A top-down view of the ecliptic plane that moves. Every position is solved live from Keplerian orbital elements, and the scale is genuinely linear — the inner planets are not enlarged to make the picture nicer. Pull back to watch Neptune complete a lap, or zoom in to see how visibly off-centre Mercury's ellipse really is.
Mercury's orbit is visibly not a circle, and the Sun is not at its centre. That is neither a drawing error nor deliberate exaggeration: Mercury's eccentricity is 0.206, and this is simply what solving Kepler's equation correctly produces. Detail that appears because the maths is right is worth more than any ornament.
In the outer view, the scatter of dots between Mars and Jupiter is the asteroid belt. The boundary between the two views is placed there because 1.52 AU to 5.20 AU is the largest relative gap anywhere in the solar system.
At the current speed. Bold means it falls in the 8-40 second range that is comfortable to watch.
Click any band to jump to that retrograde episode; the view switches to whichever one can actually resolve that planet.
At this scale the entire orbit of Mercury · Venus · Earth · Mars falls inside the Sun's own disc — Earth's whole orbit is a few pixels across, so a dot there could not say where the planet is. Those planets are shown in the inner-system inset at the bottom right instead.
Read the scale bar before comparing speeds. The inner-system view separates Mercury through Mars so their relative motion is easy to follow; the outer-system view preserves the real distance to Neptune, compressing the four inner planets beside the Sun. Changing playback speed only advances the date faster. It does not alter an orbit or a planet's period.
| Planet | a (AU) | Time for one lap |
|---|---|---|
| Mercury | 0.387 AU | 0.24 yr |
| Venus | 0.723 AU | 0.62 yr |
| Earth | 1 AU | 1 yr |
| Mars | 1.524 AU | 1.88 yr |
| Jupiter | 5.203 AU | 11.86 yr |
| Saturn | 9.537 AU | 29.45 yr |
| Uranus | 19.189 AU | 84.02 yr |
| Neptune | 30.07 AU | 164.79 yr |
No single speed makes the whole solar system watchable at once. At 3 days per second Mercury laps in 29 seconds, while Neptune takes 5.6 hours. Getting Neptune into the comfortable range means running fast enough that Mercury sweeps most of a turn every frame. That conflict is not a failure of interface design — it is Kepler's third law, period growing as the 3/2 power of orbital radius, spread across a factor of 1900.
Which makes the speed control part of the content rather than a convenience. Once a planet moves more than 90° per frame it is redrawn as a ring. The rule is computed from the refresh rate actually measured on your display, not from an assumed 60 Hz — on a 30 Hz phone more planets become rings than on a 120 Hz screen.
The date range stops at 1800 and 2050 because that is the validity window of the element table itself, not a limit of the program. Going further needs a second set of elements carrying periodic correction terms — which the precession lesson will use.
Related tools: Why planets appear to move backwards · The ecliptic plane · Ptolemaic and heliocentric
Orbital elements from NASA/JPL, "Keplerian Elements for Approximate Positions of the Major Planets" (Standish & Williams, 1992), valid 1800–2050. Positions are geometric — no light-time or aberration — because this is a diagram of the ecliptic plane, not a simulation of a telescope view.
Interactive retrograde teaching tools have a long history: Nebraska (NAAP), Foothill AstroSims, the University of New Mexico, SimuFísica, NoA at the University of Fukui, Marble Cafe, and jsOrrery. None of their code is used here; the calculation and drawing are our own.