Solar System Simulator

The Sun, eight planets, Pluto and 21 moons where they really are, at any moment from 1800 to 2100. Drag to look around, pick a world, and run time forward or backward.

What you are looking at

This is a model of the solar system at the date and time in the top-left corner. When it opens, that is right now, running in real time, and the view starts over Earth: day and night fall where they really do at this moment, city lights come on across the night side, and clouds drift over the oceans. Pick any other body from the list on the left, or click a label in the view, and the camera flies there.

Everything moves the way it really moves. The Moon keeps the same face toward Earth, Jupiter's four large moons race around it in hours and days, and Saturn's rings tilt toward or away from the Sun as the seasons of its 29-year orbit turn. The stars and the band of the Milky Way are in their true places too: 8,920 real stars, every one bright enough to see with the naked eye from a dark site.

How to use the simulator

The panel on the right shows the selected body's live distance from the Sun and from Earth, how long its light takes to reach us, and its key facts: size, mass, gravity, the length of its day and year, axial tilt and temperature. Moons of the selected planet appear as buttons at the bottom of the panel.

The address bar keeps up with you. Copy it at any point and whoever opens the link sees the same body at the same moment, which is handy for a lesson or a homework question.

Travel through time from 1800 to 2100

Time runs at speeds from real time to a year per second, forward or backward. At one day per second you can watch the inner planets lap the outer ones. At a month per second Mars traces its looping path relative to Earth. Choose a date in the date box to jump straight to it, or press Now to come back to the present.

The date range is deliberate. We compared the computed positions with NASA JPL's Horizons system across 1800 to 2100 and the simulator stays inside that tested span.

Eclipses and other sky events

The Events button lists what is coming up from the date on screen: solar and lunar eclipses, oppositions of the outer planets (when they are brightest and up all night), the greatest elongations of Mercury and Venus, and the equinoxes and solstices. Choose one and the simulator jumps to that moment and frames the scene.

Shadows are calculated for every point on each body from the size and position of the Sun and of nearby worlds. That is how the dark spot of the Moon's shadow crosses Earth during a solar eclipse, how Earth's shadow turns the Moon a coppery red in a total lunar eclipse (sunlight bent through our atmosphere still reaches it), and how the small black shadows of Io, Europa, Ganymede and Callisto slide across Jupiter's clouds.

True scale, and why space looks empty

Sizes and distances are true unless you turn on Enlarge. The distances are hard to imagine: light from the Sun takes about 8 minutes 20 seconds to reach Earth and over 4 hours to reach Neptune. Zoom out to see the whole system and the planets shrink to points, so each is marked with a small ring and its name. Enlarge draws the planets, and the orbits of their moons, 20 times larger so you can see them as discs from farther away; it is labelled because it is not to scale.

How accurate is it?

Positions come from established orbital theories rather than from a fixed animation. We test them against NASA JPL's Horizons system, the reference ephemeris used for spacecraft navigation:

• Planets and Pluto: within 30 arcseconds of Horizons at every sample from 1800 to 2100, about the width of Jupiter's disc as seen from Earth.
• The Moon: within 5 arcseconds and 25 km (2020 to 2030).
• Jupiter's four large moons: within 700 km.
• The other moons: from JPL's published mean orbits, adjusted to match Horizons; most stay within about 2 degrees of their true place around their planet.

The positions are geometric: they show where each body is, not where it appears after its light has travelled to us. Accuracy and sources explains the methods, data and tests in full.