first): Space play/pause · R reset · A add a body · T trails · C recenter · + − zoom · [ ] pick a body · Delete remove it

What you can do

How does a solar system simulator work?

It does what Isaac Newton's law of gravity says, one small step at a time. Many times a second it adds up the pull on each body from every other body, nudges each velocity, and moves each body a little. Nothing tells a planet to go round in an ellipse: the orbits come out of the pull alone. That is also how NASA's engineers plan spacecraft paths, with far more care and more bodies.

Kepler's laws fall out on their own. Each planet sweeps round on an ellipse with the Sun near one end; it moves fastest when closest, which you can see in Mercury, the most stretched orbit of the eight; and the farther out a planet is, the longer its year, by a fixed rule: the square of the period grows with the cube of the distance. Jupiter, about five times as far from the Sun as Earth, takes about twelve years to go round.

The planets start from where they really are today. Their places are worked out from NASA JPL's published orbital elements for each planet, accurate to about a degree, and the simulation runs on from there.

What does this simulation simplify?

Distances, orbit shapes and masses are real, and the orbital periods follow from them. Sizes are not: the planets and the Sun are drawn much bigger than they are, because at true size even Jupiter would be far smaller than a pixel at the zoom that shows its orbit.

It is flat. The planets' orbits tilt by up to 7 degrees (Mercury's) against Earth's, and that tilt is dropped. There are no moons, dwarf planets such as Pluto, asteroids or comets, and no relativity, which in reality turns Mercury's orbit by a tiny extra 43 arcseconds a century.

Time moves in small fixed steps with a leapfrog integrator, a method that keeps orbits from drifting over many turns; the energy drift readout shows the leftover error. Planets you add are made of the same stuff as the presets: their mass, where you drop them and how you throw them decide everything that follows.

Questions

Is this solar system simulator free?
Yes. It runs free in your web browser on phones, tablets and computers, with no download, no account and no ads. It needs only JavaScript and an HTML canvas, not WebGL, so it runs on older devices too.
Are the planets in their real positions?
Yes, when it starts. Each planet's place on today's date is worked out from NASA JPL's mean orbital elements (Standish's table, valid from 1800 to 2050), accurate to about a degree, and flattened into one plane. After that the planets move by the simulator's own gravity, so after many simulated years they drift from the real ones.
Is the solar system to scale?
The distances, orbit shapes and masses are; the sizes are not. Neptune is about 78 times as far from the Sun as Mercury, so the inner and outer planets have their own views. At true size every planet would be smaller than a pixel.
How long is a year in the simulator?
On Inner planets a year takes 8 seconds at 1× and 2 seconds at 4×. On Outer planets a year passes in under a second, so Jupiter's 12-year orbit takes about 10 seconds and Neptune's 165-year orbit about 2¼ minutes. The counter shows the years passed.
What happens if Jupiter were heavier?
Tap Jupiter and move the mass slider. A few times heavier and the others barely notice. Hundreds of times heavier, Jupiter is more like a small star: it swings the Sun round a shared center and stretches the other orbits, and on All eight a planet can be flung out within a couple of minutes.
Can I build my own solar system?
Yes. Pick Build your own for a lone Sun, then tap to drop planets on circular orbits or drag to throw them on your own paths. Set the mass first with the slider: on its scale the Sun is 1000, Jupiter is about 1 and Earth 0.003.
Is there a 3D solar system in the Everdust app?
Yes. On Apple Vision Pro, Everdust's Solar System to Scale lets you walk from the Sun to Neptune with every size and distance true, and Night Sky flies you to the planets from the real sky; on iPhone and iPad, Night Sky (since version 1.1) flies you to them too. The Everdust app is free on the App Store for Apple Vision Pro, iPhone, iPad and Apple TV, on Google Play for Android, and on the Meta Horizon Store for Meta Quest 3 and 3S.

This is one world, in your browser

The full version is in the Everdust app.

The app has many more live worlds at full detail, games built on the same physics and narrated stories you step inside. It’s free to download, with no ads, on the App Store for iPhone, iPad, Apple Vision Pro and Apple TV, on Google Play for Android phones and tablets, on the Meta Horizon Store for Meta Quest and from everdust.ai for Mac.