Solar System Simulator

How the Solar System Simulator works

Solar system simulator: what it does and why

The solar system is hard to picture because its scale defeats every diagram. Textbook posters line the planets up in a row, evenly spaced and roughly the same size, and almost everything about that picture is wrong. This simulator puts each planet where it really is on a chosen date, lets you switch between a readable view and the true proportions, and runs the clock forward so you can watch the orbits turn.

Why an accurate orrery is worth having

Knowing where the planets are explains a lot of what happens in the night sky. When Earth passes between the Sun and an outer planet, that planet is at opposition: closest, brightest and up all night. Mars reaches opposition roughly every 26 months, which is why launch windows to Mars open on the same rhythm — the next ones fall in late 2026 and early 2029. Jupiter comes round every 13 months, Saturn every 12½. When two planets share the same longitude seen from Earth they appear close together in the sky, as Jupiter and Saturn did in the "great conjunction" of 21 December 2020, the closest since 1623. All of that can be read straight off the view here.

Where the planets come from

Each planet is placed using its mean Keplerian orbital elements for the J2000 epoch, with the standard secular rates applied per century, the same approximate elements published for educational and planning use by the major ephemeris services. From the elements the tool solves Kepler's equation for the eccentric anomaly, converts to a position in the orbital plane and rotates it into the ecliptic frame. Over the years 1800 to 2050 the result is within a fraction of a degree of a full numerical ephemeris, which is more than enough to show conjunctions, oppositions and the general shape of the sky on a given date.

Where it gets used

• Teaching. Kepler's second law — planets move faster near the Sun — is visible when Mercury speeds through perihelion at a month per second.
• Observing plans. Checking which planets sit on the far side of the Sun on a given date tells you which ones are lost in its glare and which are worth going outside for.
• Anniversaries and gifts. Setting the date to a birthday and saving a 4K render gives a true picture of the sky's layout on that day.
• Space news. Mission timelines make more sense when you can see where Earth and the target planet were at launch and arrival.

Distances and sizes

At true scale the Sun is a dot and Neptune is thirty times farther out than Earth, so nothing is visible at once. The default Logarithmic setting compresses the distances so the inner planets are spread out and the outer ones still fit, while keeping the correct order and the correct angular positions. Switch to Real scale to see the real proportions of the orbits. Planet sizes are exaggerated by default for the same reason; Real-scale sizes are correct relative to the orbits and make the planets almost invisible, which is itself the lesson.

Running time

The Run time control advances the date continuously at one day, week, month or year per second of real time. Mercury completes a lap in 88 days, so at a month per second it takes about three seconds; Neptune takes 165 years, so a year per second is still nearly three minutes. The date in the stats block updates as it runs, and setting the date field resets the clock to that instant.

Orbit lines and labels

Orbit lines are traced from the elements for the date shown, so they include each orbit's eccentricity and inclination. Mercury's tilted, off-centre ellipse is obvious once you look side-on. Labels float above each planet and always face the camera; turn them off for a cleaner render before saving.

Tips and pitfalls

• Dates and times are UTC. For a local evening in the Americas or Asia the UTC date may already be the next day; the difference is small for planets but it matters if you are matching a render to a timestamp.
• Stay inside 1800–2050. The elements drift outside that range. Positions centuries away are still broadly right but should not be trusted for precise alignments.
• Logarithmic squeezes distance, not direction. Read directions from the Sun on either setting; judge how far apart two planets are only on Real scale.
• It is heliocentric. The view is from outside the solar system. Where a planet appears in your sky also depends on where Earth is, so look at the angle from Earth to the planet, not from the Sun.

How to read the result

The stats panel starts with the date and time shown, then lists each planet's distance from the Sun in astronomical units (1 AU is Earth's average distance, about 149.6 million km) and its heliocentric ecliptic longitude in degrees. Earth's distance swings between about 0.983 AU in early January and 1.017 AU in early July. Two planets with nearly the same longitude are lined up on the same side of the Sun; an outer planet whose longitude matches Earth's is at opposition, and one that differs by 180° is hidden behind the Sun.

Saving

Download PNG renders the current view at 1080p, 2K or 4K with the starfield background, ready for a slide, a worksheet or a poster. Orbit the view first, then use Fit view to re-centre.

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